Chilled water system configuration can be roughly devided into the following three types:

Constant primary flow

Load is controlled by 3-way valves installed in the downstream of cooling coil by bypassing waterflow as needed. Water

Constant primary flow and variable secondary flow

Capacity is controlled by VFD installed on secondary pumps. Primary loop water flow should be equal to or more than secondary loop water flow. Otherwise, the heated secondary loop water in the downstream of cooling coil would bypass the chiller and enter directly to the cooling again, disrupting the system. The bypass water from primary to secondary loop flows through a piping called decoupler. The flow in decouple should be one directional.

Variable primary flow

Capacity is controlled by VFDs installed on primary pumps. A bypass valve is needed to maintain the minimum required flow. If the water speed through the evaporate tube is too low, water can freeze and rupture the tube.

Summary

CPF CPF VSF VPF
Load control device 3-way valves on CC downstream VFD on secondary loop VFD on primary loop
Modulated variable Delta T Flow rate Flow rate
Bypass piping No Yes Yes
Bypass valve No No Yes

References

Hubbard, R.S.. (2011). Energy impacts of chilled-water-piping configuration. 83. 20-27.

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