Who invented air conditioning?

Air conditioning is the cooling and de-humidification of indoor air for thermal comfort. Using a system of coils as a solution to cool and remove moisture from muggy air in a printing plant that was wrinkling magazine pages, Willis Carrier invented and manufactured the world's first mechanical air conditioning unit in 1902. Carrier's invention – encompassing the first system to provide man-made control over temperature, humidity, ventilation and air quality, was first installed as a solution to the quality problems experienced at a Brooklyn printing plant, Sackett-Wilhelms Lithographing and Publishing Company. Air conditioning not only spawned a company and an industry, but also brought about profound economic, social and cultural changes.

Timeline of United States inventions (1890–1945)

A timeline of United States inventions (1890–1945) encompasses the ingenuity and innovative advancements of the United States within a historical context, dating from the Progressive Era to the end of World War II, which have been achieved by inventors who are either native-born or naturalized citizens of the United States. Copyright protection secures a person's right to his or her first-to-invent claim of the "original" invention in question, highlighted in Article I, Section 8, Clause 8 of the United States Constitution which gives the following enumerated power to the United States Congress:
In 1641, the first patent in North America was issued to Samuel Winslow by the General Court of Massachusetts for a new method of making salt. On April 10, 1790, President George Washington signed the Patent Act of 1790 (1 Stat. 109) into law which proclaimed that patents were to be authorized for "any useful art, manufacture, engine, machine, or device, or any improvement therein not before known or used." On July 31, 1790, Samuel Hopkins of Philadelphia, Pennsylvania, became the first person in the United States to file and to be granted a patent under the new U.S. patent statute. The Patent Act of 1836 (Ch. 357, 5 Stat. 117) further clarified United States patent law to the extent of establishing a patent office where patent applications are filed, processed, and granted, contingent upon the language and scope of the claimant's invention, for a patent term of 14 years with an extension of up to an additional 7 years.

From 1836 to 2011, the United States Patent and Trademark Office (USPTO) has granted a total of 7,861,317 patents relating to several well-known inventions appearing throughout the timeline below. Some examples of patented inventions between the years 1890 and 1945 include John Froelich's tractor (1892), Ransom Eli Olds' assembly line (1901), Willis Carrier's air-conditioning (1902), the Wright Brothers' airplane (1903), and Robert H. Goddard's liquid-fuel rocket (1926).

1890 Stop sign

A stop sign is a traffic sign, usually erected at road junctions such as a four-way intersection, that instructs drivers to stop and then to proceed only if the way ahead is clear. The idea of placing stop signs at road junctions was first conceived in 1890 when William Phelps Eno of Saugatuck, Connecticut proposed and devised the first set of traffic laws in an article published in "Rider and Driver". However, the first use of stop signs did not appear until 1915 when officials in Detroit, Michigan installed a stop sign with black letters on a white background. Throughout the years and with many alterations made to the stop sign, the current version with white block-lettering on a red background that is used in the United States as well as emulated in many other countries around the world today, did not come into use until the Joint Committee on Uniform Traffic Control Devices adopted the design in 1975.

1890 Tabulating machine

The tabulating machine is an electrical device designed to assist in summarizing information and, later, accounting. The results of a tabulation are electrically coupled with a sorter while displayed on clock-like dials. The concept of automated data processing had been born. In 1890, Herman Hollerith invented the mechanical tabulating machine, a design used during the 1890 Census which stored and processed demographic and statistical information on punched cards.

1890 Shredded wheat

1890 Babcock test

1890 Smoke detector

1891 Ferris wheel

A Ferris wheel is a non-building structure, consisting of an upright wheel with passenger gondolas attached to the rim. Opened on June 21, 1893 at the Chicago World's Fair, the original Ferris Wheel was invented two years earlier by the Pittsburgh, Pennsylvania bridge-builder George Washington Gale Ferris Jr. in 1891.

1891 Dow process

The Dow process is the electrolytic method of bromine extraction from brine, and was Herbert Henry Dow's second revolutionary process for generating bromine commercially in 1891.

1891 Tesla coil

A Tesla coil is a type of resonant transformer circuit invented by Nikola Tesla around 1891. Nikola Tesla used these coils to conduct innovative experiments in electrical lighting, phosphorescence, x-ray generation, high frequency alternating current phenomena, electrotherapy, and the transmission of electrical energy without wires for point-to-point telecommunications, broadcasting, and the transmission of electrical power.

1891 Rotary dial

1891 Pastry fork

1891 Schrader valve

A Schrader valve consists of a hollow cylindrical metal tube, typically brass, with the exterior end threaded. The interior end takes a variety of forms depending on its application. In the center of the exterior end is a metal pin pointing along the axis of the tube; the pin's end is flush with the end of the valve body. Generally, all Schrader valves are used on tires. They have threads and bodies of a single standard size at the exterior end, so caps and tools generally are universal for the valves on all automobile and bicycle pneumatic tires. Also, pressure valves can be used on Schrader valves in place of caps in order to measure the pressure of pneumatic tires. In 1891, George Schrader, the son of German-American immigrant August Schrader, invented the Schrader valve. A patent was issued on April 11, 1893.

1892 Bottle cap

1892 Dimmer

1892 Bicycle seat (padded)

1892 internal combustion-powered tractor
A tractor is a distinctive farm vehicle specifically designed to deliver a high tractive effort at slow speeds, for the purposes of hauling a trailer or machinery used in agriculture or construction. Agricultural implements may be towed behind or mounted on the tractor, and the tractor may also provide a source of power if the implement is mechanized. While steam powered tractors had been built earlier, In 1892, John Froelich invented and built the first gasoline-powered tractor in Clayton County, Iowa.

1893 Zipper

The zipper is a popular device for temporarily joining two edges of fabric. Zippers are found on trousers, jeans, jackets, and luggage. Whitcomb L. Judson was an American mechanical engineer from Chicago who was the first to invent, conceive of the idea, and to construct a workable zipper. Using a hook-and-eye device, Judson intended for this earliest form of the zipper to be used on shoes. He also conceived the idea of the slide fastener mechanism in conjunction with the invention of the zipper. Patents were issued to Judson for the zipper in 1891, 1894, and 1905.

1893 Spectroheliograph

The spectroheliograph is an instrument used in astronomy that captures a photographic image of the Sun at a single wavelength of light, a monochromatic image. The spectroheliograph was invented in 1893 by George Ellery Hale and independently later by Henri Alexandre Deslandres in 1894.

1893 Pinking shears

Early 1890s Phantoscope

1894 Stadimeter

A stadimeter, a type of optical rangefinder, is an optical device for estimating the range to an object of known height by measuring the angle between the top and bottom of the object as observed at the device. It is similar to a sextant, in that the device is using mirrors to measure an angle between two objects but differs in that one dials in the height of the object. The stadimeter was invented in 1894 by Bradley Allen Fiske, a Rear-Admiral in the United States Navy. The first sea tests, conducted in 1895, showed that it was equally useful for fleet sailing and for navigation. Likewise, the stadimeter proved useful during the Battle of Manila Bay during the Spanish–American War. U.S. patent #523,721 was issued to Fiske on July 31, 1894.

1894 Mousetrap

A mousetrap is a specialized type of animal trap designed primarily to catch mice. However, it may also trap other small animals. Mousetraps are usually set in an indoor location where there is a suspected infestation of rodents. The first mouse trap was invented by William C. Hooker of Abingdon, Illinois, exactly three years before James Henry Atkinson developed a prototype called the "Little Nipper". Atkinson probably saw the Hooker trap in shops or in advertisements, and copyied it as the basis for his own model. Hooker received US patent #528671 for his invention, the mousetrap, in 1894.

1894 Medical glove

Medical gloves are disposable gloves used during medical examinations and procedures that help prevent contamination between caregivers and patients. Medical gloves are made of different polymers including latex, nitrile rubber, vinyl and neoprene; they come unpowdered, or powdered with cornstarch to lubricate the gloves, making them easier to put on the hands. In 1894, William Stewart Halsted, the Surgeon-in-Chief of Johns Hopkins Hospital, invented the medical glove in an effort to make medical care safer and more sterile for patients and health care workers.

1895 Cyclocomputer

A cyclocomputer or cyclometer is a device mounted on a bicycle that calculates and displays trip information, similar to the instruments in the dashboard of a car. The computer with display, or head unit, usually is attached to the handlebar for easy viewing. In 1895, Curtis Hussey Veeder invented the cyclometer.

1895 Clipless pedal

1895 Volleyball

Volleyball is an Olympic sport in which two teams of 6 active players are separated by a net. Each team tries to score points against one another by grounding a ball on the other team's court under organized rules. William G. Morgan invented the sport first known as "Mintonnette" in 1895 while studying at a YMCA in Holyoke, Massachusetts. It was later renamed volleyball by Alfred S. Halstead.

1897 Cotton candy

Cotton candy is a soft confection made from sugar that is heated and spun into slim threads that look like a mass of cotton. It was co-invented in 1897 by William Morrison and John C. Wharton, candy-makers from Nashville, Tennessee.

1897 Muffler

A muffler is a device for reducing the amount of noise emitted by a machine. On internal combustion engines, the engine exhaust blows out through the muffler. The internal combustion engine muffler was invented by Milton O. Reeves who received a patent in 1897.

1897 Tapered roller bearing

1897 Ice cream scoop

1897 Charcoal briquette

1897 Billiards cue chalk

1898 Candy corn

Candy corn is a confection in the United States and Canada, popular primarily in autumn around Halloween, that mimics the shape and coloration of corn kernels—a broad yellow end, a tapered orange center, and a pointed white tip. Candy corn is made primarily from sugar, corn syrup, artificial coloring and binders. It is generally thought that George Renninger, an employee of the Wunderlee Candy Company, invented candy corn in the 1880s. However, the earliest references credit the Goelitz Confectionery Company, now known as the Jelly Belly Candy Company, for introducing candy corn or "chicken feed" to the American public in 1898.

A remote control is an electronic device used to operate any machine, such as a television, remotely. Many of these remotes communicate to their respective devices through infrared signals and radio control. In Madison Square Garden, at the Electrical Exhibition, Nikola Tesla gave the first demonstration of a boat propelling in water, controlled by his remote control which he designed using radio signals. Tesla received a patent for his invention in 1898.

1898 Semi-automatic shotgun

1898 Semi-truck

1898 Filing cabinet (vertical)

1898 Installer bit

1898 Sousaphone

1899 Wing warping

Wing warping consists of the twisting motion of the wings of an aircraft to produce lateral control. The entire wing structure twists slightly in a helical motion in the desired direction. The concept of wing warping is attributed to Wilbur Wright who in 1899, came up with the idea and with the conclusion that the roll of an aircraft could be controlled by the motion of that aircraft's wings. Exemplified by the twisting of a long, narrow box, the Wright brothers incorporated wing warping on their 1899 glider that used ropes to pull on the wings. Later on, the young French engineer Robert Esnault-Pelterie replaced wing warping in 1904 with the aileron on a copy he made of a 19th-century Wright glider. However, it was Henry Farman, a French aviator, who was the first to use the aileron as an integral part of the wing structure in place of wing warping in 1908.

1899 Flash-lamp

The electric flash-lamp is a device that uses an electrical circuit to trigger a fuse to ignite explosive powder such as magnesium, for a brief sudden burst of bright light "flash" from a chemical reaction of flash powder burning. It was principally used for flash photography in the early 20th century, but had other uses as well. The flash-lamp was invented and patented on November 7, 1899 by New York City resident Joshua Lionel Cowen.

1900 Duckpin bowling

Duckpin bowling is a variation of bowling that uses balls which are significantly smaller than those used in ten-pin bowling, weighing each, which are devoid of finger holes. The pins are correspondingly shorter and lighter than their ten-pin equivalents. Hence, when the pins are knocked down, they resemble a "flock of flying ducks". While the rules remained almost identical to those of the Ten-pin game, one rule change was made: A bowler is allowed to use three bowls on each turn. Strikes would still be strikes and spares still spares, but when all pins were knocked down on the third ball, it counts as a score of ten. During the summer of 1900, some bowlers at Diamond Alleys in Baltimore, Maryland thought it might be interesting to resize the pins to match the 6-inch ball. Thus, the inventor of duckpin bowling, John Van Sant, used a wood turner to do exactly that.

1900 Nickel-zinc battery

1900 Merrill-Crowe process

1900 Carbide lamp

1900 Fly swatter

1900 Thumbtack

1901 Key punch

1901 Mercury-vapor lamp

1901 Assembly line

Used globally around the world, an assembly line is a manufacturing process in which interchangeable parts are added to a product in a sequential manner in order to create a finished product more quickly than with older methods. This type of manufacturing greatly reduces the amount of time taken to assemble a product, thus reducing production, material, and labor costs so that an affordable product cost can be passed onto consumers. According to a book entitled "Michigan Yesterday & Today" authored by Robert W. Domm, the assembly line and its basic concept is credited to Ransom Olds, who used it to build the first mass-produced automobile, the Oldsmobile Curved Dash. Olds patented the assembly line concept, which he put to work in his Olds Motor Vehicle Company factory in 1901. This development is often overshadowed by Henry Ford, who perfected the assembly line by installing driven conveyor belts that could produce a Model T in ninety-three minutes.

1901 Safety razor (disposable)

A safety razor protects the skin from all but the edge of the blade while shaving skin. King Camp Gillette, a traveling hardware salesman of Fond du Lac, Wisconsin invented the double-edged, disposable safety razor attached to a re-usable razor handle. Beforehand, dull razors were taken to barbers for sharpening. With Gillette's double-edged and disposable blades, a uniform shave on a man's face could be achieved with a fresh blade and disposed after it was used. Gillette applied for a patent in 1901. It was granted in 1904.

1901 Windowed envelope

A windowed envelope is a conventional envelope with a plastic window to allow the recipient's address to be printed on the paper contained within. Windowed envelopes save the expense of printing or labor of addressing, and in addition save time in preparing the message for dispatch when the customary addresses are already on the letter paper itself. Calling it the "outlook envelope", Americus F. Callahan of Chicago was the first to patent the windowed envelope. U.S. patent #701,839 was filed on December 9, 1901 and issued on June 10, 1902.

1901 Radio direction finder

A radio direction finder (RDF) is a device for finding the direction to a radio source. Due to radio's ability to travel very long distances and "over the horizon", it makes a particularly good navigation system for ships, small boats, and aircraft that might be some distance from their destination. The radio direction finder is the earliest form of radio navigation. It was first patented by American physicist John Stone Stone. He filed on January 23, 1901 and was granted the patent (U.S. Patent 716,134) on December 16, 1902.

1902 Hearing aid

1902 Postage meter

1902 Teddy bear

1902 Periscope (collapsible)

1902 Mercury arc valve

1902 Air conditioning

Air conditioning is the cooling and de-humidification of indoor air for thermal comfort. Using a system of coils as a solution to cool and remove moisture from muggy air in a printing plant that was wrinkling magazine pages, Willis Carrier invented and manufactured the world's first mechanical air conditioning unit in 1902. Carrier's invention – encompassing the first system to provide man-made control over temperature, humidity, ventilation and air quality, was first installed as a solution to the quality problems experienced at a Brooklyn printing plant, Sackett-Wilhelms Lithographing and Publishing Company. Air conditioning not only spawned a company and an industry, but also brought about profound economic, social and cultural changes.

1903 Tea bag

A tea bag is a small, porous paper, silk or nylon sealed bag containing tea leaves for brewing tea. Tea bags were invented by Thomas Sullivan around 1903. The first tea bags were made from silk. Sullivan was a tea and coffee merchant in New York who began packaging tea samples in tiny silk bags, but many customers brewed the tea in them.

1903 Offset printing press

1903 Airplane

A fixed-wing aircraft, or airplane, is a heavier-than-air craft whose lift is generated by air pressure differential between the upper and lower wing surfaces. The Wright brothers, Wilbur and Orville Wright of Dayton, Ohio, made the first powered and sustained airplane flights under control of the pilot in the Wright Flyer I on December 17, 1903 in Kitty Hawk, North Carolina. In the two years afterward, they developed their flying machine into the world's first practical fixed-wing aircraft. By October 1905, the Wright Flyer III was capable and proven to circle in the air 30 times in 39 minutes for a total distance of 24.5 miles. The brothers' fundamental breakthrough was their invention of "three-axis control", which enabled the pilot to steer the aircraft effectively and to maintain its equilibrium. This required method has become standard on all fixed-wing aircraft. From the beginning of their aeronautical work, the Wright brothers focused on unlocking the secrets of control to conquer "the flying problem", rather than on developing more powerful engines as some other experimenters did. Charles Edward Taylor built the first aircraft engine and was a vital contributor of mechanical aspects in the building and maintaining of early Wright engines and airplanes. Although there were many earlier attempts at heavier-than-air powered flight, some of which achieved successful short hops, and disputed earlier claims of sustained flight, the Wright brothers are officially credited by the Fédération Aéronautique Internationale, the international record-setting body for aeronautics and astronautics, as achieving "the first sustained and controlled heavier-than-air powered flight". In addition, U.S. patent number #821393 for the airplane, was filed by Orville Wright on March 23, 1903 and was issued in May 1906.

1903 Windshield wipers

The windshield wiper is a bladed device used to wipe rain and dirt from a windshield. In 1903, Mary Anderson is credited with inventing the first operational windshield wiper. In Anderson's patent, she called her invention a window cleaning device for electric cars and other vehicles. Operated via a lever from inside a vehicle, her version of windshield wipers closely resembles the windshield wiper found on many early car models. Anderson had a model of her design manufactured. She then filed a patent (U.S. patent number 743,801) on June 18, 1903 that was issued to her by the U.S. Patent Office on November 10, 1903.

1903 Wood's glass

Wood's glass is a light filter used in communications during World War I. An "invisible radiation" technique which worked both in infrared daylight communication and ultraviolet night communications, it does not transmit visible light, leaving the 'invisible radiation' as a signal beam. Wood's glass was invented by Robert Williams Wood in 1903.

1903 Wood's lamp

A Wood's lamp is a diagnostic tool used in dermatology which shines ultraviolet light onto the skin of the patient; a technician then observes any subsequent fluorescence. Though the technique for producing a source of ultraviolet light was devised by Robert Williams Wood in 1903 using "Wood's glass", not until 1925 was the technique used in dermatology by Margarot and Deveze for the detection of fungal infection of hair.
1903 Baler (round)

A baler is a piece of farm machinery used to compress a cut and raked crop (such as hay, straw, or silage) into compact bales that are easy to handle, transport and store. Several different types of balers are commonly used, each producing a different type of bales – rectangular or cylindrical (round), of various sizes, bound with twine, netting, or wire. The round hay baler was invented by Ummo F. Luebben of Sutton, Nebraska, which he conceived with his brother Melchior in 1903, and then patented in 1910. The invention of the round hay baler revolutionized the laborious task of haying into a one-man, low-cost operation with a machine that automatically gathered the hay, rolled into a round bale, and ejected it.

1904 Automatic transmission

An automatic transmission is an automobile gearbox that changes gear ratios automatically as the vehicle moves, freeing the driver from having to shift gears manually. Modern automatic transmissions trace their origins to an early "horseless carriage" gearbox that was developed in 1904 by the Sturtevant brothers of Boston, Massachusetts.

1904 Banana split

1904 Pantograph (diamond-shaped)

1904 Dragline excavator

1905 Batting helmet

A batting helmet is the protective headgear worn by batters in the game of baseball or softball. It is meant to protect the batter's head from errant pitches thrown by the pitcher. A batter who is "hit by pitch", due to an inadvertent wild pitch or a pitcher's purposeful attempt to hit him, may be seriously, even fatally, injured. In 1905, a New York Giants (the team now known as the San Francisco Giants) baseball player named Roger Bresnahan, after missing thirty days of the baseball season and lying in a hospital bed due to a head injury (or beaning), created, with assistance from the A.J. Reach Company, a crude, leather, vertically sliced football helmet over his cap that is considered to be the first batting helmet. The headgear was unpopular, even with Bresnahan at the time, and it wasn't until the mid-1950s that his idea was accepted.

1905 Liquid ring pump

A liquid ring pump is a rotating positive displacement pump that is powered by an induction motor and is typically used as a vacuum pump or as a gas compressor. The liquid ring pump was invented in 1905 by Lewis H. Nash. Production soon began thereafter at the Nash Engineering Company. Nash filed U.S. patent #1,091,529 on February 24, 1910 and was issued to him on March 31, 1914.

1905 Ice pop

1906 Typesetting

1906 Flushometer

1906 Audion tube

1907 Curtain rod

1907 Electrostatic precipitator

1907 Paper towel

1908 Candy apple

Candy apples, also known as toffee apples outside of North America, are whole apples covered in a hard sugar candy coating. While the topping varies from place to place, they are almost always served with a wooden stick of sorts in the middle making them easier to eat. Toffee apples are a common treat at autumn festivals in Western culture in the Northern Hemisphere, such as Halloween and Guy Fawkes Night because these festivals fall in the wake of the annual apple harvest. Dipping fruits into a sugar syrup is an ancient tradition. However, the origin of the red candy apple is attributed to Newark, New Jersey candymaker who conceived the idea of dipping apples into a red cinnamon candy mixture he had on hand. In addition, dipping apples in hot caramel a 1950s American invention attributed to Kraft salesman Dan Walker.

1909 Skee ball

Skee ball is a common game found in arcades and one of the first redemption games. Skee ball is similar to bowling except it is played on an inclined lane and the player aims to get the ball to fall into a hole rather than knock down pins. The object of the game is to collect as many points as possible by rolling balls up an incline and into the designated point value holes. Skee ball was invented and patented in 1909 by J.D. Estes of Philadelphia.

1909 Paper shredder

Paper shredders are used to cut paper into chad, typically either strips or fine particles. Government organizations, businesses, and private individuals use shredders to destroy private, confidential, or otherwise sensitive documents. The first paper shredder is credited to prolific inventor Abbot Augustus Low of Horseshoe, New York. His patent for a "waste paper receptacle" to offer an improved method of disposing of waste paper received a U.S. patent on August 31, 1909.

1909 Suppressor

1909 Gin rummy

1910 Headset

1911 Fifth wheel coupling

1911 Erector Set

1911 Binder clip

A binder clip, or a banker's clip or foldback clip, is a simple device for binding sheets of paper together. It leaves the paper intact and can be removed quickly and easily unlike the staple. The binder clip was invented in 1911 by Washington, D.C. resident Louis E. Baltzley who was motivated by a desire to help his father, Edwin, a prolific writer and inventor, keep manuscripts in order. The original design was modified five times, but the essential mechanism has never changed.

1911 Automobile self starter

An automobile self-starter is an electric motor that initiates rotational motion in an internal combustion engine before it can power itself, therefore eliminating the hand crank used to start engines. In 1911, Charles F. Kettering invented the automobile self-starter while working at National Cash Register and then sold them for installation on cars at the Cadillac company. There had been many attempts at producing an electric starter before, but none of them were successful. Most designs at that time called for the use of an electric motor attached to the engine's flywheel. However, in order to fit in the car's engine compartment, the device would have to be small, and therefore it would be unable to produce a sufficient enough amount of torque.

1911 Road surface marking

A road surface marking is any kind of device or material that is used on a road surface in order to convey official information for drivers and pedestrians. Edward N. Hines originated the concept of painting a line down the center of a road to separate traffic in opposing directions. They were first used in Wayne County, Michigan in 1911.

1912 Autopilot

An autopilot is a mechanical, electrical, or hydraulic system used to guide a vehicle without assistance from a human being. Most people understand an autopilot to refer specifically to aircraft, but self-steering gear for ships, boats, space craft, and missiles is sometimes also called "autopilot". The first aircraft autopilot was invented by Lawrence Sperry in 1912. Sperry demonstrated it in 1914, and proved the credibility of the invention by flying the aircraft with his hands away from the controls and visible to onlookers.

1912 Electric blanket

An electric blanket is a blanket with an integrated electrical heating device usually placed above the top bed sheet. The first electric blanket was invented in 1912 by American physician Sidney I. Russell. This earliest form of an electric blanket was an 'underblanket' under the bed that covered and heated from below. In 1937, Electric 'overblankets which lie on top of the sleeping person were introduced in the United States.

1912 Traffic light (electric)

The traffic light, also known as traffic signal, is a signaling device positioned at a road intersection, pedestrian crossing, or other location. Its purpose is to indicate, using a series of colors, the correct moment to stop, drive, ride or walk, using a universal color code. The color of the traffic lights representing stop and go are likely derived from those used to identify port (red) and starboard (green) in maritime rules governing right of way, where the vessel on the left must stop for the one crossing on the right. In Salt Lake City, Utah, policeman Lester Wire invented the first red-green electric traffic lights.

1913 Formica (plastic)

Formica is a hard durable plastic laminate used for countertops, cupboard doors, and other surfaces which are heat-resistant and easy to clean. Formica was invented in 1913 by Herbert A Faber and Daniel J. O'Connor of Westinghouse Electric.

1914 Regenerative circuit

The regenerative circuit allows an electronic signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor. A regenerative circuit is often an AM detector, converting the RF signal on the antenna to an audio waveform. Their use of positive feedback greatly increases both the selectivity and sensitivity of a simple receiver. Positive feedback builds up the input signal to very high levels. Edwin Armstrong, invented and patented the regenerative circuit while he was a junior in college, in 1914.

1914 Traffic cone

1914 Fortune cookie

1915 Skeet shooting

1915 Single-sideband modulation

1916 Hamburger bun

1916 Lincoln Logs

1916 Supermarket

A supermarket is a self-service store offering a wide variety of food and household merchandise, organized into departments. It is larger in size and has a wider selection than a traditional grocery store. The concept of a "self-service" grocery store was invented by American entrepreneur Clarence Saunders and his Piggly Wiggly stores. Beforehand, customers would shop at a general store where a clerk behind a counter would fetch inventory in limited quantity for customers to purchase. With Saunders' new innovation of self-service, customers would be able to choose a wider selection of goods at competitive prices. Saunders' first store opened in Memphis, Tennessee, in 1916.

1916 Cloverleaf interchange

A cloverleaf interchange is a two-level interchange in which left turns, in countries that drive on the right, are handled by loop roads. To go left, in right-hand traffic, vehicles first pass either over or under the other road, then turn right onto a one-way three-fourths loop ramp (270°) and merge onto the intersecting road. The cloverleaf was first patented in the United States by Arthur Hale, a civil engineer in Maryland, on February 29, 1916.

1916 Tow truck

1916 Condenser microphone

1916 Light switch (toggle)

A toggle light switch is a switch, most commonly used to operate electric lights, permanently connected equipment, or electrical outlets whereby the switch handle does not control the contacts directly, but through an intermediate arrangement of internal springs and levers. The toggle light switch is safe, reliable, and durable, but produces a loud "snap" or "click" noise when a person's finger manually flips the toggle light switch into the on/off position. The design for the toggle light switch was patented in 1916 by William J. Newton and Morris Goldberg of Lynbrook, New York.

