Sequence of operation
VVT Zone II Controller
CARRIER CORPORATION ©2019
Installation and Start-up Guide
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49
Fan Heat Off Delay
– For fan-powered terminals, the controller has a configurable
Fan Off Delay
. After the heating
coil de-energizes, the fan continues to run for the length of the delay to deliver to the zone any heat stored in the
coil. The default delay of 2 minutes is optimal for ducted hot water coils. For ducted electric heat coils, the
nominal delay is approximately 1 minute. For baseboard and non-ducted heat, the delay should be set at 0.
This feature applies to parallel fan terminals in both occupied and unoccupied mode and series fan terminals in
the unoccupied mode if the air source fan is off.
Demand control ventilation (DCV) and dehumidification using optional
sensors
The VVT Zone II’s
RH/CO2
input supports an optional CO
2
sensor or Relative Humidity (RH) sensor. 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
2
sensor
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
2
sensor
The zone controller monitors the CO
2
sensor and can override the temperature control to respond to 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).
Summary of Contents for VVT Zone
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