VAV systems vary the air compressor handbook pdf at a constant temperature. The advantages of VAV systems over constant-volume systems include more precise temperature control, reduced compressor wear, lower energy consumption by system fans, less fan noise, and additional passive dehumidification.
Because the supply air temperature is constant, the air flow rate must vary to meet the rising and falling heat gains or losses within the thermal zone served. Even a simple VAV system has several advantages over a CAV system. One is more precise temperature control. To meet a space cooling load, a CAV unit operates the fan and compressor at full capacity until the temperature drops to a specified limit, and then the compressor turns off. In a single-zone VAV unit, the fan speed varies depending on the actual space temperature and the temperature setpoint, while the compressor modulates the refrigerant flow to maintain a constant supply air temperature.
The result is more precise space temperature control. Another advantage is energy savings and reduced wear. Modulating control of the compressor also reduces wear and delivers further energy savings. A final advantage is increased dehumidification. Because VAV air flow is reduced under part-load conditions, air is exposed to cooling coils for a longer time.
More moisture condenses on the coils, dehumidifying the air. Thus, although a constant-volume and a single-zone VAV unit maintain the same room temperature, the VAV unit provides more passive dehumidification and more comfortable space conditions. The air blower’s flow rate is variable. The VAV terminal unit is connected to either a local or a central control system.