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What is a Variable Air Volume (VAV) Box?


Building Technology Basics

Video Transcript:

Hi and welcome to Building Technology Basics with me Simon Berry.

Today, we are going to answer the question, What is a VAV?

The term Variable Air Volume, better known in the HVAC industry as VAV, relates to a type of system that varies the amount of air directed to different spaces within a building based on the heating or cooling needs of a particular zone. 

[As you can see by this image]

You’ll also often hear the term VAV box. The box is the housing where the VAV and its additional components reside, mounted to the ductwork. 

A typical automated VAV box consists of the VAV controller with an actuator that controls a damper. 

How far open or closed this damper is will depend on the current setpoint and temperature of the zone.

Boxes also have inlets and outlets where the air comes in and leaves. 

These inlets and outlets are often equipped with sensors that gather information such as pressure, airflow, and temperature.

Each VAV controller is generally paired with a temperature sensor that is wired on a wall in its zone.

[As you can see by this image] 

If the thermostat or the building automation system calls for a set point of 75 degrees and the current temperature is 77 degrees, the VAV will open the damper to allow more cool air into the space. 

Once the temperature in the space reaches the setpoint, the VAV will modulate (or turn) the damper

to the closed position.

Damper positions range from 0% to 100%, however, you’ll rarely see a damper position at 0%, 

because we always want to ensure a steady flow of fresh air at all times.

There are different types of VAV boxes for specific applications. 

Some of these include;

dual duct, 

single duct, 


and VAV with reheat. 

We’ll cover these specific types of VAV boxes in a future video.

And that concludes our What is a VAV video?

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