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

The term "air change rate" refers to the frequency at which cabin air is replaced, typically measured in air changes per hour (ACH). This concept is significant in the context of cabin atmosphere control systems (CACS) because maintaining a healthy and comfortable cabin environment for passengers and crew is crucial during flight.

In practice, the air change rate indicates how effectively the cabin can be refreshed with new air, helping to dilute contaminants, manage humidity levels, and ensure an adequate supply of breathable oxygen. A higher air change rate is generally desired in aircraft to enhance passenger comfort and air quality, particularly on long flights where passengers spend extended periods in the same enclosed space.

By understanding air change rates, operators can optimize ventilation systems and ensure compliance with health and safety standards, leading to better overall cabin conditions.