Application Algorithm
The VAV application algorithm is designed to maximize the user comfort and energy efficiency, achieving the set temperature by adjusting the airflow based on the occupancy status, measured temperature and CO2 levels. It functioning is formulated on the operation the following control loops.
space temperature control loop determines the demand for cooling or heating based on the room temperature measurement and the corresponding setpoint temperature. The control loops for cooling and heating are mutually exclusive, i.e., only one of them regulates the demand, while the other is disabled.
discharge air temperature control loop is used to limit the discharge air temperature specified by the current discharge air setpoint based on the discharge air temperature measurement. It has the effect of limiting the reheater control. The discharge air temperature control loop operates only when there is a need for heating. If there is no discharge air sensor, the control loop has no effect on limiting the discharge air temperature (it has a value of 0).
room CO2 concentration control loop is used to adjust the airflow according to the measured CO2 concentration. It has a priority effect on the calculated airflow setpoint. It means that the airflow can be higher than the cooling or heating demand if the CO2 concentration in the room is too high in order to ventilate the room. In the absence of a CO2 sensor, the control loop does not affect the calculated airflow setpoint (it has a value of 0).
airflow control loop is based on the currently measured airflow in relation to the calculated airflow setpoint, which is based on the demand for cooling/heating, measured CO2 concentration, and the HVAC mode settings. The demand for airflow is affected by the level of damper opening resulting from the airflow control loop.