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Note: in the broadest sense, "air conditioning" can refer to any form of "heating, ventilation, and air-conditioning." This article is specifically about the use of refrigeration for this purpose. The first album of the pop group Curved Air was Airconditioning An air conditioner (often abbreviated to AC in the United States and air-con in Australia) is an appliance or mechanism designed to extract heat from a humanly occupied space air temperature using a refrigeration cycle. An earlier form of air conditioning was invented in Persia (Iran) thousands of years ago in the form of wind shafts which was built on top of the roof in order to catch the wind and pass it through water and blow the cooled air into the building [1] (http://www.metafilter.com/comments.mefi/26911). Electrical version of air conditioning was invented by Willis Haviland Carrier (1876–1950) around 1902 to control temperature and humidity for improved manufacturing process control. Later, air conditioning was applied to increase productivity in the workplace. Later still, air conditioning use was expanded to improve comfort in homes and automobiles. Air conditioning equipment usually reduces the humidity of the air processed by the system. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In the refrigeration cycle, work is applied to cool a living or storage volume by pumping heat from a lower temperature heat source into a higher temperature heat sink. Heat naturally flows in the opposite direction. Insulation is used as means to reduce the work and energy required to achieve and maintain a lower temperature in the cooled space. The most common types of air conditioners employ a working fluid called a refrigerant in a cycle where the refrigerant repeatedly changes state from liquid to vapor and back to liquid. The refrigerant is condensed to release heat in one part of the cycle and is boiled (or evaporated) to absorb heat in another part of the cycle. The most common refrigeration cycle uses an electric motor to drive a compressor. In an automobile the compressor is driven by a pulley on the engine's crankshaft. The compressor does not create a cooling effect directly. The cooling effect is created when a suitable refrigerant boils and absorbs heat from the cooled space through a heat exchanger. You must understand the refrigerant flow and changes of state to understand the refrigeration cycle: The first part of the cycle causes refrigerant vapor to be recycled into its liquid form by extracting heat from a high temperature vapor in a condenser. The compressor compresses a relatively low-pressure and low-temperature refrigerant vapor drawn from the evaporator coil. During compression, the refrigerant vapor is heated by compression itself and the work of compression to create a high-temperature and high-pressure vapor. Then it is pushed into a heat exchanger known as a condenser located in a higher temperature heat sink that is located outside of the space being cooled. In the condenser, heat is removed from the refrigerant so that it condenses to a liquid state. The second part of the cycle begins when the liquid refrigerant leaves the condenser as a high temperature, high-pressure liquid and passes through a metering device into the cooling coil or evaporator on the low-pressure side of the system. The compressor pumps the refrigerant out of the evaporator at a rate sufficient to cause the pressure and temperature of the refrigerant to drop well below its boiling point as it is circulated through an interior heat exchanger coil. This boiling liquid refrigerant absorbs heat energy from the interior space through the walls of this interior coil. The system is designed to completely evaporate liquid refrigerant into a low-pressure vapor within the interior coil before it returns to the compressor to repeat the cycle. In very dry climates, "swamp coolers" are popular for improving comfort during hot weather. The evaporative cooler is a device that draws outside air through a wet pad. The sensible heat of the incoming air, as measured by a dry bulb thermometer, is reduced. The total heat (sensible heat plus latent heat) of the entering air 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 comfortable. These coolers cost less and are mechanically simple to understand and maintain. An early type of cooler, using ice for a further effect, was patented by John Gorrie of Apalachicola, FL in 1842, who used the device to cool the patients of his malaria hospital. "Freon" is a trade name for a family of chlorofluorocarbon refrigerants manufactured by DuPont and other companies. These refrigerants were commonly used due to their superior stability and safety properties. Unfortunately, evidence has accumulated that these chlorine bearing refrigerants reach the upper atmosphere when they escape. The chemistry is poorly understood but consensus seems to have been growing that chlorine atoms of these CFCs refrigerants are released in the presence of strong ultraviolet radiation or UV and these chlorine atoms act as a catalyst to do severe damage to the ozone layer that shields the earth’s surface from the strong UV radiation. Air conditioner equipment capacity in the U.S. is often described in terms of "tons". A "ton" is defined as the cooling capacity of one ton (2000 pounds or 909 kilograms) of ice melting in a 24-hour period. This is equal to 12,000 BTU per hour, or 3.5 kilowatts. Residential central air conditioners can be 1 to 5 tons (3.5 to 17.5 kW). The use of electric/compressive air conditioning puts a major demand on the nation's electrical power grid in warm weather, when most units are operating under heavy load. A 1995 study of various utility studies of residential air conditioning concluded that the average wasted energy is 40% of the demand. This means that there is a huge opportunity to reduce the need for new power plants and to conserve energy. In an automobile the A/C system will use around 5 hp (4 kW) of the engine's power. See alsoExternal links
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