What does air change per hour (ACH) measure?

Air changes per hour (ACH) is a vital metric that quantifies how many times the air within a defined space, such as a home, is completely replaced in one hour. This measurement is critical for understanding indoor air quality, ventilation efficiency, and the overall performance of HVAC systems.

When calculating ACH, the total volume of air in the home is considered alongside the total airflow rate. By determining how often the entire volume of air circulates in one hour, professionals can assess whether a building is adequately ventilated or whether there are concerns regarding air quality, humidity, or the potential for pollutants to accumulate.

For example, if a home has a calculated ACH of 5, this means that the total volume of air inside the home is entirely replaced five times within that hour, indicating good ventilation which can help in controlling moisture levels and maintaining a healthy indoor environment. This concept is crucial in building analysis and energy audits, as it informs decisions related to air sealing and improving ventilation strategies.

The other choices do not accurately reflect the purpose of ACH. Total airflow, frequency of maintenance checks, and temperature changes are not directly related to how often indoor air is replaced, making them less relevant in the context of understanding air changes per hour.