Basics of VAV

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 VAV - Variable Air Volume 

What is VAV?

It is a mechanical device which regulates the flow of air in ducts. It generally consists of a blade or plate of different material as per the requirement to restrict the flow. It is used to cut-off the air supplied to any room from the central air handling unit. It can be operated manually or automatically.

VAV work with a temperature sensor, It varies airflow at a constant temperature

 when the set temperature on the thermostat is acheived automatically it reduces the flow by the closing damper and when temperature increased it open the valve which supplies more air to space to achieve temperature.

VAV can be used for a single room or zone. It is available based on air quantity.

It is also called an energy-saving device.

It can be used for heating and cooling both purposes.

Video On VAV 





Construction and Working




VAV comes in rectangular, oval as well as round form as per requirement.

it has two openings on each end one for entry of air and other for the exit of air.

It consists of a damper and its shaft directly connected with the actuator. And actuator directly connected with the thermostat installed in the room.

Actuator rotates the shaft based on room temerature.

How it is Installed


VAV is selected based on Air quantity required for room to achieve design temperature. Thermostat to be installed at the centre of the room so that it can sense accurate temperature.

How To select No of VAV




VAV should be used for a single room or single zone, otherwise, it will create problem in maintaining temperature.
Ex. As per layout, single VAV is used for 6 room and thermostat is installed in the first room. If the temperature in the first room achieved it will stop the flow of air in the duct. It does not care about the temperature in the remaining room. So it is better to installed individual VAV to each room.

How VAV can be used as an energy-saving device.

Normally in large space central air handling unit is used, in which air is supplied from a single source.
It supplies air to all the space through ducts.
And in this system, it supplies to that area also where occupancy is not there. and when VAV is used for this area it stops the air supply to this area.VAV act as a personal AC for each room.



Normally multiple VAV is integrated with a single integrator and this integrator linked with BMS system. When temperature achieved in the room, VAV stops the flow in that room and backpressure is generated in the main duct. In ducts DPT sensor used which sense the backpressure in ducts and share data with the BMS system.
Based on VAV positioning BMS system changes the speed of central air handler through VFD.
And with this system AHU run for only those area where it required which saves energy.



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