换气率(air exchange rate)指单位时间（h）内进入试验舱的清洁空气量（m3/h），与试验舱容积（m3）的比率，单位为ACH，用n表示。

Air changes per hour, or air change rate, abbreviated ACH or ac/h, is a measure of the air volume added to or removed from a space (normally a room or house) divided by the volume of the space. If the air in the space is either uniform or perfectly mixed, air changes per hour is a measure of how many times the air within a defined space is replaced.