SYS-APM001-EN
40
Variable-Primary-Flow Systems
Another method for balancing the production and distribution flows is to make
them equal. Variable-flow systems require chillers that can operate properly
when evaporator flow varies.
Conceptually, the variable-primary-flow (VPF) system resembles the familiar
constant primaryvariable secondary design more commonly known as the
decoupled" system.
1
For example, both require a bypass. The bypass line for a
VPF system is required to ensure that minimum flow through chillers can be
maintained. Each chiller in the arrangement shown has a dedicated pump
whose operation coincides with the chiller it serves.
Figure 18 Variable-primary-flow system
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.
However:
n
variable-flow chiller pumps eliminate the need for a separate
distribution pump.
n
the bypass can be positioned either upstream or downstream of the
cooling coils.
n
a control valve in the bypass ensures that the amount of flow through the
operating chiller(s) never falls below the minimum limit.
Chiller 2
Chiller 1
Variable-Flow-
Chiller Pumps
Control Valve
System Coils,
Two-Way Control Valves
Multiple
Valves May Be
Three-Way
Required
Optional
"Bypass"
Check
Valves
For Minimum Chiller Flow
Summary :
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. Chiller 2 Chiller 1 Variable-Flow- Chiller Pumps Control Valve System Coils, Two-Way Control Valves Multiple Valves May Be Three-Way Required Optional "Bypass" Check Valves For Minimum Chiller Flow
Tags :
chiller,system,bypass,ales,flow,control,chillers,through,coils,ariableprimaryflow,ale,required,minimum