Specifications

52 Catalog WSC/WDC-4
Figure 14, Minimum Entering Condenser Water Temperature (TXV)
For example; at 44°F LWT, 10 degree F Delta-T, and 50% full load operation, the entering
condenser water temperature could be as low as 50.5°F. This provides excellent operation with
water-side economizer systems.
Depending on local climatic conditions, using the lowest possible entering condenser water
temperature may be more costly in total system power consumed than the expected savings in
chiller power would suggest, due to the excessive fan power required.
Cooling tower fans must continue to operate at 100% capacity at low wet bulb temperatures. As
chillers are selected for lower kW per ton, the cooling tower fan motor power becomes a higher
percentage of the total peak load chiller power. McQuay’s Energy Analyzer program can optimize
the chiller/tower operation for specific buildings in specific locales.
Even with tower fan control, some form of water flow control, such as tower bypass, is
recommended.
Figure 15 illustrates two temperature actuated tower bypass arrangements. The “Cold Weather”
scheme provides better startup under cold ambient air temperature conditions. The check valve
may be required to prevent entraining air at the pump inlet.
Figure 15, Bypass, Mild Weather Operation
Bypass, Cold Weather Operation
Minimum Entering Condenser Water Temperature - 10 F Range
30.0
35.0
40.0
45.0
50.0
55.0
60.0
65.0
0 102030405060708090100110
Percent Load
ECWT, F
44 LChWT
42 LChWT
46 LChWT