Evaporative-Cooling Air Conditioning SystemsĮvaporative-cooling air conditioning systems use the cooling effect of the evaporation of liquid water to cool an airstream directly or indirectly. Individual systems are usually used only for the perimeter zone of the building. Outdoor air is introduced through an opening or through a small air damper. Most of the individual systems do not employ connecting ductwork. Individual air conditioning systems are characterized by the use of a DX coil for a single room. This is the simplest and most direct way of cooling the air. Sometimes room air conditioners are separated into two split units: an outdoor condensing unit with compressor and condenser, and an indoor air handler in order to have the air handler in a more advantageous location and to reduce the compressor noise indoors. The difference between a room air conditioner and a room heat pump, and a packaged terminal air conditioner and a packaged terminal heat pump, is that a four-way reversing valve is added to all room heat pumps. A temperature control system senses the space air temperature (sensor) and starts or stops the compressor to control its cooling and heating capacity through a thermostat (refer to Chap. A condenser liquefies refrigerant from hot gas to liquid and rejects heat through a coil and a condenser fan. A compressor compresses the refrigerant from a lower evaporating pressure to a higher condensing pressure. An air filter removes airborne particulates. When the hot refrigerant releases heat energy to the conditioned space during the heating season, it acts as a heat pump. In tubeand- fin coil, the refrigerant evaporates, expands directly inside the tubes, and absorbs the heat energy from the ambient air during the cooling season it is called a direct expansion (DX) coil. The major components in a factory-assembled and ready-for-use room air conditioner include the following: An evaporator fan pressurizes and supplies the conditioned air to the space. Packaged terminal air conditioner (PTAC), installed in a sleeve through the outside wall.Individual air conditioning systems can be classified into two categories: Unlike other systems, these systems normally use a totally independent unit or units in each room. A heat pump extracts heat from a heat source and rejects heat to air or water at a higher temperature for heating. Individual room, or simply individual air conditioning systems employ a single, self-contained room air conditioner, a packaged terminal, a separated indoor-outdoor split unit, or a heat pump. Air conditioning systems can also be classified according to their construction and operating characteristics as follows.
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