Throughout the centuries, people have devised many methods of manipulating the heat and humidity of the air surrounding them. Ancient Egyptians, Indians, Greeks, and Romans hung wet mats over doors and windows (wind blowing through the mats was cooled by evaporation), while their rulers were cooled by slave-operated fans. Leonardo da Vinci invented a water-driven fan in the middle ages. In the nineteenth century, the textile industry used various devices to humidify factory air; South Carolina physician John Gorrie (1803-1855) invented an air-conditioning and refrigeration machine; and In New York City, both Carnegie Hall and the Stock Exchange building had air-cooling systems around the turn of the century.
None of these systems was truly effective, however. The breakthrough came in 1902 from a young mechanical engineer named Willis H. Carrier (1876-1950). Carrier had grown up on a farm in New York and then attended Cornell University on scholarship, where he studied engineering. While working for the Buffalo Forge Company, Carrier was assigned to solve the problem of a Brooklyn, New York, printing company. Humid weather seriously compromised the quality of color printing. Noting that very cold air would absorb humidity from very warm air, Carrier devised a cold-water-spray apparatus that dehumidified and cleaned interior air, and added a dew-point control that automatically regulated interior air humidity by adjusting the water-spray temperature. Carrier patented his system in 1904. By 1911 he had codified the laws of psychrometry --the science measuring the water-vapor content of air--and presented a paper outlining the basis of a complete air-conditioning system. For this, he became known as "the Father of Air Conditioning." The term air conditioning itself was first used by engineer Stuart W. Cramer in 1906. In 1919, the first air-conditioned movie theater opened in Chicago, Illinois, along with the first air-conditioned department store, Abraham & Straus, in New York City. The first fully air-conditioned high-rise structure, the Milam Building in San Antonio, Texas, was erected in 1929. The Baltimore & Ohio railway line introduced air conditioning to that industry in 1931; Packard did the same for automobiles in 1939, followed by Greyhound for buses in 1940.
Individual room air conditioners were developed in the 1930s by the Americans H. H. Schutz and J. Q. Sherman, with compact versions becoming available in the 1950s. Early air conditioners used ammonia, an irritating and corrosive substance, as a refrigerant. In 1930, Thomas Midgley, Jr. (1889-1944) of the Du Pont company discovered freon, a nontoxic, nonflammable, highly efficient refrigerant gas which, in various forms, was the industry standard. Freon is a halogenated hydrocarbon, also known as a chlorofluorocarbon. When these compounds escape from freon production facilities or refrigeration systems and find their way into the upper atmosphere of the earth, they break down and release chlorine. This contributes to the destruction of the ozone layer, which screens dangerous ultraviolet radiation from sunlight, preventing possible skin cancers. The production of freon was therefore banned as of 1996.
Alternatives to freon are being developed that are less environmentally destructive, such as the chemical R134a for the air-conditioning (A/C) systems of automobiles. Cars built prior to 1992 must convert their A/C system once their existing freon system empties.
Scientists are exploring other ways to cool air, especially for smaller systems like refrigerators. Acoustic cooling uses a loudspeaker to create pressure fluctuations in a gas, decompressing it, and therefore cooling it. Another experimental freon-free refrigerator uses a thermocouple device that cools by passing electric current between two semiconductors, though it requires larger amounts of power than conventional refrigerators.
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