Carrier RTU Open v3 - Pre-Occupancy Purge; Unoccupied Free Cooling; Optimal Start

Sequence of Operation
RTU Open v3 CARRIER CORPORATION ©2019
Installation and Start-up Guide All rights reserved
48
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
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.