Air Changes per Hour (ACH) is a measure of how many times the air in a defined space is replaced within a 60-minute period. This value is determined by dividing the volume of air exchanged in an hour by the volume of the space. For instance, if a room’s air volume is 500 cubic feet and 1000 cubic feet of air are exchanged per hour, the ACH is 2.
The calculation of air exchange rates is important in maintaining indoor air quality and controlling temperature and humidity levels. Proper air exchange can reduce concentrations of indoor pollutants, improve thermal comfort, and contribute to a healthier indoor environment. Historically, understanding and managing air exchange was paramount for ensuring adequate ventilation in mines and other enclosed spaces, preventing the build-up of hazardous gases. Today, it informs building design, HVAC system implementation, and strategies for mitigating airborne disease transmission.
