What is a Constant Air Volume HVAC System?

In the realm of heating, ventilation, and air conditioning (HVAC) systems, various designs cater to diverse needs. One such configuration is the Constant Air Volume (CAV) HVAC system. This article aims to shed light on the fundamental concepts behind CAV systems, their operation, benefits, and potential limitations. By the end, readers will have a comprehensive understanding of CAV HVAC systems and their relevance in modern building environments.

What is a Constant Air Volume HVAC System?

A Constant Air Volume HVAC system is a configuration that maintains a fixed and unvarying volume of air delivered to different zones or spaces within a building. Unlike other HVAC systems, such as Variable Air Volume (VAV) systems, where the air volume varies according to demand, CAV systems deliver a constant airflow rate regardless of the heating or cooling requirements.

Operation of Constant Air Volume HVAC Systems

CAV systems comprise several key components working together to regulate temperature, humidity, and air quality in a building. These components include:

  1. Air Handling Unit (AHU): The AHU acts as the central point of control for the CAV system. It consists of a fan, filters, heating or cooling coils, dampers, and controls.
  2. Dampers: Dampers are used to control the flow of air within the system. In a CAV system, these dampers are generally fixed, allowing a consistent airflow rate.
  3. Heating and Cooling Coils: These components help regulate the temperature of the air supplied to the spaces. Heating coils warm the air during colder periods, while cooling coils lower the temperature during warmer periods.
  4. Controls: Controls in a CAV system play a crucial role in maintaining a constant airflow rate. They monitor temperature, humidity, and other environmental parameters, adjusting the heating or cooling accordingly.

Benefits of Constant Air Volume HVAC Systems

  1. Simplicity: CAV systems are relatively straightforward in design and operation compared to more complex HVAC configurations. Their simplicity often leads to lower installation and maintenance costs.
  2. Cost-effective: CAV systems are generally more affordable to install and maintain due to their simpler design. They may be particularly suitable for buildings with consistent and predictable cooling or heating needs.
  3. Energy Efficiency: While CAV systems may not be as energy-efficient as some variable systems, they can still incorporate energy-saving measures. For example, integrating efficient fans, motors, and controls can help optimize energy consumption and reduce operational costs.
  4. Zoning Flexibility: CAV systems can easily accommodate multi-zone setups, allowing different areas of a building to have individual temperature control. This zoning flexibility enables enhanced comfort and personalized climate control.

Limitations and Considerations

  1. Limited Flexibility: CAV systems may not be ideal for buildings with varying occupancy levels or spaces with significantly different heating or cooling demands. The fixed airflow rate can lead to potential over-conditioning or under-conditioning in certain areas.
  2. Energy Consumption: Compared to more advanced HVAC systems like VAV, CAV systems may consume more energy, particularly during periods of lower demand. This aspect should be considered when evaluating energy efficiency goals.
  3. Occupant Comfort: Since CAV systems supply a constant airflow rate, they may not be as effective in maintaining precise temperature control in each zone. Areas farther from the AHU may experience temperature variations, potentially affecting occupant comfort.


Constant Air Volume HVAC systems offer a simple and cost-effective solution for many buildings with consistent heating and cooling requirements. While they may not provide the same level of energy efficiency and zone-specific control as some other HVAC configurations, CAV systems remain a reliable choice for applications where simplicity and lower costs are priorities. Understanding the principles behind CAV systems empowers building owners and HVAC professionals to make informed decisions.