Constant air volume (CAV) systems are consistently used on medium to large projects to supply regulated fresh-air requirements to each zone/floor as well as extracting ‘used’ air from the building. Constant volume units are used particularly on Fan Coil projects to deliver specific fan coils and zones with ‘guaranteed’ fresh air volumes. These can also be reset via the BMS in order to accommodate the change in fresh air requirements. All units are pressure independent and can be placed anywhere in the system and used with any BMS.
CAV systems are well-suited for applications where the ventilation load is constant for large periods of time. Facilities like warehouses, call centers and manufacturing facilities that operate 24/7 are good examples of places where CAV can be deployed effectively. These facilities are places where the number of occupants and ventilation requirements show almost no variation. In concert halls or other event venues that are used sporadically, CAV ventilation can also be used. As the name suggests, constant air volume controls (CAV) provide a constant volume of air to all parts of the building when the system is in operation. CAV systems are either “on” or “off”. When the system is on, heated or cooled air is blown through the air ducts at a constant rate. When the system is off, no air blows through the air ducts and registers.
It may have some shortcomings, but still, CAV ventilation systems may have variable applications. In general, if ventilation requirements are constant over time, CAV systems can be deployed. VAV ventilation systems cannot save much energy if there are no chances for them to reduce airflow.
CAV ventilation systems can be divided into three subtypes, which are –
Single Duct Systems are the simplest type of CAV ventilation. A single set of ducts distribute conditioned air throughout indoor spaces, using common heating and cooling equipment, so they can provide either heating or cooling, but not both simultaneously.
Reheat systems also use centralized mechanical equipment but have reheat coils further downstream in the ducts to serve specific zones. This configuration can provide different air temperatures for separate zones if required.
Mixed-air systems have two sets of ducts, one for space heating and the other for cooling. Each zone has a mixing box where both airstreams meet, and the proportions of warm and cool air are adjusted according to the requirements of each zone.