Trane SYS-APM001-EN manual System Configurations, Parallel Chillers

System Configurations

Multiple chilled-water systems are more common than single chilled-water systems for the same reason that most commercial airplanes have more than one engine—the balance of reliability and cost. The most typical system configuration, by far, has two chillers. Since system loads can vary throughout a wide spectrum, multiple chilled-water systems can often operate with one chiller. During these periods, if the system is designed properly, the energy required to operate a second chiller and its auxiliaries can be conserved.

This section examines:

•Constant flow systems

•Systems in which flow is constant through chillers, but variable through the rest of the system

•Systems in which flow varies throughout the entire system—including the chillers

Parallel Chillers

Figure 25 shows a system with two chillers piped in parallel, using a single chilled-water pump.

Figure 25. Parallel chillers with a single, common chiller pump

54°F [12.2°C]	54°F [12.2°C]
	Chiller 2 (Off)
	49°F [9.4°C]

Constant

Flow

Pump

Chiller 1 (On)

44°F [6.6°C]

With constant flow loads, water flows in both chillers continually, whether the chiller is operating or not. Clearly, this can disrupt the supply chilled-water temperature when only one chiller is operating. The temperatures indicated in Figure 25 show how the supply water temperature rises when one chiller is cycled off in response to a part-load condition. This may result in inadequate dehumidification capabilities or the inability to satisfy specific loads.

42 Chiller System Design and Control SYS-APM001-EN