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38 TRG-TRC010-EN
notes
period five
Application Considerations
Controlling the refrigerant pressure difference between the evaporator and
condenser of a water-cooled chiller is accomplished by varying the temperature
or flow rate of the water flowing through the condenser. The following are 5
common methods used to control condensing temperature:
1) Cycling or varying the speed of the cooling tower fans to control the
temperature of the water leaving the cooling tower
2) Using a cooling tower bypass pipe to mix warmer leaving-condenser water
with the colder tower water and control the temperature entering the condenser
as illustrated here
3) Modulating a throttling valve to restrict the flow of water through the
condenser
4) Using a chiller bypass pipe to vary the flow rate of water through the
condenser
5) Using a variable-speed drive on the condenser water pump to vary the water
flow rate through the condenser
Each of these strategies has its advantages and disadvantages. Selecting the
appropriate condensing temperature control scheme will depend on the
specific requirements of the application.
The water flow rate through the chiller condenser must stay between the
minimum and maximum condenser bundle flow rates specified by the chiller
manufacturer.
condensing temperature control
Cooling Tower Bypass
condenser
condenser
bypass
bypass
cooling tower
cooling tower
55°F
55°F
[13°C]
[13°C]
40°F
40°F
[4°C]
[4°C]
65°F
65°F
[18°C]
[18°C]
diverting
diverting
valve
valve
Figure 53
trgtrc010_book.book Page 38 Wednesday, September 1, 1999 10:42 AM