The VAV system is an air conditioning system that Control the room temperature by adjusting the “air volume” instead of adjusting the “air temperature,” which is different from CAV systems where the air volume is constant.
🔹 Working principle of VAV system
1. VAV Box installed in the supply duct to each zone.
2. Sensor in the room detects the room temperature → sends the value back to the Controller.
3. Controller commands the VAV Box to adjust the Damper (air adjustment plate) to open more or less.
• If the room is too hot → turn on more.
• If the room is too cold → Partially shut down.
4. The result is that the amount of air supplied into the area will More-less according to the needs (Load) of each zone.
🔸 Example of air volume adjustment (VAV Logic)
Room temperature (°C) VAV Box response Air supply volume
Higher than Setpoint, open Damper more, air supply increases.
Below the setpoint, partially close the damper, air supply decreases.
Equal to Setpoint, constant Damper level, constant wind.
🔧 Related equipment
• VAV Box: Air volume adjustment box with Damper and Actuator.
• Thermostat / Temp Sensor: Measures room temperature.
• Controller: Controls the position of the Damper.
• Reheat Coil (in some cases): Used when warm air is needed in winter.
✅ Advantages of the VAV system
• More energy efficient than CAV.
• Control the temperature in each zone precisely.
• Reduce noise because it can reduce wind speed.
📌 Note:
Adjusting the air volume of a VAV must take into account:
• Min / Max CFM of each zone.
• Adjusting the balance of the entire system.
• Relationship with Static Pressure of AHU.
• Use of VAV with Reheat for overcooled zones.