1917 Stream cipher

In cryptography, a stream cipher is a symmetric key cipher where plaintext bits are combined with a pseudorandom cipher bit stream, typically by an exclusive-or (xor) operation. In a stream cipher the plaintext digits are encrypted one at a time, and the transformation of successive digits varies during the encryption. Also known as a state cipher, the stream cipher was invented in 1917 by Gilbert Sandford Vernam at Bell Labs.

1917 Marshmallow creme

1918 Superheterodyne receiver

1918 French dip sandwich

1918 Torque wrench

1918 Crystal oscillator

1918 Grocery bag

1918 Hydraulic brake

1919 Blender

1919 Silica gel

1919 Toaster (pop-up)

1920 Eskimo Pie

1920 Jungle gym

1921 Polygraph

Not to be confused with an earlier and different invention with the same name, a polygraph, popularly referred to as a lie detector, is an instrument that measures and records several physiological indices such as blood pressure, pulse, respiration, and skin conductivity while the subject is asked and answers a series of questions, in the belief that deceptive answers will produce physiological responses that can be differentiated from those associated with non-deceptive answers. The polygraph was invented in 1921 by John Augustus Larson, a medical student at the University of California at Berkeley and a police officer of the Berkeley Police Department in Berkeley, California. According to Encyclopædia Britannica, the polygraph was on its 2003 list of the 325 greatest inventions.

1921 Flowchart

A flowchart is common type of chart, representing an algorithm or process, showing the steps as boxes of various kinds, and their order by connecting these with arrows. Flowcharts are used in analyzing, designing, documenting or managing a process or program in various fields. The second structured method for documenting process flow, the "flow process chart", was invented by Frank Gilbreth to members of ASME in 1921 as the presentation "Process Charts—First Steps in Finding the One Best Way".

1921 Adhesive bandage

Popularly known by the brand name Band-Aid, an adhesive bandage is a self-sticking taped and small dressing used for injuries not serious enough to require a full-size bandage. This easy-to-use dressing with adhesive tape was invented by Earle Dickson in 1921.

1921 Headrest

In an automobile, the headrest or head restraint is a device attached to the top of the seat behind the occupant's head. Most headrests are cushioned for comfort, are height adjustable and most commonly finished in the same material as the rest of the seat. The automobile headrest was invented by Benjamin Katz, a resident of Oakland, California, in 1921. U.S. patent #1,471,168 for the headrest was issued to Katz on October 16, 1923.

1921 Garage door

A garage door is a large door on a garage that can either be opened manually or by a garage door opener. Garage doors are necessarily large to allow passage of automobiles and/or trucks. In 1921, C. G. Johnson of Detroit, Michigan invented the "Overhead Door", the first upward-lifting garage door. To market the garage door, Johnson mounted a small prototype of his door on the back of his Model T Ford and drove around the United States signing up distributors.

1922 Blowout preventer (ram)

A ram blowout preventer is a large valve that can seal off a wellhead by using ram-types employing steel cut off rams to seal the borehole. During drilling or well interventions, the valve may be closed if overpressure from an underground zone causes formation fluids such as oil or natural gas to enter the wellbore and threaten the rig. In 1922, James Smither Abercrombie collaborated with Harry S. Cameron with the idea of creating a mechanically operated ram-type blowout preventer. A patent was issued in January 1926.

1922 Convertible

1922 Water skiing

Water skiing is a sport where one or more persons is pulled behind a motor boat or a cable ski installation on a body of water wearing one or more skis. Water skiing began in 1922 when Ralph Samuelson used two boards as skis and a clothesline as a tow rope on Lake Pepin in Lake City, Minnesota. The sport remained a little-known activity for several years. Samuelson took stunts on the road, performing shows from Michigan to Florida. In 1966 the American Water Ski Association formally acknowledged Samuelson as the first on record. Samuelson was also the first ski racer, first to go over a jump ramp, first to slalom ski, and the first to put on a water ski show.

1922 Radial arm saw

A radial arm saw has a circular saw mounted on a sliding horizontal arm. In addition to making length cuts a radial arm saw may be configured with a dado blade to create cuts for dado, rabbet or half lap joints. Some radial arm saws allow the blade to be turned parallel to the back fence allowing a rip cut to be performed. In 1922, Raymond De Walt of Bridgeton, New Jersey invented the radial arm saw. A patent was applied for in 1923 and awarded to De Walt in 1925.

1922 Audiometer

1922 Neutrodyne

1923 Bulldozer

A bulldozer is a crawler or a continuous tracked tractor, equipped with a substantial metal plate or blade, used to push large quantities of soil, sand, or rubble during construction work. In 1923, a farmer named James Cummings and a draftsman named J. Earl McLeod co-invented and created the first designs. A replica is on display at the city park in Morrowville, Kansas where the two built the first bulldozer.

1923 Cotton swab

Cotton swabs consist of a small wad of cotton wrapped around either one or both ends of a small rod. They are commonly used in a variety of applications including first aid, cosmetics application, for cleaning, and arts & crafts. The cotton swab was invented by Leo Gerstenzang in 1923, who invented the product after attaching wads of cotton to a toothpick. His product, which he named "Baby Gays", went on to become the most widely sold brand name, "Q-tip".

1923 Instant camera

An instant camera is a type of camera with self-developing film. The earliest instant camera, which consisted of a camera and portable darkroom in a single compartment, was invented in 1923 by Samuel Shlafrock. In 1947, Edwin H. Land invented a new camera that produced photographic images in 60 seconds. A colored photograph model would follow in the 1960s and eventually receive more than 500 patents for Land's innovations in light and plastic technologies.

1924 Locking pliers

1924 Cheeseburger

A cheeseburger is a hamburger with cheese added to it. Traditionally the cheese is placed on top of the patty, but the burger can include many variations in structure, ingredients, and composition. The term itself is a portmanteau of the words "cheese" and "hamburger." The cheese is usually sliced, and then added to the cooking hamburger patty shortly before the patty finishes cooking which allows the cheese to melt. Lionel C. Sternberger is believed to have invented the "cheese hamburger" in the 1920s in the Northeast portion of Los Angeles County. The earliest year attributed to the invention of the cheeseburger by Sternberger is in 1924, while others claimed that he invented it as late as 1926. According to "American Heritage", "a local restaurateur was identified as the inventor of the cheeseburger at his death in 1964. Cooking at his father's short-order joint in Pasadena in the early 1920s, the lad experimentally tossed a slice (variety unknown) on a hamburger 'and lo! the cheeseburger sizzled to life."

1924 Earth inductor compass

The Earth inductor compass is a device for determining aircraft direction using the magnetic field of the Earth. The operation of the compass is based on the principle of electromagnetic induction with the Earth's magnetic field acting as the induction field for an electric generator. A variation generated voltage, thus allows the Earth inductor compass to determine direction. The earth inductor compass is an American invention. It was designed in 1924 by Morris Titterington at the Pioneer Instrument Company. Designed to compensate for the weaknesses of the magnetic compass, the Earth inductor compass provided pilots with a more stable and reliable reference instrument.

1924 Gas chamber execution

1924 Moviola

1924 Radio altimeter

1925 Automatic volume control

1925 Masking tape

1925 Reuben sandwich

1926 Tilt-A-Whirl

1926 Garage door opener

A garage door opener is a motorized device that opens and closes a garage door. Most are controlled by switches on the garage wall, as well as by a remote control carried in the garage owner's vehicle. In 1926, the electric garage door opener was invented by C.G. Johnson, the inventor of the garage door and founder of the Overhead Door Corporation.

1926 Power steering
Power steering is a system for reducing the steering effort on vehicles by using an external power source to assist in turning the roadwheels. In 1926, Francis W. Davis of Waltham, Massachusetts invented power steering.

1926 Drive through
A drive-through, or drive-thru, allows customers to purchase products without leaving their cars. In 1926, City Center Bank, which became UMB Financial Corporation under R. Crosby Kemper opened what is considered the first drive-up window. In-n-Out Burger claims to have built the first drive-through restaurant in 1948. Harry and Esther Snyder, the chain's founders, built their first restaurant in Baldwin Park, California, with a two-way speaker to enable patrons to order directly from their cars without the intermediation of a carhop.

1926 Liquid-fuel rocket

The liquid-fuel rocket is a rocket with an engine that uses propellants in liquid form. On March 16, 1926 in Auburn, Massachusetts, Dr. Robert H. Goddard, the "father of modern rocketry", launched the first liquid-fueled rocket in history, which used liquid oxygen and gasoline as propellants.

1927 Bread slicer
Sliced bread is a loaf of bread which has been pre-sliced and packaged for commercial convenience. The automatic commercial bread slicer was invented in 1927 by Otto Frederick Rohwedder. His machine both sliced and wrapped a loaf of bread. In 1928, the bread slicer was improved by Gustav Papendick, a baker from St. Louis, Missouri.

1927 Jukebox
A jukebox is a partially automated music-playing device, usually a coin-operated machine, that can play specially selected songs from self-contained media. The traditional jukebox is rather large with a rounded top and has colored lighting on the front of the machine on its vertical sides. The classic jukebox has buttons with letters and numbers on them that, when combined, are used to indicate a specific song from a particular record. The Automatic Music Instrument Company built and introduced the first electric automated musical instrument which later became known as the jukebox during the 1930s.

1927 Garbage disposal
A garbage disposal is a device, usually electrically powered, installed under a kitchen sink between the sink's drain and the trap which shreds food waste into pieces small enough to pass through plumbing. The garbage disposal was invented in 1927 by John W. Hammes. After eleven years of development, his InSinkErator company put his disposer on the market in 1968.

1927 Pressure washer

A pressure washer is a high pressure mechanical sprayer that can be used to remove loose paint, mold, grime, dust, mud, and dirt from surfaces and objects such as buildings, vehicles, and concrete road surfaces. Frank Ofeldt in the United States invented the steam pressure washer or "high-pressure Jenny" in 1927.

1927 Resonator guitar
A resonator guitar or resophonic guitar is an acoustic guitar whose sound is produced by one or more spun metal cones resonators instead of the wooden sound board (guitar top/face). The resonator guitar was invented in 1927 by John Dopyera.

1927 Kool-Aid
Kool-Aid is a powdered drink mix that comes in an assortment of different flavors. "Kool-Ade" was invented in 1927 by Edwin Perkins in Hastings, Nebraska. Perkins devised a method of removing the liquid from a drink called "Fruit Smack" so the remaining powder could be re-packaged in envelopes, which Perkins designed and printed, all under a new name to be called "Kool-Ade". The name of the powdered drink was later to be changed at a later time to Kool-Aid.

1927 Corn dog

The corn dog, pogo, dagwood dog, pluto pup or corny dog is a hot dog coated in cornbread batter and deep fried in hot oil, although some are baked. Almost all corn dogs are served on wooden sticks, though some early versions were stickless. Although a contending topic as numerous claims of the origins of the corn dog have surfaced, the earliest reference to what resembles a corn dog appeared in U.S. patent 1,706,491 filed in 1927 by Stanley S. Jenkins and issued in 1929. A competing claim to the invention of the corn dog is by George Boyington, the creator of Pronto Pups (made of pancake batter) who in 1938 or 1939, created a "batter-dipped, deep fried hot dog" after a rain storm in Rockaway Beach, Oregon ruined and made his hot dogs mushy. Another story is that Neil Fletcher supposedly invented corn dogs, first selling them at the Texas State Fair in 1942.

1927 Negative feedback amplifier

1927 Quartz clock

1928 Recliner

1928 Ice cube tray

1928 Bubble gum

1928 Clip-on tie

1928 Electric razor

1928 Iron lung

1929 Freon

1929 Tampon (applicator)

1929 Eyelash curler

1929 Sunglasses

Sunglasses or sun glasses are a visual aid which feature lenses that are coloured or darkened to prevent strong light from reaching the eyes. For centuries, Chinese judges had routinely worn smoke-colored quartz lenses to conceal their eye expressions in court. However, these were not intended for blocking sunlight from eyes. It wasn't until the 20th century that what is now considered to be sunglasses were invented. In 1929, Sam Foster invented and mass-produced the first tinted eyewear pieces solely intended to block out sunlight.

1929 Frozen food

Frozen food is food preserved by the process of freezing. Freezing food is a common method of food preservation which slows both food decay and, by turning water to ice, makes it unavailable for most bacterial growth and slows down most chemical reactions. Clarence Birdseye offered his quick-frozen foods to the public. Birdseye got the idea during fur-trapping expeditions to Labrador in 1912 and 1916, where he saw the natives use freezing to preserve foods.

1929 Cyclotron

1930 Tiltrotor

A tiltrotor is an aircraft which uses a pair or more of powered rotors (sometimes called "proprotors") mounted on rotating shafts or nacelles at the end of a fixed wing for lift and propulsion, and combines the vertical lift capability of a helicopter with the speed and range of a conventional fixed-wing aircraft. In September 1930, George Lehberger devised the basic concept of tilt rotor aircraft, that is, a relatively low disc loading thruster (propeller) that can tilt its axis from the vertical (for vertical lift) to the horizontal (for propulsive thrust). On September 16, 1930, Lehberger was issued U.S. patent #1,775,861.

1930 Car audio

Car audio/video (car AV) is a sound or video system fitted in an automobile. In 1930, the Galvin Corporation introduced the first commercial car radio, the Motorola model 5T71, which sold for between $110 and $130 and could be installed in most popular automobiles. Inventors Paul Galvin and Joe Galvin came up with the name Motorola when their company started manufacturing car radios.

1930 Cheesesteak

A cheesesteak, or a Philly cheesesteak, is a long, crusty roll filled with thinly sliced sautéed ribeye beef and melted cheese. Generally, the cheese of choice is Cheez Whiz, but American and provolone are common substitutions. The art of cheesesteak preparation lies in the balance of flavors, textures and what is often referred to as the "drip" factor. Other toppings may include fried onions, sautéed mushrooms, ketchup and hot or sweet peppers. The cheesesteak was invented in 1930 by Philadelphian hot dog vendor Pat Olivieri who one day decided to substitute beef instead of a hot dog in a hoagie bun. A taxicab driver noticed the alluring aroma and asked for his own sandwich. Through word of mouth, Olivieri's sandwiches the following day were highly sought after by taxi cab drivers around Philadelphia. Due to booming business, Olivieri soon opened up his own shop, Pat's King of Steaks on 9th Street and Passyunk Avenue. Eventually, according to legend, he added cheese to the steak. The cheesesteak is considered to be a cultural icon of the city of Philadelphia.

1930 Bathysphere

1930 Chocolate chip cookie

1930 Thermistor

1931 Electric guitar

An electric guitar is a guitar using pickups to convert its metal string vibration into electricity. This is amplified with an instrument amplifier. The output is altered with guitar effects such as reverb or distortion. The earliest electric guitar, known as a "frying pan", was a hollow bodied acoustic instrument with tungsten steel pickups invented by George Beauchamp and Adolph Rickenbacker in 1931. The electric guitar was a key instrument in the development of musical styles that emerged since the late 1940s, such as Chicago blues, early rock and roll, rockabilly, and 1960s blues rock. Electric guitars are used in almost every popular music genre. U.S. patent #2,089,171 was filed by Beauchamp on June 2, 1934 and issued on August 10 1937.

1931 Strobe light

The strobe light, commonly called a strobe, is a device used to produce regular flashes of light. Modern uses of strobe lights serve a purpose for safety warning, and motion detection. Strobes can be found atop most police cars, ambulances, and fire trucks. The origin of strobe lighting dates to 1931, when Harold Eugene Edgerton invented a flashing lamp to make an improved stroboscope for the study of moving objects, eventually resulting in dramatic photographs of objects such as bullets in flight.

1931 Aerogel

Aerogel is a low-density solid-state material derived from gel in which the liquid component of the gel has been replaced with gas. The result is an extremely low-density solid with several remarkable properties, most notably its effectiveness as a thermal insulator. It was first invented by Samuel Stephens Kistler in 1931, as a result of a bet with Charles Learned over who could replace the liquid inside of a Fruit preserves jar with gas without causing shrinkage.

1931 Bug zapper

1932 Miniature snap-action switch

1932 Toilet brush

1932 Golf cart

1932 Staple remover

1932 Radio telescope

A radio telescope is a form of directional radio antenna used in radio astronomy. They differ from optical telescopes in that they operate in the radio frequency portion of the electromagnetic spectrum where they can detect and collect data on radio sources. Radio telescopes are typically large parabolic or dish antenna used singularly or in an array. Karl Guthe Jansky started the field of radio astronomy serendipitous in 1932 when his directional antenna found radio static that he later identified as coming from the Milky Way.

1932 Tape dispenser

A tape dispenser holds a roll of tape and has a mechanism on one end to easily shear the tape. Dispensers vary widely based on the tape they dispense. Clear tape dispensers are commonly made of plastic, and may be disposable. Other dispensers are stationary and may have sophisticated features to control tape usage and improve ergonomics. The first tape dispenser with a built-in cutting edge was invented in 1932 by John A. Borden, another 3M employee.

1933 Landing Vehicle Tracked

A Landing Vehicle Tracked (LVT), also known as amtracks, alligators, or in their fire support variants as buffaloes, were amphibious tracked vehicles capable of crawling out of the water and onto the beach and beyond. Used primarily by the United States Armed Forces in the Pacific War against the Empire of Japan during World War II, later versions were thinly armored, and some were equipped with a light tank turret to provide fire support, making them equivalent to light amphibious tanks. Highly versatile in their use, LVT's landed supplies ashore at Guadalcanal and soldiers ashore at Tarawa, other variations of the LVT were equipped with flamethrowers during the Peleliu Campaign. The LVT was derived from the "Alligator", an amphibious vehicle invented by Donald Roebling in 1933 as a rescue vehicle for downed aviators in the Florida Everglades.

1933 Multiplane camera

The multiplane camera is a special motion picture camera used in the traditional animation process that moves a number of pieces of artwork past the camera at various speeds and at various distances from one another, creating a three-dimensional effect, although not stereoscopic. Various parts of the artwork layers are left transparent, to allow other layers to be seen behind them. The movements are calculated and photographed frame-by-frame, with the result being an illusion of depth by having several layers of artwork moving at different speeds. The further away from the camera, the slower the speed. The multiplane effect is sometimes referred to as a parallax process. As a former director and animator of Walt Disney Studios, Ub Iwerks in 1933 invented the multiplane camera using four layers of flat artwork before a horizontal camera.

1933 Frequency modulation

1933 Impact sprinkler

An impact sprinkler is a type of irrigation sprinkler that pivots on a bearing on top of its threaded attachment nut, and is driven in a circular motion by a spring-loaded arm that is pushed back by the water stream, then returning to "impact" the stream. This produces an intermittent diffusion of the stream that provides a uniform waterfall closer to the sprinkler. In 1933, the impact sprinkler was invented and patented by lemon tree grower and farmer Orton Englehardt of Glendora, California.

1934 Trampoline (modern)

A trampoline is a gymnastic and recreational device consisting of a piece of taut, strong fabric stretched over a steel frame using many coiled springs to provide a rebounding force which propels the jumper high into the air. In a trampoline, the fabric is not elastic itself; the elasticity is provided by the springs which connect it to the frame. While the trampoline is an old invention which relied on crude and flawed designs, the modern trampoline was invented by George Nissen and Larry Griswold around 1934.

1934 Acrostic (puzzle)

An acrostic is a type of word puzzle, related somewhat to crossword puzzles, that uses an acrostic form with lettered clues and numbered blanks. The acrostic puzzle was invented in 1934 by Elizabeth Kingsley, first appearing in the March 31 edition of the "Saturday Evening Post".

1935 Richter magnitude scale

1935 Black light

1935 Parking meter

1935 Surfboard fin

1935 pH meter

1935 Gomco clamp

1936 Reed switch

A reed switch is an electrical switch consisting of two ferromagnetic and specially shaped contact blades (reeds) positioned in a hermetically sealed glass tube with a gap between them and in a protective atmosphere. Operated by an applied magnetic field, reed switches are used as reed relays, automotive sensors, robotics sensors, security sensors and are found in many toys and games. The reed switch was invented in 1936 by W. B. Elwood at Bell Telephone Laboratories.

1936 Phillips-head screw

The Phillips-head screw is a crosshead screw design lying in its self-centering property, useful on automated production lines that use power screwdrivers. The Phillips-head screw was invented and patented by Henry F. Phillips in 1936.

1936 Stock car racing

Stock car racing is a form of automobile racing. Shorter ovals are called short tracks, unpaved short tracks are called dirt tracks, and longer ovals are known as superspeedways. On March 8, 1936, the first stock car race was held on the Daytona Beach Road Course, promoted by local racer Sig Haugdahl. The race was 78 laps (250 miles) long for street-legal family sedans sanctioned by the American Automobile Association (AAA) for cars built in 1935 and 1936. The city posted a $5000 purse with $1700 for the winner. In 1948, stock car racing became a regulated sport when Bill France, Sr. created NASCAR.

1936 Programming languages

A programming language is a machine-readable artificial language. Programming languages can be used to create programs that specify the behavior of a machine, to express algorithms precisely, or as a mode of human communication. The first programming languages predate the modern computer. In mathematical logic and computer science, lambda calculus, also written as λ-calculus, is a formal system designed to investigate function definition, function application and recursion. It was invented by Alonzo Church and Stephen Cole Kleene in the 1930s as part of an investigation into the foundations of mathematics, but has now emerged as a useful tool in the investigation of problems in computability, recursion theory, and as a fundamental basis and a modern paradigm to computer programming and software languages.

1936 Compact fluorescent lamp

A compact fluorescent lamp is a fluorescent lamp designed to replace an incandescent lightbulb. Some CFL's fit into light fixtures formerly used for incandescent lamps and they are designed to produce the same amount of visible light found in incandescent light. CFLs generally use 70% less energy and have a longer rated life. In 1941, George Inman devised the first practical fluorescent lamp while working for General Electric. The key patent for this light source, U.S. patent #2,259,040 was filed by Inman on April 22, 1936 and issued to him on October 14, 1941. In 1976, Edward E. Hammer invented the first helical or spiraled compact fluorescent lamp, but due to the difficulty of the manufacturing process for coating the interior of the spiral glass tube, General Electric did not manufacture or sell the device. Other companies began manufacturing and selling the device in 1995.

1936 Chair lift

A chair lift is a type of aerial lift, which consists of a continuously circulating steel cable loop strung between two end terminals and usually over intermediate towers, carrying a series of chairs. They are the primary onhill transport at most ski areas, but are also found at amusement parks, various tourist attractions, and increasingly, in urban transport. James Curran, an engineer from the Union Pacific Railroad, invented and built the first chair lift in the world. Known as the Proctor Mountain Ski Lift, it was located in Sun Valley, Idaho.

1936 Strain gauge

A strain gauge is a device used to measure the strain of an object. As the object is deformed, the foil is deformed, causing its electrical resistance to change. The strain gauge was invented in 1936 by Edward E. Simmons, a professor at the California Institute of Technology, and re-invented in 1938 by Arthur C. Ruge, an earthquake specialist at the Massachusetts Institute of Technology.

1936 Bass guitar

The bass guitar is a stringed instrument played primarily with the fingers or thumb (either by plucking, slapping, popping, tapping, or thumping), or by using a plectrum. The bass guitar is similar in appearance and construction to an electric guitar, but with a longer neck and scale length, and four, five, or six strings. In 1936, the Audiovox bass, the earliest electric solidbody bass guitar made out of walnut and neck-through construction, was invented by Paul Tutmarc of Seattle, Washington. Later in 1951, the bass guitar was perfected when Leo Fender introduced the precision bass, a fretted, solidbody instrument.

1937 O-ring

1937 Photosensitive glass

1937 Digital computer

1937 Shopping cart

A shopping cart is a metal or plastic basket on wheels supplied by a shop, especially a supermarket, for use by customers inside the shop for transport of merchandise to the check-out counter during shopping. Often, customers are allowed to leave the carts in the parking lot, and store personnel return the carts to the shop. The first shopping cart was invented by Sylvan Goldman in 1937, owner of the Humpty Dumpty supermarket chain in Oklahoma City.

1937 Sunglasses (polarized)

Polarized sunglasses are protective eyewear which incorporate oscillated lenses shifting the sun's rays in the opposite direction. Polarized sunglasses were invented in 1937 by Edwin Land.

1937 Klystron

A klystron is a specialized linear-beam vacuum tube. Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern particle accelerator. Russell and Sigurd Varian of Stanford University are generally considered to be the inventors. Their prototype was completed in August 1937.

1937 Cyclamate

1938 Beach ball

A beach ball is an inflatable ball for beach and water games. Their large size and light weight take little effort to propel; they travel very slowly and generally must be caught with two hands, making them ideal for lazy games and for children. Their lightness and size make them difficult to use in even moderate wind. The beach ball was invented in California by Jonathon DeLonge in 1938.

1938 Fiberglass

The technique of heating and drawing glass into fine fibers has been used for millennia. The use of these fibers for textile applications is more recent. The first commercial production of fiberglass was in 1936. In 1938, fiberglass was invented by Russell Games Slayter of Owens-Corning.

1938 Xerography

Xerography, which means "dry writing" in Greek, is a process of making copies. Xerography makes copies without using ink. In this process, static electricity charges a lighted plate; a plastic powder is applied to the areas of the page to remain white. The photocopier was invented in 1938 by Chester Floyd Carlson who marketed his revolutionary device to about 20 companies before he could interest any. The Haloid Company, later called the Xerox Corporation, marketed it, and xerography eventually became common and inexpensive.

1938 Nylon

1938 Operant conditioning chamber

1938 Soft serve ice cream

Not to be confused with regular ice cream of the slow, churned type which was invented in China over two millennia ago, soft serve is a distinctive type of frozen dessert that is similar to, but much softer than, ice cream. In 1938, J.F. "Grandpa" McCullough and his son Alex co-invented soft serve ice cream, devising a new way to serve ice cream in its soft, creamy form that it takes before going into the deep freeze to make it scoopable. After Alex McCullough commissioned Harry Oltz in 1939 to design the first soft serve ice cream machine, similar to ones used for making frozen custard, the Dairy Queen franchise was founded when Sherb Noble opened the first store in 1940.

1938 Teflon

In chemistry, polytetrafluoroethylene is a synthetic fluoropolymer which finds numerous applications. PTFE is best known by the DuPont brand name Teflon. PTFE was accidentally invented by Roy Plunkett of Kinetic Chemicals in 1938.

1939 Yield sign

In road transport, a yield sign or give way sign indicates that a vehicle driver must prepare to stop if necessary to let a driver on another approach proceed. However, there is no need to stop if his way is clear. A driver who stops has yielded his right of way to another. The yield sign, but not the yield traffic rule itself, was invented in 1939 by Tulsa police officer Clinton Riggs.

