This section describes the duct pressure control setpoints and related data, inputs, outputs, and operation.
Setpoints and related data
The setpoints and related data include the following items:
- Duct pressure setpoint (DctPrs-SP)
- Duct static pressure (DctPrs)
- Duct pressure shutdown setpoint (DctShutdownSp)
Inputs
The input for duct pressure control is 0 to 5 VDC from the duct pressure sensor to terminal DCT PRS.
Outputs
The outputs include the following items:
- 24 VAC from the FAN to energize the fan motor or enable VFD
- 2 to 10 VDC from the VFD terminal.
Operation
When the fan is energized, the 2 to 10 VDC output from VFD terminal is used to maintain the supply duct pressure to the duct pressure setpoint. If the duct pressure is above setpoint, the VFD output decreases. If the duct pressure is below setpoint, the VFD output increases.
The rate of change of the VFD output is determined by the deviation from setpoint and length of time away from the setpoint.
If the duct pressure reaches the duct pressure shutdown setpoint, the fan and all other outputs of the unit de-energize.