Vapor Compression Units
The vapor compression chilled water circulating
system differs from a refrigerant circulating (direct
expansion) air-conditioning system. In vapor
compression chilled water circulating systems, the air is
conditioned by using a secondary refrigerant (chilled
water) that is circulated to the various cooling coils. Heat
from the air-conditioned space is absorbed by the
circulating chilled water. Heat is then removed from the
water by the primary refrigerant system in the water
chiller. In large ton vapor compression systems, the
compressor is a centrifugal type that uses R-11 or R-114
as the primary refrigerant.
The operating cycle of the centrifugal refrigeration
plant (fig. 10-18) is basically the same as other
refrigeration plants except for the method of
compression. The refrigerant gas is pressurized in the
centrifugal turbocompressor. This then is discharged
into the condenser where it is condensed by circulating
seawater flowing through the condenser tubes. The
condensed liquid refrigerant drains to the bottom of the
condenser into a float chamber. When the refrigerant
level is high enough, a float-operated valve opens.
(NOTE: In some R-11 units, an orifice is installed
instead of a float valve.) This allows the liquid
high-pressure refrigerant to spray out into the water
chiller (evaporator). Water to be chilled flows through
the tubes of the water chiller. As the refrigerant from the
condenser sprays out over the tubes, the water within
the tubes is chilled or cooled due to the vaporization of
the liquid refrigerant. Then, the vaporized refrigerant
reenters the suction side of the compressor to start the
cycle again.
Figure 10-18.-Vapor compressor (centrifugal) unit.
10-20
