D–EIMWC00808-16HU - 15/64
Figure 3, Minimum Entering Condenser Water Temperature (EXV)
Min. ECWT = 5.25 + 0.88*(LWT) - DT
FL*
(PLD/100) + 22*(PLD/100)
2
•
ECWT = Entering condenser water temperature
•
LWT = Leaving chilled water temperature
•
DT
FL
= Chilled Water Delta-T at full load
•
PLD = The percent chiller load point to be checked
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 44.5
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.
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.
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
E
CW
T
,
F
Percent Load
Minimum Entering Condenser Water Temperature - 10 F Range
44
LChWT
42
LChWT
