Constant air volume (CAV) provides a constant level of airflow at two temperatures and maintains standard air pressure. It requires two sets of ductwork, but is easy to maintain and best for large open spaces. Variable air volume (VAV) is more complex, energy efficient, and suitable for smaller rooms.
Constant air volume (CAV) is a method for air conditioning systems in buildings that provides a constant level of airflow at two different temperatures and maintains a standard air pressure throughout the system. Because it’s one of the ways a standard heating, ventilation, and air conditioning (HVAC) system is built, the actual function of the machinery can vary based on the needs of the building. The alternative to a constant air volume system is a variable air volume (VAV) system. While both are used in building design, each has some unique advantages over the other.
The main challenge in using a constant air volume system is that it usually requires two sets of ductwork throughout the building: one for heated air and one for cooled air. These air supplies are provided by individual air handlers or a central unit known as a CAV box, which can switch back and forth between heating and cooling the air it pumps into the ductwork. Individual rooms or businesses in an office building then control room temperature by regulating the mix of hot and cold air that is allowed into the room. This gives a constant air volume system the advantage over its alternative in that ambient temperatures can be changed more rapidly than with a VAV system.
Variable air volume systems tend to be much more complex than their CAV counterparts because they must employ temperature controls and manipulate the actual volume of air being pumped into each room. Variable speed fans and dampers are built into the duct to facilitate this, and the system controls automatically open and close them, or turn them on and off, as required. While a VAV system is more difficult to design and implement, it is more energy efficient than a CAV system, as the components of the variable air design operate only when needed. The air supply from a constant air volume system is supplied continuously in quantities that satisfy the building’s thermostat settings.
Incorporating a CAV system into a building can be physically more extensive to build from the ground up, but is often used in smaller buildings with simple HVAC needs or large open floor plan buildings, such as those with auditoriums, gymnasiums, or classrooms. Public spaces often have CAV systems for climate control, such as shopping malls, government centers, and libraries. The constant air volume approach relies on machinery that is easy to maintain and relatively maintenance free compared to a VAV system. Works best for spaces like large, open sports arenas with few restrictions on airflow. If a building layout is changed over time to provide smaller and smaller rooms, a CAV system is changed to provide multi-zone capabilities making it more like a VAV system, with each room being given a more individual treatment for controls environmental.
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