Sequence of Operation
RTU Open v5
CARRIER CORPORATION ©2019
Integration Guide
All rights reserved
25
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.
