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TRG-TRC016-EN 77
period three
System Variations
notes
The final method of “free” cooling is to transfer heat between the cooling tower
water and the chilled water inside a centrifugal chiller through the use of
refrigerant migration. When the temperature of the water from the cooling
tower is colder than the desired chilled-water temperature, the compressor is
turned off and automatic shutoff valves inside the chiller refrigerant circuit are
opened. This allows refrigerant to circulate between the evaporator and
condenser without the need to operate the compressor. Because refrigerant
vapor migrates to the area with the lowest temperature, refrigerant boils in the
evaporator and the vapor migrates to the cooler condenser. After the refrigerant
condenses into a liquid, it flows by gravity back into the evaporator.
There are no additional fouling concerns because the cooling-tower water flows
through the chiller condenser and is separated from the chilled-water loop.
Although not as effective as a plate-and-frame heat exchanger, it is possible for
refrigerant migration in a centrifugal chiller to satisfy many cooling load
requirements (up to 40 percent of the chiller’s design capacity) without
operating the compressor. This can increase further if the system can
accommodate warmer chilled-water temperatures at part-load conditions.
waterside economizer
Refrigerant Migration
from
from
compressor
compressor
to
to
compressor
compressor
evaporator
evaporator
condenser
condenser
shutoff
shutoff
valve
valve
shutoff
shutoff
valve
valve
vapor
vapor
migration
migration
liquid
liquid
flow
flow
Figure 85