Variable Air Volume (VAV)

The VAV system has a central air-processing unit to produce air at a specified temperature and relative humidity. The conditioned air from the main unit is conveyed in ductwork to ceiling diffusers which incorporate thermostatically controlled actuators. These can change the air volume to suit each room load. In a large room, several of these VAV ceiling units may be controlled by one room thermostat. Several rooms/zones may have separate thermostats to control the air flow to each room. The inlet fan may have variable pitched impellers operated by compressed air. A pressure switch controls the pitch angle. Air distribution is usually medium to high velocity. The air temperature in each zone can be varied with the heat energy in the delivery air volume, but the system is only suitable for buildings having a fairly evenly distributed cooling load.

Note: The lighting fittings may require a fire damper Section through plenum ceiling

FREQUENTLY ASKED QUESTIONS

What are the main components of a VAV system?
A VAV system consists of a central air-processing unit, ductwork, ceiling diffusers, and thermostatically controlled actuators. The central unit produces air at a specified temperature and relative humidity, which is then conveyed through the ductwork to the ceiling diffusers. The actuators in the diffusers can change the air volume to suit each room’s load.
How do VAV ceiling units control the air flow in a room?

VAV ceiling units incorporate thermostatically controlled actuators that can change the air volume to suit each room’s load. These actuators are typically controlled by a room thermostat, which senses the room temperature and adjusts the air flow accordingly. In a large room, several VAV ceiling units may be controlled by one room thermostat.

What are the advantages of using VAV systems in buildings with varying cooling loads?

VAV systems are suitable for buildings with fairly evenly distributed cooling loads. They offer several advantages, including energy efficiency, improved indoor air quality, and increased flexibility. By adjusting the air flow to each room based on its specific needs, VAV systems can reduce energy waste and provide a more comfortable indoor environment.

How does the inlet fan in a VAV system control the air flow?

The inlet fan in a VAV system may have variable pitched impellers operated by compressed air. A pressure switch controls the pitch angle of the impellers, which in turn adjusts the air flow. This allows the system to maintain a consistent air pressure and flow rate, even as the cooling load varies.

What is the typical air distribution velocity in a VAV system?

The air distribution velocity in a VAV system is usually medium to high velocity. This allows for efficient air distribution and mixing, which helps to maintain a consistent indoor air quality and temperature. The exact velocity may vary depending on the specific system design and the building’s requirements.

Can VAV systems be used in buildings with highly variable cooling loads?

VAV systems are generally not suitable for buildings with highly variable cooling loads. They are designed to work best in buildings with fairly evenly distributed cooling loads, where the air flow can be adjusted to meet the specific needs of each room. In buildings with highly variable cooling loads, other HVAC systems, such as constant air volume (CAV) systems, may be more appropriate.