1939 VU meter

A VU meter is often included in analog circuit, audio equipment to display a signal level in Volume Units. It is intentionally a "slow" measurement, averaging out peaks and troughs of short duration to reflect the perceived loudness of the material. It was originally invented in 1939 by the combined effort of Bell Labs and broadcasters CBS and NBC for measuring and standardizing the levels of telephone lines. The instrument used to measure VU is called the volume indicator (VI) instrument. Most users ignore this and call it a VU meter.

1939 Starting gate

1939 Twist tie

1939 Automated teller machine

An automated teller machine (ATM) is a computerized telecommunications device that provides the clients of a financial institution with access to financial transactions in a public space without the need for a cashier, human clerk or bank teller. ATMs are known by various other names including automatic banking machine, cash machine, and various regional variants derived from trademarks on ATM systems held by particular banks. Financial transcationssuch as deposits, withdrawals, and transfers of accounts may be conducted at ATM's by inserting an ATM card. In 1939, Armenian-American inventor Luther George Simjian initially came up with the idea of creating a hole-in-the-wall machine that would allow customers to make financial transactions. The idea was met with a great deal of skepticism after Citicorp tested it. In later years and after Simjian filed 20 patents related to the device, the idea and the gradual usage of ATM's became more widespread around the world.

1939 Vocoder

A vocoder, a portmanteau of the words voice and encoder, is an analysis and synthesis system, mostly used for speech. In the encoder, the input is passed through a multiband filter, each band is passed through an envelope follower, and the control signals from the envelope followers are communicated to the decoder. The decoder applies these control signals to corresponding filters in the (re)synthesizer. Research physicist Homer Dudley invented the Vocoder at Bell Labs in 1939 which served the purpose of improving the voice-carrying capabilities of his employer's telephone lines.

1940 Fluxgate magnetometer

1941 Aerosol Bomb
1941 Deodorant

1941 Acrylic fiber

1941 Electric guitar (solid body)

1942 Bazooka

A bazooka is a shoulder-fired, man-portable recoilless rocket anti-tank weapon that features a solid rocket motor for propulsion, allowing for high explosive (HE) and high-explosive anti-tank (HEAT) warheads to be delivered against armored vehicles, machine gun nests, and fortified bunkers at ranges beyond that of a standard thrown grenade or mine. The bazooka was co-invented in February 1942 by Edward Uhl, then a lieutenant in the United States Army, and Colonel Leslie Skinner.

1943 Magnetic proximity fuze

A magnetic proximity fuze is a type of proximity fuze that initiates a detonator in a piece of ordnance such as a land mine, naval mine, depth charge, or shell when the fuse's magnetic equilibrium is upset by a magnetic object such as a tank or a submarine. In 1943, Panayottis John Eliomarkakis of Philiadelphia filed U.S. patent #2,434,551 which was issued on January 13, 1948.

1943 Modern Coal Burning Steam Locomotive

This invention was only primarily used with steam locomotives that had booster valves or superchargers to heat the fire even hotter to produce extra power. The coal used was semi-bituminous and bituminous coal only inside the steam locomotives. Sadly, this invention lasted until 1960 when Diesel's fully replaced American railroads.

1943 Slinky

A Slinky or "Lazy Spring" is a toy consisting of a helical spring that stretches and can bounce up and down. It can perform a number of tricks, including traveling down a flight of steps end-over-end as it stretches and re-forms itself with the aid of gravity and its own momentum. The Slinky was invented in 1943 by American engineer Richard T. James while working in his home laboratory to invent a set of springs that could be used to support sensitive instruments on board ships and stabilize them even in rough seas. When he once accidentally knocked one of his springs off a shelf, James saw that, rather than flopping in a heap onto the floor, the spring "stepped" in a series of arcs from the shelf, to a stack of books, to a tabletop, to the floor, where it re-coiled itself and stood upright. In 1945, the James first exhibited his new toy at the Gimbels, a department store located in Philadelphia. He sold 400 Slinkys in 90 minutes which was the start of a sensation that continues to this day.

A microwave oven cooks or heats food by dielectric heating. Cooking food with microwaves was discovered by Percy Spencer on October 8, 1945, while building magnetrons for radar sets at Raytheon. Spencer was working on an active radar set when he noticed a strange sensation, and saw that a peanut candy bar he had in his pocket started to melt. Although he was not the first to notice this phenomenon, as the holder of 120 patents, Spencer was no stranger to discovery and experiment, and realized what was happening. The radar had melted his candy bar with microwaves. The first food to be deliberately cooked with microwaves was popcorn, and the second was an egg. In 1947, Raytheon under Percy Spencer demonstrated the world's first microwave oven built at the company which was called the "Radarange".

1945 Cruise control

Cruise control automatically controls the rate of motion of a motor vehicle. The driver sets the speed and the system will take over the throttle of the car to maintain the same speed. Cruise control was invented in 1945 by a blind inventor and mechanical engineer named Ralph Teetor. His idea was born out of the frustration of riding in a car driven by his lawyer, who kept speeding up and slowing down as he talked. The first car with Teetor's system was the Chrysler Imperial in 1958. This system calculated ground speed based on driveshaft rotations and used a solenoid to vary throttle position as needed.

1945 Block heater

Timelines of United States inventions
Related topics

Willis Haviland Carrier (November 26, 1876 – October 7, 1950) was an American engineer, best known for inventing modern air conditioning. Carrier invented the first electrical air conditioning unit in 1902. In 1915, he founded Carrier Corporation, a company specializing in the manufacture and distribution of heating, ventilation, and air conditioning (HVAC) systems.

Willis Carrier

Willis Carrier was born on November 26, 1876, in Angola, New York, the son of Duane Williams Carrier (1836–1908) and Elizabeth R. Haviland (1845–1888).

He studied at Cornell University, graduating in 1901 with a BSE degree.

In Buffalo, New York, on July 17, 1902, in response to an air quality problem experienced at the Sackett-Wilhelms Lithographing & Publishing Company of Brooklyn, Willis Carrier submitted drawings for what became recognized as the world's first modern air conditioning system. The 1902 installation marked the birth of air conditioning because of the addition of humidity control, which led to the recognition by authorities in the field that A/C must perform four basic functions:After several more years of refinement and field testing, on January 2, 1906, Carrier was granted for an "Apparatus for Treating Air," the world's first spray-type air conditioning equipment. It was designed to humidify or dehumidify air, heating water for the first function and cooling it for the second.

In 1906 Carrier discovered that "constant dew-point depression provided practically constant relative humidity," which later became known among air conditioning engineers as the "law of constant dew-point depression." On this discovery he based the design of an automatic control system, for which he filed a patent claim on May 17, 1907. was issued on February 3, 1914.

On December 3, 1911, Carrier presented what is perhaps the most significant document ever prepared on air conditioning –
"Rational Psychrometric Formulae" – at the annual meeting of the American Society of Mechanical Engineers. It became known as the "Magna Carta of Psychrometrics." This document tied together the concepts of relative humidity, absolute humidity, and dew-point temperature, thus making it possible to design air-conditioning systems to precisely fit the requirements at hand.

With the onset of World War I in late 1914, the Buffalo Forge Company, where Carrier had been employed for 12 years, decided to confine its activities entirely to manufacturing. The result was that seven young engineers pooled together their life savings of $32,600 to form the Carrier Engineering Corporation in New York on June 26, 1915. The seven were Carrier, J. Irvine Lyle, Edward T. Murphy, L. Logan Lewis, Ernest T. Lyle, Frank Sanna, Alfred E. Stacey, Jr., and Edmund P. Heckel. The company eventually settled on Frelinghuysen Avenue in Newark, New Jersey.

Despite the development of the centrifugal refrigeration machine and the commercial growth of air conditioning to cool buildings in the 1920s, the company ran into financial difficulties, as did many others, as a result of the Wall Street Crash in October 1929. In 1930, Carrier Engineering Corp. merged with Brunswick-Kroeschell Company and York Heating & Ventilating Corporation to form the Carrier Corporation, with Willis Carrier named Chairman of the Board.

The Great Depression slowed residential and commercial use of air conditioning. The company spread out over four cities in New Jersey and Pennsylvania until Carrier consolidated and moved his company to Syracuse, New York, in 1937. The company became one of the largest employers in central New York.

Willis Carrier's igloo in the 1939 New York World's Fair gave visitors a glimpse into the future of air conditioning, but before it became popular, World War II began. During the post-war economic boom of the 1950s, air conditioning began its tremendous growth in popularity. Today, air-conditioning and HVAC is a staple in many American homes. Ceiling fans and air conditioning are often used in conjunction; in summer, a ceiling fan allows the thermostat to be set several degrees higher; in winter, a fan can be set to a low speed on reverse direction to bring down stratified heat from the heating system.

In 1930, Carrier started Toyo Carrier and Samsung Applications in Japan and Korea. South Korea is now the largest producer for air conditioning in the world. The Carrier Corporation pioneered the design and manufacture of refrigeration machines to cool large spaces. By increasing industrial production in the summer months, air conditioning revolutionized American life. The introduction of residential air conditioning in the 1920s helped start the great migration to the Sunbelt. The company became a subsidiary of United Technologies Corporation in 1980. The Carrier Corporation remains a world leader in commercial and residential HVAC and refrigeration. In 2007, the Carrier Corporation had sales of more than $15 billion and employed some 45,000 people.

Carrier and all three of his wives, (Claire Seymour, d. 1912; Jennie Martin, d. 1939; Elizabeth Marsh Wise, d. 1964), are buried in Forest Lawn Cemetery in Buffalo, New York. Despite being married three times, Willis Carrier fathered only one child, Howard Carter Willis.

Carrier was a Presbyterian.

For his contributions to science and industry, Willis Carrier was awarded an engineering degree by Lehigh University in 1935 and an honorary Doctor of Letters degree by Alfred (NY) University in 1942; Carrier was awarded the Frank P. Brown Medal in 1942; and was inducted posthumously in the National Inventors Hall of Fame (1985) and the Buffalo Science Museum Hall of Fame (2008).

Modern air conditioning emerged from advances in chemistry during the 19th century, and the first large-scale electrical air conditioning was invented and used in 1902 by US inventor Willis Carrier. The introduction of residential air conditioning in the 1920s helped enable the great migration to the Sun Belt in the United States.

Air conditioning

Air conditioning (often referred to as AC, A/C, or air con) is the process of removing heat and moisture from the interior of an occupied space, to improve the comfort of occupants. Air conditioning can be used in both domestic and commercial environments. This process is most commonly used to achieve a more comfortable interior environment, typically for humans and other animals; however, air conditioning is also used to cool/dehumidify rooms filled with heat-producing electronic devices, such as computer servers, power amplifiers, and even to display and store some delicate products, such as artwork.

Air conditioners often use a fan to distribute the conditioned air to an occupied space such as a building or a car to improve thermal comfort and indoor air quality. Electric refrigerant-based AC units range from small units that can cool a small bedroom, which can be carried by a single adult, to massive units installed on the roof of office towers that can cool an entire building. The cooling is typically achieved through a refrigeration cycle, but sometimes evaporation or free cooling is used. Air conditioning systems can also be made based on desiccants (chemicals which remove moisture from the air) and subterraneous pipes that can distribute the heated refrigerant to the ground for cooling.

In the most general sense, air conditioning can refer to any form of technology that modifies the condition of air (heating, (de-) humidification, cooling, cleaning, ventilation, or air movement). In common usage, though, "air conditioning" refers to systems which cool air. In construction, a complete system of heating, ventilation, and air conditioning is referred to as HVAC.

Since prehistoric times, snow and ice were used for cooling. The business of harvesting ice during winter and storing for use in summer became popular towards the late 17th century. This practice was replaced by mechanical ice-making machines.

The basic concept behind air conditioning is said to have been applied in ancient Egypt, where reeds were hung in windows and were moistened with trickling water. The evaporation of water cooled the air blowing through the window. This process also made the air more humid, which can be beneficial in a dry desert climate. In ancient Rome, water from aqueducts was circulated through the walls of certain houses to cool them. Other techniques in medieval Persia involved the use of cisterns and wind towers to cool buildings during the hot season.

The 2nd-century Chinese mechanical engineer and inventor Ding Huan of the Han Dynasty invented a rotary fan for air conditioning, with seven wheels in diameter and manually powered by prisoners of the time. In 747, Emperor Xuanzong (r. 712–762) of the Tang Dynasty (618–907) had the "Cool Hall" ("Liang Dian" ) built in the imperial palace, which the "Tang Yulin" describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song Dynasty (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.

In the 17th century, the Dutch inventor Cornelis Drebbel demonstrated "Turning Summer into Winter" as an early form of modern air conditioning for James I of England by adding salt to water.

In 1758, Benjamin Franklin and John Hadley, a chemistry professor at Cambridge University, conducted an experiment to explore the principle of evaporation as a means to rapidly cool an object. Franklin and Hadley confirmed that evaporation of highly volatile liquids (such as alcohol and ether) could be used to drive down the temperature of an object past the freezing point of water. They conducted their experiment with the bulb of a mercury thermometer as their object and with a bellows used to speed up the evaporation. They lowered the temperature of the thermometer bulb down to while the ambient temperature was. Franklin noted that, soon after they passed the freezing point of water, a thin film of ice formed on the surface of the thermometer's bulb and that the ice mass was about thick when they stopped the experiment upon reaching. Franklin concluded: "From this experiment one may see the possibility of freezing a man to death on a warm summer's day."

In 1820, English scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida. He hoped to eventually use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities. Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. Though his process improved the artificial production of ice, his hopes for its success vanished soon afterwards when his chief financial backer died and Gorrie did not get the money he needed to develop the machine. According to his biographer, Vivian M. Sherlock, he blamed the "Ice King", Frederic Tudor, for his failure, suspecting that Tudor had launched a smear campaign against his invention. Dr. Gorrie died impoverished in 1855, and the dream of commonplace air conditioning went away for 50 years.

James Harrison's first mechanical ice-making machine began operation in 1851 on the banks of the Barwon River at Rocky Point in Geelong, Australia. His first commercial ice-making machine followed in 1853, and his patent for an ether vapor compression refrigeration system was granted in 1855. This novel system used a compressor to force the refrigeration gas to pass through a condenser, where it cooled down and liquefied. The liquefied gas then circulated through the refrigeration coils and vaporized again, cooling down the surrounding system. The machine produced of ice per day.

Though Harrison had commercial success establishing a second ice company back in Sydney in 1860, he later entered the debate over how to compete against the American advantage of ice-refrigerated beef sales to the United Kingdom. He wrote: "Fresh meat frozen and packed as if for a voyage, so that the refrigerating process may be continued for any required period", and in 1873 prepared the sailing ship "Norfolk" for an experimental beef shipment to the United Kingdom. His choice of a cold room system instead of installing a refrigeration system upon the ship itself proved disastrous when the ice was consumed faster than expected.

In 1902, the first modern electrical air conditioning unit was invented by Willis Carrier in Buffalo, New York. After graduating from Cornell University, Carrier found a job at the Buffalo Forge Company. There, he began experimenting with air conditioning as a way to solve an application problem for the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, New York. The first air conditioner, designed and built in Buffalo by Carrier, began working on 17 July 1902.

Designed to improve manufacturing process control in a printing plant, Carrier's invention controlled not only temperature but also humidity. Carrier used his knowledge of the heating of objects with steam and reversed the process. Instead of sending air through hot coils, he sent it through cold coils (filled with cold water). The air was cooled, and thereby the amount of moisture in the air could be controlled, which in turn made the humidity in the room controllable. The controlled temperature and humidity helped maintain consistent paper dimensions and ink alignment. Later, Carrier's technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of America was formed to meet rising demand. Over time, air conditioning came to be used to improve comfort in homes and automobiles as well. Residential sales expanded dramatically in the 1950s.

In 1906, Stuart W. Cramer of Charlotte was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning", using it in a patent claim he filed that year as an analogue to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company.

Shortly thereafter, the first private home to have air conditioning was built in Minneapolis in 1914, owned by Charles Gates. Realizing that air conditioning would one day be a standard feature of private homes, particularly in regions with warmer climate, David St. Pierre DuBose (1898-1994) designed a network of ductwork and vents for his home "Meadowmont", all disguised behind intricate and attractive Georgian-style open moldings. This building is believed to be one of the first private homes in the United States equipped for central air conditioning.

In 1945, Robert Sherman of Lynn, Massachusetts invented a portable, in-window air conditioner that cooled, heated, humidified, dehumidified, and filtered the air.

The first air conditioners and refrigerators employed toxic or flammable gases, such as ammonia, methyl chloride, or propane, that could result in fatal accidents when they leaked. Thomas Midgley, Jr. created the first non-flammable, non-toxic chlorofluorocarbon gas, "Freon", in 1928. The name is a trademark name owned by DuPont for any chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), or hydrofluorocarbon (HFC) refrigerant. The refrigerant names include a number indicating the molecular composition (e.g., R-11, R-12, R-22, R-134A). The blend most used in direct-expansion home and building comfort cooling is an HCFC known as chlorodifluoromethane (R-22).

Dichlorodifluoromethane (R-12) was the most common blend used in automobiles in the U.S. until 1994, when most designs changed to R-134A due to the ozone-depleting potential of R-12. R-11 and R-12 are no longer manufactured in the U.S. for this type of application, so the only source for air-conditioning repair purposes is the cleaned and purified gas recovered from other air conditioner systems. Several non-ozone-depleting refrigerants have been developed as alternatives, including R-410A. It was first commercially used by Carrier Corp. under the brand name "Puron".

Modern refrigerants have been developed to be more environmentally safe than many of the early chlorofluorocarbon-based refrigerants used in the early- and mid-twentieth century. These include HCFCs (R-22, as used in most U.S. homes before 2011) and HFCs (R-134a, used in most cars) have replaced most CFC use. HCFCs, in turn, are supposed to have been in the process of being phased out under the Montreal Protocol and replaced by HFCs such as R-410A, which lack chlorine. HFCs, however, contribute to climate change problems. Moreover, policy and political influence by corporate executives resisted change. Corporations insisted that no alternatives to HFCs existed. The environmental organization Greenpeace provided funding to a former East German refrigerator company to research an alternative ozone- and climate-safe refrigerant in 1992. The company developed a hydrocarbon mix of isopentane and isobutane, but as a condition of the contract with Greenpeace could not patent the technology, which led to its widespread adoption by other firms. Their activist marketing first in Germany led to companies like Whirlpool, Bosch, and later LG and others to incorporate the technology throughout Europe, then Asia, although the corporate executives resisted in Latin America, so that it arrived in Argentina produced by a domestic firm in 2003, and then finally with giant Bosch's production in Brazil by 2004.

In 1995, Germany made CFC refrigerators illegal. DuPont and other companies blocked the refrigerant in the U.S. with the U.S. EPA, disparaging the approach as "that German technology". Nevertheless, in 2004, Greenpeace worked with multinational corporations like Coca-Cola and Unilever, and later Pepsico and others, to create a corporate coalition called Refrigerants Naturally!. Then, four years later, Ben & Jerry's of Unilever and General Electric began to take steps to support production and use in the U.S. In 2011 the EPA decided in favor of the ozone- and climate-safe refrigerant for U.S. manufacture.

In the refrigeration cycle, heat is transported from a colder location to a hotter area. As heat would naturally flow in the opposite direction, work is required to achieve this. A refrigerator is an example of such a system, as it transports the heat out of the interior and into its environment. The refrigerant is used as the medium which absorbs and removes heat from the space to be cooled and subsequently ejects that heat elsewhere.

Circulating refrigerant vapor enters the compressor, where its pressure and temperature are increased. The hot, compressed refrigerant vapor is now at a temperature and pressure at which it can be condensed and is routed through a condenser. Here it is cooled by air flowing across the condenser coils and condensed into a liquid. Thus, the circulating refrigerant removes heat from the system and the heat is carried away by the air. The removal of this heat can be greatly augmented by pouring water over the condenser coils, making it much cooler when it hits the expansion valve.

The condensed, pressurized, and still usually somewhat hot liquid refrigerant is next routed through an expansion valve (often nothing more than a pinhole in the system's copper tubing) where it undergoes an abrupt reduction in pressure. That pressure reduction results in flash evaporation of a part of the liquid refrigerant, greatly lowering its temperature. The cold refrigerant is then routed through the evaporator. A fan blows the interior warm air (which is to be cooled) across the evaporator, causing the liquid part of the cold refrigerant mixture to evaporate as well, further lowering the temperature. The warm air is therefore cooled and is pumped by an exhaust fan/ blower into the room. To complete the refrigeration cycle, the refrigerant vapor is routed back into the compressor. In order for the process to have any efficiency, the cooling/evaporative portion of the system must be separated by some kind of physical barrier from the heating/condensing portion, and each portion must have its own fan to circulate its own "kind" of air (either the hot air or the cool air).

Modern air conditioning systems are not designed to draw air into the room from the outside, they only recirculate the increasingly cool air on the inside. Because this inside air always has some amount of moisture suspended in it, the cooling portion of the process always causes ambient warm water vapor to condense on the cooling coils and to drip from them down onto a catch tray at the bottom of the unit from which it must then be routed outside, usually through a drain hole. As this moisture has no dissolved minerals in it, it will not cause mineral buildup on the coils. This will happen even if the ambient humidity level is low. If ice begins to form on the evaporative fins, it will reduce circulation efficiency and cause the development of more ice, etc. A clean and strong circulatory fan can help prevent this, as will raising the target cool temperature of the unit's thermostat to a point that the compressor is allowed to turn off occasionally. A failing thermistor may also cause this problem. Refrigerators without a defrost cycle may have this same issue. Dust can also cause the fins to begin blocking air flow with the same undesirable result: ice.

By running an air conditioner's compressor in the opposite direction, the overall effect can be completely reversed and the indoor area will become heated instead of cooled (see heat pump). The engineering of physical and thermodynamic properties of gas–vapor mixtures is called psychrometrics.

A heat pump is an air conditioner in which the refrigeration cycle can be reversed, producing heating instead of cooling in the indoor environment. They are also commonly referred to as a "reverse cycle air conditioner". The heat pump is significantly more energy efficient than electric resistance heating. Some homeowners elect to have a heat pump system installed as a feature of a central air conditioner. When the heat pump is in heating mode, the indoor evaporator coil switches roles and becomes the condenser coil, producing heat. The outdoor condenser unit also switches roles to serve as the evaporator, and discharges cold air (colder than the ambient outdoor air).

Air-source heat pumps are more popular in milder winter climates where the temperature is frequently in the range of 4–13 °C (40–55 °F), because heat pumps become inefficient in more extreme cold. This is because ice forms on the outdoor unit's heat exchanger coil, which blocks air flow over the coil. To compensate for this, the heat pump system must temporarily switch back into the regular air conditioning mode to switch the outdoor evaporator coil "back" to being the condenser coil, so that it can heat up and defrost. A heat pump system will therefore have a form of electric resistance heating in the indoor air path that is activated only in this mode in order to compensate for the temporary indoor air cooling, which would otherwise be uncomfortable in the winter.

The icing problem becomes much more severe with lower outdoor temperatures, so heat pumps are commonly installed in tandem with a more conventional form of heating, such as a natural gas or oil furnace, which is used instead of the heat pump during harsher winter temperatures. In this case, the heat pump is used efficiently during the milder temperatures, and the system is switched to the conventional heat source when the outdoor temperature is lower.

Absorption heat pumps are a kind of air-source heat pump, but they do not depend on electricity to power them. Instead, gas, solar power, or heated water is used as a main power source. An absorption pump dissolves ammonia gas in water, which gives off heat. Next, the water and ammonia mixture is depressurized to induce boiling, and the ammonia is boiled off, which absorbs heat from the outdoor air.

Some more expensive fixed window air conditioning units have a true heat pump function. However, a window unit may only have an electric resistance heater.

In very dry climates, evaporative coolers, sometimes referred to as swamp coolers or desert coolers, are popular for improving coolness during hot weather. An evaporative cooler is a device that draws outside air through a wet pad, such as a large sponge soaked with water. The sensible heat of the incoming air, as measured by a dry bulb thermometer, is reduced. The temperature of the incoming air is reduced, but it is also more humid, so the total heat (sensible heat plus latent heat) is unchanged. Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite substantial.

Evaporative coolers tend to feel as if they are not working during times of high humidity, when there is not much dry air with which the coolers can work to make the air as cool as possible for dwelling occupants. Unlike other types of air conditioners, evaporative coolers rely on the outside air to be channeled through cooler pads that cool the air before it reaches the inside of a house through its air duct system; this cooled outside air must be allowed to push the warmer air within the house out through an exhaust opening such as an open door or window. These coolers cost less and are mechanically simple to understand and maintain.

Air conditioning can also be provided by a process called free cooling which uses pumps to circulate a coolant (typically water or a glycol mix) from a cold source, which in turn acts as a heat sink for the energy that is removed from the cooled space. Common storage media are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter boreholes, equipped with heat exchanger. Some systems with small storage capacity are hybrid systems, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added because the temperature of the storage gradually increases during the cooling season, thereby declining its effectiveness.

Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage (STES) so the cold of winter can be used for summer air conditioning. Free cooling and hybrid systems are mature technology.

Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 50% to 60% relative humidity in the occupied space.

Refrigeration air conditioning equipment usually reduces the absolute humidity of the air processed by the system. The relatively cold (below the dewpoint) evaporator coil condenses water vapor from the processed air, much like an ice-cold drink will condense water on the outside of a glass. Therefore, water vapor is removed from the cooled air and the relative humidity in the room is lowered. The water is usually sent to a drain or may simply drip onto the ground outdoors.
The heat is ejected by the air conditioners condenser, which is located outside of the area being cooled.

Most modern air-conditioning systems feature a dehumidification cycle during which the compressor runs while the fan is slowed as much as possible to reduce the evaporator temperature and therefore condense more water. When the temperature falls below a threshold, both the fan and compressor are shut off to mitigate further temperature drops; this prevents moisture on the evaporator from being blown back into the room. When the temperature rises again, the compressor restarts and the fan returns to low speed.

Occasionally, to thaw any ice produced, the fan runs with the compressor shut down; this function is less effective when ambient temperatures are low.

Inverter air conditioners use the inside coil temperature sensor to keep the evaporator as cold as possible. When the evaporator is too cold, the compressor is slowed or stopped with the indoor fan running.

A specialized air conditioner that is used only for dehumidifying is called a dehumidifier. It also uses a refrigeration cycle, but differs from a standard air conditioner in that both the evaporator and the condenser are placed in the same air path. A standard air conditioner transfers heat energy out of the room because its condenser coil releases heat outside. However, since all components of the dehumidifier are in the "same" room, no heat energy is removed. Instead, the electric power consumed by the dehumidifier remains in the room as heat, so the room is actually "heated", just as by an electric heater that draws the same amount of power.

