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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. Daikin'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 5 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 5, Bypass, Mild Weather Operation
14
Minimum Entering Condenser Water Temperature - 10 F Range
65.0
44 LChWT
42 LChWT
46 LChWT
60.0
55.0
50.0
45.0
40.0
35.0
30.0
0
10
20
30
Centrifugal Chillers
40
50
60
70
Percent Load
80
90
100
110
Bypass, Cold Weather Operation
D-EIMWC00804-14EN
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