VAV box (variable air volume)

A VAV (variable air volume) box is a damper unit in the ductwork that varies the amount of cooled air delivered to a zone, rather than blasting a constant volume everywhere. On a central AHU / chilled-water system, the AHU supplies cool air at a steady temperature and each zone's VAV box opens or closes — under its own thermostat — to hold that zone's temperature. It's how a big office, floor or mall keeps a boardroom, an open-plan area and a corner office all comfortable from one central plant, and it saves energy by throttling air back where it isn't needed (a cousin of demand-controlled ventilation). When a VAV box sticks, loses its actuator or its controller drifts, you get the classic complaint: one room is freezing while the room next door is warm, even though 'the AC is working' — it's not the chiller, and often not the AHU, it's that zone's box. Diagnosing and resetting VAV boxes and their controls is part of a proper central-system service by Al Ghubaiba's chiller team, and it depends on the system holding the right static pressure in the ducts.