Changeover Mode Detection; Indoor Air Quality - United Technologies Carrier Unit Vent Open Integration Manual

Changeover mode detection

The Unit Vent determines the changeover mode for 2-pipe heating/cooling systems. The controller monitors a
local changeover thermistor sensor or switch, dependent upon the configuration. For thermistor applications, the
heat or cool mode is determined by user-configurable temperature setpoints. When the sensed temperature
exceeds the Changeover Heat Limit, the system changeover mode is set to heat. When the sensed temperature
falls below the Changeover Cool Limit, the system changeover mode is set to cool. For applications using a switch,
the heat mode is determined when the input is open, while a closed switch indicates cool mode.
Additionally, an Analog Network Input point and a BACnet Analog Value input variable are also provided to allow a
network-supplied analog value of the system water temperature to be used to determine the changeover mode.
The Analog Network Input point has the highest priority, followed by the BACnet AV point, then the local input if
multiple inputs are supplied simultaneously.

Indoor Air Quality

If used with a modulating-type mixed air damper, the controller can provide Demand Controlled Ventilation (DCV)
to properly ventilate an occupied space. To meet ventilation requirement, the fan must be configured for the
Continuous or Always On mode of operation.
Demand Control Ventilation (DCV) - If the optional CO
modulating mixed air damper is installed, the controller will increase the minimum damper opening to outdoor air
as required by the CO
control monitors the CO
position as required. The control provides proportional ventilation to meet the requirements of ASHRAE
specifications by providing a base ventilation rate and then increasing the rate as the CO
control begins to proportionally increase ventilation when the CO
and reaches the full ventilation rate when the CO
The configurable Minimum Damper Pos insures that proper base ventilation is delivered when occupants are not
present. The DCV Max Vent Damper Pos (default 60%) limits the maximum amount of outdoor air. An automatic
minimum mixed air temperature override control prevents unacceptable mixed air temperatures when the outdoor
air is extremely cold. It proportionally resets the maximum amount of outdoor air used for DCV from the configured
DCV Max Vent Damper Pos as the OA drops below the Minimum Cooling SAT limit and ends at the Minimum
Damper Pos when the OAT reaches 10°F (-12.2°C).
If this additional outdoor air being introduced for ventilation causes an unacceptable drop in the supply air
temperature or could cause a potential coil freeze-up condition, then the control can be set to temper the supply
air during DCV control. The control uses heating to prevent the supply air from falling below the configurable Min
DCV Override SAT setpoint, when the DCV control is active. The IAQ configurations are accessed on the Properties
page > Equipment tab > Configuration.
The following conditions must be true for this algorithm to run:

Damper Control is configured for Modulating

Valid space temperature must be available

The unit is in an occupied mode

Supply Fan must be on and not in alarm

IAQ sensor value reading is greater than the DCV Start Control Setpoint

The DCV calculated damper position must be > the economizer position
Unit Ventilator
Integration Guide
levels within the occupied space. The control provides DCV during occupied periods. The
2
level and compares it to the configured setpoints and adjusts the minimum damper
2
sensor (or a CO sensor value) is available and a
2 2
level rises above the start ventilation setpoint
2
level is at or above the maximum setpoint.
2
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Communications wiring
level increases. The
2
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