Air conditioning
Air conditioning, often abbreviated as A/C or air con, is the process of removing heat from an enclosed space to achieve a more comfortable interior temperature and, in some cases, controlling the humidity of internal air. Air conditioning can be achieved using a mechanical 'air conditioner' or through other methods, such as passive cooling and ventilative cooling. Air conditioning is a member of a family of systems and techniques that provide heating, ventilation, and air conditioning. Heat pumps are similar in many ways to air conditioners but use a reversing valve, allowing them to both heat and cool an enclosed space.
In hot weather, air conditioning can prevent heat stroke, dehydration due to excessive sweating, electrolyte imbalance, kidney failure, and other issues due to hyperthermia. An estimated 190,000 heat-related deaths are averted annually owing to air conditioning. Air conditioners increase productivity in hot climates, and historians rank air conditioning as a key factor that shaped postwar metropolitan growth, alongside highways, automobiles, shopping malls, and suburban housing., air conditioning used about 7% of global electricity and emitted 3% of greenhouse gas.
Air conditioners, which typically use vapor-compression refrigeration, range in size from small units used in vehicles or single rooms to massive units that can cool large buildings. Air source heat pumps, which can be used for heating as well as cooling, are becoming increasingly common in cooler climates. According to the International Energy Agency 1.6 billion air conditioning units were used globally in 2016. The United Nations has called for the technology to be made more sustainable to mitigate climate change and for the use of alternatives, like passive cooling, evaporative cooling, selective shading, windcatchers, and thermal insulation.
History
Air conditioning dates back to prehistory. Double-walled living quarters, with a gap between the two walls to encourage air flow, were found in the ancient city of Hamoukar, in modern Syria. Ancient Egyptian buildings also used a wide variety of passive air-conditioning techniques. These became widespread from the Iberian Peninsula through North Africa, the Middle East, and Northern India.Passive techniques remained widespread until the 20th century when they fell out of fashion and were replaced by powered air conditioning. Using information from engineering studies of traditional buildings, passive techniques are being revived and modified for 21st-century architectural designs.
Air conditioners allow the building's indoor environment to remain relatively constant, largely independent of changes in external weather conditions and internal heat loads. They also enable deep plan buildings to be created and have allowed people to live comfortably in hotter parts of the world.
Development
Preceding discoveries
In 1558, Giambattista della Porta described a method of chilling ice to temperatures far below its freezing point by mixing it with potassium nitrate in his popular science book Natural Magic. In 1620, Cornelis Drebbel demonstrated "Turning Summer into Winter" for James I of England, chilling part of the Great Hall of Westminster Abbey with an apparatus of troughs and vats. Drebbel's contemporary Francis Bacon, like della Porta a believer in science communication, may not have been present at the demonstration, but in a book published later the same year, he described it as "experiment of artificial freezing" and said that "Nitre is very cold, and hence nitre or salt when added to snow or ice intensifies the cold of the latter, the nitre by adding to its cold, but the salt by supplying activity to the cold of the snow."In 1758, Benjamin Franklin and John Hadley, a chemistry professor at the University of Cambridge, conducted experiments applying the principle of evaporation as a means to cool an object rapidly. Franklin and Hadley confirmed that the evaporation of highly volatile liquids could be used to drive down the temperature of an object past the freezing point of water. They experimented with the bulb of a mercury-in-glass thermometer as their object. They used a bellows 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."
The 19th century included many developments in compression technology. 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 envisioned centralized air conditioning that could cool entire cities. Gorrie was granted a patent in 1851, but following the death of his main backer, he was not able to realize his invention. In 1851, James Harrison created the first mechanical ice-making machine in Geelong, Australia, and was granted a patent for an ether vapor-compression refrigeration system in 1855 that produced three tons of ice per day. In 1860, Harrison established a second ice company. He later entered the debate over competing against the American advantage of ice-refrigerated beef sales to the United Kingdom.
First devices
While early cooling systems typically relied on bulky reciprocating steam engines for power, a significant technological shift occurred in 1894 when Hungarian engineer István Röck began manufacturing industrial ammonia compressors driven by electric motors. This innovation made the systems more compact and suitable for urban environments. By 1896, his factory produced 'dry air cooling apparatuses' specifically designed for the cooling and dehumidification of residential rooms, hospitals, theaters, large public halls, and even residential rooms, several years before the widespread commercialization of modern air conditioning. This system operated by using an electric motor-driven ammonia compressor to chill a secondary refrigerant, typically brine. This cold brine was circulated through pipes to a 'dry air cooling unit', where a fan forced ambient air over the chilled coils. This process not only lowered the temperature but also dehumidified the air by condensing moisture on the cold surfaces, providing a complete climate control solution.Electricity made the development of effective units possible. In 1901, American inventor Willis H. Carrier built what is considered the first modern electrical air conditioning unit. In 1902, he installed his first air-conditioning system in the Sackett-Wilhelms Lithographing & Publishing Company in Brooklyn, New York. He patented "air conditioning" in 1906, and by 1914, the first domestic air conditioning was installed. His invention controlled both the temperature and humidity, which helped maintain consistent paper dimensions and ink alignment at the printing plant. Later, together with six other employees, Carrier formed The Carrier Air Conditioning Company of America, a business that in 2020, employed 53,000 people and was valued at $18.6 billion.
In 1906, Stuart W. Cramer of Charlotte, North Carolina, was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning" in a patent claim which he filed that year, where he suggested that air conditioning was analogous 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, thus controlling the humidity that is necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company.
Domestic air conditioning soon took off. In 1914, the first domestic air conditioning was installed in Minneapolis in the home of Charles Gilbert Gates. It is, however, possible that the considerable device was never used, as the house remained uninhabited
In 1931, H.H. Schultz and J.Q. Sherman developed what would become the most common type of individual room air conditioner: one designed to sit on a window ledge. The units went on sale in 1932 at US$10,000 to $50,000 A year later, the first air conditioning systems for cars were offered for sale. Chrysler Motors introduced the first practical semi-portable air conditioning unit in 1935, and Packard became the first automobile manufacturer to offer an air conditioning unit in its cars in 1939.
Further development
Innovations in the latter half of the 20th century allowed more ubiquitous air conditioner use. 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 inverter air conditioners were released in 1980–1981.In 1954, Ned Cole, a 1939 architecture graduate from the University of Texas at Austin, developed the first experimental "suburb" with inbuilt air conditioning in each house. 22 homes were developed on a flat, treeless track in northwest Austin, Texas, and the community was christened the 'Austin Air-Conditioned Village.' The residents were subjected to a year-long study of the effects of air conditioning led by the nation's premier air conditioning companies, builders, and social scientists. In addition, researchers from UT's Health Service and Psychology Department studied the effects on the "artificially cooled humans." One of the more amusing discoveries was that each family reported being troubled with scorpions, the leading theory being that scorpions sought cool, shady places. Other reported changes in lifestyle were that mothers baked more, families ate heavier foods, and they were more apt to choose hot drinks.
Air conditioner adoption tends to increase above around $10,000 annual household income in warmer areas. Global GDP growth explains around 85% of increased air condition adoption by 2050, while the remaining 15% can be explained by climate change.