What is the primary advantage of using a variable air volume (VAV) system over a constant air volume (CAV) system?

The primary advantage of using a variable air volume (VAV) system over a constant air volume (CAV) system is its ability to provide improved energy efficiency by varying the airflow to different zones based on their individual cooling or heating demands. In a VAV system, the volume of conditioned air supplied to each zone is adjusted according to the zone's specific load requirements, which can vary throughout the day depending on factors such as occupancy, solar gain, and equipment usage. This contrasts with a CAV system, where a constant volume of air is supplied to each zone regardless of its actual needs. Because VAV systems can reduce airflow when cooling or heating demands are lower, they require less fan energy compared to CAV systems, which operate at a constant fan speed. This reduction in fan energy consumption translates to significant energy savings, particularly in buildings with diverse zone loads and fluctuating occupancy patterns. For example, a conference room that is only occupied for a few hours a day can have its airflow reduced significantly when unoccupied, saving energy. Additionally, VAV systems often incorporate variable frequency drives (VFDs) on the supply fans, allowing the fan speed and airflow to be adjusted to match the overall building load, further enhancing energy efficiency. Also, since VAV systems use less energy they also reduce the load on the central heating and cooling plant.