Pre-occupancy purge - Johnson Controls - LIT-12011950 - Building automation software - Smart Equipment Controller - 5.0

Smart Equipment Controls Sequence of Operation Technical Bulletin

Product name
Smart Equipment Controller
Document type
Technical Bulletin
Document number
LIT-12011950
Version
5.0
Revision date
2024-06-06
Product status
Active

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.