# VAV System: Variable Air Volume Cooling

> A VAV — variable air volume — system cools different zones by varying how much conditioned air each receives, through motorised VAV boxes in the ductwork controlled by zone thermostats. Rooms that need less cooling get less air, rather than everything getting the same airflow.

## Why it matters

Comfort complaints in new offices are very often VAV complaints. The system is
good at zoned control, but only if its zones match the layout — which they
rarely do after a fit-out unless someone re-balances them.

## How it works in practice

| Component | Role |
| --- | --- |
| AHU | Supplies conditioned air |
| VAV box | Varies airflow to one zone |
| Zone thermostat | Tells the box how much air is needed |
| BMS | Coordinates boxes and the AHU |

## Common mistakes

- **Not re-balancing after a fit-out.** The most common cause of hot and cold
  rooms.
- **One box serving rooms with different loads.** Neither room is comfortable.
- **Blocking the return path.** Walls to slab can starve the system of return air.

## Standards referenced

HVAC energy requirements under **ECBC 2017**.

## Frequently asked questions

### Why do offices use VAV?

Because different parts of a floor need different amounts of cooling — a sunny perimeter, a full meeting room and an empty corner are not the same. VAV lets each zone be controlled separately and saves energy compared with constant-volume systems.

### What happens to VAV when a floor is re-partitioned?

Zones change. A VAV box that served one open area may now serve two rooms with different loads, making one too cold and the other stuffy. Re-zoning and re-balancing are a normal and necessary part of a fit-out.

## Sources

- [ECBC 2017](https://beeindia.gov.in/) — HVAC system requirements

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Source: https://hagerstone.com/glossary/vav-system