What does air change rate measure?

Air change rate specifically measures the frequency at which air within a building is replaced due to air leakage. This is a critical factor in understanding the building's airtightness and overall energy efficiency. A higher air change rate indicates that more outside air is entering the building, which can lead to increased heating or cooling costs and potential comfort issues for occupants. It is an essential component in assessing how well a building is sealed against unwanted airflow, which directly impacts energy consumption and indoor air quality.

In contrast, the other options pertain to different aspects of building performance. Temperature changes relate to thermal dynamics and do not directly measure air movement. Humidity levels are concerned with moisture content in the air, which is an entirely different measurement context. Air pressure changes, while relevant to airflow dynamics, do not quantify how often the air in a space is completely exchanged. Thus, the air change rate provides a distinct and crucial measurement that informs building performance related to air leakage.