AAON Auto-Zone 2 GPC-XP - WSHP Unit Compressor Enable; Heat Rejection; Heat Addition; Emergency Shutdown

Operation Of The WSHP Loop Controller
WSHP Unit Compressor Enable
If after the Lead/Lagged pump activates and Proof of Water Flow has
been established, the System Active relay is energized and when AZ
2 Controllers are being used for the WSHP units, a Global enable is
broadcast to the controllers letting them know to enable their compres-
sors. If using another control system for the WSHP units the System
Active relay would be used to send a 24 V relay signal to the units to run.
Heat Rejection
Staged Cooling
The GPC-XP Loop Controller monitors the loop water temperature to
determine if the loop water needs to be cooled. If the loop water tempera-
ture rises above a user dened setpoint the GPC-XP Loop Controller will
energize the cooling tower spray pump. This will remain on if the spray
pump proof of ow proves ow until the setpoint temperature is satised.
This acts as the rst stage of heat rejection. If the loop water temperature
continues to rises above a second set of user dened setpoints the cooling
tower fan will be energized providing a second stage of cooling for the
water owing through the cooling tower.
Modulating Cooling
The GPC-XP Loop Controller has the ability of sending a modulating
signal to the cooling tower fan if equipped with a VFD, to provide an
increase or decrease using a direct acting oating point control of the
output signal for modulating the cooling tower fan VFD.
Heat Addition
Staged Heating
The GPC-XP Loop Controller monitors the loop water temperature to
determine if the loop water needs to be heated. If the loop water tem-
perature falls below a user dened setpoint the GPC-XP Loop Control-
ler will energize the Cool Bypass Valve and enable the heat addition
device. This will remain on if the boiler proof of ow proves ow until
the setpoint temperature is satised.
Modulating Heating
The GPC-XP Loop Controller has the ability of sending a modulating
signal to a modulating mixing valve or a variable heat source. When
the loop water temperature drops below a user dened setpoint, the
Cool Bypass Valve will be energized and the analog output voltage
will increase or decrease using a reverse acting oating point control to
modulate a valve or variable heat source.
Emergency Shutdown
The GPC-XP Loop Controller uses an Emergency Shutdown input on
one of the binary inputs from a restat or smoke detector (by others) to
force shutdown of the entire system should a safety condition be initi-
ated by the safety device. It is congured as a Normally Closed (NC)
contact that is only active when the circuit is opened.
Operation
7
WSHP Loop Controller GPC-XP Guide