When the deviation calculation is enabled, a determination is made if the setpoint is greater than the air flow for a period of time an analog deviation value is mode available to the central function for additional control logic or reporting.
The supply airflow deviation signal (VavSuAirFlDvn) is used for fan speed (static pressure) reset strategies at the air handling unit. It is obtained by measuring the airflow from the supply duct and comparing it to the airflow setpoint.
VavSuAirFlDvn (in percent) = VavSuSpAflRel minus VavSuAirFlRel
VavSuAirFlDvn will equal 0 in case of invalid condition