In addition, if water is condensed in the room, the amount of heat previously needed to evaporate that water also is re-released in the room (the latent heat of vaporization). The dehumidification process is the inverse of adding water to the room with an evaporative cooler, and instead releases heat. Therefore, an in-room dehumidifier always will warm the room and reduce the relative humidity indirectly, as well as reducing the humidity directly by condensing and removing water.

Inside the unit, the air passes over the evaporator coil first, and is cooled and dehumidified. The now dehumidified, cold air then passes over the condenser coil where it is warmed up again. Then the air is released back into the room. The unit produces warm, dehumidified air and can usually be placed freely in the environment (room) that is to be conditioned.

Dehumidifiers are commonly used in cold, damp climates to prevent mold growth indoors, especially in basements. They are also used to protect sensitive equipment from the adverse effects of excessive humidity in tropical countries.

In a thermodynamically closed system, any power dissipated into the system that is being maintained at a set temperature (which is a standard mode of operation for modern air conditioners) requires that the rate of energy removal by the air conditioner increase. This increase has the effect that, for each unit of energy input into the system (say to power a light bulb in the closed system), the air conditioner removes that energy. To do so, the air conditioner must increase its power consumption by the inverse of its "efficiency" (coefficient of performance) times the amount of power dissipated into the system. As an example, assume that inside the closed system a 100 W heating element is activated, and the air conditioner has a coefficient of performance of 200%. The air conditioner's power consumption will increase by 50 W to compensate for this, thus making the 100 W heating element cost a total of 150 W of power.

It is typical for air conditioners to operate at "efficiencies" of significantly greater than 100%. However, it may be noted that the input electrical energy is of higher thermodynamic quality (lower entropy) than the output thermal energy (heat energy).

Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration", with each approximately equal to the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. The value is defined as 12,000 BTU per hour, or 3517 watts. Residential central air systems are usually from 1 to 5 tons (3.5 to 18 kW) in capacity.

For residential homes, some countries set minimum requirements for energy efficiency. In the United States, the efficiency of air conditioners is often (but not always) rated by the seasonal energy efficiency ratio (SEER). The higher the SEER rating, the more energy efficient is the air conditioner. The SEER rating is the BTU of cooling output during its normal annual usage divided by the total electric energy input in watt hours (W·h) during the same period.

this can also be rewritten as:

For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, would consume 5000/10 = 500 Watts of power on average.

The electrical energy consumed per year can be calculated as the average power multiplied by the annual operating time:

Assuming 1000 hours of operation during a typical cooling season (i.e., 8 hours per day for 125 days per year).

Another method that yields the same result, is to calculate the total annual cooling output:

Then, for a SEER of 10, the annual electrical energy usage would be:

SEER is related to the coefficient of performance (COP) commonly used in thermodynamics and also to the Energy Efficiency Ratio (EER). The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures, while SEER is calculated over a whole range of external temperatures (i.e., the temperature distribution for the geographical location of the SEER test). SEER is unusual in that it is composed of an Imperial unit divided by an SI unit. The COP is a ratio with the same metric units of energy (joules) in both the numerator and denominator. They cancel out, leaving a dimensionless quantity. Formulas for the approximate conversion between SEER and EER or COP are available.

From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43 units of heat energy are pumped per unit of work energy.

The United States now requires that residential systems manufactured in 2006 have a minimum SEER rating of 13 (although window-box systems are exempt from this law, so their SEER is still around 10).

Window unit air conditioners are installed in an open window. The interior air is cooled as a fan blows it over the evaporator. On the exterior the heat drawn from the interior is dissipated into the environment as a second fan blows outside air over the condenser. A large house or building may have several such units, allowing each room to be cooled separately.

In 1971, General Electric introduced a popular portable in-window air conditioner designed for convenience and portability.

Packaged terminal air conditioner (PTAC) systems are also known as wall-split air conditioning systems. They are ductless systems. PTACs, which are frequently used in hotels, have two separate units (terminal packages), the evaporative unit on the interior and the condensing unit on the exterior, with an opening passing through the wall and connecting them. This minimizes the interior system footprint and allows each room to be adjusted independently. PTAC systems may be adapted to provide heating in cold weather, either directly by using an electric strip, gas, or other heater, or by reversing the refrigerant flow to heat the interior and draw heat from the exterior air, converting the air conditioner into a heat pump. While room air conditioning provides maximum flexibility, when used to cool many rooms at a time it is generally more expensive than central air conditioning.

The first practical semi-portable air conditioning unit was invented by engineers at Chrysler Motors and offered for sale starting in 1935.

Split-system air conditioners come in two forms: mini-split and central systems. In both types, the inside-environment (evaporative) heat exchanger is separated by some distance from the outside-environment (condensing unit) heat exchanger.

A mini-split system typically supplies air conditioned and heated air to a single or a few rooms of a building. Multi-zone systems are a common application of ductless systems and allow up to 8 rooms (zones) to be conditioned from a single outdoor unit. Multi-zone systems typically offer a variety of indoor unit styles including wall-mounted, ceiling-mounted, ceiling recessed, and horizontal ducted. Mini-split systems typically produce per hour of cooling. Multi-zone systems provide extended cooling and heating capacity up to 60,000 Btu's.

Advantages of the ductless system include smaller size and flexibility for zoning or heating and cooling individual rooms. The inside wall space required is significantly reduced. Also, the compressor and heat exchanger can be located farther away from the inside space, rather than merely on the other side of the same unit as in a PTAC or window air conditioner. Flexible exterior hoses lead from the outside unit to the interior one(s); these are often enclosed with metal to look like common drainpipes from the roof. In addition, ductless systems offer higher efficiency, reaching above 30 SEER.

The primary disadvantage of ductless air conditioners is their cost. Such systems cost about US$1,500 to US$2,000 per ton (12,000 BTU per hour) of cooling capacity. This is about 30% more than central systems (not including ductwork) and may cost more than twice as much as window units of similar capacity."

An additional possible disadvantage is that the cost of installing mini splits can be higher than some systems. However, lower operating costs and rebates or other financial incentives—offered in some areas—can help offset the initial expense.

Central (ducted) air conditioning offers whole-house or large-commercial-space cooling, and often offers moderate multi-zone temperature control capability by the addition of air-louver-control boxes.

In central air conditioning, the inside heat-exchanger is typically placed inside the central furnace/AC unit of the forced air heating system which is then used in the summer to distribute chilled air throughout a residence or commercial building.

The heat-exchanger cools the air that is being forced through it by the furnace blower. As the warm air comes in contact with this cool surface the water in the air condenses. By pulling the water molecules from the air. According to the psychometric chart as relative humidity decreases in order to feel cool you will have to lower the temperature even more. A common way to counteract this effect is by installing a whole-home humidifier. Similarly, installing a high efficient system this need to turn the temperature down wont have such and influence on your energy costs.

A multi-split system is a conventional split system, which is divided into two parts (evaporator and condenser) and allows cooling or heating of several rooms with one external unit. In the outdoor unit of this air conditioner there is a more powerful compressor, ports for connecting several traces and automation with locking valves for regulating the volume of refrigerant supplied to the indoor units located in the room.

A large Multi Split System is called a Variable refrigerant flow system and can be used instead of a central air conditioner system, as it allows for higher energy efficiency but it is more expensive to purchase and install.

"Difference between split system and multi-split system":

Other common types of air conditioning system are multi-split systems, the difference between separate split system and multi-split system in several indoor units. All of them are connected to the main external unit, but the principle of their operation is similar to a simple split-system.

Its unique feature is the presence of one main external unit that connected to several indoor units. Such systems might be the right solution for maintaining the microclimate in several offices, shops, large living spaces. Just few of outdoor units do not worsen the aesthetic appearance of the building.The main external unit can be connected to several different indoor types: floor, ceiling, cassette, etc.

Before selecting the installation location of air conditioner, several main factors need to be considered. First of all, the direction of air flow from the indoor units should not fall on the place of rest or work area. Secondly, there should not be any obstacles on the way of the airflow that might prevent it from covering the space of the premises as much as possible. The outdoor unit must also be located in an open space, otherwise the heat from the house will not be effectively discharged outside and the productivity of the entire system will drop sharply. It is highly advisable to install the air conditioner units in easily accessible places, for further maintenance during operation.

The main problem when installing a multi-split system is the laying of long refrigerant lines for connecting the external unit to the internal ones. While installing a separate split system, workers try to locate both units opposite to each other, where the length of the line is minimal. Installing a multi-split system creates more difficulties, since some of indoor units can be located far from the outside. The first models of multi-split systems had one common control system that did not allow you to set the air conditioning individually for each room. However, now the market has a wide selection of multi-split systems, in which the functional characteristics of indoor units operate separately from each other.

The selection of indoor units has one restriction: their total power should not exceed the capacity of the outdoor unit. In practice, however, it is very common to see a multi-split system with a total capacity of indoor units greater than the outdoor capacity by at least 20%. However, it is wrong to expect better performance when all indoor units are turned on at the same time, since the total capacity of the whole system is limited by the capacity of the outdoor unit. Simply put, the outdoor unit will distribute all its power to all operating indoor units in such a way that some of the rooms may not have a very comfortable temperature level. However, the calculation of the total power is not simple, since it takes into account not only the nominal power of the units, but also the cooling capacity, heating, dehumidification, humidification, venting, etc.

A portable air conditioner can be easily transported inside a home or office. They are currently available with capacities of about and with or without electric-resistance heaters. Portable air conditioners are either evaporative or refrigerative.

The compressor-based refrigerant systems are air-cooled, meaning they use air to exchange heat, in the same way as a car radiator or typical household air conditioner does. Such a system dehumidifies the air as it cools it. It collects water condensed from the cooled air and produces hot air which must be vented outside the cooled area; doing so transfers heat from the air in the cooled area to the outside air.

A portable system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit.The portable units draw indoor air and expel it outdoors through a single duct. Many portable air conditioners come with heat as well as dehumidification function.

Hose systems, which can be "monoblock" or "air-to-air", are vented to the outside via air ducts. The "monoblock" type collects the water in a bucket or tray and stops when full. The "air-to-air" type re-evaporates the water and discharges it through the ducted hose and can run continuously.

A single-hose unit uses air from within the room to cool its condenser, and then vents it outside. This air is replaced by hot air from outside or other rooms (due to the negative pressure inside the room), thus reducing the unit's overall efficiency.

Modern units might have a coefficient of performance of approximately 3 (i.e., 1 kW of electricity will produce 3 kW of cooling). A dual-hose unit draws air to cool its condenser from outside instead of from inside the room, and thus is more effective than most single-hose units. These units create no negative pressure in the room.

Evaporative coolers, sometimes called "swamp coolers", do not have a compressor or condenser. Liquid water is evaporated on the cooling fins, releasing the vapor into the cooled area. Evaporating water absorbs a significant amount of heat, the latent heat of vaporisation, cooling the air. Humans and animals use the same mechanism to cool themselves by sweating.

Evaporative coolers have the advantage of needing no hoses to vent heat outside the cooled area, making them truly portable. They are also very cheap to install and use less energy than refrigerative air conditioners.

Air-conditioning engineers broadly divide air conditioning applications into "comfort" and "process" applications.

Comfort applications aim to provide a building indoor environment that remains relatively constant despite changes in external weather conditions or in internal heat loads.

Air conditioning makes deep plan buildings feasible, for otherwise they would have to be built narrower or with light wells so that inner spaces received sufficient outdoor air via natural ventilation. Air conditioning also allows buildings to be taller, since wind speed increases significantly with altitude making natural ventilation impractical for very tall buildings. Comfort applications are quite different for various building types and may be categorized as:

Women have, on average, a significantly lower resting metabolic rate than men. Using inaccurate metabolic rate guidelines for air conditioning sizing can result in oversized and less efficient equipment, and setting system operating setpoints too cold can result in reduced worker productivity.

In addition to buildings, air conditioning can be used for many types of transportation, including automobiles, buses and other land vehicles, trains, ships, aircraft, and spacecraft.

Air conditioning is common in the US, with 88% of new single-family homes constructed in 2011 including air conditioning, ranging from 99% in the South to 62% in the West. In Canada, air conditioning use varies by province. In 2013, 55% of Canadian households reported having an air conditioner, with high use in Manitoba (80%), Ontario (78%), Saskatchewan (67%), and Quebec (54%) and lower use in Prince Edward Island (23%), British Columbia (21%), and Newfoundland and Labrador (9%). In Europe, home air conditioning is generally less common. Southern European countries such as Greece have seen a wide proliferation of home air-conditioning units in recent years. In another southern European country, Malta, it is estimated that around 55% of households have an air conditioner installed.
In India AC sales have dropped by 40% due to higher costs and stricter energy efficiency regulations.

Process applications aim to provide a suitable environment for a process being carried out, regardless of internal heat and humidity loads and external weather conditions. It is the needs of the process that determine conditions, not human preference. Process applications include these:

In both comfort and process applications, the objective may be to not only control temperature, but also humidity, air quality, and air movement from space to space.

In hot weather, air conditioning can prevent heat stroke, dehydration from excessive sweating and other problems related to hyperthermia. Heat waves are the most lethal type of weather phenomenon in developed countries. Air conditioning (including filtration, humidification, cooling and disinfection) can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where proper atmosphere is critical to patient safety and well-being. It is sometimes recommended for home use by people with allergies.

Poorly maintained water cooling towers can promote the growth and spread of microorganisms, such as "Legionella pneumophila", the infectious agent responsible for Legionnaires' disease, or thermophilic actinomycetes. As long as the cooling tower is kept clean (usually by means of a chlorine treatment), these health hazards can be avoided or reduced. Excessive air conditioning can have a negative effect on skin, causing it to dry out, and can also cause dehydration.

Innovation in air conditioning technologies continues, with much recent emphasis placed on energy efficiency. Production of the electricity used to operate air conditioners has an environmental impact, including the release of greenhouse gases.

Cylinder unloaders are a method of load control used mainly in commercial air conditioning systems. On a semi-hermetic (or open) compressor, the heads can be fitted with unloaders which remove a portion of the load from the compressor so that it can run better when full cooling is not needed. Unloaders can be electrical or mechanical.

According to a 2015 government survey, 87% of the homes in the United States use air conditioning and 65% of those homes have central air conditioning. Most of the homes with central air conditioning have programmable thermostats, but approximately two-thirds of the homes with central air do not use this feature to make their homes more energy efficient.

Alternatives to continual air conditioning can be used with less energy, lower cost, and with less environmental impact. These include:

In an automobile, the A/C system will use around 4 horsepower (3 kW) of the engine's power, thus increasing fuel consumption of the vehicle.

The selection of the working fluids (refrigerants) has a significant impact not only on the performance of the air conditioners but on the environment as well. Most refrigerants used for air conditioning contribute to global warming, and many also deplete the ozone layer. CFCs, HCFCs, and HFCs are potent greenhouse gases when leaked to the atmosphere.

The use of CFC as a refrigerant was once common, including the refrigerants R-11 and R-12 (sold under the brand name "Freon-12"). Freon refrigerants were commonly used during the 20th century in air conditioners due to their superior stability and safety properties. When they are released accidentally or deliberately, these chlorine-bearing refrigerants eventually reach the upper atmosphere. Once the refrigerant reaches the stratosphere, UV radiation from the Sun homolytically cleaves the chlorine-carbon bond, yielding a chlorine radical. These chlorine radicals catalyze the breakdown of ozone into diatomic oxygen, depleting the ozone layer that shields the Earth's surface from strong UV radiation. Each chlorine radical remains active as a catalyst until it binds with another radical, forming a stable molecule and quenching the chain reaction.

Prior to 1994, most automotive air conditioning systems used R-12 as a refrigerant. It was replaced with R-134a refrigerant, which has no ozone depletion potential. Old R-12 systems can be retrofitted to R-134a by a complete flush and filter/dryer replacement to remove the mineral oil, which is not compatible with R-134a.

R22 (also known as HCFC-22) has a global warming potential about 1,800 times higher than CO. It was phased out for use in new equipment by 2010, and is to be completely discontinued by 2020. Although these gasses can be recycled when air conditioning units are disposed of, uncontrolled dumping and leaking can release gas directly into the atmosphere.

In the UK, the Ozone Regulations came into force in 2000 and banned the use of ozone depleting HCFC refrigerants such as R22 in new systems. The Regulation banned the use of R22 as a "top-up" fluid for maintenance between 2010 (for virgin fluid) and 2015 (for recycled fluid). This means that equipment that uses R22 can still operate, as long as it does not leak. Although R22 is now banned, units that use the refrigerant can still be serviced and maintained.

The manufacture and use of CFCs has been banned or severely restricted due to concerns about ozone depletion (see also Montreal Protocol). In light of these environmental concerns, beginning on November 14, 1994, the U.S. Environmental Protection Agency has restricted the sale, possession and use of refrigerant to only licensed technicians, per rules under sections 608 and 609 of the Clean Air Act.

As an alternative to conventional refrigerants, other gases, such as CO (R-744), have been proposed. R-744 is being adopted as a refrigerant in Europe and Japan. It is an effective refrigerant with a global warming potential of 1, but it must use higher compression to produce an equivalent cooling effect.

In 1992, a non-governmental organization, Greenpeace, was spurred by corporate executive policies and requested that a European lab find substitute refrigerants. This led to two alternatives, one a blend of propane (R290) and isobutane (R600a), and one of pure isobutane. Industry resisted change in Europe until 1993, and in the U.S. until 2011, despite some supportive steps in 2004 and 2008 (see Refrigerant Development above).

In 1902, the first modern electrical air conditioning unit was invented by Willis Carrier in Buffalo, New York. After graduating from Cornell University, Carrier found a job at the Buffalo Forge Company. There, he began experimenting with air conditioning as a way to solve an application problem for the Sackett-Wilhelms Lithographing and Publishing Company in Brooklyn, New York. The first air conditioner, designed and built in Buffalo by Carrier, began working on 17 July 1902.

Air conditioning

Air conditioning (often referred to as AC, A/C, or air con) is the process of removing heat and moisture from the interior of an occupied space, to improve the comfort of occupants. Air conditioning can be used in both domestic and commercial environments. This process is most commonly used to achieve a more comfortable interior environment, typically for humans and other animals; however, air conditioning is also used to cool/dehumidify rooms filled with heat-producing electronic devices, such as computer servers, power amplifiers, and even to display and store some delicate products, such as artwork.

Air conditioners often use a fan to distribute the conditioned air to an occupied space such as a building or a car to improve thermal comfort and indoor air quality. Electric refrigerant-based AC units range from small units that can cool a small bedroom, which can be carried by a single adult, to massive units installed on the roof of office towers that can cool an entire building. The cooling is typically achieved through a refrigeration cycle, but sometimes evaporation or free cooling is used. Air conditioning systems can also be made based on desiccants (chemicals which remove moisture from the air) and subterraneous pipes that can distribute the heated refrigerant to the ground for cooling.

In the most general sense, air conditioning can refer to any form of technology that modifies the condition of air (heating, (de-) humidification, cooling, cleaning, ventilation, or air movement). In common usage, though, "air conditioning" refers to systems which cool air. In construction, a complete system of heating, ventilation, and air conditioning is referred to as HVAC.

Since prehistoric times, snow and ice were used for cooling. The business of harvesting ice during winter and storing for use in summer became popular towards the late 17th century. This practice was replaced by mechanical ice-making machines.

The basic concept behind air conditioning is said to have been applied in ancient Egypt, where reeds were hung in windows and were moistened with trickling water. The evaporation of water cooled the air blowing through the window. This process also made the air more humid, which can be beneficial in a dry desert climate. In ancient Rome, water from aqueducts was circulated through the walls of certain houses to cool them. Other techniques in medieval Persia involved the use of cisterns and wind towers to cool buildings during the hot season.

The 2nd-century Chinese mechanical engineer and inventor Ding Huan of the Han Dynasty invented a rotary fan for air conditioning, with seven wheels in diameter and manually powered by prisoners of the time. In 747, Emperor Xuanzong (r. 712–762) of the Tang Dynasty (618–907) had the "Cool Hall" ("Liang Dian" ) built in the imperial palace, which the "Tang Yulin" describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song Dynasty (960–1279), written sources mentioned the air conditioning rotary fan as even more widely used.

In the 17th century, the Dutch inventor Cornelis Drebbel demonstrated "Turning Summer into Winter" as an early form of modern air conditioning for James I of England by adding salt to water.

Modern air conditioning emerged from advances in chemistry during the 19th century, and the first large-scale electrical air conditioning was invented and used in 1902 by US inventor Willis Carrier. The introduction of residential air conditioning in the 1920s helped enable the great migration to the Sun Belt in the United States.

James Harrison's first mechanical ice-making machine began operation in 1851 on the banks of the Barwon River at Rocky Point in Geelong, Australia. His first commercial ice-making machine followed in 1853, and his patent for an ether vapor compression refrigeration system was granted in 1855. This novel system used a compressor to force the refrigeration gas to pass through a condenser, where it cooled down and liquefied. The liquefied gas then circulated through the refrigeration coils and vaporized again, cooling down the surrounding system. The machine produced of ice per day.

Though Harrison had commercial success establishing a second ice company back in Sydney in 1860, he later entered the debate over how to compete against the American advantage of ice-refrigerated beef sales to the United Kingdom. He wrote: "Fresh meat frozen and packed as if for a voyage, so that the refrigerating process may be continued for any required period", and in 1873 prepared the sailing ship "Norfolk" for an experimental beef shipment to the United Kingdom. His choice of a cold room system instead of installing a refrigeration system upon the ship itself proved disastrous when the ice was consumed faster than expected.

Designed to improve manufacturing process control in a printing plant, Carrier's invention controlled not only temperature but also humidity. Carrier used his knowledge of the heating of objects with steam and reversed the process. Instead of sending air through hot coils, he sent it through cold coils (filled with cold water). The air was cooled, and thereby the amount of moisture in the air could be controlled, which in turn made the humidity in the room controllable. The controlled temperature and humidity helped maintain consistent paper dimensions and ink alignment. Later, Carrier's technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of America was formed to meet rising demand. Over time, air conditioning came to be used to improve comfort in homes and automobiles as well. Residential sales expanded dramatically in the 1950s.

In 1906, Stuart W. Cramer of Charlotte was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning", using it in a patent claim he filed that year as an analogue to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company.

Shortly thereafter, the first private home to have air conditioning was built in Minneapolis in 1914, owned by Charles Gates. Realizing that air conditioning would one day be a standard feature of private homes, particularly in regions with warmer climate, David St. Pierre DuBose (1898-1994) designed a network of ductwork and vents for his home "Meadowmont", all disguised behind intricate and attractive Georgian-style open moldings. This building is believed to be one of the first private homes in the United States equipped for central air conditioning.

In 1945, Robert Sherman of Lynn, Massachusetts invented a portable, in-window air conditioner that cooled, heated, humidified, dehumidified, and filtered the air.

The first air conditioners and refrigerators employed toxic or flammable gases, such as ammonia, methyl chloride, or propane, that could result in fatal accidents when they leaked. Thomas Midgley, Jr. created the first non-flammable, non-toxic chlorofluorocarbon gas, "Freon", in 1928. The name is a trademark name owned by DuPont for any chlorofluorocarbon (CFC), hydrochlorofluorocarbon (HCFC), or hydrofluorocarbon (HFC) refrigerant. The refrigerant names include a number indicating the molecular composition (e.g., R-11, R-12, R-22, R-134A). The blend most used in direct-expansion home and building comfort cooling is an HCFC known as chlorodifluoromethane (R-22).

Dichlorodifluoromethane (R-12) was the most common blend used in automobiles in the U.S. until 1994, when most designs changed to R-134A due to the ozone-depleting potential of R-12. R-11 and R-12 are no longer manufactured in the U.S. for this type of application, so the only source for air-conditioning repair purposes is the cleaned and purified gas recovered from other air conditioner systems. Several non-ozone-depleting refrigerants have been developed as alternatives, including R-410A. It was first commercially used by Carrier Corp. under the brand name "Puron".

In 1995, Germany made CFC refrigerators illegal. DuPont and other companies blocked the refrigerant in the U.S. with the U.S. EPA, disparaging the approach as "that German technology". Nevertheless, in 2004, Greenpeace worked with multinational corporations like Coca-Cola and Unilever, and later Pepsico and others, to create a corporate coalition called Refrigerants Naturally!. Then, four years later, Ben & Jerry's of Unilever and General Electric began to take steps to support production and use in the U.S. In 2011 the EPA decided in favor of the ozone- and climate-safe refrigerant for U.S. manufacture.

In the refrigeration cycle, heat is transported from a colder location to a hotter area. As heat would naturally flow in the opposite direction, work is required to achieve this. A refrigerator is an example of such a system, as it transports the heat out of the interior and into its environment. The refrigerant is used as the medium which absorbs and removes heat from the space to be cooled and subsequently ejects that heat elsewhere.

Circulating refrigerant vapor enters the compressor, where its pressure and temperature are increased. The hot, compressed refrigerant vapor is now at a temperature and pressure at which it can be condensed and is routed through a condenser. Here it is cooled by air flowing across the condenser coils and condensed into a liquid. Thus, the circulating refrigerant removes heat from the system and the heat is carried away by the air. The removal of this heat can be greatly augmented by pouring water over the condenser coils, making it much cooler when it hits the expansion valve.

By running an air conditioner's compressor in the opposite direction, the overall effect can be completely reversed and the indoor area will become heated instead of cooled (see heat pump). The engineering of physical and thermodynamic properties of gas–vapor mixtures is called psychrometrics.

A heat pump is an air conditioner in which the refrigeration cycle can be reversed, producing heating instead of cooling in the indoor environment. They are also commonly referred to as a "reverse cycle air conditioner". The heat pump is significantly more energy efficient than electric resistance heating. Some homeowners elect to have a heat pump system installed as a feature of a central air conditioner. When the heat pump is in heating mode, the indoor evaporator coil switches roles and becomes the condenser coil, producing heat. The outdoor condenser unit also switches roles to serve as the evaporator, and discharges cold air (colder than the ambient outdoor air).

Air-source heat pumps are more popular in milder winter climates where the temperature is frequently in the range of 4–13 °C (40–55 °F), because heat pumps become inefficient in more extreme cold. This is because ice forms on the outdoor unit's heat exchanger coil, which blocks air flow over the coil. To compensate for this, the heat pump system must temporarily switch back into the regular air conditioning mode to switch the outdoor evaporator coil "back" to being the condenser coil, so that it can heat up and defrost. A heat pump system will therefore have a form of electric resistance heating in the indoor air path that is activated only in this mode in order to compensate for the temporary indoor air cooling, which would otherwise be uncomfortable in the winter.

The icing problem becomes much more severe with lower outdoor temperatures, so heat pumps are commonly installed in tandem with a more conventional form of heating, such as a natural gas or oil furnace, which is used instead of the heat pump during harsher winter temperatures. In this case, the heat pump is used efficiently during the milder temperatures, and the system is switched to the conventional heat source when the outdoor temperature is lower.

