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TRG-TRC010-EN 45
period five
Application Considerations
notes
This leads to the discussion of a free cooling principle called refrigerant
migration. It involves adapting a water chiller so that it functions as a simple
heat exchanger.
When the available condenser water is cooler than the desired chilled water
temperature, the compressor is turned off and bypass valves in the chiller
refrigerant circuit are opened to let the refrigerant circulate without help from
the compressor. Because refrigerant migrates to the area with the lowest
temperature, refrigerant boils in the evaporator and the vapor flows to the
cooler condenser bundle. After the refrigerant condenses, it flows (by gravity)
back to the evaporator.
The advantages of refrigerant migration are these: no extra components are
required in the system, control is performed by the chiller itself, and there are
no additional fouling concerns. It is possible for the free cooling chiller to satisfy
many cooling load requirements without operating the compressor, especially
when the system can accommodate warmer chilled water temperatures at part-
load conditions.
free cooling
Refrigerant Migration
from
from
compressor
compressor
to
to
compressor
compressor
evaporator
evaporator
condenser
condenser
Figure 61
trgtrc010_book.book Page 45 Wednesday, September 1, 1999 10:42 AM