TRG-TRC012-EN 35
period five
Application Considerations
notes

Constant or Variable Evaporator Water Flow

In previous designs, chillers were required to maintain a constant flow rate of
water through the evaporator. This requirement has changed due to advances
in chiller controls. Increased sensing and control capabilities now allow chiller
manufacturers to design controls that monitor, and respond faster to,
fluctuating conditions.
While the chiller may be able to handle variable water flow through the
evaporator, the specific application of a chilled water system may not warrant
variable flow. As always, each application should be analyzed to determine if
variable evaporator water flow is warranted.
The controls on many current chiller designs can properly control the chiller in
response to varying evaporator flow rates, with the following limitations:
evaporator water flow…
Constant or Variable Flow
variable
variable
speed
speed
drive
drive
chilled
chilled
water
water
pump
pump evaporator
evaporator
Figure 50
variable evaporator water flow

Limitations

▲Maintain minimum and maximum water flow
rates through the chiller evaporator
▲Rate at which evaporator water flow changes
must be kept below the corresponding limit to:
◆Maintain the chilled water set point control
◆Keep the chiller on line
◆Protect the chiller from damage
Figure 51