Variable air volume (VAV) systems and constant volume (CV) systems are two types of centralized air systems. In a CV system, the airflow rate remains constant, while the temperature is controlled by adjusting the cooling or heating coil output. In contrast, VAV systems vary the airflow rate to match the changing cooling or heating demands of the building. VAV systems are more energy-efficient and can provide better zone control, but they require more complex controls and may be more expensive to install. CV systems, on the other hand, are simpler and less expensive, but may waste energy by constantly circulating air at a fixed rate.