Air Conditioning and Global Warming
Air conditioning systems use energy to remove heat from a given location, transferring it to the exterior in the form of exhaust. Some of the energy is invariably wasted as heat, and this additional heat must also be exhausted. Thus, air conditioning results in net heat release to the environment. The warming effect is aggravated, moreover, because higher forms of energy such as electricity are used to power air conditioners. Generating and transmitting this electricty entails further production of waste heat, as well as greenhouse gas (GHG) emission. Demand for air conditioning peaks along with other demand for electricity during summer days. Auxiliary generators used to meet peak demand are less efficient and often burn fossil fuels.
In 1998, for example, the total equivalent warming impact (TEWI) of European air conditioning was 156 million metric tons of carbon dioxide (CO2) equivalent. Of that TEWI, 25.6 million metric tons were attributable to direct hydrofluorocarbon emissions and around 130 million metric tons were attributable to indirect emissions. In the same year, the TEWI of 303 million automotive air conditioning systems worldwide represented 0.14 percent of total anthropogenic TEWI. There are two basic approaches to cooling the air in an enclosure: refrigeration and evaporation. In the refrigeration cycle, a fluid is compressed so that its temperature rises and is circulated through pipes over which air or water is forced, thus removing heat. The compressed, cooled refrigerant is then expanded through a nozzle, so that its temperature drops sharply before it absorbs heat in an exchanger from the air in the enclosure. The refrigerant with the heat absorbed is then compressed and its heat removed in the exhaust heat exchanger. This process need not include phase change. When a substance evaporates, it absorbs a great deal of heat from the environment, called the latent heat. In large industrial systems, the...
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