Different air conditioners use various amounts of electricity to remove the same amount of heat. Engineers use a number, called the Energy Efficiency Ratio (EER), to measure how economically an air conditioner uses electricity. To find an air conditioner's EER, its Btu per hour rating is pided by the number of watts of electricity used by the unit. For example, an air conditioner that uses 600 watts to remove 5,000 Btu's per hour has an EER of 5,000 pided by 600, or 8.33. Most air conditioners have an EER of from 8 to 9. The higher the EER of a unit, the less electricity it uses--and the less it costs to operate.
History
The ancient Egyptians, Greeks, and Romans used wet mats to cool indoor air. They hung the mats over the doors to their tents and other dwellings. When wind blew through the mats, evaporation of the water cooled the air. The people of India later used this method to cool the royal palaces. About 1500, Leonardo da Vinci, the great Italian artist and scientist, built the first mechanical fan to provide ventilation. Water power turned the fan. In 1553, the English developed a rotary fan to ventilate mines.
Textile manufacturers made the first attempts at air conditioning. In 1719, a silk company in Derwent, England, installed a central system to heat and ventilate its mill. Early cloth makers in New England boiled water in huge pots near their looms to keep the air moist. Unfortunately, the heat injured the health of the workers and this method was discontinued.
About 1838, David B. Reid, an English scientist, provided the British House of Commons with a system to ventilate and humidify the air. In the mid-1800's, John Gorrie, an American, invented a cold-air machine to cool hospital rooms.
During the late 1800's, textile manufacturers in New England began using sprays of water to condition the air in their mills. In 1897, Joseph McCreery of Toledo, Ohio, received a patent for the type of spray now used in air conditioners.
By 1902, Alfred R. Wolff, a consulting engineer, had designed air-cooling systems for Carnegie Hall and several other buildings in New York City. That same year, Willis H. Carrier, a research engineer, designed the first scientific system to clean, circulate, and control the temperature and humidity of air.
In 1906, Stuart W. Cramer, a textile engineer from Charlotte, N.C., used the term air conditioning for the first time. Air conditioning became a recognized branch of engineering in 1911.
The Baltimore & Ohio Railroad installed the first air-conditioning system for trains in 1931. Air conditioning of apartments and homes also began during the 1930's. In 1939, Packard Motors introduced air-conditioning units for automobiles. The Greyhound Corporation installed the first bus air-conditioning systems in 1940. By the 1990's, about 70 percent of all of the housing in the United States had some form of air conditioning. In addition, most of the new single-family homes that were built in the United States were equipped with central air conditioning.
Careers in air conditioning
Careers in air conditioning can be pided into five main fields: (1) designing, (2) manufacturing, (3) selling, (4) installing and servicing, and (5) teaching and research. College-educated engineers research and design air-conditioning systems. Skilled machinists, toolmakers, cabinetmakers, and similar craftworkers help manufacture air conditioners. Technical training, such as a degree in engineering, is often essential for positions in the selling and executive branches of air conditioning. Specially trained technicians, and operating and service engineers, install and maintain air conditioners.
Contributor: James E. Hill, Ph.D., Chief, Building Environment Division, National Institute of Standards and Technology.
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