Absorption heat pumps are a kind of air-source heat pump, but they do not depend on electricity to power them. Instead, gas, solar power, or heated water is used as a main power source. An absorption pump dissolves ammonia gas in water, which gives off heat. Next, the water and ammonia mixture is depressurized to induce boiling, and the ammonia is boiled off, which absorbs heat from the outdoor air.

Some more expensive fixed window air conditioning units have a true heat pump function. However, a window unit may only have an electric resistance heater.

In very dry climates, evaporative coolers, sometimes referred to as swamp coolers or desert coolers, are popular for improving coolness during hot weather. An evaporative cooler is a device that draws outside air through a wet pad, such as a large sponge soaked with water. The sensible heat of the incoming air, as measured by a dry bulb thermometer, is reduced. The temperature of the incoming air is reduced, but it is also more humid, so the total heat (sensible heat plus latent heat) is unchanged. Some of the sensible heat of the entering air is converted to latent heat by the evaporation of water in the wet cooler pads. If the entering air is dry enough, the results can be quite substantial.

Evaporative coolers tend to feel as if they are not working during times of high humidity, when there is not much dry air with which the coolers can work to make the air as cool as possible for dwelling occupants. Unlike other types of air conditioners, evaporative coolers rely on the outside air to be channeled through cooler pads that cool the air before it reaches the inside of a house through its air duct system; this cooled outside air must be allowed to push the warmer air within the house out through an exhaust opening such as an open door or window. These coolers cost less and are mechanically simple to understand and maintain.

Air conditioning can also be provided by a process called free cooling which uses pumps to circulate a coolant (typically water or a glycol mix) from a cold source, which in turn acts as a heat sink for the energy that is removed from the cooled space. Common storage media are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter boreholes, equipped with heat exchanger. Some systems with small storage capacity are hybrid systems, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added because the temperature of the storage gradually increases during the cooling season, thereby declining its effectiveness.

Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage (STES) so the cold of winter can be used for summer air conditioning. Free cooling and hybrid systems are mature technology.

Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 50% to 60% relative humidity in the occupied space.

Refrigeration air conditioning equipment usually reduces the absolute humidity of the air processed by the system. The relatively cold (below the dewpoint) evaporator coil condenses water vapor from the processed air, much like an ice-cold drink will condense water on the outside of a glass. Therefore, water vapor is removed from the cooled air and the relative humidity in the room is lowered. The water is usually sent to a drain or may simply drip onto the ground outdoors.
The heat is ejected by the air conditioners condenser, which is located outside of the area being cooled.

Most modern air-conditioning systems feature a dehumidification cycle during which the compressor runs while the fan is slowed as much as possible to reduce the evaporator temperature and therefore condense more water. When the temperature falls below a threshold, both the fan and compressor are shut off to mitigate further temperature drops; this prevents moisture on the evaporator from being blown back into the room. When the temperature rises again, the compressor restarts and the fan returns to low speed.

Occasionally, to thaw any ice produced, the fan runs with the compressor shut down; this function is less effective when ambient temperatures are low.

Inverter air conditioners use the inside coil temperature sensor to keep the evaporator as cold as possible. When the evaporator is too cold, the compressor is slowed or stopped with the indoor fan running.

A specialized air conditioner that is used only for dehumidifying is called a dehumidifier. It also uses a refrigeration cycle, but differs from a standard air conditioner in that both the evaporator and the condenser are placed in the same air path. A standard air conditioner transfers heat energy out of the room because its condenser coil releases heat outside. However, since all components of the dehumidifier are in the "same" room, no heat energy is removed. Instead, the electric power consumed by the dehumidifier remains in the room as heat, so the room is actually "heated", just as by an electric heater that draws the same amount of power.

In addition, if water is condensed in the room, the amount of heat previously needed to evaporate that water also is re-released in the room (the latent heat of vaporization). The dehumidification process is the inverse of adding water to the room with an evaporative cooler, and instead releases heat. Therefore, an in-room dehumidifier always will warm the room and reduce the relative humidity indirectly, as well as reducing the humidity directly by condensing and removing water.

Inside the unit, the air passes over the evaporator coil first, and is cooled and dehumidified. The now dehumidified, cold air then passes over the condenser coil where it is warmed up again. Then the air is released back into the room. The unit produces warm, dehumidified air and can usually be placed freely in the environment (room) that is to be conditioned.

Dehumidifiers are commonly used in cold, damp climates to prevent mold growth indoors, especially in basements. They are also used to protect sensitive equipment from the adverse effects of excessive humidity in tropical countries.

In a thermodynamically closed system, any power dissipated into the system that is being maintained at a set temperature (which is a standard mode of operation for modern air conditioners) requires that the rate of energy removal by the air conditioner increase. This increase has the effect that, for each unit of energy input into the system (say to power a light bulb in the closed system), the air conditioner removes that energy. To do so, the air conditioner must increase its power consumption by the inverse of its "efficiency" (coefficient of performance) times the amount of power dissipated into the system. As an example, assume that inside the closed system a 100 W heating element is activated, and the air conditioner has a coefficient of performance of 200%. The air conditioner's power consumption will increase by 50 W to compensate for this, thus making the 100 W heating element cost a total of 150 W of power.

It is typical for air conditioners to operate at "efficiencies" of significantly greater than 100%. However, it may be noted that the input electrical energy is of higher thermodynamic quality (lower entropy) than the output thermal energy (heat energy).

Air conditioner equipment power in the U.S. is often described in terms of "tons of refrigeration", with each approximately equal to the cooling power of one short ton (2000 pounds or 907 kilograms) of ice melting in a 24-hour period. The value is defined as 12,000 BTU per hour, or 3517 watts. Residential central air systems are usually from 1 to 5 tons (3.5 to 18 kW) in capacity.

For residential homes, some countries set minimum requirements for energy efficiency. In the United States, the efficiency of air conditioners is often (but not always) rated by the seasonal energy efficiency ratio (SEER). The higher the SEER rating, the more energy efficient is the air conditioner. The SEER rating is the BTU of cooling output during its normal annual usage divided by the total electric energy input in watt hours (W·h) during the same period.

this can also be rewritten as:

For example, a 5000 BTU/h air-conditioning unit, with a SEER of 10, would consume 5000/10 = 500 Watts of power on average.

The electrical energy consumed per year can be calculated as the average power multiplied by the annual operating time:

Assuming 1000 hours of operation during a typical cooling season (i.e., 8 hours per day for 125 days per year).

Another method that yields the same result, is to calculate the total annual cooling output:

Then, for a SEER of 10, the annual electrical energy usage would be:

SEER is related to the coefficient of performance (COP) commonly used in thermodynamics and also to the Energy Efficiency Ratio (EER). The EER is the efficiency rating for the equipment at a particular pair of external and internal temperatures, while SEER is calculated over a whole range of external temperatures (i.e., the temperature distribution for the geographical location of the SEER test). SEER is unusual in that it is composed of an Imperial unit divided by an SI unit. The COP is a ratio with the same metric units of energy (joules) in both the numerator and denominator. They cancel out, leaving a dimensionless quantity. Formulas for the approximate conversion between SEER and EER or COP are available.

From equation (2) above, a SEER of 13 is equivalent to a COP of 3.43, which means that 3.43 units of heat energy are pumped per unit of work energy.

The United States now requires that residential systems manufactured in 2006 have a minimum SEER rating of 13 (although window-box systems are exempt from this law, so their SEER is still around 10).

Window unit air conditioners are installed in an open window. The interior air is cooled as a fan blows it over the evaporator. On the exterior the heat drawn from the interior is dissipated into the environment as a second fan blows outside air over the condenser. A large house or building may have several such units, allowing each room to be cooled separately.

In 1971, General Electric introduced a popular portable in-window air conditioner designed for convenience and portability.

Packaged terminal air conditioner (PTAC) systems are also known as wall-split air conditioning systems. They are ductless systems. PTACs, which are frequently used in hotels, have two separate units (terminal packages), the evaporative unit on the interior and the condensing unit on the exterior, with an opening passing through the wall and connecting them. This minimizes the interior system footprint and allows each room to be adjusted independently. PTAC systems may be adapted to provide heating in cold weather, either directly by using an electric strip, gas, or other heater, or by reversing the refrigerant flow to heat the interior and draw heat from the exterior air, converting the air conditioner into a heat pump. While room air conditioning provides maximum flexibility, when used to cool many rooms at a time it is generally more expensive than central air conditioning.

The first practical semi-portable air conditioning unit was invented by engineers at Chrysler Motors and offered for sale starting in 1935.

Split-system air conditioners come in two forms: mini-split and central systems. In both types, the inside-environment (evaporative) heat exchanger is separated by some distance from the outside-environment (condensing unit) heat exchanger.

A mini-split system typically supplies air conditioned and heated air to a single or a few rooms of a building. Multi-zone systems are a common application of ductless systems and allow up to 8 rooms (zones) to be conditioned from a single outdoor unit. Multi-zone systems typically offer a variety of indoor unit styles including wall-mounted, ceiling-mounted, ceiling recessed, and horizontal ducted. Mini-split systems typically produce per hour of cooling. Multi-zone systems provide extended cooling and heating capacity up to 60,000 Btu's.

Advantages of the ductless system include smaller size and flexibility for zoning or heating and cooling individual rooms. The inside wall space required is significantly reduced. Also, the compressor and heat exchanger can be located farther away from the inside space, rather than merely on the other side of the same unit as in a PTAC or window air conditioner. Flexible exterior hoses lead from the outside unit to the interior one(s); these are often enclosed with metal to look like common drainpipes from the roof. In addition, ductless systems offer higher efficiency, reaching above 30 SEER.

The primary disadvantage of ductless air conditioners is their cost. Such systems cost about US$1,500 to US$2,000 per ton (12,000 BTU per hour) of cooling capacity. This is about 30% more than central systems (not including ductwork) and may cost more than twice as much as window units of similar capacity."

An additional possible disadvantage is that the cost of installing mini splits can be higher than some systems. However, lower operating costs and rebates or other financial incentives—offered in some areas—can help offset the initial expense.

Central (ducted) air conditioning offers whole-house or large-commercial-space cooling, and often offers moderate multi-zone temperature control capability by the addition of air-louver-control boxes.

In central air conditioning, the inside heat-exchanger is typically placed inside the central furnace/AC unit of the forced air heating system which is then used in the summer to distribute chilled air throughout a residence or commercial building.

The heat-exchanger cools the air that is being forced through it by the furnace blower. As the warm air comes in contact with this cool surface the water in the air condenses. By pulling the water molecules from the air. According to the psychometric chart as relative humidity decreases in order to feel cool you will have to lower the temperature even more. A common way to counteract this effect is by installing a whole-home humidifier. Similarly, installing a high efficient system this need to turn the temperature down wont have such and influence on your energy costs.

A multi-split system is a conventional split system, which is divided into two parts (evaporator and condenser) and allows cooling or heating of several rooms with one external unit. In the outdoor unit of this air conditioner there is a more powerful compressor, ports for connecting several traces and automation with locking valves for regulating the volume of refrigerant supplied to the indoor units located in the room.

A large Multi Split System is called a Variable refrigerant flow system and can be used instead of a central air conditioner system, as it allows for higher energy efficiency but it is more expensive to purchase and install.

"Difference between split system and multi-split system":

Other common types of air conditioning system are multi-split systems, the difference between separate split system and multi-split system in several indoor units. All of them are connected to the main external unit, but the principle of their operation is similar to a simple split-system.

Its unique feature is the presence of one main external unit that connected to several indoor units. Such systems might be the right solution for maintaining the microclimate in several offices, shops, large living spaces. Just few of outdoor units do not worsen the aesthetic appearance of the building.The main external unit can be connected to several different indoor types: floor, ceiling, cassette, etc.

Before selecting the installation location of air conditioner, several main factors need to be considered. First of all, the direction of air flow from the indoor units should not fall on the place of rest or work area. Secondly, there should not be any obstacles on the way of the airflow that might prevent it from covering the space of the premises as much as possible. The outdoor unit must also be located in an open space, otherwise the heat from the house will not be effectively discharged outside and the productivity of the entire system will drop sharply. It is highly advisable to install the air conditioner units in easily accessible places, for further maintenance during operation.

The main problem when installing a multi-split system is the laying of long refrigerant lines for connecting the external unit to the internal ones. While installing a separate split system, workers try to locate both units opposite to each other, where the length of the line is minimal. Installing a multi-split system creates more difficulties, since some of indoor units can be located far from the outside. The first models of multi-split systems had one common control system that did not allow you to set the air conditioning individually for each room. However, now the market has a wide selection of multi-split systems, in which the functional characteristics of indoor units operate separately from each other.

The selection of indoor units has one restriction: their total power should not exceed the capacity of the outdoor unit. In practice, however, it is very common to see a multi-split system with a total capacity of indoor units greater than the outdoor capacity by at least 20%. However, it is wrong to expect better performance when all indoor units are turned on at the same time, since the total capacity of the whole system is limited by the capacity of the outdoor unit. Simply put, the outdoor unit will distribute all its power to all operating indoor units in such a way that some of the rooms may not have a very comfortable temperature level. However, the calculation of the total power is not simple, since it takes into account not only the nominal power of the units, but also the cooling capacity, heating, dehumidification, humidification, venting, etc.

A portable air conditioner can be easily transported inside a home or office. They are currently available with capacities of about and with or without electric-resistance heaters. Portable air conditioners are either evaporative or refrigerative.

The compressor-based refrigerant systems are air-cooled, meaning they use air to exchange heat, in the same way as a car radiator or typical household air conditioner does. Such a system dehumidifies the air as it cools it. It collects water condensed from the cooled air and produces hot air which must be vented outside the cooled area; doing so transfers heat from the air in the cooled area to the outside air.

A portable system has an indoor unit on wheels connected to an outdoor unit via flexible pipes, similar to a permanently fixed installed unit.The portable units draw indoor air and expel it outdoors through a single duct. Many portable air conditioners come with heat as well as dehumidification function.

Hose systems, which can be "monoblock" or "air-to-air", are vented to the outside via air ducts. The "monoblock" type collects the water in a bucket or tray and stops when full. The "air-to-air" type re-evaporates the water and discharges it through the ducted hose and can run continuously.

A single-hose unit uses air from within the room to cool its condenser, and then vents it outside. This air is replaced by hot air from outside or other rooms (due to the negative pressure inside the room), thus reducing the unit's overall efficiency.

Modern units might have a coefficient of performance of approximately 3 (i.e., 1 kW of electricity will produce 3 kW of cooling). A dual-hose unit draws air to cool its condenser from outside instead of from inside the room, and thus is more effective than most single-hose units. These units create no negative pressure in the room.

Evaporative coolers, sometimes called "swamp coolers", do not have a compressor or condenser. Liquid water is evaporated on the cooling fins, releasing the vapor into the cooled area. Evaporating water absorbs a significant amount of heat, the latent heat of vaporisation, cooling the air. Humans and animals use the same mechanism to cool themselves by sweating.

Evaporative coolers have the advantage of needing no hoses to vent heat outside the cooled area, making them truly portable. They are also very cheap to install and use less energy than refrigerative air conditioners.

Air-conditioning engineers broadly divide air conditioning applications into "comfort" and "process" applications.

Comfort applications aim to provide a building indoor environment that remains relatively constant despite changes in external weather conditions or in internal heat loads.

Air conditioning makes deep plan buildings feasible, for otherwise they would have to be built narrower or with light wells so that inner spaces received sufficient outdoor air via natural ventilation. Air conditioning also allows buildings to be taller, since wind speed increases significantly with altitude making natural ventilation impractical for very tall buildings. Comfort applications are quite different for various building types and may be categorized as:

Women have, on average, a significantly lower resting metabolic rate than men. Using inaccurate metabolic rate guidelines for air conditioning sizing can result in oversized and less efficient equipment, and setting system operating setpoints too cold can result in reduced worker productivity.

In addition to buildings, air conditioning can be used for many types of transportation, including automobiles, buses and other land vehicles, trains, ships, aircraft, and spacecraft.

Air conditioning is common in the US, with 88% of new single-family homes constructed in 2011 including air conditioning, ranging from 99% in the South to 62% in the West. In Canada, air conditioning use varies by province. In 2013, 55% of Canadian households reported having an air conditioner, with high use in Manitoba (80%), Ontario (78%), Saskatchewan (67%), and Quebec (54%) and lower use in Prince Edward Island (23%), British Columbia (21%), and Newfoundland and Labrador (9%). In Europe, home air conditioning is generally less common. Southern European countries such as Greece have seen a wide proliferation of home air-conditioning units in recent years. In another southern European country, Malta, it is estimated that around 55% of households have an air conditioner installed.
In India AC sales have dropped by 40% due to higher costs and stricter energy efficiency regulations.

Process applications aim to provide a suitable environment for a process being carried out, regardless of internal heat and humidity loads and external weather conditions. It is the needs of the process that determine conditions, not human preference. Process applications include these:

In both comfort and process applications, the objective may be to not only control temperature, but also humidity, air quality, and air movement from space to space.

In hot weather, air conditioning can prevent heat stroke, dehydration from excessive sweating and other problems related to hyperthermia. Heat waves are the most lethal type of weather phenomenon in developed countries. Air conditioning (including filtration, humidification, cooling and disinfection) can be used to provide a clean, safe, hypoallergenic atmosphere in hospital operating rooms and other environments where proper atmosphere is critical to patient safety and well-being. It is sometimes recommended for home use by people with allergies.

Poorly maintained water cooling towers can promote the growth and spread of microorganisms, such as "Legionella pneumophila", the infectious agent responsible for Legionnaires' disease, or thermophilic actinomycetes. As long as the cooling tower is kept clean (usually by means of a chlorine treatment), these health hazards can be avoided or reduced. Excessive air conditioning can have a negative effect on skin, causing it to dry out, and can also cause dehydration.

Innovation in air conditioning technologies continues, with much recent emphasis placed on energy efficiency. Production of the electricity used to operate air conditioners has an environmental impact, including the release of greenhouse gases.

Cylinder unloaders are a method of load control used mainly in commercial air conditioning systems. On a semi-hermetic (or open) compressor, the heads can be fitted with unloaders which remove a portion of the load from the compressor so that it can run better when full cooling is not needed. Unloaders can be electrical or mechanical.

According to a 2015 government survey, 87% of the homes in the United States use air conditioning and 65% of those homes have central air conditioning. Most of the homes with central air conditioning have programmable thermostats, but approximately two-thirds of the homes with central air do not use this feature to make their homes more energy efficient.

Alternatives to continual air conditioning can be used with less energy, lower cost, and with less environmental impact. These include:

In an automobile, the A/C system will use around 4 horsepower (3 kW) of the engine's power, thus increasing fuel consumption of the vehicle.

The selection of the working fluids (refrigerants) has a significant impact not only on the performance of the air conditioners but on the environment as well. Most refrigerants used for air conditioning contribute to global warming, and many also deplete the ozone layer. CFCs, HCFCs, and HFCs are potent greenhouse gases when leaked to the atmosphere.

The use of CFC as a refrigerant was once common, including the refrigerants R-11 and R-12 (sold under the brand name "Freon-12"). Freon refrigerants were commonly used during the 20th century in air conditioners due to their superior stability and safety properties. When they are released accidentally or deliberately, these chlorine-bearing refrigerants eventually reach the upper atmosphere. Once the refrigerant reaches the stratosphere, UV radiation from the Sun homolytically cleaves the chlorine-carbon bond, yielding a chlorine radical. These chlorine radicals catalyze the breakdown of ozone into diatomic oxygen, depleting the ozone layer that shields the Earth's surface from strong UV radiation. Each chlorine radical remains active as a catalyst until it binds with another radical, forming a stable molecule and quenching the chain reaction.

Prior to 1994, most automotive air conditioning systems used R-12 as a refrigerant. It was replaced with R-134a refrigerant, which has no ozone depletion potential. Old R-12 systems can be retrofitted to R-134a by a complete flush and filter/dryer replacement to remove the mineral oil, which is not compatible with R-134a.

R22 (also known as HCFC-22) has a global warming potential about 1,800 times higher than CO. It was phased out for use in new equipment by 2010, and is to be completely discontinued by 2020. Although these gasses can be recycled when air conditioning units are disposed of, uncontrolled dumping and leaking can release gas directly into the atmosphere.

In the UK, the Ozone Regulations came into force in 2000 and banned the use of ozone depleting HCFC refrigerants such as R22 in new systems. The Regulation banned the use of R22 as a "top-up" fluid for maintenance between 2010 (for virgin fluid) and 2015 (for recycled fluid). This means that equipment that uses R22 can still operate, as long as it does not leak. Although R22 is now banned, units that use the refrigerant can still be serviced and maintained.

The manufacture and use of CFCs has been banned or severely restricted due to concerns about ozone depletion (see also Montreal Protocol). In light of these environmental concerns, beginning on November 14, 1994, the U.S. Environmental Protection Agency has restricted the sale, possession and use of refrigerant to only licensed technicians, per rules under sections 608 and 609 of the Clean Air Act.

As an alternative to conventional refrigerants, other gases, such as CO (R-744), have been proposed. R-744 is being adopted as a refrigerant in Europe and Japan. It is an effective refrigerant with a global warming potential of 1, but it must use higher compression to produce an equivalent cooling effect.

In 1992, a non-governmental organization, Greenpeace, was spurred by corporate executive policies and requested that a European lab find substitute refrigerants. This led to two alternatives, one a blend of propane (R290) and isobutane (R600a), and one of pure isobutane. Industry resisted change in Europe until 1993, and in the U.S. until 2011, despite some supportive steps in 2004 and 2008 (see Refrigerant Development above).

The inventor Ding Huan (fl. 180 AD) of the Han dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered. In 747, Emperor Xuanzong had a "Cool Hall" built in the imperial palace, which the "Tang Yulin" () describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song dynasty, written sources mentioned the air conditioning rotary fan as even more widely used.

Tang dynasty

The Tang dynasty (; ) or the Tang Empire was an imperial dynasty of China, preceded by the Sui dynasty and followed by the Five Dynasties and Ten Kingdoms period. Historians generally regard the Tang as a high point in Chinese civilization, and a golden age of cosmopolitan culture. Tang territory, acquired through the military campaigns of its early rulers, rivaled that of the Han dynasty. The Tang capital at Chang'an (present-day Xi'an) was the most populous city in the world in its day.

The Lǐ family () founded the dynasty, seizing power during the decline and collapse of the Sui Empire. The dynasty was briefly interrupted when Empress Wu Zetian seized the throne, proclaiming the Second Zhou dynasty (690–705) and becoming the only Chinese empress regnant. In two censuses of the 7th and 8th centuries, the Tang records estimated the population by number of registered households at about 50 million people. Yet, even when the central government was breaking down and unable to compile an accurate census of the population in the 9th century, it is estimated that the population had grown by then to about 80 million people. With its large population base, the dynasty was able to raise professional and conscripted armies of hundreds of thousands of troops to contend with nomadic powers in dominating Inner Asia and the lucrative trade-routes along the Silk Road. Various kingdoms and states paid tribute to the Tang court, while the Tang also conquered or subdued several regions which it indirectly controlled through a protectorate system. Besides political hegemony, the Tang also exerted a powerful cultural influence over neighboring East Asian states such as those in Japan and Korea.

The Tang dynasty was largely a period of progress and stability in the first half of the dynasty's rule, until the An Lushan Rebellion and the decline of central authority in the later half of the dynasty. Like the previous Sui dynasty, the Tang dynasty maintained a civil-service system by recruiting scholar-officials through standardized examinations and recommendations to office. The rise of regional military governors known as "jiedushi" during the 9th century undermined this civil order. Chinese culture flourished and further matured during the Tang era; it is traditionally considered the greatest age for Chinese poetry. Two of China's most famous poets, Li Bai and Du Fu, belonged to this age, as did many famous painters such as Han Gan, Zhang Xuan, and Zhou Fang. Scholars of this period compiled a rich variety of historical literature, as well as encyclopedias and geographical works. The adoption of the title Tängri Qaghan by the Tang Emperor Taizong in addition to his title as emperor was eastern Asia's first "simultaneous kingship".

Many notable innovations occurred under the Tang, including the development of woodblock printing. Buddhism became a major influence in Chinese culture, with native Chinese sects gaining prominence. However, in the 840s the Emperor Wuzong of Tang enacted policies to persecute Buddhism, which subsequently declined in influence. Although the dynasty and central government had gone into decline by the 9th century, art and culture continued to flourish. The weakened central government largely withdrew from managing the economy, but the country's mercantile affairs stayed intact and commercial trade continued to thrive regardless. However, agrarian rebellions in the latter half of the 9th century resulted in damaging atrocities such as the Guangzhou massacre of 878-879.

The Li family belonged to the northwest military aristocracy prevalent during the Sui dynasty and claimed to be paternally descended from the Daoist founder, Laozi (whose personal name was Li Dan or Li Er) the Han dynasty General Li Guang and Western Liang ruler Li Gao. This family was known as the Longxi Li lineage (; ), which includes the Tang poet Li Bai. The Tang Emperors also had Xianbei maternal ancestry, from Emperor Gaozu of Tang's Xianbei mother, Duchess Dugu.

Li Yuan was Duke of Tang and governor of Taiyuan, modern Shanxi, during the Sui dynasty's collapse, which was caused in part by the Sui failure to conquer the northern part of the Korean peninsula during the Goguryeo–Sui War. He had prestige and military experience, and was a first cousin of Emperor Yang of Sui (their mothers were sisters). Li Yuan rose in rebellion in 617, along with his son and his equally militant daughter Princess Pingyang (d. 623), who raised and commanded her own troops. In winter 617, Li Yuan occupied Chang'an, relegated Emperor Yang to the position of "Taishang Huang" or retired emperor, and acted as regent to the puppet child-emperor, Yang You. On the news of Emperor Yang's murder by General Yuwen Huaji on June 18, 618, Li Yuan declared himself the emperor of a new dynasty, the Tang.

Li Yuan, known as Emperor Gaozu of Tang, ruled until 626, when he was forcefully deposed by his son Li Shimin, the Prince of Qin. Li Shimin had commanded troops since the age of 18, had prowess with bow and arrow, sword and lance and was known for his effective cavalry charges. Fighting a numerically superior army, he defeated Dou Jiande (573–621) at Luoyang in the Battle of Hulao on May 28, 621. In a violent elimination of royal family due to fear of assassination, Li Shimin ambushed and killed two of his brothers, Li Yuanji (b. 603) and Crown prince Li Jiancheng (b. 589), in the Xuanwu Gate Incident on July 2, 626. Shortly thereafter, his father abdicated in his favor and Li Shimin ascended the throne. He is conventionally known by his temple name Taizong.

