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Variable Air Volume (VAV) is a type of heating, ventilating, and/or air-conditioning (HVAC) system. Unlike constant air volume (CAV) systems, which supply a constant airflow at a variable temperature, VAV systems vary the airflow 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. ==Simple VAV systems== The simplest VAV system incorporates one supply duct that, when in cooling mode, distributes supply air at a constant temperature of approximately .〔(【引用サイトリンク】url=http://aec.us.com/variable-air-volume-systems.html )〕 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. This on/off cycling causes the temperature to fluctuate above and below the temperature setpoint. 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. VAV fan control, especially with modern electronic variable-speed drives, reduces the energy consumed by fans, which can be a substantial part of the total cooling energy requirements of a building. 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.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Variable air volume」の詳細全文を読む スポンサード リンク
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