The Thrilling World of VAV Boxes

Buildings’ conditions change due to numerous factors such as occupancy, external weather conditions, and room sizes. Therefore, the amount of cool air required to keep the occupants’ comfort and to cool in different zones of a building is usually variant.

That’s the reason why VAV boxes are so important. In the 4th episode of our podcast, Stephen Higgins talks a little bit more about these units.

VAV boxes, or Variable Air Volume boxes, are units ducted from air handlers that allow controlling the amount of cooling in a room of a building without affecting the temperature in other ones.

Each VAV box serves a particular zone, and a damper in the box opens and closes depending on the need, assuring that the correct amount of air is delivered to that zone. A damper is never fully close but can close to a point in which only provides 15% to 30% of the original design cubic feet per minute for a particular space. When the temperature of an area rises, the damper opens to send more cool air to the room in order to lower the temperature.

The damper shaft of a VAV box is connected to a motor (actuator), which is interlocked with the room thermostat. The thermostat is placed in the space and allows the occupants to have total control over the temperature.

By regulating the volume of air delivered, a VAV system can control the temperature of a space without changing the temperature of the supply air, improving efficiency that results in big savings.

Watch the video to understand more.

Why are VAV boxes a great deal? There are 4 main reasons.

  1. Efficiency: VAV Systems use the minimum amount of air required to keep a space at its design temperature. In addition, it positively impacts other pieces of equipment because it allows air handlers, chillers, and boilers to operate at part load conditions.
  2. Individual Temperature Control: because a VAV box is attached to a thermostat, the temperature in a room can be controlled regardless of the temperature in other spaces of the building.
  3. Cost: In addition to inexpensive operation cost, the initial cost of a traditional VAV system is low because it does not require piping or coils.
  4. Flexibility: The boxes can be easily moved from one ductwork branch to another as long as the condition of the space is similar

There are 3 types of VAV systems: traditional, fan-powered, and coil reheat.

Traditional – It is basically the VAV box with the damper. The damper opens and closes to deliver more or less cool air to the area.

Fan-powered – If the room is near its design temperature and the air supply is low, a fan is placed to improve air movement. This procedure impacts energy efficiency, but the fan only starts running when the damper is half-way closed, which means that the fan is not always on.

Coil reheat – A hot water or electric coil (fed from hot water system or heat pumps) is placed in the VAV box to increase air volume and movement. When the damper is 50% close, then the coil heats up the air, which is delivered to the room.

The best option for your application depends on several factors because one solution does not fit all. Choosing  VAV boxes seems to be a very simple task, but it actually requires the understanding of different types of damper, insulation, and sound delivery of air.