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WattMaster WHP Section 1
Design Guide 1-11
pump exceeds the first pumps run time by the same amount. This keeps both pumps with
roughly the same number of hours on each pump. Changeover occurs at the time the run
time setpoint is exceeded. The running pump is shut off at the same time the standby
pump is energized, this prevents any down time or alarms. The unit can be configured to
control either the Loop Inlet temperature or the loop outlet temperature.
A user adjustable low outdoor air temperature setting of XX degrees will allow the unit to
run the pumps continuously for protection against freezing.
If the pump is constant volume, and the pump has been started, it has 3 seconds to
generate flow or the standby pump is activated. If the pump is controlled by a VFD, once
it starts, it has 60 seconds to generate flow and if it doesn’t the standby pump is activated.
If the standby pump fails, an alarm is generated and the Loop controller deactivates any
active heat rejection or addition stages. At the same time an alarm is generated, we
energize relay #5 on the Loop Controller board so that it may used to turn on a local
alarm signal.
Loop flow can be determined by a binary contact closure on input #3 or a 0 to 50 PSI
pressure sensor on input #3. If a pressure sensor is used, the user can program the
pressure setpoint that needs to be met for proof of flow.
Pump VFD Control
An optional Pump VFD signal can be modulated if the system is configured for
proportional control and a pressure sensor is attached to analog input #3.
At a user defined rate, the VFD signal is ramped up when the pressure is below
a user defined setpoint by a user defined deadband. The signal ramps down when the
pressure exceeds the setpoint by the deadband value. If the pressure ever exceeds the high
pressure setpoint, an emergency override activates and begins cutting the VFD signal in
half each time the control loop is polled by the software. This protects against run away
over-pressurization.
The pump relay outputs are still activated and Lead/Lagged as described above
and the pump relay remains on until the Request signal is removed, provided it
has been operating for at least 15 minutes.
Compressor Control
Anytime a pump is running and proof of flow has been established, the compressor output
is activated.