AAON Auto-Zone 2 GPC-XP - Operation of the WSHP Loop Controller; Overview; Typical Sequence; Pump On;Off -Control

Overview
The GPC-XP Controller can be congured to control the water loop
to the individual water source heat pumps installed in a typical water
source heat pump system. The GPC-XP can operate stand-alone or be
used with the AZ 2 Control System to utilize the transfer of commonly
shared information , such as outside air temperature and system active
conditions over a communication network.
The main goal of the GPC-XP Loop Controller is to provide water ow
and to maintain the loop water temperature by monitoring either the Loop
Return Water Temperature or the Loop Supply Water Temperature. If
a higher temperature is required, a water heating device is enabled. If
the temperature needs to be lowered, a water cooling device is enabled.
The AZ 2 Controller can be congured to control individual water
source heat pumps. The AZ 2 Controller will work in conjunction with
the GPC-XP Loop Controller to send and receive data critical to an ef-
cient WSHP system.
Typical Sequence
On a typical system as is shown and congured in this manual the GPC-
XP WSHP Loop Controller waits for a Request to Run from an AZ 2
Controller on a Global Binary Channel or a Binary Contact Closure from
another source when the AZ 2 Controllers are not being used. Once the
request is received the GPC-XP energizes the Request to Run Relay and
the System Active relay. The System Pump (usually using a Lead/Lag
pump conguration) is then activated to initiate water ow in the system.
Once the System Pump is activated and Proof of Water Flow has been
determined a Global broadcast or 24 VAC from the System Active relay
is sent to the Heat Pumps to enable their compressors to run as needed.
The GPC-XP monitors the System Return Water Temperature or the
System Supply Water Temperature to determine if the water needs to
be heated or cooled to maintain the desired loop water temperature. The
typical conguration uses the Return Water Temperature to determine
the need for Heating or Cooling of the loop water.
Pump On/Off -Control
When a Request to Run is received, the GPC-XP Loop Controller
activates the System Pump to initiate water ow to the heat pumps
and other devices on the loop. The pumps can either be constant ow
or controlled by a VFD (see “Pump VFD Control”). If controlled by
a VFD, a water pressure transducer must be used for pump control. In
addition if the Request To Run goes away or if the Proof of Water Flow
is lost, the pump will turn off.
Typically the System Pumps are Lead/Lag controlled based on a user
denable number of hours of operation. If one pump exceeds the other
pump’s run time by this amount, the lead is changed until that pump
exceeds the rst pump’s run time by the same amount. This keeps both
pumps with roughly the same number of hours on each pump. The run-
ning pump is shut off at the same time the standby pump is energized,
this prevents any down time or alarms.
The GPC-XP Loop Controller monitors water ow in the loop with either
a Binary contact closure (BIN1) or a 0 to 50 PSI pressure transducer
from one of the analog inputs congured for this. The user can congure
the pressure setpoint that needs to be met to initiate the System Pump.
Pump VFD Control
The GPC-XP Loop Controller has 4 optional modulating output signals
available for control of pumps, boilers and cooling towers utilizing
VFD control. If the system is using a Pressure Transducer instead of a
pressure switch for System Pump control, the GPC-XP can monitor the
loop pressure and use a Reverse Acting PID Loop to maintain a user
dened Loop Pressure Setpoint.
The Loop Pressure is maintained by decreasing the signal output voltage
when the pressure exceeds the user dened setpoint plus the deadband
and increasing the voltage output signal with the pressure is below the
setpoint.
The pump relays are still activated and Lead/Lagged as described in the
previous section. Both output signals are enabled by their correspond-
ing relays.
Operation Of The WSHP Loop Controller
Operation
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WSHP Loop Controller GPC-XP Guide