Although killing two brothers and deposing his father contradicted the Confucian value of filial piety, Taizong showed himself to be a capable leader who listened to the advice of the wisest members of his council. In 628, Emperor Taizong held a Buddhist memorial service for the casualties of war, and in 629 he had Buddhist monasteries erected at the sites of major battles so that monks could pray for the fallen on both sides of the fight. This was during the Tang campaign against the Eastern Turks, a Turkic Khaganate that was destroyed after the capture of its ruler, Illig Qaghan by the famed Tang military officer Li Jing (571–649); who later became a Chancellor of the Tang dynasty. With this victory, the Turks accepted Taizong as their khagan, a title rendered as Tian Kehan in addition to his rule as emperor of China under the traditional title "Son of Heaven".

Although she entered Emperor Gaozong's court as the lowly consort Wu Zhao, Wu Zetian rose to the highest seat of power in 690, establishing the short-lived Wu Zhou. Empress Wu's rise to power was achieved through cruel and calculating tactics: a popular conspiracy theory stated that she killed her own baby girl and blamed it on Gaozong's empress so that the empress would be demoted. Emperor Gaozong suffered a stroke in 655, and Wu began to make many of his court decisions for him, discussing affairs of state with his councilors, who took orders from her while she sat behind a screen. When Empress Wu's eldest son, the crown prince, began to assert his authority and advocate policies opposed by Empress Wu, he suddenly died in 675. Many suspected he was poisoned by Empress Wu. Although the next heir apparent kept a lower profile, in 680 he was accused by Wu of plotting a rebellion and was banished. (He was later obliged to commit suicide.)

In 683, Emperor Gaozong died. He was succeeded by Emperor Zhongzong, his eldest surviving son by Wu. Zhongzong tried to appoint his wife's father as chancellor: after only six weeks on the throne, he was deposed by Empress Wu in favor of his younger brother, Emperor Ruizong. This provoked a group of Tang princes to rebel in 684. Wu's armies suppressed them within two months. She proclaimed the Tianshou era of Wu Zhou on, and three days later demoted Emperor Ruizong to crown prince. He was also forced to give up his father's surname Li in favor of the Empress Wu. She then ruled as China's only empress regnant.

A palace coup on, forced Empress Wu to yield her position on February 22. The next day, her son Zhongzong was restored to power; the Tang was formally restored on March 3. She died soon after. To legitimize her rule, she circulated a document known as the "Great Cloud Sutra", which predicted that a reincarnation of the Maitreya Buddha would be a female monarch who would dispel illness, worry, and disaster from the world. She even introduced numerous revised written characters to the written language, which reverted to the originals after her death. Arguably the most important part of her legacy was diminishing the hegemony of the Northwestern aristocracy, allowing people from other clans and regions of China to become more represented in Chinese politics and government.

There were many prominent women at court during and after Wu's reign, including Shangguan Wan'er (664–710), a poet, writer, and trusted official in charge of Wu's private office. In 706 the wife of Emperor Zhongzong of Tang, Empress Wei (d. 710), persuaded her husband to staff government offices with his sister and her daughters, and in 709 requested that he grant women the right to bequeath hereditary privileges to their sons (which before was a male right only). Empress Wei eventually poisoned Zhongzong, whereupon she placed his fifteen-year-old son upon the throne in 710. Two weeks later, Li Longji (the later Emperor Xuanzong) entered the palace with a few followers and slew Empress Wei and her faction. He then installed his father Emperor Ruizong (r. 710–712) on the throne. Just as Emperor Zhongzong was dominated by Empress Wei, so too was Ruizong dominated by Princess Taiping. This was finally ended when Princess Taiping's coup failed in 712 (she later hanged herself in 713) and Emperor Ruizong abdicated to Emperor Xuanzong.

During the 44-year reign of Emperor Xuanzong, the Tang dynasty reached its height, a golden age with low economic inflation and a toned down lifestyle for the imperial court. Seen as a progressive and benevolent ruler, Xuanzong even abolished the death penalty in the year 747; all executions had to be approved beforehand by the emperor himself (these were relatively few, considering that there were only 24 executions in the year 730). Xuanzong bowed to the consensus of his ministers on policy decisions and made efforts to staff government ministries fairly with different political factions. His staunch Confucian chancellor Zhang Jiuling (673–740) worked to reduce deflation and increase the money supply by upholding the use of private coinage, while his aristocratic and technocratic successor Li Linfu (d. 753) favored government monopoly over the issuance of coinage. After 737 most of Xuanzong's confidence rested in his long-standing chancellor Li Linfu, who championed a more aggressive foreign policy employing non-Chinese generals. This policy ultimately created the conditions for a massive rebellion against Xuanzong.

The Tang Empire was at its height of power up until the middle of the 8th century, when the An Lushan Rebellion (December 16, 755 – February 17, 763) destroyed the prosperity of the empire. An Lushan was a half-Sogdian, half-Turk Tang commander since 744, had experience fighting the Khitans of Manchuria with a victory in 744, yet most of his campaigns against the Khitans were unsuccessful. He was given great responsibility in Hebei, which allowed him to rebel with an army of more than 100,000 troops. After capturing Luoyang, he named himself emperor of a new, but short-lived, Yan state. Despite early victories scored by Tang General Guo Ziyi (697–781), the newly recruited troops of the army at the capital were no match for An Lushan's frontier veterans, so the court fled Chang'an. While the heir apparent raised troops in Shanxi and Xuanzong fled to Sichuan province, they called upon the help of the Uyghur Khaganate in 756. The Uyghur khan Moyanchur was greatly excited at this prospect, and married his own daughter to the Chinese diplomatic envoy once he arrived, receiving in turn a Chinese princess as his bride. The Uyghurs helped recapture the Tang capital from the rebels, but they refused to leave until the Tang paid them an enormous sum of tribute in silk. Even Abbasid Arabs assisted the Tang in putting down An Lushan's rebellion. The Tibetans took hold of the opportunity and raided many areas under Chinese control, and even after the Tibetan Empire had fallen apart in 842 (and the Uyghurs soon after) the Tang were in no position to reconquer Central Asia after 763. So significant was this loss that half a century later "jinshi" examination candidates were required to write an essay on the causes of the Tang's decline. Although An Lushan was killed by one of his eunuchs in 757, this time of troubles and widespread insurrection continued until rebel Shi Siming was killed by his own son in 763.

One of the legacies that the Tang government left since 710 was the gradual rise of regional military governors, the jiedushi, who slowly came to challenge the power of the central government. After the An Lushan Rebellion, the autonomous power and authority accumulated by the jiedushi in Hebei went beyond the central government's control. After a series of rebellions between 781 and 784 in today's Hebei, Shandong, Hubei and Henan provinces, the government had to officially acknowledge the jiedushi's hereditary ruling without accreditation. The Tang government relied on these governors and their armies for protection and to suppress locals that would take up arms against the government. In return, the central government would acknowledge the rights of these governors to maintain their army, collect taxes and even to pass on their title to heirs. As time passed, these military governors slowly phased out the prominence of civil officials drafted by exams, and became more autonomous from central authority. The rule of these powerful military governors lasted until 960, when a new civil order under the Song dynasty was established. Also, the abandonment of the equal-field system meant that people could buy and sell land freely. Many poor fell into debt because of this, forced to sell their land to the wealthy, which led to the exponential growth of large estates. With the breakdown of the land allocation system after 755, the central Chinese state barely interfered in agricultural management and acted merely as tax collector for roughly a millennium, save a few instances such as the Song's failed land nationalization during the 13th-century war with the Mongols.

With the central government collapsing in authority over the various regions of the empire, it was recorded in 845 that bandits and river pirates in parties of 100 or more began plundering settlements along the Yangtze River with little resistance. In 858, enormous floods along the Grand Canal inundated vast tracts of land and terrain of the North China Plain, which drowned tens of thousands of people in the process.
The Chinese belief in the Mandate of Heaven granted to the ailing Tang was also challenged when natural calamities occurred, forcing many to believe the Heavens were displeased and that the Tang had lost their right to rule. Then in 873 a disastrous harvest shook the foundations of the empire; in some areas only half of all agricultural produce was gathered, and tens of thousands faced famine and starvation. In the earlier period of the Tang, the central government was able to meet crises in the harvest, as it was recorded from 714–719 that the Tang government responded effectively to natural disasters by extending the price-regulation granary system throughout the country. The central government was able then to build a large surplus stock of foods to ward off the rising danger of famine and increased agricultural productivity through land reclamation. In the 9th century, however, the Tang government was nearly helpless in dealing with any calamity.

Although these natural calamities and rebellions stained the reputation and hampered the effectiveness of the central government, the early 9th century is nonetheless viewed as a period of recovery for the Tang dynasty. The government's withdrawal from its role in managing the economy had the unintended effect of stimulating trade, as more markets with less bureaucratic restrictions were opened up. By 780, the old grain tax and labor service of the 7th century was replaced by a semiannual tax paid in cash, signifying the shift to a money economy boosted by the merchant class. Cities in the Jiangnan region to the south, such as Yangzhou, Suzhou, and Hangzhou prospered the most economically during the late Tang period. The government monopoly on the production of salt, weakened after the An Shi Rebellion, was placed under the Salt Commission, which became one of the most powerful state agencies, run by capable ministers chosen as specialists. The commission began the practice of selling merchants the rights to buy monopoly salt, which they would then transport and sell in local markets. In 799 salt accounted for over half of the government's revenues. S.A.M. Adshead writes that this salt tax represents "the first time that an indirect tax, rather than tribute, levies on land or people, or profit from state enterprises such as mines, had been the primary resource of a major state." Even after the power of the central government was in decline after the mid 8th century, it was still able to function and give out imperial orders on a massive scale. The "Tangshu" (Old Book of Tang) compiled in the year 945 recorded that in 828 the Tang government issued a decree that standardized irrigational square-pallet chain pumps in the country:

In the second year of the Taihe reign period [828], in the second month...a standard model of the chain pump was issued from the palace, and the people of Jingzhao Fu (d footnote: the capital) were ordered by the emperor to make a considerable number of machines, for distribution to the people along the Zheng Bai Canal, for irrigation purposes.|

The last great ambitious ruler of the Tang dynasty was Emperor Xianzong (r. 805–820), whose reign was aided by the fiscal reforms of the 780s, including a government monopoly on the salt industry. He also had an effective well trained imperial army stationed at the capital led by his court eunuchs; this was the Army of Divine Strategy, numbering 240,000 in strength as recorded in 798. Between the years 806 and 819, Emperor Xianzong conducted seven major military campaigns to quell the rebellious provinces that had claimed autonomy from central authority, managing to subdue all but two of them. Under his reign there was a brief end to the hereditary jiedushi, as Xianzong appointed his own military officers and staffed the regional bureaucracies once again with civil officials. However, Xianzong's successors proved less capable and more interested in the leisure of hunting, feasting, and playing outdoor sports, allowing eunuchs to amass more power as drafted scholar-officials caused strife in the bureaucracy with factional parties. The eunuchs' power became unchallenged after Emperor Wenzong's (r. 826–840) failed plot to have them overthrown; instead the allies of Emperor Wenzong were publicly executed in the West Market of Chang'an, by the eunuchs' command.
However, the Tang did manage to restore at least indirect control over former Tang territories as far west as the Hexi Corridor and Dunhuang in Gansu. In 848 the ethnic Han Chinese general Zhang Yichao (799–872) managed to wrestle control of the region from the Tibetan Empire during its civil war. Shortly afterwards Emperor Xuānzong of Tang (r. 846–859) acknowledged Zhang as the protector (防禦使, "Fangyushi") of Sha Prefecture and "jiedushi" military governor of the new Guiyi Circuit.

In addition to natural calamities and jiedushi amassing autonomous control, the Huang Chao Rebellion (874–884) resulted in the sacking of both Chang'an and Luoyang, and took an entire decade to suppress. Although the rebellion was defeated by the Tang, it never recovered from that crucial blow, weakening it for the future military powers to take over. There were also large groups of bandits, in the size of small armies, that ravaged the countryside in the last years of the Tang, who smuggled illicit salt, ambushed merchants and convoys, and even besieged several walled cities.

Zhu Wen, originally a salt smuggler who had served under the rebel Huang Chao, surrendered to Tang forces. By helping to defeat Huang, he was granted a series of rapid military promotions. In 907 the Tang dynasty was ended when Zhu Wen, now a military governor, deposed the last emperor of Tang, Emperor Ai of Tang, and took the throne for himself (known posthumously as Emperor Taizu of Later Liang). He established the Later Liang, which inaugurated the Five Dynasties and Ten Kingdoms period. A year later Zhu Wen had the deposed Emperor Ai poisoned to death.

Taizong set out to solve internal problems within the government which had constantly plagued past dynasties. Building upon the Sui legal code, he issued a new legal code that subsequent Chinese dynasties would model theirs upon, as well as neighboring polities in Vietnam, Korea, and Japan. The earliest law code to survive was the one established in the year 653, which was divided into 500 articles specifying different crimes and penalties ranging from ten blows with a light stick, one hundred blows with a heavy rod, exile, penal servitude, or execution.

The legal code distinguished different levels of severity in meted punishments when different members of the social and political hierarchy committed the same crime. For example, the severity of punishment was different when a servant or nephew killed a master or an uncle than when a master or uncle killed a servant or nephew.

The Tang Code was largely retained by later codes such as the early Ming dynasty (1368–1644) code of 1397, yet there were several revisions in later times, such as during the Song dynasty (960–1279).

The Tang had three departments (), which were obliged to draft, review, and implement policies respectively. There were also six ministries () under the administrations that implemented policy, each of which was assigned different tasks. These Three Departments and Six Ministries included the personnel administration, finance, rites, military, justice, and public works—an administrative model which would last until the fall of the Qing dynasty (1644–1912).

Although the founders of the Tang related to the glory of the earlier Han dynasty (3rd century –3rd century ), the basis for much of their administrative organization was very similar to the previous Northern and Southern dynasties. The Northern Zhou (6th century) fubing system of divisional militia was continued by the Tang, along with farmer-soldiers serving in rotation from the capital or frontier in order to receive appropriated farmland. The equal-field system of the Northern Wei (4th–6th centuries) was also kept, although there were a few modifications.

Although the central and local governments kept an enormous number of records about land property in order to assess taxes, it became common practice in the Tang for literate and affluent people to create their own private documents and signed contracts. These had their own signature and that of a witness and scribe in order to prove in court (if necessary) that their claim to property was legitimate. The prototype of this actually existed since the ancient Han dynasty, while contractual language became even more common and embedded into Chinese literary culture in later dynasties.

The center of the political power of the Tang was the capital city of Chang'an (modern Xi'an), where the emperor maintained his large palace quarters and entertained political emissaries with music, sports, acrobatic stunts, poetry, paintings, and dramatic theater performances. The capital was also filled with incredible amounts of riches and resources to spare. When the Chinese prefectural government officials traveled to the capital in the year 643 to give the annual report of the affairs in their districts, Emperor Taizong discovered that many had no proper quarters to rest in and were renting rooms with merchants. Therefore, Emperor Taizong ordered the government agencies in charge of municipal construction to build every visiting official his own private mansion in the capital.

Students of Confucian studies were potential candidates for the imperial examinations, the graduates of which could be appointed as state bureaucrats in the local, provincial, and central government. There were two types of exams that were given, "mingjing" (; "illuminating the classics") and "jinshi" (; "presented scholar"). The "mingjing" was based upon the Confucian classics and tested the student's knowledge of a broad variety of texts. The "jinshi" tested a student's literary abilities in writing essay-style responses to questions on matters of governance and politics, as well as their skills in composing poetry. Candidates were also judged on their skills of deportment, appearance, speech, and level of skill in calligraphy, all of which were subjective criteria that allowed the already wealthy members of society to be chosen over ones of more modest means who were unable to be educated in rhetoric or fanciful writing skills. There was a disproportionate number of civil officials coming from aristocratic as opposed to non-aristocratic families. The exams were open to all male subjects whose fathers were not of the artisan or merchant classes, although having wealth or noble status was not a prerequisite in receiving a recommendation. In order to promote widespread Confucian education, the Tang government established state-run schools and issued standard versions of the Five Classics with selected commentaries.

This competitive procedure was designed to draw the best talent into government. But perhaps an even greater consideration for the Tang rulers, aware that imperial dependence on powerful aristocratic families and warlords would have destabilizing consequences, was to create a body of career officials having no autonomous territorial or functional power base. The Tang law code ensured equal division of inherited property amongst legitimate heirs, allowing a bit of social mobility and preventing the families of powerful court officials from becoming landed nobility through primogeniture. As it turned out, these scholar-officials acquired status in their local communities and in family ties, while they also shared values that connected them to the imperial court. From Tang times until the end of the Qing dynasty in 1912, scholar-officials functioned often as intermediaries between the grassroots level and the government. Yet the potential of a widespread examination system was not fully realized until the Song dynasty, when the merit-driven scholar official largely shed his aristocratic habits and defined his social status through the examination system. As historian Patricia Ebrey states of the Song period scholar-officials:
From the outset, religion played a role in Tang politics. In his bid for power, Li Yuan had attracted a following by claiming descent from the Daoist sage Laozi ( 6th century ). People bidding for office would have monks from Buddhist temples pray for them in public in return for cash donations or gifts if the person was selected. Before the persecution of Buddhism in the 9th century, Buddhism and Daoism were accepted side by side, and Emperor Xuanzong (r. 712–756) invited monks and clerics of both religions to his court. At the same time Xuanzong exalted the ancient Laozi by granting him grand titles, wrote commentary on the Daoist "Laozi", set up a school to prepare candidates for examinations on Daoist scriptures, and called upon the Indian monk Vajrabodhi (671–741) to perform Tantric rites to avert a drought in the year 726. In 742 Emperor Xuanzong personally held the incense burner during a ceremony led by Amoghavajra (705–774, patriarch of the Shingon school) reciting "mystical incantations to secure the victory of Tang forces."

While religion played a role in politics, politics also played a role in religion. In the year 714, Emperor Xuanzong forbade shops and vendors in the city of Chang'an to sell copied Buddhist sutras, instead giving the Buddhist clergy of the monasteries the sole right to distribute sutras to the laity. In the previous year of 713, Emperor Xuanzong had liquidated the highly lucrative Inexhaustible Treasury, which was run by a prominent Buddhist monastery in Chang'an. This monastery collected vast amounts of money, silk, and treasures through multitudes of anonymous people's repentances, leaving the donations on the monastery's premise. Although the monastery was generous in donations, Emperor Xuanzong issued a decree abolishing their treasury on grounds that their banking practices were fraudulent, collected their riches, and distributed the wealth to various other Buddhist monasteries and Daoist abbeys, and to repair statues, halls, and bridges in the city.

The Tang dynasty government attempted to create an accurate census of the size of their empire's population, mostly for effective taxation and matters of military conscription for each region. The early Tang government established both the grain tax and cloth tax at a relatively low rate for each household under the empire. This was meant to encourage households to enroll for taxation and not avoid the authorities, thus providing the government with the most accurate estimate possible. In the census of 609, the population was tallied by efforts of the government at a size of 9 million households, or about 50 million people. The Tang census of 742 again approximated the size of China's population at about 50 million people. Patricia Ebrey writes that even if a rather significant number of people had avoided the registration process of the tax census, the population size during the Tang had not grown significantly since the earlier Han dynasty (the census of the year 2 recording a population of roughly 58 million people in China). S.A.M. Adshead disagrees, estimating that there were about 75 million people by 750.

In the Tang census of the year 754, there were 1,859 cities, 321 prefectures, and 1,538 counties throughout the empire. Although there were many large and prominent cities during the Tang, the rural and agrarian areas comprised the majority of China's population at some 80 to 90%. There was also a dramatic migratory shift of the population from northern to southern China, as the North held 75% of the overall population at the dynasty's inception, but by its end was reduced to 50%.

Chinese population size would not dramatically increase until the Song dynasty period, when the population doubled to 100 million people because of extensive rice cultivation in central and southern China, coupled with rural farmers holding more abundant yields of food that they could easily provide to the growing market.

The 7th and first half of the 8th century are generally considered to be the era in which the Tang reached the zenith of its power. In this period, Tang control extended further west than any previous dynasty, stretching from north Vietnam in the south, to a point north of Kashmir bordering Persia in the west, to northern Korea in the north-east.

Some of the kingdoms paying tribute to the Tang dynasty included Kashmir, Nepal, Khotan, Kucha, Kashgar, Korea, Champa, and kingdoms located in Amu Darya and Syr Darya valley. Turkic nomads addressed the Emperor of Tang China as "Tian Kehan". After the widespread Göktürk revolt of Shabolüe Khan (d. 658) was put down at Issyk Kul in 657 by Su Dingfang (591–667), Emperor Gaozong established several protectorates governed by a Protectorate General or Grand Protectorate General, which extended the Chinese sphere of influence as far as Herat in Western Afghanistan. Protectorate Generals were given a great deal of autonomy to handle local crises without waiting for central admission. After Xuanzong's reign, military governors (jiedushi) were given enormous power, including the ability to maintain their own armies, collect taxes, and pass their titles on hereditarily. This is commonly recognized as the beginning of the fall of Tang's central government.

By the year 737, Emperor Xuanzong discarded the policy of conscripting soldiers that were replaced every three years, replacing them with long-service soldiers who were more battle-hardened and efficient. It was more economically feasible as well, since training new recruits and sending them out to the frontier every three years drained the treasury. By the late 7th century, the "fubing" troops began abandoning military service and the homes provided to them in the equal-field system. The supposed standard of 100 "mu" of land allotted to each family was in fact decreasing in size in places where population expanded and the wealthy bought up most of the land. Hard-pressed peasants and vagrants were then induced into military service with benefits of exemption from both taxation and corvée labor service, as well as provisions for farmland and dwellings for dependents who accompanied soldiers on the frontier. By the year 742 the total number of enlisted troops in the Tang armies had risen to about 500,000 men.

In East Asia, Tang Chinese military campaigns were less successful elsewhere than in previous imperial Chinese dynasties. Like the emperors of the Sui dynasty before him, Taizong established a military campaign in 644 against the Korean kingdom of Goguryeo in the Goguryeo–Tang War; however, this led to its withdrawal in the first campaign because they failed to overcome the successful defense led by General Yeon Gaesomun. Allying with the Korean Silla Kingdom, the Chinese fought against Baekje and their Yamato Japanese allies in the Battle of Baekgang in August 663, a decisive Tang–Silla victory. The Tang dynasty navy had several different ship types at its disposal to engage in naval warfare, these ships described by Li Quan in his "Taipai Yinjing" (Canon of the White and Gloomy Planet of War) of 759. The Battle of Baekgang was actually a restoration movement by remnant forces of Baekje, since their kingdom was toppled in 660 by a joint Tang–Silla invasion, led by Chinese general Su Dingfang and Korean general Kim Yushin (595–673). In another joint invasion with Silla, the Tang army severely weakened the Goguryeo Kingdom in the north by taking out its outer forts in the year 645. With joint attacks by Silla and Tang armies under commander Li Shiji (594–669), the Kingdom of Goguryeo was destroyed by 668.

Although they were formerly enemies, the Tang accepted officials and generals of Goguryeo into their administration and military, such as the brothers Yeon Namsaeng (634–679) and Yeon Namsan (639–701). From 668 to 676, the Tang Empire would control northern Korea. However, in 671 Silla broke the alliance and began the Silla–Tang War to expel the Tang forces. At the same time the Tang faced threats on its western border when a large Chinese army was defeated by the Tibetans on the Dafei River in 670. By 676, the Tang army was expelled out of Korea by Unified Silla. Following a revolt of the Eastern Turks in 679, the Tang abandoned its Korean campaigns.

Although the Tang had fought the Japanese, they still held cordial relations with Japan. There were numerous Imperial embassies to China from Japan, diplomatic missions that were not halted until 894 by Emperor Uda (r. 887–897), upon persuasion by Sugawara no Michizane (845–903). The Japanese Emperor Tenmu (r. 672–686) even established his conscripted army on that of the Chinese model, his state ceremonies on the Chinese model, and constructed his palace at Fujiwara on the Chinese model of architecture.

Many Chinese Buddhist monks came to Japan to help further the spread of Buddhism as well. Two 7th-century monks in particular, Zhi Yu and Zhi You, visited the court of Emperor Tenji (r. 661–672), whereupon they presented a gift of a south-pointing chariot that they had crafted. This 3rd century mechanically driven directional-compass vehicle (employing a differential gear) was again reproduced in several models for Tenji in 666, as recorded in the "Nihon Shoki" of 720. Japanese monks also visited China; such was the case with Ennin (794–864), who wrote of his travel experiences including travels along China's Grand Canal. The Japanese monk Enchin (814–891) stayed in China from 839 to 847 and again from 853 to 858, landing near Fuzhou, Fujian and setting sail for Japan from Taizhou, Zhejiang during his second trip to China.

The Sui and Tang carried out very successful military campaigns against the steppe nomads. Chinese foreign policy to the north and west now had to deal with Turkic nomads, who were becoming the most dominant ethnic group in Central Asia. To handle and avoid any threats posed by the Turks, the Sui government repaired fortifications and received their trade and tribute missions. They sent four royal princesses to form marriage alliances with Turkic clan leaders, in 597, 599, 614, and 617. The Sui stirred trouble and conflict amongst ethnic groups against the Turks. As early as the Sui dynasty, the Turks had become a major militarized force employed by the Chinese. When the Khitans began raiding northeast China in 605, a Chinese general led 20,000 Turks against them, distributing Khitan livestock and women to the Turks as a reward. On two occasions between 635 and 636, Tang royal princesses were married to Turk mercenaries or generals in Chinese service. Throughout the Tang dynasty until the end of 755, there were approximately ten Turkic generals serving under the Tang. While most of the Tang army was made of "fubing" Chinese conscripts, the majority of the troops led by Turkic generals were of non-Chinese origin, campaigning largely in the western frontier where the presence of "fubing" troops was low. Some "Turkic" troops were nomadicised Han Chinese, a desinicized people.

Civil war in China was almost totally diminished by 626, along with the defeat in 628 of the Ordos Chinese warlord Liang Shidu; after these internal conflicts, the Tang began an offensive against the Turks. In the year 630, Tang armies captured areas of the Ordos Desert, modern-day Inner Mongolia province, and southern Mongolia from the Turks. After this military victory, Emperor Taizong won the title of Great Khan amongst the various Turks in the region who pledged their allegiance to him and the Chinese empire (with several thousand Turks traveling into China to live at Chang'an). On June 11, 631, Emperor Taizong also sent envoys to the Xueyantuo bearing gold and silk in order to persuade the release of enslaved Chinese prisoners who were captured during the transition from Sui to Tang from the northern frontier; this embassy succeeded in freeing 80,000 Chinese men and women who were then returned to China.

