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22 TRG-TRC016-EN
notes
period one
Types of Water Chillers
In the example system shown in Figure 25, the chilled water is cooled from 57°F
[13.9°C] to 41°F [5°C] for a 16°F [8.9°C] ∆T. This reduces the water flow rate
required from 2.4 gpm/ton [0.043 L/s/kW] to 1.5 gpm/ton [0.027 L/s/kW].
Reducing water flow rates either: 1) lowers system installed costs by reducing
pipe, pump, valve, and cooling tower sizes, or 2) lowers system operating costs
by using smaller pumps and smaller cooling tower fans. In some cases, both
installed and operating costs can be saved. Low-flow systems will be discussed
in more detail in Period Three.
The two ARI rating standards mentioned previously, as well as ASHRAE/IESNA
Standard 90.1–1999 (the energy standard), allow reduced chilled-water
temperatures and flow rates. System design engineers should examine the use
of reduced flow rates to offer value to building owners.
Flow Rates and Temperatures
2.4 gpm/ton
[0.043 L/s/kW]
44°F
44°F
[6.7°C]
[6.7°C]
54°F
54°F
[12.2°C]
[12.2°C]
85°F
85°F
[29.4°C]
[29.4°C]
95°F
95°F
[35°C]
[35°C]
3.0 gpm/ton
[0.054 L/s/kW]
ARI conditions
1.5 gpm/ton
[0.027 L/s/kW]
41°F
41°F
[5°C]
[5°C]
57°F
57°F
[13.9°C]
[13.9°C]
85°F
85°F
[29.4°C]
[29.4°C]
100°F
100°F
[37.8°C]
[37.8°C]
2.0 gpm/ton
[0.036 L/s/kW]
low-flow conditions
evaporator
flow rate
condenser
flow rate
evaporator
flow rate
condenser
flow rate
Figure 25