Figure 4-10.-FIoor-mounted air-conditioning unit (shown withcover panels removed).Cooling equipment for air conditioning must be ofa type that will satisfactorily cool the air for a particularspace that is being air conditioned. One method used tocool air in air-conditioning units is to evaporate water.A discussion of this method, called evaporative cooling,can be found in chapter 10 of the UT3 TRAMAN.Another method, and one of the most important, ismechanical refrigeration. In this method, the air thatis to be conditioned and cooled is blown through coolingcoils having a temperature of about 50°F. This not onlycools, but dehumidifies the air. A discussion of thismethod can also be found in chapter 10 of the UT3TRAMAN.There are various types of air-conditioning units andsystems. A few of the common types are discussedbelow.Self-Contained (Package) UnitsSelf-contained refrigerative air-conditioning unitsare either window units (figs. 4-8 and 4-9) or largerFigure 4-11.-Refrigerating cycle of a package type air-conditioning unit.floor-mounted units (fig. 4-10). Both types of unitscontain a complete system of refrigeration components.The window units need not be installed in windows.They also can be installed in transoms, or they can beframed into outside walls. The use of outside walls isimportant for proper performance. When the unit isoperating, the compressor (fig. 4-11) forces a high--pressure (high-temperature) refrigerant gas to thecondenser. The condenser fan draws in and blowsoutside air over the condenser coils. This movement ofthe relatively cooler outside air over the hot condensercoils changes the gas to a liquid, giving off heat that isexhausted to the outside. The liquid then passes througha control device that regulates the flow of the liquid tothe evaporator. In the evaporator, the liquid changes toa low-pressure (low-temperature) gas that is circulatedthrough the evaporator coils. The inside or room air isthen circulated by an evaporator fan over the coldevaporator coils. This action removes heat from the airand returns the cooled air back to the room.A variation of this type of unit is the heat pump. Ina heat pump, the roles of the condenser and theevaporator can be reversed so that the unit draws in andheats outside air and expels cold inside air. In this way,the unit functions as a heating unit, rather than a coolingunit.4-9
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