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Section 1 WattMaster WHP
1-10 Design Guide
WHP Loop Controller
Sequence of Operations
Summary
The Water Source Heat Pump Loop Controller waits for a Request to Run signal from a
Heat Pump or from a Binary Contact Closure. Once the request is received the Loop
Controller activates a Pump to initiate water flow to the Heat Pumps. Once the pump is
activated and proof of flow has been determined, a Global is broadcast to all Heat Pumps
to enable them to go ahead and run their compressors. The main goal of the Loop
Controller is to provide water flow and to maintain the loop water temperature by
monitoring either the Loop Inlet or Loop Outlet temperature. If a higher temperature is
required, Heat Addition is enabled. If the temperature needs to be lowered, Heat
Rejection is enabled.
Once the Loop Controller has been activated by a request, it will run for a minimum of 15
minutes to prevent cycling on and off due to borderline requests from the Heat Pumps.
If a Fire Alarm is detected, the Loop Controller generates a Global broadcast to all Heat
Pumps to turn off.
If the High Pressure option is configured, the Loop Controller can generate a Global
broadcast to force the Heat Pumps to open their Isolation Valves to reduce loop pressure
if the high limit has been exceeded.
Pump Control
If WattMaster Water Source Heat Pump Controllers are used in conjunction with the
Loop Controller, a Global Binary signal from the attached Heat Pumps sends a Request to
run or Enable to Run command to the Loop Controller. If the Loop Controller is used in a
stand alone configuration, a contact closure on the AIN 2 of the Analog Expansion board
gives the controller a request to run. When a request to run is received, the Loop
Controller activates a pump to initiate water flow to the heat pumps. The pumps can
either be constant flow or controlled by a VFD. If the request goes away for at least one
minute, the request to run command is removed. If the loop controller has been running a
minimum of 15 minutes then it can be turned off, since there is no longer a request to run.
If the proof of flow is lost while the pumps are running, the pump is shut off immediately
if the changeover to the Standby Pump had already been made.
The pumps are Lead/Lag controlled based on a user definable number of hours. If one
pump exceeds the other pumps run time by this amount, the lead is changed until that