A variable air volume box, more commonly known as a VAV box, is an essential part of air conditioning in any large industrial or commercial building. Air conditioning is part of a larger entity called a HVAC system, which encompasses heating, ventilation, air conditioning, and control systems. The variable air volume box is a HVAC component alongside other pieces of hardware such as coils and drain pans, humidification and dehumidification equipment, air dampers, air filters, ducts, exhaust systems, return air plenums, and so on. A VAV system exists in contrast to a CAV, or constant air volume system.

A variable air volume box is just what it sounds like -- a box that can hold a variable amount of air. It helps make air conditioning systems more efficient by regulating the amount of cooling targeted toward any specific room or area. This is referred to as the cooling/heating load. A room whose windows face the sun for most of the day will have a higher cooling load than a room in the shade. When a VAV box constricts a valve to let less air through, it decreases the amount of energy consumed by fans that direct the air around the building.

Modern VAV boxes come with advanced control equipment that supports automated changes to air flow as efficiency dictates. This control equipment is also linked to central computers for the entire HVAC system for a building. Small pressure sensors detect the pressure of air in the box and hinges open and close doors to manipulate airflow and air volume.

Research continues to improve variable air volume boxes, millions of which are installed throughout the country. Areas for improvement include minimizing noise, reducing the need for maintenance, fine-tuning the control systems, and creating diagnostic response systems that alert maintenance teams and give them accurate information about malfunctions before they even need to look at the device physically.