Variable Air Volume (VAV) boxes, also called VAV terminal units or VAV dampers, are zone-level air distribution devices that regulate airflow to maintain comfortable conditions in individual spaces. They are the workhorses of modern commercial HVAC systems, providing independent temperature control. Variable Air Volume (VAV) is the most used HVAC system in commercial buildings. In this article we'll discuss the Variable Air Volume system and single duct VAV boxes with reheat coils. The Air Handler varies the amount of air flow (CFM) at the overall system level based on the demand required by. Daikin's single duct VAV boxes, from 80 to 8000 CFM, provide high performance and set the standard in the industry for construction, performance, and quality. The advantages of VAV.