While the Turks were settled in the Ordos region (former territory of the Xiongnu), the Tang government took on the military policy of dominating the central steppe. Like the earlier Han dynasty, the Tang dynasty (along with Turkic allies) conquered and subdued Central Asia during the 640s and 650s. During Emperor Taizong's reign alone, large campaigns were launched against not only the Göktürks, but also separate campaigns against the Tuyuhun, the oasis city-states, and the Xueyantuo. Under Emperor Gaozong, a campaign led by the general Su Dingfang was launched against the Western Turks ruled by Ashina Helu.

The Tang Empire competed with the Tibetan Empire for control of areas in Inner and Central Asia, which was at times settled with marriage alliances such as the marrying of Princess Wencheng (d. 680) to Songtsän Gampo (d. 649). A Tibetan tradition mentions that Chinese troops captured Lhasa after Songtsän Gampo's death, but no such invasion is mentioned in either Chinese annals or the Tibetan manuscripts of Dunhuang.
There was a long string of conflicts with Tibet over territories in the Tarim Basin between 670–692, and in 763 the Tibetans even captured the capital of China, Chang'an, for fifteen days during the An Shi Rebellion. In fact, it was during this rebellion that the Tang withdrew its western garrisons stationed in what is now Gansu and Qinghai, which the Tibetans then occupied along with the territory of what is now Xinjiang. Hostilities between the Tang and Tibet continued until they signed a formal peace treaty in 821. The terms of this treaty, including the fixed borders between the two countries, are recorded in a bilingual inscription on a stone pillar outside the Jokhang temple in Lhasa.

During the Islamic conquest of Persia (633–656), the son of the last ruler of the Sassanid Empire, Prince Pirooz, fled to Tang China. According to the "Old Book of Tang", Pirooz was made the head of a Governorate of Persia in what is now Zaranj, Afghanistan. During this conquest of Persia, the Rashidun Islamic Caliph Uthman Ibn Affan (r. 644–656) sent an embassy to the Tang court at Chang'an. Arab sources claim Umayyad commander Qutayba ibn Muslim briefly took Kashgar from China and withdrew after an agreement, but modern historians entirely dismiss this claim. The Arab Umayyad Caliphate in 715 desposed Ikhshid, the king the Fergana Valley, and installed a new king Alutar on the throne. The deposed king fled to Kucha (seat of Anxi Protectorate), and sought Chinese intervention. The Chinese sent 10,000 troops under Zhang Xiaosong to Ferghana. He defeated Alutar and the Arab occupation force at Namangan and reinstalled Ikhshid on the throne. The Tang dynasty Chinese defeated the Arab Umayyad invaders at the Battle of Aksu (717). The Arab Umayyad commander Al-Yashkuri and his army fled to Tashkent after they were defeated. The Turgesh then crushed the Arab Umayyads and drove them out. By the 740s, the Arabs under the Abbasid Caliphate in Khurasan had re-established a presence in the Ferghana basin and in Sogdiana. At the Battle of Talas in 751, Qarluq mercenaries under the Chinese defected, helping the Arab armies of the Islamic Caliphate to defeat the Tang force under commander Gao Xianzhi. Although the battle itself was not of the greatest significance militarily, this was a pivotal moment in history; it marks the spread of Chinese papermaking into regions west of China as captured Chinese soldiers revealed secrets of Chinese papermaking to the Arabs. These techniques ultimately reached Europe by the 12th century through Arab-controlled Spain. Although they had fought at Talas, on June 11, 758, an Abbasid embassy arrived at Chang'an simultaneously with the Uyghur Turks bearing gifts for the Tang Emperor. In 788–9 the Chinese concluded a military alliance with the Uighur Turks who twice defeated the Tibetans, in 789 near the town of Gaochang in Dzungaria, and in 791 near Ningxia on the Yellow River.
Joseph Needham writes that a from the Patriarch of Antioch. However, Friedrich Hirth and other sinologists such as S.A.M. Adshead have identified "Fu lin" (拂菻) in the "Old" and "New Book of Tang" as the Byzantine Empire, which those histories directly associated with "Daqin" (i.e. the Roman Empire). The embassy sent in 643 by "Boduoli" (波多力) was identified as Byzantine ruler Constans II Pogonatos ("Kōnstantinos Pogonatos", or "Constantine the Bearded") and further embassies were recorded as being sent into the 8th century. S.A.M. Adshead offers a different transliteration stemming from "patriarch" or "patrician", possibly a reference to one of the acting regents for the young Byzantine monarch. The "Old" and "New Book of Tang" also provide a description of the Byzantine capital Constantinople, including how it was besieged by the "Da shi" (大食, i.e. Umayyad Caliphate) forces of Muawiyah I, who forced them to pay tribute to the Arabs. The 7th-century Byzantine historian Theophylact Simocatta wrote about the reunification of northern and southern China by the Sui dynasty (dating this to the time of Emperor Maurice); the capital city "Khubdan" (from Old Turkic "Khumdan", i.e. Chang'an); the basic geography of China including its previous political division around the Yangzi River; the name of China's ruler "Taisson" meaning "Son of God", but possibly derived from the name of the contemporaneous ruler Emperor Taizong.

Through use of the land trade along the Silk Road and maritime trade by sail at sea, the Tang were able to acquire and gain many new technologies, cultural practices, rare luxury, and contemporary items. From Europe, the Middle East, Central and South Asia, the Tang dynasty were able to acquire new ideas in fashion, new types of ceramics, and improved silver-smithing techniques. The Tang Chinese also gradually adopted the foreign concept of stools and chairs as seating, whereas the Chinese beforehand always sat on mats placed on the floor. In the Middle East, the Islamic world coveted and purchased in bulk Chinese goods such as silks, lacquerwares, and porcelain wares. Songs, dances, and musical instruments from foreign regions became popular in China during the Tang dynasty. These musical instruments included oboes, flutes, and small lacquered drums from Kucha in the Tarim Basin, and percussion instruments from India such as cymbals. At the court there were nine musical ensembles (expanded from seven in the Sui dynasty) representing music from throughout Asia.

There was great contact and interest in India as a hub for Buddhist knowledge, with famous travelers such as Xuanzang (d. 664) visiting the South Asian state. After a 17-year-long trip, Xuanzang managed to bring back valuable Sanskrit texts to be translated into Chinese. There was also a Turkic–Chinese dictionary available for serious scholars and students, while Turkic folksongs gave inspiration to some Chinese poetry. In the interior of China, trade was facilitated by the Grand Canal and the Tang government's rationalization of the greater canal system that reduced costs of transporting grain and other commodities. The state also managed roughly of postal service routes by horse or boat.

Although the Silk Road from China to Europe and the Western World was initially formulated during the reign of Emperor Wu (141–87 ) during the Han, it was reopened by the Tang in 639 when Hou Junji ( 643) conquered the West, and remained open for almost four decades. It was closed after the Tibetans captured it in 678, but in 699, during Empress Wu's period, the Silk Road reopened when the Tang reconquered the Four Garrisons of Anxi originally installed in 640, once again connecting China directly to the West for land-based trade. The Tang captured the vital route through the Gilgit Valley from Tibet in 722, lost it to the Tibetans in 737, and regained it under the command of the Goguryeo-Korean General Gao Xianzhi. When the An Lushan Rebellion ended in 763, the Tang Empire had once again lost control over its western lands, as the Tibetan Empire largely cut off China's direct access to the Silk Road. An internal rebellion in 848 ousted the Tibetan rulers, and Tang China regained its northwestern prefectures from Tibet in 851. These lands contained crucial grazing areas and pastures for raising horses that the Tang dynasty desperately needed.

Despite the many expatriate European travelers coming into China to live and trade, many travelers, mainly religious monks and missionaries, recorded the strict border laws that the Chinese enforced. As the monk Xuanzang and many other monk travelers attested to, there were many Chinese government checkpoints along the Silk Road that examined travel permits into the Tang Empire. Furthermore, banditry was a problem along the checkpoints and oasis towns, as Xuanzang also recorded that his group of travelers were assaulted by bandits on multiple occasions.

The Silk Road also affected Tang dynasty art. Horses became a significant symbol of prosperity and power as well as an instrument of military and diplomatic policy. Horses were also revered as a relative of the dragon.

Chinese envoys have been sailing through the Indian Ocean to India since perhaps the 2nd century BC, yet it was during the Tang dynasty that a strong Chinese maritime presence could be found in the Persian Gulf and Red Sea, into Persia, Mesopotamia (sailing up the Euphrates River in modern-day Iraq), Arabia, Egypt in the Middle East and Aksum (Ethiopia), and Somalia in the Horn of Africa.

During the Tang dynasty, thousands of foreign expatriate merchants came and lived in numerous Chinese cities to do business with China, including Persians, Arabs, Hindu Indians, Malays, Bengalis, Sinhalese, Khmers, Chams, Jews and Nestorian Christians of the Near East, among many others. In 748, the Buddhist monk Jian Zhen described Guangzhou as a bustling mercantile business center where many large and impressive foreign ships came to dock. He wrote that "many big ships came from Borneo, Persia, Qunglun (Indonesia/Java)...with...spices, pearls, and jade piled up mountain high", as written in the "Yue Jue Shu" (Lost Records of the State of Yue). During the An Lushan Rebellion Arab and Persian pirates burned and looted Guangzhou in 758, and foreigners were massacred at Yangzhou in 760. The Tang government reacted by shutting the port of Canton down for roughly five decades, and foreign vessels docked at Hanoi instead. However, when the port reopened it continued to thrive. In 851 the Arab merchant Sulaiman al-Tajir observed the manufacturing of Chinese porcelain in Guangzhou and admired its transparent quality. He also provided a description of Guangzhou's mosque, its granaries, its local government administration, some of its written records, the treatment of travelers, along with the use of ceramics, rice-wine, and tea. However, in another bloody episode at Guangzhou in 879, the Chinese rebel Huang Chao sacked the city, and purportedly slaughtered thousands of native Han Chinese, along with foreign Jews, Christians, Zoroastrians, and Muslims in the process. Huang's rebellion was eventually suppressed in 884.

Vessels from neighboring East Asian states such as Silla and Balhae of Korea and the Hizen Province of Japan were all involved in the Yellow Sea trade, which Silla dominated. After Silla and Japan reopened renewed hostilities in the late 7th century, most Japanese maritime merchants chose to set sail from Nagasaki towards the mouth of the Huai River, the Yangzi River, and even as far south as the Hangzhou Bay in order to avoid Korean ships in the Yellow Sea. In order to sail back to Japan in 838, the Japanese embassy to China procured nine ships and sixty Korean sailors from the Korean wards of Chuzhou and Lianshui cities along the Huai River. It is also known that Chinese trade ships traveling to Japan set sail from the various ports along the coasts of Zhejiang and Fujian provinces.

The Chinese engaged in large-scale production for overseas export by at least the time of the Tang. This was proven by the discovery of the Belitung shipwreck, a silt-preserved shipwrecked Arabian dhow in the Gaspar Strait near Belitung, which had 63,000 pieces of Tang ceramics, silver, and gold (including a Changsha bowl inscribed with a date: "16th day of the seventh month of the second year of the Baoli reign", or 826, roughly confirmed by radiocarbon dating of star anise at the wreck). Beginning in 785, the Chinese began to call regularly at Sufala on the East African coast in order to cut out Arab middlemen, with various contemporary Chinese sources giving detailed descriptions of trade in Africa. The official and geographer Jia Dan (730–805) wrote of two common sea trade routes in his day: one from the coast of the Bohai Sea towards Korea and another from Guangzhou through Malacca towards the Nicobar Islands, Sri Lanka and India, the eastern and northern shores of the Arabian Sea to the Euphrates River. In 863 the Chinese author Duan Chengshi (d. 863) provided a detailed description of the slave trade, ivory trade, and ambergris trade in a country called Bobali, which historians suggest was Berbera in Somalia. In Fustat (old Cairo), Egypt, the fame of Chinese ceramics there led to an enormous demand for Chinese goods; hence Chinese often traveled there (this continued into later periods such as Fatimid Egypt). From this time period, the Arab merchant Shulama once wrote of his admiration for Chinese seafaring junks, but noted that their draft was too deep for them to enter the Euphrates River, which forced them to ferry passengers and cargo in small boats. Shulama also noted that Chinese ships were often very large, with capacities up to 600–700 passengers.

Both the Sui and Tang Dynasties had turned away from the more feudal culture of the preceding Northern Dynasties, in favor of staunch civil Confucianism. The governmental system was supported by a large class of Confucian intellectuals selected through either civil service examinations or recommendations. In the Tang period, Daoism and Buddhism reigned as core ideologies as well, and played a large role in people's daily lives. The Tang Chinese enjoyed feasting, drinking, holidays, sports, and all sorts of entertainment, while Chinese literature blossomed and was more widely accessible with new printing methods.

Although Chang'an was the capital of the earlier Han and Jin dynasties, after subsequent destruction in warfare, it was the Sui dynasty model that comprised the Tang era capital. The roughly square dimensions of the city had six miles (10 km) of outer walls running east to west, and more than five miles (8 km) of outer walls running north to south. The royal palace, the Taiji Palace, stood north of the city's central axis. From the large Mingde Gates located mid-center of the main southern wall, a wide city avenue stretched from there all the way north to the central administrative city, behind which was the Chentian Gate of the royal palace, or Imperial City. Intersecting this were fourteen main streets running east to west, while eleven main streets ran north to south. These main intersecting roads formed 108 rectangular wards with walls and four gates each, and each ward filled with multiple city blocks. The city was made famous for this checkerboard pattern of main roads with walled and gated districts, its layout even mentioned in one of Du Fu's poems. During the Heian period, the city of Heian kyō (present-day Kyoto) of Japan like many cities was arranged in the checkerboard street grid pattern of the Tang capital and in accordance with traditional geomancy following the model of Chang'an. Of these 108 wards in Chang'an, two of them (each the size of two regular city wards) were designated as government-supervised markets, and other space reserved for temples, gardens, ponds, etc. Throughout the entire city, there were 111 Buddhist monasteries, 41 Daoist abbeys, 38 family shrines, 2 official temples, 7 churches of foreign religions, 10 city wards with provincial transmission offices, 12 major inns, and 6 graveyards. Some city wards were literally filled with open public playing fields or the backyards of lavish mansions for playing horse polo and cuju football. In 662, Emperor Gaozong moved the imperial court to the Daming Palace, which became the political center of the empire and served as the royal residence of the Tang emperors for more than 220 years.

The Tang capital was the largest city in the world at its time, the population of the city wards and its suburban countryside reaching two million inhabitants. The Tang capital was very cosmopolitan, with ethnicities of Persia, Central Asia, Japan, Korea, Vietnam, Tibet, India, and many other places living within. Naturally, with this plethora of different ethnicities living in Chang'an, there were also many different practiced religions, such as Buddhism, Nestorian Christianity, Manichaeism, Zoroastrianism, Judaism, and Islam being practiced within. With widely open access to China that the Silk Road to the west facilitated, many foreign settlers were able to move east to China, while the city of Chang'an itself had about 25,000 foreigners living within. Exotic green-eyed, blonde-haired Tocharian ladies serving wine in agate and amber cups, singing, and dancing at taverns attracted customers. If a foreigner in China pursued a Chinese woman for marriage, he was required to stay in China and was unable to take his bride back to his homeland, as stated in a law passed in 628 to protect women from temporary marriages with foreign envoys. Several laws enforcing segregation of foreigners from Chinese were passed during the Tang dynasty. In 779 the Tang dynasty issued an edict which forced Uighurs in the capital, Chang'an, to wear their ethnic dress, stopped them from marrying Chinese females, and banned them from passing off as Chinese.
Chang'an was the center of the central government, the home of the imperial family, and was filled with splendor and wealth. However, incidentally it was not the economic hub during the Tang dynasty. The city of Yangzhou along the Grand Canal and close to the Yangtze River was the greatest economic center during the Tang era.

Yangzhou was the headquarters for the Tang's government monopoly on salt, and the greatest industrial center of China; it acted as a midpoint in shipping of foreign goods that would be organized and distributed to the major cities of the north. Much like the seaport of Guangzhou in the south, Yangzhou boasted thousands of foreign traders from all across Asia.

There was also the secondary capital city of Luoyang, which was the favored capital of the two by Empress Wu. In the year 691 she had more than 100,000 families (more than 500,000 people) from around the region of Chang'an move to populate Luoyang instead. With a population of about a million, Luoyang became the second largest city in the empire, and with its close proximity to the Luo River it benefited from southern agricultural fertility and trade traffic of the Grand Canal. However, the Tang court eventually demoted its capital status and did not visit Luoyang after the year 743, when Chang'an's problem of acquiring adequate supplies and stores for the year was solved. As early as 736, granaries were built at critical points along the route from Yangzhou to Chang'an, which eliminated shipment delays, spoilage, and pilfering. An artificial lake used as a transshipment pool was dredged east of Chang'an in 743, where curious northerners could finally see the array of boats found in southern China, delivering tax and tribute items to the imperial court.

The Tang period was a golden age of Chinese literature and art. There are over 48,900 poems penned by some 2,200 Tang authors that have survived until modern times. Skill in the composition of poetry became a required study for those wishing to pass imperial examinations, while poetry was also heavily competitive; poetry contests amongst guests at banquets and courtiers were common. Poetry styles that were popular in the Tang included "gushi" and "jintishi", with the renowned poet Li Bai (701–762) famous for the former style, and poets like Wang Wei (701–761) and Cui Hao (704–754) famous for their use of the latter. "Jintishi" poetry, or regulated verse, is in the form of eight-line stanzas or seven characters per line with a fixed pattern of tones that required the second and third couplets to be antithetical (although the antithesis is often lost in translation to other languages). Tang poems remained popular and great emulation of Tang era poetry began in the Song dynasty; in that period, Yan Yu (嚴羽; active 1194–1245) was the first to confer the poetry of the High Tang (c. 713–766) era with "canonical status within the classical poetic tradition." Yan Yu reserved the position of highest esteem among all Tang poets for Du Fu (712–770), who was not viewed as such in his own era, and was branded by his peers as an anti-traditional rebel.

The Classical Prose Movement was spurred in large part by the writings of Tang authors Liu Zongyuan (773–819) and Han Yu (768–824). This new prose style broke away from the poetry tradition of the "piantiwen" (, "parallel prose") style begun in the Han dynasty. Although writers of the Classical Prose Movement imitated "piantiwen", they criticized it for its often vague content and lack of colloquial language, focusing more on clarity and precision to make their writing more direct. This "guwen" (archaic prose) style can be traced back to Han Yu, and would become largely associated with orthodox Neo-Confucianism.

Short story fiction and tales were also popular during the Tang, one of the more famous ones being "Yingying's Biography" by Yuan Zhen (779–831), which was widely circulated in his own time and by the Yuan dynasty (1279–1368) became the basis for plays in Chinese opera. Timothy C. Wong places this story within the wider context of Tang love tales, which often share the plot designs of quick passion, inescapable societal pressure leading to the abandonment of romance, followed by a period of melancholy. Wong states that this scheme lacks the undying vows and total self-commitment to love found in Western romances such as "Romeo and Juliet", but that underlying traditional Chinese values of inseparableness of self from one's environment (including human society) served to create the necessary fictional device of romantic tension.

There were large encyclopedias published in the Tang. The "Yiwen Leiju" encyclopedia was compiled in 624 by the chief editor Ouyang Xun (557–641) as well as Linghu Defen (582–666) and Chen Shuda (d. 635). The encyclopedia "Treatise on Astrology of the Kaiyuan Era" was fully compiled in 729 by Gautama Siddha (fl. 8th century), an ethnic Indian astronomer, astrologer, and scholar born in the capital Chang'an.

Chinese geographers such as Jia Dan wrote accurate descriptions of places far abroad. In his work written between 785 and 805, he described the sea route going into the mouth of the Persian Gulf, and that the medieval Iranians (whom he called the people of Luo-He-Yi) had erected 'ornamental pillars' in the sea that acted as lighthouse beacons for ships that might go astray. Confirming Jia's reports about lighthouses in the Persian Gulf, Arabic writers a century after Jia wrote of the same structures, writers such as al-Mas'udi and al-Muqaddasi. The Tang dynasty Chinese diplomat Wang Xuance traveled to Magadha (modern northeastern India) during the 7th century. Afterwards he wrote the book "Zhang Tianzhu Guotu" (Illustrated Accounts of Central India), which included a wealth of geographical information.

Many histories of previous dynasties were compiled between 636 and 659 by court officials during and shortly after the reign of Emperor Taizong of Tang. These included the "Book of Liang", "Book of Chen", "Book of Northern Qi", "Book of Zhou", "Book of Sui", "Book of Jin", "History of Northern Dynasties" and the "History of Southern Dynasties". Although not included in the official "Twenty-Four Histories", the "Tongdian" and "Tang Huiyao" were nonetheless valuable written historical works of the Tang period. The "Shitong" written by Liu Zhiji in 710 was a meta-history, as it covered the history of Chinese historiography in past centuries until his time. The "Great Tang Records on the Western Regions", compiled by Bianji, recounted the journey of Xuanzang, the Tang era's most renowned Buddhist monk.

Other important literary offerings included Duan Chengshi's (d. 863) "Miscellaneous Morsels from Youyang", an entertaining collection of foreign legends and hearsay, reports on natural phenomena, short anecdotes, mythical and mundane tales, as well as notes on various subjects. The exact literary category or classification that Duan's large informal narrative would fit into is still debated amongst scholars and historians.

Since ancient times, the Chinese believed in a folk religion and Daoism that incorporated many deities. The Chinese believed Tao and the afterlife was a reality parallel to the living world, complete with its own bureaucracy and afterlife currency needed by dead ancestors. Funerary practices included providing the deceased with everything they might need in the afterlife, including animals, servants, entertainers, hunters, homes, and officials. This ideal is reflected in Tang dynasty art. This is also reflected in many short stories written in the Tang about people accidentally winding up in the realm of the dead, only to come back and report their experiences.

Buddhism, originating in India around the time of Confucius, continued its influence during the Tang period and was accepted by some members of imperial family, becoming thoroughly sinicized and a permanent part of Chinese traditional culture. In an age before Neo-Confucianism and figures such as Zhu Xi (1130–1200), Buddhism had begun to flourish in China during the Northern and Southern dynasties, and became the dominant ideology during the prosperous Tang. Buddhist monasteries played an integral role in Chinese society, offering lodging for travelers in remote areas, schools for children throughout the country, and a place for urban literati to stage social events and gatherings such as going-away parties. Buddhist monasteries were also engaged in the economy, since their land property and serfs gave them enough revenues to set up mills, oil presses, and other enterprises. Although the monasteries retained'serfs', these monastery dependents could actually own property and employ others to help them in their work, including their own slaves.

The prominent status of Buddhism in Chinese culture began to decline as the dynasty and central government declined as well during the late 8th century to 9th century. Buddhist convents and temples that were exempt from state taxes beforehand were targeted by the state for taxation. In 845 Emperor Wuzong of Tang finally shut down 4,600 Buddhist monasteries along with 40,000 temples and shrines, forcing 260,000 Buddhist monks and nuns to return to secular life; this episode would later be dubbed one of the Four Buddhist Persecutions in China. Although the ban would be lifted just a few years after, Buddhism never regained its once dominant status in Chinese culture. This situation also came about through new revival of interest in native Chinese philosophies, such as Confucianism and Daoism. Han Yu (786–824)—who Arthur F. Wright stated was a "brilliant polemicist and ardent xenophobe"—was one of the first men of the Tang to denounce Buddhism. Although his contemporaries found him crude and obnoxious, he would foreshadow the later persecution of Buddhism in the Tang, as well as the revival of Confucian theory with the rise of Neo-Confucianism of the Song dynasty. Nonetheless, Chán Buddhism gained popularity amongst the educated elite. There were also many famous Chan monks from the Tang era, such as Mazu Daoyi, Baizhang, and Huangbo Xiyun. The sect of Pure Land Buddhism initiated by the Chinese monk Huiyuan (334–416) was also just as popular as Chan Buddhism during the Tang.

Rivaling Buddhism was Daoism, a native Chinese philosophical and religious belief system that found its roots in the book of the "Daodejing" (attributed to a 6th-century BC figure named Laozi) and the "Zhuangzi". The ruling Li family of the Tang dynasty actually claimed descent from the ancient Laozi. On numerous occasions where Tang princes would become crown prince or Tang princesses taking vows as Daoist priestesses, their lavish former mansions would be converted into Daoist abbeys and places of worship. Many Daoists were associated with alchemy in their pursuits to find an elixir of immortality and a means to create gold from concocted mixtures of many other elements. Although they never achieved their goals in either of these futile pursuits, they did contribute to the discovery of new metal alloys, porcelain products, and new dyes. The historian Joseph Needham labeled the work of the Daoist alchemists as "proto-science rather than pseudo-science." However, the close connection between Daoism and alchemy, which some sinologists have asserted, is refuted by Nathan Sivin, who states that alchemy was just as prominent (if not more so) in the secular sphere and practiced more often by laymen.

The Tang dynasty also officially recognized various foreign religions. The Assyrian Church of the East, otherwise known as the Nestorian Christian Church, was given recognition by the Tang court. In 781, the Nestorian Stele was created in order to honor the achievements of their community in China. A Christian monastery was established in Shaanxi province where the Daqin Pagoda still stands, and inside the pagoda there is Christian-themed artwork. Although the religion largely died out after the Tang, it was revived in China following the Mongol invasions of the 13th century.

Although the Sogdians had been responsible for transmitting Buddhism to China from India during the 2nd to 4th centuries, soon afterwards they largely converted to Zoroastrianism due to their links to Sassanid Persia. Sogdian merchants and their families living in cities such as Chang'an, Luoyang, and Xiangyang usually built a Zoroastrian temple once their local communities grew larger than 100 households. Sogdians were also responsible for spreading Manichaeism in Tang China and the Uyghur Khaganate. The Uyghurs built the first Manichaean monastery in China in 768, yet in 843 the Tang government ordered that the property of all Manichaean monasteries be confiscated in response to the outbreak of war with the Uyghurs. With the blanket ban on foreign religions two years later, Manichaeism was driven underground and never flourished in China again.

