VAV-SVX07F-EN 45
Calibration, Operation Modes, and Control
Parallel Fan
The parallel fan is the first stage of heat. When the supply air temperature is cold, the parallel fan:
• Cycles ON as the first stage of heat during occupied mode or occupied standby mode.
• Cycles ON with a call for heat during unoccupied mode.
When the supply air temperature is warm
or hot, the parallel fan is OFF, unless the local reheat is
ON. Two (2) methods of control are supported for energizing the parallel fan:
• One method is based on space temperature.
• One method is based on supply airflow.
The parallel fan start points for each method of control are able to be configured.
Parallel Fan Start based on Space Temperature
The parallel fan turns ON when the space temperature falls below the heat setpoint, plus the
configured parallel fan temperature enable setpoint. It turns OFF when the space temperature rises
above the heat setpoint, plus the configured parallel fan temperature enable setpoint by 0.5°F
(0.28°C).
Parallel Fan Start Based on Supply Airflow
The parallel fan turns ON when the supply airflow falls below the configured parallel fan airflow
enable setpoint, or the supply airflow is less than the active minimum flow setpoint, plus 2% of the
configured nominal airflow. The parallel fan turns OFF when:
• The supply airflow rises above the conf
igured parallel fan airflow enable setpoint, plus 5% of
the configured nominal airflow.
• When the supply airflow is greater than the acti
ve mini
mum flow setpoint, plus 5% of the
configured nominal airflow.
In pressure dependent mode, the air valve position is
substituted for the supply airflow.
Parallel Fan Operation During Calibration
During calibration, the parallel fan is in the same state (ON or OFF) prior to the start of calibration.
It remains in that state until one minute after calibration ends. One minute after calibration ends,
normal control of the parallel fan resumes. The one-minute period is ignored if reheat is active or
if the parallel fan is overridden.
Fan OFF Delay
There is a 15-second fan OFF delay. When reheat is turned OFF, the controller turns the fan OFF 15
seconds later.
Ventilation Flow Control (VFC)
Ventilation flow control is applied to a VAV terminal and used to temper cold outdoor air (OA) that
is brought into a building for ventilation purposes. The tempered air is intended to supply an air
handler unit (AHU), which provides comfort control to the zones it serves. The VAV terminal
supplies the correct amount of ventilation air and, when possible, tempers the ventilation air to
reduce the load on the air handler. Refer to Table 11, p. 46 for ventilation flow control outputs.
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