Trane TRG-TRC016-EN manual Chiller Evaporator Flow, Three-way modulating valve

period two

Chilled-Water System Design

notes

Load-Terminal Control Options

▲ Three-way modulating valve

◆ Constant water flow

◆ Variable system return-water temperature

▲ Two-way modulating valve

◆ Variable water flow (pump energy savings) ◆ Constant system return-water temperature

▲ Face-and-bypass dampers

◆ Constant water flow
◆ Variable system return-water temperature
◆ Enhanced dehumidification capability with “wild” coils	Figure 37

Properly designed, operated, and maintained, any of these three methods can result in good space comfort control. However, they have different effects on the chilled-water system.

The use of three-way valves or face-and-bypass dampers results in variable return-water temperature and relatively constant chilled-water flow through the entire system. The use of two-way valves results in constant return-water temperature and variable water flow through the entire system. Before choosing one of these control methods, it is necessary to determine the effect that it will have on the other parts of the chilled-water system.

Chiller Evaporator Flow

▲Constant flow is most common

▲Variable flow is possible

◆Can reduce energy

consumption	evaporator
◆ Use only with
advanced chiller and
system controls

Figure 38

In the past, the water flow rate through the chiller evaporator was to remain as constant as possible. The vast majority of chilled-water systems employ pumping schemes that maintain a constant flow rate of water through each chiller evaporator. Even in the most-carefully-designed chilled-water systems, however, the flow through the chillers will still vary slightly due to system

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