What does the term "air change rate" refer to in CACS?

The term "air change rate" in the context of the Cabin Atmosphere Control System (CACS) specifically refers to the frequency at which cabin air is replaced. This is a critical factor in maintaining a healthy and comfortable environment for passengers and crew aboard an aircraft. The measurement is typically expressed in terms of air changes per hour (ACH), which quantifies how many times the total cabin air is refreshed within an hour.

This rate is important because it ensures that any contaminants or carbon dioxide buildup from breathing and other cabin activities are effectively removed from the cabin space, promoting better air quality. A higher air change rate indicates a more rapid replacement of stale air with fresh air, which is essential especially in pressurized environments like an aircraft cabin. This understanding is vital for ensuring optimal cabin conditions and compliance with safety regulations concerning air quality.