What Is a VAV System in BMS?

The Bus Analogy

A bus runs from one end of a city to the other. At some stops — many passengers get on. At others — few. The bus still runs the same route at the same speed regardless. That is inefficient.

Now imagine a smart bus that adjusts speed based on passenger demand. Fewer passengers — runs slower, saves fuel. Many passengers — runs at full capacity. That is VAV.

VAV — Variable Air Volume — a motorised box in each zone's duct. Opens or closes based on that zone's actual demand:

Room warm — occupancy sensor shows 30 people:
  VAV damper opens fully — maximum cool air
Room cool — nearly empty:
  VAV damper partially closes — minimum air
Room empty for 2 hours:
  VAV damper at minimum — almost no air

BMS coordinates all VAV boxes across the floor and adjusts AHU supply fan speed via VFD accordingly. If most rooms are cool and VAV boxes are nearly closed — fan slows down. Energy saved automatically.

Related Topics

• What is BMS integration? — how a BMS connects with VFDs, energy meters, BACnet/Modbus devices and other building systems
• How to design a BMS system step by step — the complete BMS design methodology covering site survey, IO list, controller selection, sequence of operations
• What is a Building Management System (BMS)? — fundamentals of BMS controls and architecture for HVAC, lighting, energy and access
• What is BMS commissioning? — the disciplined commissioning process that turns a BMS install into a working building brain
• Browse all HVAC Systems topics — more from this section of the EnSmart BMS Library