Air changes per hour (ACH) is a measure of how many times the air within a defined space is replaced in one hour. It is calculated by dividing the volumetric airflow rate (typically in cubic feet per minute or CFM) by the volume of the space (in cubic feet) and then multiplying by 60 minutes. For example, a 1,000 cubic foot room with an airflow rate of 250 CFM has an ACH of (250 * 60) / 1000 = 15.
Understanding ventilation rates is crucial for maintaining healthy indoor air quality, controlling humidity and temperature, and minimizing the concentration of airborne pollutants. Historically, ventilation was primarily achieved through natural means like open windows and doors. However, with the advent of modern building practices and increased emphasis on energy efficiency, mechanical ventilation systems have become essential for controlling airflow and achieving desired indoor environmental conditions. This metric is vital in various applications, including residential buildings, offices, hospitals, and laboratories, where specific ventilation requirements exist.
