CNT-SVX17G-EN 65
Sequence of Operations
Parallel Fan
The parallel fan is the first stage of heat. When the primary air temperature is cold, the
parallel fan:
•Cycles ON a
s the first stage of heat during occupied mode or occupied standby mode;
•Cycles ON with a call
for heat during unoccupied mode.
When the primary air temperature is warm or hot, the parallel fan is OF
F unless the local
reheat is ON. Two methods of control are supported for energizing the parallel fan. One
method is based on space temperature; the other method is based on primary 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 delta temperature enable setpoint. It turns OFF when the
space temperature rises above the heat setpoint plus the configured parallel fan delta
temperature enable setpoint by 0.5°F (0.28°C).
Parallel fan start based on primary airflow
The parallel fan turns ON
when the primary airflow falls below the configured parallel fan
airflow enable setpoint or the primary airflow is less than the active minimum flow
setpoint plus 2% of the configured nominal airflow. The parallel fan turns OFF when the
primary airflow rises above the configured parallel fan airflow enable setpoint plus 5%
of the configured nominal airflow and the primary airflow is greater than the active
minimum flow setpoint plus 5% of the configured nominal airflow. In pressure
dependent mode, the air valve position is substituted for the primary airflow.
Parallel fan operation during calibration
During calibration, the parallel fan is in the same state (ON or OF
F) as it was before
calibration started. 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.
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