CAV vs VAV in HVAC Systems: Differences, Advantages & Applications
In HVAC design, understanding the difference between Constant Air Volume (CAV) and Variable Air Volume (VAV) systems is essential for proper system selection and energy efficiency.
What is a CAV System?
A Constant Air Volume (CAV) system delivers a fixed airflow rate to a space while varying the air temperature to maintain comfort conditions.
How CAV Works
The supply fan runs at a constant speed, and airflow remains the same at all times. Temperature control is achieved by adjusting the cooling or heating coil output.
Advantages of CAV
- Simple design and control
- Lower initial cost
- Easy maintenance
Disadvantages of CAV
- Higher energy consumption
- Less flexible for multi-zone buildings
- Limited part-load efficiency
What is a VAV System?
A Variable Air Volume (VAV) system adjusts the airflow rate based on the cooling or heating demand of each zone.
How VAV Works
The supply fan speed changes according to system demand. Each zone has a VAV box that controls airflow using a modulating damper.
Advantages of VAV
- Energy efficient at part load
- Better zone control
- Improved occupant comfort
Disadvantages of VAV
- Higher initial cost
- More complex control system
Key Differences Between CAV and VAV
| Parameter | CAV | VAV |
|---|---|---|
| Airflow | Constant | Variable |
| Energy Efficiency | Lower | Higher |
| Initial Cost | Lower | Higher |
| Control Flexibility | Limited | High |
| Application | Small buildings | Medium to large buildings |
When to Use CAV?
CAV systems are suitable for small commercial spaces or buildings with stable load conditions.
When to Use VAV?
VAV systems are ideal for office buildings, hospitals, and large facilities where load varies throughout the day.
To properly size ducts for CAV or VAV systems, use our HVAC Duct Sizing Calculator and calculate airflow using the Air Velocity Calculator.
Conclusion
Both CAV and VAV systems have their applications. However, modern HVAC design increasingly favors VAV systems due to improved energy efficiency and flexibility.
Disclaimer: This article is for educational purposes only. Final HVAC design should be completed by a qualified engineer.
