Vapor Compression UnitsThe vapor compression chilled water circulatingsystem differs from a refrigerant circulating (directexpansion) air-conditioning system. In vaporcompression chilled water circulating systems, the air isconditioned by using a secondary refrigerant (chilledwater) that is circulated to the various cooling coils. Heatfrom the air-conditioned space is absorbed by thecirculating chilled water. Heat is then removed from thewater by the primary refrigerant system in the waterchiller. In large ton vapor compression systems, thecompressor is a centrifugal type that uses R-11 or R-114as the primary refrigerant.The operating cycle of the centrifugal refrigerationplant (fig. 10-18) is basically the same as otherrefrigeration plants except for the method ofcompression. The refrigerant gas is pressurized in thecentrifugal turbocompressor. This then is dischargedinto the condenser where it is condensed by circulatingseawater flowing through the condenser tubes. Thecondensed liquid refrigerant drains to the bottom of thecondenser into a float chamber. When the refrigerantlevel is high enough, a float-operated valve opens.(NOTE: In some R-11 units, an orifice is installedinstead of a float valve.) This allows the liquidhigh-pressure refrigerant to spray out into the waterchiller (evaporator). Water to be chilled flows throughthe tubes of the water chiller. As the refrigerant from thecondenser sprays out over the tubes, the water withinthe tubes is chilled or cooled due to the vaporization ofthe liquid refrigerant. Then, the vaporized refrigerantreenters the suction side of the compressor to start thecycle again.Figure 10-18.-Vapor compressor (centrifugal) unit.10-20
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