Air Conditioning
ALTERNATIVE NAME/S: AC, air con, Egg-Nishna
Modern air conditioning controls the temperature, humidity, purity and circulation of the air within a selected environment. In industrial use, other factors such as the air pressure and the removal of smells may also be controlled. An air-cooling system was invented in the 1840’s by the American doctor John Gorrie* for the treatment of his feverish patients. At the end of the nineteenth century, ideas about cooling air were given a boost by the new techniques of refrigeration for cold storage and transportation of perishable foods, and the invention of refrigeration apparatus by scientists such as Carl von Linde*.
In St Louis, Missouri, the Automatic Refrigerating company supplied refrigeration to a restaurant and beerhall who, in 1891, devised their own air conditioning system by attaching expansion coils to the wall of the restaurant and so keeping their crowded restaurant at around 73 degrees Fahrenheit even when the temperature outside was up to 90 degrees Fahrenheit.
Professional air conditioning began in industries where products were affected by temperature and humidity. Willis H Carrier is recognized as the founder of modern air conditioning. In 1902 he was asked to solve a humidity problem in a printing firm where the ink would not stick to the paper in very hot weather. Carrier, who worked for manufacturers of heating plants and drying equipment, had already seen the need for accurate data on air pressure, humidity and temperature.
In 1902, he used data from the Weather Bureau to design what was probably the first scientific air conditioning system. He worked out how much water per hour needed to be removed from the air in the printers and then installed two sections of chilled coil, one to circulate cold artesian well water, the other connected to an ammonia refrigerating compressor. The coils cooled the air around them, and as chilled air holds less moisture than hot air, the humidity of the air fell (air at 70 degrees Fahrenheit holds only half as much water vapor as air at 90 degrees Fahrenheit). Carrier’s system worked and other industries such as drug manufacturers, who required humidity control, became interested.
The name ‘air conditioning’ originated in a paper on humidity control in textile mills presented to the National Cotton Manufacturers Association by Stuart W Cramer in 1907. The measurement and control of the moisture content in textiles was then generally known as conditioning. Cranmer devised a system in which humidified air was circulated in the building where the textiles were processed and he went on to design a system in which a machine drew in fresh air and conditioned it before circulating it. He had therefore made the leap between providing moisture and conditioning air. Air was drawn in both from outdoors and from the factory, taken through a fine water spray and then through a cloth filter before being circulated. His system combined humidification, ventilation and cleansing.
Movie theatres were the first to realize the commercial value of offering customers a controlled environment in hot weather. Department stores followed, and then offices as management realized their staff worked a lot better when they were not wilting in high temperatures and humidity. In the 1920’s, the rich began to install air conditioning in their private residences. By 1930, the term air conditioning had become synonymous with air cooling to ordinary Americans although the engineers resisted this interpretation.
The technology kept pace and accelerated demand. In 1922, Carrier invented the centrifugal compressor which supplied a much more reliable form of mechanical refrigeration, and around the same time a new method was developed to circulate refrigerated air without sudden cold blasts. As the technology advanced, it became clear that to maintain a perfectly controlled indoor environment, it was necessary to seal it off from the outside air. Technological innovations included improved automatic controls such as thermostats, automatically fired furnaces and boilers, thermal insulation and refrigeration compressors.
In winter, when a room thermostat registers a demand for more heat, the furnace automatically starts up and heats the air around it. When the air reaches a certain temperature, a blower circulates the warm air through ducts into the room. The warm air displaces cooler room air, and the room air temperature rises. When room air temperature reaches the level at which the thermostat is set, the burner is shut off and the furnace cools. The blower continues to introduce air into the room but the circulating air temperature gradually drops and when the thermostat demands heat the process starts up again. In summer, the room thermostat again controls the air temperature.
A rise in the room temperature causes the thermostat switch to close and a refrigerating compressor to start operating. A cooled refrigerant fluid flows through the inside of the cooling coil and a fan circulates the room air over the outside of the coil. The contact of the room air with the cold surface of the coil cools the air. Part of the moisture in the air is condensed on the coil and drained away from the house. The cool, dry air introduced into the room replaces the warm, humid air and both the room air temperature and the relative humidity are gradually lowered.
In large scale air conditioning, water-cooled condensers are used because air-cooled condensers operate too slowly. Water-cooled condensers are usually installed in a separate cooling tower in which the condenser water is cooled by the evaporation into outdoor air. In 1950’s and ‘60’s, many new buildings featured sealed windows. Today, many people in smaller and domestic environment prefer the greater control gained by portable plug-in conditioners.
ONELINER: Air conditioning
OTHER CONNECTIONS: AC has altered demographics and arguably politics (See Johnson). As global temperatures increase, particularly as developing counties are emulating First World lifestyles, AC is boosting demand for electricity, which contributes to amplifying feedback in the climate emergency. CFC’s were banned in the Montreal Protocol treaty, which has led to a recovery of the earth’s protective ozone layer.
BIBLIOGRAPHY:
Carrier, Willis H, Cherne, Realto E, Grant, Walter A. Modern Air-Conditioning, Heating and Ventilating, Pitman Publishing Corporation, New York, 1950
Cooper, Gail, Air-Conditioning America, Engineers and the Controlled Environment 1900-1960, John Hopkins University Press, Baltimore and London, 1998
Stangle, William Hull, An Air-Conditioning Primer, McGraw-Hill Book Company, Inc., New York and London, 1940
Johnson, Steven HWGTN: AC migration to Sun Belt leads to election of President Reagan