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Demand control ventilation (DCV) and dehumidification using optional
sensors
The VVT Zone Controller's RH/CO2 input supports an optional CO
The sensor can have a 5-volt maximum output. The range is configurable as either 0–5 or 1–5 volts (1–5 volt
supports 4–20 mA sensors with a 250 ohm resistor). The controller's low and high sensor input configuration
allows for a wide range of sensors.
The controller can also support both DCV and dehumidification functions, by using a system RH or CO
input connected to another controller.
NOTE If the connected sensor and/or system sensor value are used by the air source through Linkage, set
the appropriate control type to Enable. If you do not need local control at the zone, set DCV Max Vent Airflow
or Maximum RH Override Airflow to 0.
Demand Control Ventilation (DCV) – Requires CO
The zone controller monitors the CO
increasing CO2 levels when the zone is occupied. If the sensor's value exceeds the DCV Start Ctrl Setpoint
and the air source is in cooling or ventilation mode, the controller increases airflow to the zone at a base rate
defined by ASHRAE, and then proportionally increases ventilation if the CO2 level continues to increase. If the
sensor's value exceeds the DCV Max Ctrl Setpoint, the controller modulates the damper to its DCV Max Vent
Damper Position.
When the zone is unoccupied, the Cooling Min Damper Position and Heating Min Damper Position provide
base ventilation.
If the controller is configured for reheat, the heating setpoint is temporarily increased to a value halfway
between the heating and cooling setpoints. If the zone temperature drops below the heating setpoint, the DCV
override is temporarily suspended and the damper returns to normal control until the zone temperature is
satisfied.
Dehumidification – Requires RH sensor
The zone controller monitors the RH sensor and can provide dehumidification if the sensor's value exceeds
the Occupied RH Control Setpoint. If the zone is occupied and does not require heating, and the air source is
operating in a cooling mode and providing primary air with a sufficiently low dew point, the controller
overrides the damper control to increase airflow to the zone. During the dehumidification mode, the heating
setpoint is temporarily increased to a value halfway between the heating and cooling setpoints to prevent
overcooling the zone. The controller uses a PID control loop to provide dehumidification. The controller has a
Maximum RH Override Airflow setting to prevent excessive airflow during dehumidification.
NOTE If both control functions are enabled, the zone will control to the greatest calculated damper position of
the three values (temperature, RH, or IAQ
VVT Zone Controller
sensor
2
sensor and can override the temperature control to respond to
2
sensor or Relative Humidity (RH) sensor.
2
sensor
2
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