8
Centrifugal Chillers
IM 1044-2
Figure 4, 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.
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
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
10
20
30
40
50
60
70
80
90
100
110
Percent Load
E
CW
T
, F
44 LChWT
42 LChWT
46 LChWT
