VAV and CAV HVAC Systems: Features, Benefits and Best Uses

Variable Air Volume (VAV) and Constant Air Volume (CAV) are two different and widely used heating and cooling systems. However, there may be good reasons to switch from a VAV to a CAV system in your commercial building, and here are some reasons why.

The CAV System

The Constant Air Volume (CAV) heating and cooling was widely used in commercial spaces as a method of cooling, heating and ventilation twenty or thirty years ago. This type of system employs a simple on/off fan and compressor cycle, operating at full capacity until the desired temperature level is achieved. Think of it as the air conditioning and heating unit in your small motel room. If you turn the temperature to 65 degrees, the unit will function at a constant rate until the desired temperature level is reached. Once it attains the 65-degree temperature, it shuts off.

A CAV system, by nature of its design, uses higher energy because it relies on a constant high flow of air and consequently, a higher energy output. The CAV system may still be an effective option in commercial spaces with single zones that have less variation in air temperature. However, in buildings with multiple heating and cooling zones, using the older CAV heating and cooling system will most likely result in a higher energy bill and less effective temperature, humidity and ventilation regulation.

The VAV System

A VAV system is more energy efficient and more precise in delivering the required air flow to different zones. The fans and compressors operate at variable rates to accommodate the temperature requirements of each zone, thereby reducing the amount of work the components are tasked to perform and the amount of energy utilized to achieve those temperature, ventilation and de-humidifying elements.

CAVs are still a viable and effective option in spaces such as smaller warehouses, or commercial spaces where there is only one thermal zone that does not need a variable control of air velocity and flow. In spaces such as hospitals, colleges, manufacturing facilities and restaurants, a VAV system makes the most sense, both in terms of efficiency, effectiveness and cost savings because these environments rely heavily on variable air pressure, velocity and flow. Unlike the CAV system, fan speeds in a VAV system operate at varying levels, depending on the temperature levels in the zones it is servicing.

When determining if your existing heating and cooling system is best for your commercial space, your facilities manager should be tracking things like efficiency levels, maintenance, servicing and repair/replacement of various components of the air handling systems. Tracking ongoing utility costs over time is also necessary when determining if it is appropriate to change your existing HVAC system.

If your facility’s physical space has grown over time and you are now operating with multiple heating and cooling zones, it might be an appropriate time to change your CAV system to a more efficient and cost-savings VAV system. VAV systems have been shown to save as much as 20 to 30 percent in your utility and maintenance and repair bills.

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