Trane SYS-APM001-EN manual Variable-Primary-Flow Systems, Other plant designs

System Configurations

with a surplus that may, or may not, be large enough to indicate stopping a chiller in that plant.

Other plant designs

There are many other ways to connect chillers to distributed loops and each provides its own challenges and opportunities. The advent of variable- primary-flow chilled-water systems offers some new opportunities as does distributed pumping. In any case, getting system design advice specific to your system early in the process can prevent or identify many operational challenges.

Variable-Primary-Flow Systems

Two main physical differences distinguish this type of system from the more familiar primary–secondary design, which hydraulically “decouples” the constant-flow production side of the chilled-water loop from the variable-flow distribution side. The variable-primary-flow (VPF) design eliminates the constant-flow chiller pumps and uses the variable-flow pumps to circulate water throughout the entire chilled water loop (Figure 37). Both systems include a bypass line, but the VPF bypass will be smaller.

Figure 37. Variable-primary-flow system

Typ

Chiller 1

Isolation Valves

Chiller 2

Flow Meter
(Alternative to Chiller ΔP)
Bypass Line
Modulating	Airside Coils with Two-Way
Control Valve	Control Valves
	Bypass Line
	Alternate
	Location

In a VPF system, water flow varies throughout the entire system— through the evaporator of each operating chiller as well as through the cooling coils. Two-way control valves on coils, check (or isolation) valves on chillers, and a bypass pipe with a control valve are required to implement a VPF system.

•Variable-flow chiller pumps eliminate the need for a separate distribution pump.

SYS-APM001-EN Chiller System Design and Control 55