Inputs
The inputs include the following items:
- Thermostat only is set to No (TStatOnly)
- Occupancy mode is set to Schedule (OccMode)
- Pre-occupancy purge enable is set to Enable (PreOccPurgeEna)
- Pre-occupancy purge time (PreOccPurgeTime)
- Pre-occupancy purge upper SAT setpoint (PreOccUpSAT_SP)
- Pre-occupancy purge lower SAT setpoint (PreOccLowSAT_SP)
- Economizer controller installed and online (EconCntlr)
- Supply Air Temperature (SAT)
Outputs
The outputs include the following items:
- Fan Command (Fan)
- Economizer Damper % Command (Econ)
- Exhaust Fan Command (ExFan) (if installed)
- Exhaust Fan VFD % Command (ExFanVFD) (if installed)
Operation
Pre-occupancy purge is an economizer function that inputs the time before occupancy from the schedule and compares it to the pre-occupancy purge time point. If the time before occupancy is less than the pre-occupancy purge time and the control is unoccupied, the control enters pre-occupancy purge mode. The economizer opens all the way, the indoor fan turns on, and it begins monitoring the SAT.
If the supply air temperature rises above the pre-occupancy purge upper SAT setpoint, the control modulates the economizer in an attempt to maintain the pre-occupancy purge upper SAT setpoint.
If the supply air temperature falls below the pre-occupancy purge lower SAT setpoint, the control modulates the economizer in an attempt to maintain the pre-occupancy purge lower SAT setpoint.
Power exhaust during pre-occupancy purge
If a non-modulating power exhaust is installed, the control forces the exhaust fan on and off based on economizer position setpoints.
If a variable frequency power exhaust is installed, the control forces the exhaust fan modulation using the building static pressure setpoint.
If a modulating exhaust damper is installed, the control forces the damper modulation to the building static pressure setpoint.
Termination
The control remains in pre-occupancy purge mode until the system time matches the occupied time. The control then switches to occupied operation.