Communications wiring
Unit Ventilator
CARRIER CORPORATION ©2019
Integration Guide
All rights reserved
22
Mixed air damper (Modulating)
The Unit Vent operates a mixed air damper to maintain the desired cooling setpoint without mechanical cooling,
while also providing the required ventilation. The modulating mixed air damper is controlled by the PI
(Proportional-integral) cooling algorithm and integrated with mechanical cooling while also maintaining a minimum
OA intake if the optional CO
2
sensor is available. See
Indoor Air Quality
(page 23) for additional information.
The desired
Damper Setpoint
is calculated by the controller when cooling is required. The
Damper Setpoint
Override Value
provides the capability to maintain a user-defined fixed supply air temperature when cooling is
required and available. It will override the PI temperature control algorithm when the
Damper Setpoint Override
Value
is not equal to 0 (and must be greater than 45°F (7.2°C). The
Damper Setpoint
is compared to the actual
supply air temperature and used to determine the
Mixed Air Damper
position.
The following conditions must be true in order for the modulating damper (economizer) algorithm to run:
Damper Type
is Modulating
Space temperature reading is valid
Supply Fan
must be on and not in Alarm
OAT is valid
Heat mode is not active
Fire/Smoke Detector
(FSD) is
Normal
OAT is less than
Damper Lockout Temperature
limit
OAT is less than RAT/SPT sensor
If occupied, the SPT is greater than the
Occupied Cooling
setpoint
If unoccupied, the SPT is greater than the
Unoccupied Cooling
setpoint
If all the above conditions are met, the mixed air damper will operate as an economizer as required, otherwise it
will be disabled and maintain either a closed or minimum damper position.
The configuration screens contain the
Min Cooling SAT
and
Damper Lockout
parameter based on outdoor air
temperature (OAT). Both can be adjusted to meet various specifications.
Mixed air damper (2-position)
The control can operate a 2-position (0-10 Vdc or 2-10 Vdc) type minimum outdoor air damper to maintain the
desired ventilation during occupied periods. The damper output provides a 10 Vdc signal when the control is
occupied or in an occupancy override mode. When the control is unoccupied or the fan is off, the damper output
will go to 0 Vdc. To control the maximum amount of outdoor air entering the unit, a mechanical actuator stop must
be set.
The following conditions must be true in order for the 2-position damper algorithm to run:
Damper Type
is
2-Pos
Supply Fan
must be on and not in alarm
The unit is in an occupied mode
