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32 Chiller System Design and Control SYS-APM001-EN
System Design Options
The total system power is now as follows:
* Low-flow conditions represented in Table 5 through Table 8 are 1.5 gpm/ton [0.027 L/s/kW] chilled water
and 2.0 gpm/ton [0.036 L/s/kW] condenser water.
Figure 20. System summary at full load
It becomes clear that flow rates can affect full-load system power (Figure 20).
Even though the chiller requires more power in the low-flow system, the
power reductions experienced by the pumps and cooling tower result in an
overall savings for the system.
What happens at part-load conditions? Figure 21 shows the part-load
performance based on the following assumptions:
• The chilled-water pump includes a variable-frequency drive.
• The condenser-water pump remains at constant power.
• The cooling tower is controlled to produce water temperatures lower than
design.
Table 8. Total system power
Component Power (kW) Base Case Low Flow*
Chiller 256.0 292.0
Chilled-water pump 32.0 8.4
Condenser-water pump 25.2 8.8
Cooling tower 24.1 16.0
Total power for chilled-water system 337.3 325.2
Energy Consumption, kW
300
250
200
150
100
50
0
2.4/3.0 1.5/3.0 2.4/2.0 1.5/2.0
Chilled/Condenser Water Flows, gpm/ton
Tower
Condenser Water
Pumps
Chilled Water
Pump
Chiller (100%
Load)