Power Exhaust; Pre-Occupancy Purge; Unoccupied Free Cooling - Carrier RTU Open v3 Integration Manual

Power Exhaust

The RTU Open may enable and disable an exhaust fan, based on either the controller's occupancy or its
economizer damper position. If the Fan Control is set to Two Speed or Variable Speed, the Power Exhaust
Setpoint is automatically adjusted based on the fan's air delivery. The Calculated PE Setpoint used for control is
displayed in the Maintenance section.
If Continuous Occupied Exhaust is Yes, the Power Exhaust binary output (BO-8) is energized while the RTU Open
is occupied and de-energized when unoccupied.
If Continuous Occupied Exhaust is No, the Power Exhaust binary output (BO-8) is energized when the economizer
damper output exceeds the Calculated Power Exhaust (PE) Setpoint value. The output remains energized until the
economizer output falls below the Power Exhaust Setpoint value by a fixed hysteresis of 10%.

Pre-Occupancy Purge

Pre Occupancy Purge allows the rooftop equipment with an economizer damper to use outdoor air to purge the
space of contaminants just prior to the beginning of the occupied period.
The following conditions must be true for pre-occupancy purge to operate:
•
Pre-Occupancy Purge set to Enable
•
Economizer Exists set to Yes
• A local time schedule is configured
•
The local time schedule is currently unoccupied and the remaining time is less than the configured Purge
Time
When the RTU Open schedule is unoccupied and the remaining unoccupied time is less than the purge time, the
supply fan starts. The economizer damper opens to the configured Economizer Purge Min Pos. The RTU Open
continues to operate in this mode until the occupied start time is reached. The Pre-Occ Purge state is displayed in
the Maintenance section.

Unoccupied Free Cooling

Unocc Free Cool Enable allows rooftop equipment with an economizer damper to use outdoor air for free cooling
during unoccupied periods.
The following conditions must be true for unoccupied free cooling to operate:
•
Unocc Free Cool Enable set to Enable
• The system is unoccupied
•
The outside air temperature is below the Economizer High OAT Lockout Temp setpoint
•
The outside air temperature is less than the space temperature
•
Enthalpy (if enabled) is Low
RTU Open v3
Integration Guide
Carrier Proprietary and Confidential
21
Sequence of Operation
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