Sequence of Operation
RTU Open v3
Carrier Proprietary and Confidential
CARRIER CORPORATION ©2016
Integration Guide
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23
Temperature Compensated Optimal Start
is a second start method used for gas or electric heating applications. It
switches from unoccupied to the occupied setpoints at a calculated time prior to occupancy. This minimizes the
operation of the unit’s fan. The Optimal Start recovery period may begin as early as 4 hours prior to occupancy.
The time at which the setpoints move is based on the difference between the current space temperature and the
desired setpoint, multiplied by the "K" factor, or recovery rate, for the required mode of operation.
The following conditions must be true for Temperature Compensated Optimal Start to operate:
•
On the
Properties
page >
Equipment
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
To change Temperature Compensated Optimal Start settings:
1
In the navigation tree, select the equipment that you want to change.
2
On the
Properties
page >
Equipment
tab >
Configuration
>
Setpoints
, click
Heat Start K factor
or
Cool Start
K factor
. This defines the equipment’s recovery rate in minutes / deg.
Enthalpy control
You may use an enthalpy switch to indicate the suitability of outdoor air for economizer cooling. You can use either
an outdoor air or differential enthalpy switch. A differential enthalpy switch has a sensing device in both the
outdoor and return air streams. A differential enthalpy switch indicates when outside air is more suitable to be
used than the return air and is available for economizer cooling. If no enthalpy switch is configured, a network
point (Object Name: oae) is available. This point is displayed in the i-Vu® application and an Equipment Touch as
Enthalpy
(BACnet).
The sequence of operation for economizer cooling is the same with or without an enthalpy switch, except that an
enthalpy switch imposes one more validation on the suitability of outside air for economizer cooling. An
Enthalpy
Status
that is
High
disables the economizer and the outside air damper goes to its minimum position. An
Enthalpy Status
that is
Low
enables the economizer if a call for cooling exists and the remaining preconditions are
met.
Indoor Air CO2
Indoor Air CO2
is controlled on rooftop equipment with an economizer.
Indoor Air CO2
sequence is enabled by
installing an air quality (CO2) sensor. A CO2 sensor may be terminated at the RTU Open, or a subordinate zone
controller, when part of a zoned system.
An outdoor air quality sensor may also be installed and terminated at the RTU Open, but it is not required. When
an outdoor air quality sensor is not installed, the algorithm uses 400ppm as the fixed outdoor air CO2 level.
The following conditions must be true for the
Indoor Air CO2
algorithm to operate:
•
The system is occupied
•
The supply fan has been started for at least 30 seconds
•
The CO2 sensor has a valid reading