Variable air volume (VAV) controllers are used in VAV systems to supply different rooms according to demand. Pressure-independent controllers maintain the set volume flow constant regardless of pressure fluctuations in the duct network. The control cone or damper is positioned via a differential pressure sensor and actuator. Motorized versions allow remote adjustment via building automation systems (BAS/BMS). Constant volume controllers are used in cleanrooms or laboratories where precise air quantities are required. Variable controllers adapt airflow to CO₂ concentration, occupancy, or temperature, saving fan energy. Design follows EN 16798 and manufacturer-specific performance curves.