VAV Box (Variable Air Volume)
CSI Division 23, HVAC
A mechanical device installed in a building's ductwork that modulates the amount of conditioned air delivered to a specific zone based on that zone's actual temperature, allowing a single central air handling system to serve many zones with different, changing heating and cooling needs rather than delivering a constant volume of air everywhere.
Why it matters
A VAV box has to be balanced correctly for its specific zone's airflow requirement during commissioning, since a box that's stuck fully open or fully closed either wastes energy overcooling a zone or leaves it without adequate airflow, a problem that shows up as an occupant comfort complaint rather than an obvious equipment failure.
On a real project
A building's mechanical engineer designs a VAV system with a separate box serving each perimeter zone, since each zone's solar exposure and occupancy create different, independently varying heating and cooling loads throughout the day.
Who this matters most to
A HVAC Technician or specialty controls technician installs and balances VAV boxes. A MEP Engineer designs the zoning and airflow each box has to deliver.
Where this goes wrong
A controls technician commissions a VAV box but doesn't verify its minimum airflow setpoint against the zone's actual ventilation requirement. The box modulates down to a setting that technically satisfies temperature but delivers less outside air than code requires for that occupancy, a deficiency that isn't caught until an indoor air quality complaint prompts a closer review.