The SimplyVAV controllers use up to three PID loops.
l The heating PID loop.
l The cooling PID loop.
l The discharge air temperature (DAT) loop.
For SimplyVAV controllers, the output of either the cooling and heating PID loop is used to
calculate the position of the damper. If present, the DAT input and DAT loop controls the
Reheat loop.
The PID loops in the SimplyVAV controllers are standard BACnetobjects and are described
in the topic BACnet objects on page 67.
Airflow setpoints sequence
Airflow Setpoint is calculated based on the demand for cooling or heating depending on
whether the Cooling loop or Heating loop is greater than zero.
If no room sensor is connected to the controller, the controller uses the Minimum Cooling
Airflow setpoint to maintain airflow.
Cool Air Sequence
As the Cooling loop increases from 0% to 100%, Primary Airflow Setpoint is proportionally
calculated between Minimum Cooling Airflow and Maximum Cooling Airflow.
If there is a call for reheat to maintain room temperature, the primary airflow is set to the
value of Auxiliary Flow.
Warm Air Available
In the heating mode, as the Heating Loop increases from 0% to 100%, Primary Airflow
Setpoint is proportionally calculated between Minimum Heating Airflow and Maximum
Heating Airflow.
See also the topics, Changeover on page 53 and Input sources on page 49.
Changeover
The Discharge Air Temperature input is used by the controller to determine the type of air
that is being supplied by the AHU. The sensor is required for applications that require
automatic change over between cooling and heating.
When the Heating loop is inactive, the Discharge Air Temperature input is compared to the
SAT Changeover Temp. If the Discharge Air Temperature is below the SAT Changeover
Temp minus 2°, the SAT Changeover Mode is set to COOL. If the Discharge Air
Temperature is above the SAT Changeover Temp plus 2° Fahrenheit, the SAT Changeover
Mode is set to HEAT. The default changeover temperature is 74° Fahrenheit.
See the topic Discharge Air Temperature (DAT) limiting on page 53 and Input sources
on page 49.
Discharge Air Temperature (DAT) limiting
A Discharge Air Temperature senor and DAT limiting is required to control VAV units with
reheat. If a Discharge Air Temperature (DAT) sensor is detected and DAT Limiting is
SimplyVAV Section 7: Sequences of operation
Revision H 53
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