Unoccupied Free Cooling; Optimal Start - Carrier RTU Open v5 Integration Manual


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
When the RTU Open schedule is unoccupied and the space temperature rises at least 1 °F (.5 °C) above the
Occupied Cooling Setpoint, the supply fan starts. The economizer damper opens as necessary to cool the space.
The RTU Open continues to operate in this mode until the space is satisfied or the outside air conditions are no
longer suitable for free cooling.

Optimal Start

The RTU Open may use either of 2 different Optimal Start methods. Learning Adaptive Optimal Start is used for
heat pump applications and adjusts the effective setpoints to achieve the occupied setpoints by the time
scheduled occupancy begins. This prevents or minimizes the need for auxiliary heat. The Optimal Start recovery
period may begin as early as 4 hours prior to occupancy. The algorithm works by moving the unoccupied setpoints
toward the occupied setpoints. The rate at which the setpoints move is based on the outside air temperature,
design temperatures, and capacities.
The following conditions must be true for learning adaptive optimal start to operate:

On the Properties page > Control Program tab > Configuration > Setpoints > Optimal Start, the default value
is set to 1 and must be set greater than 0 (0.00 disables Optimal Start) and less than or equal to 4.

The system is unoccupied
NOTE If the controller does not have a valid outside air temperature, then a constant of 65°F (18.3°C) is used.
This value is not adjustable.
RTU Open v5
Integration Guide
25
Sequence of Operation
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