Definitions for

**"Air Changes"**Ratio of the volume of air flowing through a space in a certain period of time (air flow rate) to the volume of that space (room volume);usually expressed as the number of room air changes per hour (ACH).

a measure of the air exchange in a building. One air change is an exchange of a volume of air equal to the interior volume of a building.

A way to express ventilation rates, which are the number of time the air volume of a given space will be replaced in a one hour periods, assuming the air distribution within the space is uniformly mixed.