Much more than earlier periods, the Tang era was renowned for the time reserved for leisure activity, especially for those in the upper classes. Many outdoor sports and activities were enjoyed during the Tang, including archery, hunting, horse polo, cuju football, cockfighting, and even tug of war. Government officials were granted vacations during their tenure in office. Officials were granted 30 days off every three years to visit their parents if they lived away, or 15 days off if the parents lived more than away (travel time not included). Officials were granted nine days of vacation time for weddings of a son or daughter, and either five, three, or one days/day off for the nuptials of close relatives (travel time not included). Officials also received a total of three days off for their son's capping initiation rite into manhood, and one day off for the ceremony of initiation rite of a close relative's son.
Traditional Chinese holidays such as Chinese New Year, Lantern Festival, Cold Food Festival, and others were universal holidays. In the capital city of Chang'an there was always lively celebration, especially for the Lantern Festival since the city's nighttime curfew was lifted by the government for three days straight. Between the years 628 and 758, the imperial throne bestowed a total of sixty-nine grand carnivals nationwide, granted by the emperor in the case of special circumstances such as important military victories, abundant harvests after a long drought or famine, the granting of amnesties, the installment of a new crown prince, etc. For special celebration in the Tang era, lavish and gargantuan-sized feasts were sometimes prepared, as the imperial court had staffed agencies to prepare the meals. This included a prepared feast for 1,100 elders of Chang'an in 664, a feast for 3,500 officers of the Divine Strategy Army in 768, and a feast for 1,200 women of the palace and members of the imperial family in the year 826. Drinking wine and alcoholic beverages was heavily ingrained into Chinese culture, as people drank for nearly every social event. A court official in the 8th century allegedly had a serpentine-shaped structure called the 'Ale Grotto' built with 50,000 bricks on the groundfloor that each featured a bowl from which his friends could drink.

Concepts of women's social rights and social status during the Tang era were notably liberal-minded for the period. However, this was largely reserved for urban women of elite status, as men and women in the rural countryside labored hard in their different set of tasks; with wives and daughters responsible for more domestic tasks of weaving textiles and rearing of silk worms, while men tended to farming in the fields. There were many women in the Tang era who gained access to religious authority by taking vows as Daoist priestesses. The head mistresses of the bordellos in the North Hamlet of the capital Chang'an acquired large amounts of wealth and power. Their high-class courtesans, who likely influenced the Japanese geishas, were well respected. These courtesans were known as great singers and poets, supervised banquets and feasts, knew the rules to all the drinking games, and were trained to have the utmost respectable table manners.

Although they were renowned for their polite behavior, the courtesans were known to dominate the conversation amongst elite men, and were not afraid to openly castigate or criticize prominent male guests who talked too much or too loudly, boasted too much of their accomplishments, or had in some way ruined dinner for everyone by rude behavior (on one occasion a courtesan even beat up a drunken man who had insulted her). When singing to entertain guests, courtesans not only composed the lyrics to their own songs, but they popularized a new form of lyrical verse by singing lines written by various renowned and famous men in Chinese history.

It was fashionable for women to be full-figured (or plump). Men enjoyed the presence of assertive, active women. The foreign horse-riding sport of polo from Persia became a wildly popular trend amongst the Chinese elite, and women often played the sport (as glazed earthenware figurines from the time period portray). The preferred hairstyle for women was to bunch their hair up like "an elaborate edifice above the forehead", while affluent ladies wore extravagant head ornaments, combs, pearl necklaces, face powders, and perfumes. A law was passed in 671 which attempted to force women to wear hats with veils again in order to promote decency, but these laws were ignored as some women started wearing caps and even no hats at all, as well as men's riding clothes and boots, and tight-sleeved bodices.

There were some prominent court women after the era of Empress Wu, such as Yang Guifei (719–756), who had Emperor Xuanzong appoint many of her relatives and cronies to important ministerial and martial positions.

During the earlier Northern and Southern dynasties (420–589), and perhaps even earlier, the drinking of tea ("Camellia sinensis") became popular in southern China. Tea was viewed then as a beverage of tasteful pleasure and with pharmacological purpose as well. During the Tang dynasty, tea became synonymous with everything sophisticated in society. The poet Lu Tong (790–835) devoted most of his poetry to his love of tea. The 8th-century author Lu Yu (known as the Sage of Tea) even wrote a treatise on the art of drinking tea, called "The Classic of Tea". Although wrapping paper had been used in China since the 2nd century BC, during the Tang dynasty the Chinese were using wrapping paper as folded and sewn square bags to hold and preserve the flavor of tea leaves. Indeed, paper found many other uses besides writing and wrapping during the Tang era.

Earlier, the first recorded use of toilet paper was made in 589 by the scholar-official Yan Zhitui (531–591), and in 851 an Arab Muslim traveler commented on how he believed the Tang era Chinese were not careful about cleanliness because they did not wash with water (as was his people's habit) when going to the bathroom; instead, he said, the Chinese simply used paper to wipe themselves.

In ancient times, the Chinese had outlined the five most basic foodstuffs known as the five grains: sesamum, legumes, wheat, panicled millet, and glutinous millet. The Ming dynasty encyclopedist Song Yingxing (1587–1666) noted that rice was not counted amongst the five grains from the time of the legendary and deified Chinese sage Shennong (the existence of whom Yingxing wrote was "an uncertain matter") into the 2nd millenniums BC, because the properly wet and humid climate in southern China for growing rice was not yet fully settled or cultivated by the Chinese. But Song Yingxing also noted that in the Ming Dynasty, seven tenths of civilians' food was rice. In fact, in the Tang Dynasty rice was not only the most important staple in southern China, but had also became popular in the north, which was for a long time the center of China.

During the Tang dynasty, wheat replaced the position of millet and became the main staple crop. As a consequence, wheat cake shared a considerable amount in the staple of Tang. There were four main kinds of cake: steamed cake, boiled cake, pancake, and Hu cake.

Steamed cake was consumed commonly by both civilians and aristocrats. Like the Rougamo in modern Chinese cuisine, steamed cake was usually stuffed by meat and vegetable. There were plenty of shops and packmen selling steamed cake in Chang’an, and its price was also far from expensive. "Taiping Guangji" recorded a civilian in Chang'an named Zou Luotuo, who was poor and "often push his cart out selling steamed cake."

Boiled cake was the staple of the Northern Dynasty, and it kept its popularity in the Tang dynasty. The definition here was very broad, including current day wonton, noodles, and many other kinds of food that soak wheat in water. Consuming boiled cake was treated as an effective and popular way of diet therapy. While aristocrats favored wonton, civilians usually consumed noodles and noodle slice soup, because the process to make wonton was heavy and complicated.

Pancake was hard to find in China before the Tang. But in the Tang dynasty pancake started becoming popular. There were also many shops in Tang cities selling pancakes. A story in "Taiping Guangji" recorded that a merchant in early Tang bought a large vacant lot in Chang’an to set up several shops selling pancake and dumplings.

Hu cake, which means foreign cake, was extremely popular in Tang. Hu cake was toasted in oven and covered by sesame. Restaurants in Tang usually treated Hu cake as an indispensable food in their menu. A Japanese Buddhist monk Ennin recorded in "The Record of a Pilgrimage to China in Search of the Law" that at that time Hu cake was popular among all civilians.
During the Tang, the many common foodstuffs and cooking ingredients in addition to those already listed were barley, garlic, salt, turnips, soybeans, pears, apricots, peaches, apples, pomegranates, jujubes, rhubarb, hazelnuts, pine nuts, chestnuts, walnuts, yams, taro, etc. The various meats that were consumed included pork, chicken, lamb (especially preferred in the north), sea otter, bear (which was hard to catch, but there were recipes for steamed, boiled, and marinated bear), and even Bactrian camels. In the south along the coast meat from seafood was by default the most common, as the Chinese enjoyed eating cooked jellyfish with cinnamon, Sichuan pepper, cardamom, and ginger, as well as oysters with wine, fried squid with ginger and vinegar, horseshoe crabs and red swimming crabs, shrimp and pufferfish, which the Chinese called "river piglet".

Some foods were also off-limits, as the Tang court encouraged people not to eat beef (since the bull was a valuable working animal), and from 831 to 833 Emperor Wenzong of Tang even banned the slaughter of cattle on the grounds of his religious convictions to Buddhism.

From the trade overseas and over land, the Chinese acquired peaches from Samarkand, date palms, pistachios, and figs from Greater Iran, pine nuts and ginseng roots from Korea and mangoes from Southeast Asia. In China, there was a great demand for sugar; during the reign of Harsha over North India (r. 606–647), Indian envoys to the Tang brought two makers of sugar who successfully taught the Chinese how to cultivate sugarcane. Cotton also came from India as a finished product from Bengal, although it was during the Tang that the Chinese began to grow and process cotton, and by the Yuan dynasty it became the prime textile fabric in China.

Methods of food preservation were important, and practiced throughout China. The common people used simple methods of preservation, such as digging deep ditches and trenches, brining, and salting their foods. The emperor had large ice pits located in the parks in and around Chang'an for preserving food, while the wealthy and elite had their own smaller ice pits. Each year the emperor had laborers carve 1000 blocks of ice from frozen creeks in mountain valleys, each block with the dimension of by 3 ft by. Frozen delicacies such as chilled melon were enjoyed during the summer.

Technology during the Tang period was built also upon the precedents of the past. Previous advancements in clockworks and timekeeping included the mechanical gear systems of Zhang Heng (78–139) and Ma Jun (fl. 3rd century), which gave the Tang engineer, astronomer, and monk Yi Xing (683–727) inspiration when he invented the world's first clockwork escapement mechanism in 725. This was used alongside a clepsydra clock and waterwheel to power a rotating armillary sphere in representation of astronomical observation. Yi Xing's device also had a mechanically timed bell that was struck automatically every hour, and a drum that was struck automatically every quarter-hour; essentially, a striking clock. Yi Xing's astronomical clock and water-powered armillary sphere became well known throughout the country, since students attempting to pass the imperial examinations by 730 had to write an essay on the device as an exam requirement. However, the most common type of public and palace timekeeping device was the inflow clepsydra. Its design was improved c. 610 by the Sui-dynasty engineers Geng Xun and Yuwen Kai. They provided a steelyard balance that allowed seasonal adjustment in the pressure head of the compensating tank and could then control the rate of flow for different lengths of day and night.

There were many other mechanical inventions during the Tang era. These included a 3 ft (0.91 m) tall mechanical wine server of the early 8th century that was in the shape of an artificial mountain, carved out of iron and rested on a lacquered-wooden tortoise frame. This intricate device used a hydraulic pump that siphoned wine out of metal dragon-headed faucets, as well as tilting bowls that were timed to dip wine down, by force of gravity when filled, into an artificial lake that had intricate iron leaves popping up as trays for placing party treats. Furthermore, as the historian Charles Benn describes it:

Yet the use of a teasing mechanical puppet in this wine-serving device wasn't exactly a novel invention of the Tang, since the use of mechanical puppets in China date back to the Qin dynasty (221–207 BC). In the 3rd century Ma Jun had an entire mechanical puppet theater operated by the rotation of a waterwheel. There was also an automatic wine-server known in the ancient Greco-Roman world, a design of the Greek inventor Heron of Alexandria that employed an urn with an inner valve and a lever device similar to the one described above. There are many stories of automatons used in the Tang, including general Yang Wulian's wooden statue of a monk who stretched his hands out to collect contributions; when the amount of coins reached a certain weight, the mechanical figure moved his arms to deposit them in a satchel. This weight-and-lever mechanism was exactly like Heron's penny slot machine. Other devices included one by Wang Ju, whose "wooden otter" could allegedly catch fish; Needham suspects a spring trap of some kind was employed here.

In the realm of structural engineering and technical Chinese architecture, there were also government standard building codes, outlined in the early Tang book of the "Yingshan Ling" (National Building Law). Fragments of this book have survived in the "Tang Lü" (The Tang Code), while the Song dynasty architectural manual of the "Yingzao Fashi" (State Building Standards) by Li Jie (1065–1101) in 1103 is the oldest existing technical treatise on Chinese architecture that has survived in full. During the reign of Emperor Xuanzong of Tang (712–756) there were 34,850 registered craftsmen serving the state, managed by the Agency of Palace Buildings (Jingzuo Jian).

Woodblock printing made the written word available to vastly greater audiences. One of the world's oldest surviving printed documents is a miniature Buddhist "dharani" sutra unearthed at Xi'an in 1974 and dated roughly from 650 to 670. The "Diamond Sutra" is the first full-length book printed at regular size, complete with illustrations embedded with the text and dated precisely to 868. Among the earliest documents to be printed were Buddhist texts as well as calendars, the latter essential for calculating and marking which days were auspicious and which days were not. With so many books coming into circulation for the general public, literacy rates could improve, along with the lower classes being able to obtain cheaper sources of study. Therefore, there were more lower-class people seen entering the Imperial Examinations and passing them by the later Song dynasty. Although the later Bi Sheng's movable type printing in the 11th century was innovative for his period, woodblock printing that became widespread in the Tang would remain the dominant printing type in China until the more advanced printing press from Europe became widely accepted and used in East Asia. The first use of the playing card during the Tang dynasty was an auxiliary invention of the new age of printing.

In the realm of cartography, there were further advances beyond the map-makers of the Han dynasty. When the Tang chancellor Pei Ju (547–627) was working for the Sui dynasty as a Commercial Commissioner in 605, he created a well-known gridded map with a graduated scale in the tradition of Pei Xiu (224–271). The Tang chancellor Xu Jingzong (592–672) was also known for his map of China drawn in the year 658. In the year 785 the Emperor Dezong had the geographer and cartographer Jia Dan (730–805) complete a map of China and her former colonies in Central Asia. Upon its completion in 801, the map was 9.1 m (30 ft) in length and 10 m (33 ft) in height, mapped out on a grid scale of one inch equaling one hundred "li" (Chinese unit of measuring distance). A Chinese map of 1137 is similar in complexity to the one made by Jia Dan, carved on a stone stele with a grid scale of 100 li. However, the only type of map that has survived from the Tang period are star charts. Despite this, the earliest extant terrain maps of China come from the ancient State of Qin; maps from the 4th century BC that were excavated in 1986.
The Chinese of the Tang era were also very interested in the benefits of officially classifying all of the medicines used in pharmacology. In 657, Emperor Gaozong of Tang (r. 649–683) commissioned the literary project of publishing an official "materia medica", complete with text and illustrated drawings for 833 different medicinal substances taken from different stones, minerals, metals, plants, herbs, animals, vegetables, fruits, and cereal crops. In addition to compiling pharmacopeias, the Tang fostered learning in medicine by upholding imperial medical colleges, state examinations for doctors, and publishing forensic manuals for physicians. Authors of medicine in the Tang include Zhen Chuan (d. 643) and Sun Simiao (581–682), the former who first identified in writing that patients with diabetes had an excess of sugar in their urine, and the latter who was the first to recognize that diabetic patients should avoid consuming alcohol and starchy foods. As written by Zhen Chuan and others in the Tang, the thyroid glands of sheep and pigs were successfully used to treat goiters; thyroid extracts were not used to treat patients with goiter in the West until 1890. The use of the dental amalgam, manufactured from tin and silver, was first introduced in the medical text "Xinxiu Bencao" written by Su Gong in 659.

Chinese scientists of the Tang period employed complex chemical formulas for an array of different purposes, often found through experiments of alchemy. These included a waterproof and dust-repelling cream or varnish for clothes and weapons, fireproof cement for glass and porcelain wares, a waterproof cream applied to silk clothes of underwater divers, a cream designated for polishing bronze mirrors, and many other useful formulas. The vitrified, translucent ceramic known as porcelain was invented in China during the Tang, although many types of glazed ceramics preceded it.

Ever since the Han dynasty (202 BC – 220 AD), the Chinese had drilled deep boreholes to transport natural gas from bamboo pipelines to stoves where cast iron evaporation pans boiled brine to extract salt. During the Tang dynasty, a gazetteer of Sichuan province stated that at one of these 182 m (600 ft) 'fire wells', men collected natural gas into portable bamboo tubes which could be carried around for dozens of km (mi) and still produce a flame. These were essentially the first gas cylinders; Robert Temple assumes some sort of tap was used for this device.

The inventor Ding Huan (fl. 180 AD) of the Han dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered. In 747, Emperor Xuanzong had a "Cool Hall" built in the imperial palace, which the "Tang Yulin" () describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song dynasty, written sources mentioned the air conditioning rotary fan as even more widely used.

The first classic work about the Tang is the "Old Book of Tang" by Liu Xu (887–946) et al. of the Later Jin, who redacted it during the last years of his life. This was edited into another history (labelled the "New Book of Tang") in order to distinguish it, which was a work by the Song historians Ouyang Xiu (1007–1072), Song Qi (998–1061), et al. of the Song dynasty (between the years 1044 and 1060). Both of them were based upon earlier annals, yet those are now lost. Both of them also rank among the "Twenty-Four Histories" of China. One of the surviving sources of the "Old Book of Tang", primarily covering up to 756, is the "Tongdian", which Du You presented to the emperor in 801. The Tang period was again placed into the enormous universal history text of the "Zizhi Tongjian", edited, compiled, and completed in 1084 by a team of scholars under the Song dynasty Chancellor Sima Guang (1019–1086). This historical text, written with three million Chinese characters in 294 volumes, covered the history of China from the beginning of the Warring States (403 BC) until the beginning of the Song dynasty (960).

The inventor Ding Huan (fl. 180 AD) of the Han dynasty invented a rotary fan for air conditioning, with seven wheels 3 m (10 ft) in diameter and manually powered. In 747, Emperor Xuanzong had a "Cool Hall" built in the imperial palace, which the "Tang Yulin" (唐語林) describes as having water-powered fan wheels for air conditioning as well as rising jet streams of water from fountains. During the subsequent Song dynasty, written sources mentioned the air conditioning rotary fan as even more widely used.

Science and technology of the Tang dynasty

The Tang dynasty (618–907) of ancient China witnessed many advancements in Chinese science and technology, with various developments in woodblock printing, timekeeping, mechanical engineering, medicine, structural engineering, cartography, and alchemy.

The popularization of woodblock printing during the Tang dynasty made the written word available to greater audiences. As a result of the much wider distribution and circulation of reading materials, the general populace were for the first time able to purchase affordable copies of texts, which correspondingly led to greater literacy. While the immediate effects of woodblock printing did not create a drastic change in Chinese society, in the long term, the accumulated effects of increased literacy enlarged the talent pool to encompass civilians of broader social-economic circumstances and backgrounds, who would be seen entering the imperial examinations and passing them by the later Song dynasty. The extent of woodblock printing is attested to by one of the world's oldest surviving printed documents, a miniature Buddhist "dharani" sutra unearthed at Xi'an in 1974, dating roughly from 650 to 670. A copy of the "Diamond Sutra" found at Dunhuang is the earliest surviving full-length book printed at regular size, complete with illustrations embedded within the text and dated precisely to 868. Among the earliest documents to be printed were Buddhist texts as well as calendars, the latter essential for calculating and marking which days were auspicious and which days were not. The commercial success and profitability of woodblock printing was attested to by one British observer at the end of the nineteenth century, who noted that even before the arrival of western printing methods, the price of books and printed materials in China had already reached an astoundingly low price compared to what could be found in his home country. Of this, he said:

Although Bi Sheng later invented the movable type system in the 11th century, Tang dynasty style woodblock printing would remain the dominant mode of printing in China until the more advanced printing press from Europe became widely accepted and used in East Asia. However it was not Gutenberg's letterpress that made the decisive breakthrough for Western methods in China as it is commonly believed, but lithography, a nineteenth century technological marvel almost wholly forgotten in Europe.

Playing cards may have been invented during the Tang dynasty around the 9th century AD as a result of the usage of woodblock printing technology. The first possible reference to card games comes from a 9th-century text known as the "Collection of Miscellanea at Duyang", written by Tang dynasty writer Su E. It describes Princess Tongchang, daughter of Emperor Yizong of Tang, playing the "leaf game" in 868 with members of the clan of Wei Baoheng, the family of the princess' husband. The first known book on the "leaf" game was called the "Yezi Gexi" and allegedly written by a Tang woman. It received commentary by writers of subsequent dynasties. The Song dynasty (960–1279) scholar Ouyang Xiu (1007–1072) asserts that the "leaf" game existed at least since the mid-Tang dynasty and associated its invention with the development of printed sheets as a writing medium. However, Ouyang also claims that the "leaves" were pages of a book used in a board game played with dice, and that the rules of the game were lost by 1067.

Other games revolving around alcoholic drinking involved using playing cards of a sort from the Tang dynasty onward. However these cards did not contain suits or numbers. Instead, they were printed with instructions or forfeits for whoever drew them.

The earliest dated instance of a card game involving cards with suits and numerals occurred on 17 July 1294 when "Yan Sengzhu and Zheng Pig-Dog were caught playing cards [zhi pai] and that wood blocks for printing them had been impounded, together with nine of the actual cards."

William Henry Wilkinson suggests that the first cards may have been actual paper currency which doubled as both the tools of gaming and the stakes being played for, similar to trading card games. Using paper money was inconvenient and risky so they were substituted by play money known as "money cards". One of the earliest games in which we know the rules is Madiao, a trick-taking game, which dates to the Ming Dynasty (1368–1644). Fifteenth century scholar Lu Rong described it is as being played with 38 "money cards" divided into four suits: 9 in coins, 9 in strings of coins (which may have been misinterpreted as sticks from crude drawings), 9 in myriads (of coins or of strings), and 11 in tens of myriads (a myriad is 10,000). The two latter suits had "Water Margin" characters instead of pips on them with Chinese characters to mark their rank and suit. The suit of coins is in reverse order with 9 of coins being the lowest going up to 1 of coins as the high card.

Technology during the Tang period was built also upon the precedents of the past. The mechanical gear systems of Zhang Heng (78-139) and Ma Jun (fl. 3rd century) gave the Tang engineer, astronomer, and monk Yi Xing (683-727) inspiration when he invented the world's first clockwork escapement mechanism in 725. This was used alongside a clepsydra clock and waterwheel to power a rotating armillary sphere in representation of astronomical observation. Yi Xing's device also had a mechanically timed bell that was struck automatically every year, and a drum that was struck automatically every quarter-hour; essentially, a striking clock. Yi Xing's astronomical clock and water-powered armillary sphere became well known throughout the country, since students attempting to pass the imperial examinations by 730 had to write an essay on the device as an exam requirement. However, the most common type of public and palace timekeeping device was the inflow clepsydra. Its design was improved "c". 610 by the Sui-dynasty engineers Geng Xun and Yuwen Kai. They provided a steelyard balance that allowed seasonal adjustment in the pressure head of the compensating tank and could then control the rate of flow for different lengths of day and night.

There were many other mechanical inventions during the Tang era. This included a 0.91 m (3 ft) tall mechanical wine server of the early 8th century that was in the shape of an artificial mountain, carved out of iron and rested on a lacquered-wooden tortoise frame. This intricate device used a hydraulic pump that siphoned wine out of metal dragon-headed faucets, as well as tilting bowls that were timed to dip wine down, by force of gravity when filled, into an artificial lake that had intricate iron leaves popping up as trays for placing party treats. Furthermore, as the historian Charles Benn describes it:

Although the use of a teasing mechanical puppet in this wine-serving device was certainly ingenious, the use of mechanical puppets in China date back to the Qin dynasty (221–207 BC) while Ma Jun in the 3rd century had an entire mechanical puppet theater operated by the rotation of a waterwheel. There was also an automatic wine-server known in the ancient Greco-Roman world, a design of Heron of Alexandria that employed an urn with an inner valve and a lever device similar to the one described above. There are many stories of automatons used in the Tang, including general Yang Wulian's wooden statue of a monk who stretched his hands out to collect contributions; when the amount of coins reached a certain weight, the mechanical figure moved his arms to deposit them in a satchel. This weight-and-lever mechanism was exactly like Heron's penny slot machine. Other devices included one by Wang Ju, whose "wooden otter" could allegedly catch fish; Needham suspects a spring trap of some kind was employed here.

The Chinese of the Tang era were also very interested in the benefits of officially classifying all of the medicines used in pharmacology. In 657, Emperor Gaozong of Tang (r. 649-683) commissioned the literary project of publishing an official "materia medica", complete with text and illustrated drawings for 833 different medicinal substances taken from different stones, minerals, metals, plants, herbs, animals, vegetables, fruits, and cereal crops. In addition to compiling pharmacopeias, the Tang fostered learning in medicine by upholding imperial medical colleges, state examinations for doctors, and publishing forensic manuals for physicians. Authors of medicine in the Tang include Zhen Qian (d. 643) and Sun Simiao (581-682), the former who first identified in writing that patients with diabetes had an excess of sugar in their urine, and the latter who was the first to recognize that diabetic patients should avoid consuming alcohol and starchy foods. As written by Zhen Qian and others in the Tang, the thyroid glands of sheep and pigs were successfully used to treat goiters; thyroid extracts were not used to treat patients with goiter in the West until 1890.

In the realm of technical Chinese architecture, there were also government standard building codes, outlined in the early Tang book of the "Yingshan Ling" (National Building Law). Fragments of this book have survived in the "Tang Lü" (The Tang Code), while the Song architectural manual of the "Yingzao Fashi" (State Building Standards) by Li Jie (1065–1101) in 1103 is the oldest existing technical treatise on Chinese architecture that has survived in full. During the reign of Emperor Xuanzong of Tang (712-756) there were 34,850 registered craftsmen serving the state, managed by the Agency of Palace Buildings (Jingzuo Jian).

In the realm of cartography, there were further advances beyond the map-makers of the Han dynasty. When the Tang chancellor Pei Ju (547-627) was working for the Sui dynasty as a Commercial Commissioner in 605, he created a well-known gridded map with a graduated scale in the tradition of Pei Xiu (224-271). The Tang chancellor Xu Jingzong (592-672) was also known for his map of China drawn in the year 658. In the year 785 the Emperor Dezong had the geographer and cartographer Jia Dan (730-805) complete a map of China and her former colonies in Central Asia. Upon its completion in 801, the map was 9.1 m (30 ft) in length and 10 m (33 ft) in height, mapped out on a grid scale of one inch equaling one hundred "li" (Chinese unit of measuring distance). A Chinese map of 1137 is similar in complexity to the one made by Jia Dan, carved on a stone stele with a grid scale of 100 li. However, the only type of map that has survived from the Tang period are star charts. Despite this, the earliest extant terrain maps of China come from the ancient State of Qin; maps from the 4th century BC that were excavated in 1986.

The Chinese of the Tang period employed complex chemical formulas for an array of different purposes, often found through experiments of alchemy. These included a waterproof and dust-repelling cream or varnish for clothes and weapons, fireproof cement for glass and porcelain wares, a waterproof cream applied to silk clothes of underwater divers, a cream designated for polishing bronze mirrors, and many other useful formulas. The vitrified, translucent ceramic known as porcelain was invented in China during the Tang, although many types of glazed ceramics preceded it.

Ever since the Han dynasty (202 BC - 220 AD), the Chinese had drilled deep boreholes to transport natural gas from bamboo pipelines to stoves where cast iron evaporation pans boiled brine to extract salt. During the Tang dynasty, a gazetteer of Sichuan province stated that at one of these 182 m (600 ft) 'fire wells', men collected natural gas into portable bamboo tubes which could be carried around for dozens of km (mi) and still produce a flame. These were essentially the first gas cylinders; Robert Temple assumes some sort of tap was used for this device.