Air Changes per Hour (ACH) is a metric used to measure the ventilation rate or the number of times that the entire volume of air within a space is replaced with fresh outdoor air per hour. It quantifies the effectiveness of air exchange and ventilation in a building or specific area.
The ACH value indicates how quickly the indoor air is being replaced with outdoor air. For example, an ACH value of 6 means that the entire volume of air within a space is completely exchanged with fresh outdoor air six times in one hour.
ACH is commonly used to assess and determine the ventilation requirements for various spaces, such as residential homes, commercial buildings, and industrial facilities. It is a crucial parameter in maintaining good indoor air quality and providing a healthy and comfortable environment for occupants.
The appropriate ACH value depends on several factors, including the space’s purpose, occupancy level, pollutant sources, and outdoor air quality. Different standards and guidelines may recommend specific ACH targets for different types of spaces.
Mechanical ventilation systems are often utilized to achieve the desired ACH values. These systems supply and distribute outdoor air while extracting and expelling indoor air, facilitating adequate air exchange and controlling indoor pollutants.
Understanding the ACH value helps building professionals design and evaluate ventilation systems, assess indoor air quality levels, and ensure compliance with ventilation standards and regulations.