Unit Functions
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IOM 1206-13 • TRAILBLAZER
®
MODEL AGZ CHILLERS
6. Evaporator LWT target must be at least 4.44°C because
below that the discharge temperatures are notadequate
to support heat recovery operation
Heat Recovery Operation Per State
When State = Off
•
Heat Recovery Pump is off
• Heat Recovery Position/Speed signal is 0%
• Circuits use normal condenser targets
When State = Recirculate
• Heat Recovery Pump is on
• Heat Recovery Position/Speed signal is at the minimum
position/speed as defined by the settings
• Circuits transition to heat recovery condenser targets
When State = On
• Heat Recovery Pump is on
• Heat Recovery Position/Speed signal is determined by
PID loop
• Circuits continue to use heat recovery condenser targets
PID Loop
A PID loop will be used for controlling valve position or pump
speed. This loop should allow for a smooth transition from
Recirculate to On control states, meaning that when output
control is handed off to the PID there isn’t a sudden large
change in the position/speed from the minimum value used
during Recirculate state.
In addition, there should be a smooth transition between auto
and manual control modes. When changing between these
modes, there should not be a sudden large change in position/
speed.
The controlled parameter for the PID is a calculated value:
• Heat Recovery LWT – [maximum condenser saturated
temperature of running circuits] The set point for the PID
is the Heat Recovery Control Offset set point.
