Constant Air Volume (CAV) is a type of heating, ventilating, and air-conditioning (HVAC) system. In a simple CAV system, the supply air flow rate is constant, but the supply air temperature is varied to meet the thermal loads of a space.

 

The temperature of this air is what is regulated to achieve the desired comfort level of the occupants. Other comfort factors such as humidity, gases, particulates, and pressure are indirectly controlled by the user, or are available as additions onto the single zone system. For example, a humidifier can be added to regulate humidity, and filters can be utilized to control gases or particulates. The pressure experienced by the user is affected by the velocity of the system, and whether or not a return fan is going to be used.

 

Most CAV systems are small, and serve a single thermal zone. However, variations such as CAV with reheat, CAV multizone, and CAV primary-secondary systems can serve multiple zones and larger buildings.

 

In mid to large-size buildings, new central CAV systems are somewhat rare. Due to fan energy savings potential, variable air volume (VAV) systems are more common. However, in small buildings and residences, CAV systems are often the system of choice due to their simplicity, low cost, and reliability. Such small CAV systems often have on/off control, rather than supply air temperature modulation, to vary their heating or cooling capacities.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CAV Types:

 

There are two main types of CAV: single duct and mixed air. In a single duct, air is conditioned and supplied through a single duct. This is the simplest and easiest to maintain CAV system.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The mixed air system has two air streams, typically one for the coldest and one for the hottest needed air temperature in the zone. The two air streams are strategically combined in a mixing box which controls the proportions of hot and cold air. This mixing box then supplies a constant volume of this mixed air to properly control the temperature of the zone. The mixed air system option is not as proficient at controlling the humidity, yet it does do well at controlling the temperature.