The process of determining how many times the air within a defined space is replaced per unit of time, typically an hour, is a critical element in indoor environmental control. This assessment involves quantifying the volume of fresh or filtered air introduced into the area and correlating it to the room’s volume. For instance, if a room with a volume of 50 cubic meters receives 250 cubic meters of fresh air per hour, the exchange rate is calculated to be 5 air changes per hour (ACH).
Adequate ventilation, gauged by this rate, is essential for diluting indoor pollutants, reducing the concentration of airborne pathogens, and maintaining acceptable air quality for occupants. Historically, ensuring sufficient ventilation has been paramount in mitigating the spread of diseases and providing a comfortable and healthy indoor environment. This parameter directly impacts energy efficiency, occupant health, and the operational effectiveness of HVAC systems.