Variable Air Volume (VAV) systems are HVAC systems that regulate the flow of air into a building based on the changing needs of the space. They work by controlling the volume of air that is delivered to each room or space, instead of controlling the temperature of the air itself.

Here's how it works:

1. Air is drawn into the system and filtered before being heated or cooled to the desired temperature.
2. The air is then delivered to each room or space through ducts and diffusers.
3. The VAV system includes a VAV box installed in each room or space, which is connected to a thermostat and a control system.
4. When the thermostat senses a change in temperature, it sends a signal to the control system to adjust the flow of air into the room.
5. The VAV box then opens or closes a damper to regulate the amount of air that is delivered, maintaining a constant temperature in the room.

VAV systems provide efficient heating and cooling by only delivering the amount of air that is needed to maintain a comfortable temperature, reducing energy waste.