Pressure independent type VAV: Model – PAC-PIDVAV-3L/3M

3L – For Low-pressure applications; 3M – For Medium pressure applications.
PACVENT pressure independent type VAV is a single duct pressure independent air terminal unit, designed to use with low and medium pressure air handling systems. Pressure independent control involves an additional input to the control of the VAV terminal unit. The pressure-independent control options also monitor and respond to the velocity of the airflow, generally at the inlet of the unit. The terminal unit damper is positioned from a signal sent from the zone thermostat through a velocity reset controller to the damper actuator. The velocity reset controller then responds to changes in the inlet pressure conditions to maintain the required airflow. Pressure-independent controls are frequently used for single duct variable volume control. For a given thermostat setting, the controller can position the damper further open if the airflow at the inlet is insufficient to meet the requirement, or it can position the damper further closed if the inlet airflow is greater than the requirement.
Pressure-independent controllers do have their limitations. The selection of air flows must be given careful consideration. The reset controllers respond to an input signal from the differential inlet sensor in the range of 0.0” WC to 1.35” WC which reflects the CFM range of a given terminal unit size. Electronic controllers cannot accurately control the airflow when the differential pressure signal falls much below 0.04” WC. For this reason, PACVENT publishes minimum airflow setting limitations and suggested airflow ranges for each unit size.