Which term is used to describe the rate at which air is exchanged in a space, measured in cycles per hour?

Which term is used to describe the rate at which air is exchanged in a space, measured in cycles per hour?

• A. Air Pressure Differential
• B. Air Changes Per Hour (ACH)
• C. Walk-off mats
• D. Acute health effects

Answer: (B)

Air changes per hour describes how often the air in a space is completely replaced in one hour. This rate, measured in cycles per hour, is a key measure of ventilation effectiveness because higher ACH dilutes and removes airborne contaminants more quickly, reducing infection risk. You can think of it as how many times the entire room’s air is refreshed each hour. The calculation is straightforward: multiply the supply airflow rate (in cubic meters per minute or cubic feet per minute) by 60, then divide by the room’s volume. For example, if a room receives 4 cubic meters of air per minute and is 200 cubic meters in volume, the ACH is (4 × 60) / 200 = 1.2. In healthcare settings, typical targets vary by space, with patient rooms often around 6–12 ACH and operating rooms higher, around 15–20 ACH. Other terms, like air pressure differential, describe pressure differences between spaces, not how quickly air is exchanged.

Air changes per hour describes how often the air in a space is completely replaced in one hour. This rate, measured in cycles per hour, is a key measure of ventilation effectiveness because higher ACH dilutes and removes airborne contaminants more quickly, reducing infection risk. You can think of it as how many times the entire room’s air is refreshed each hour. The calculation is straightforward: multiply the supply airflow rate (in cubic meters per minute or cubic feet per minute) by 60, then divide by the room’s volume. For example, if a room receives 4 cubic meters of air per minute and is 200 cubic meters in volume, the ACH is (4 × 60) / 200 = 1.2. In healthcare settings, typical targets vary by space, with patient rooms often around 6–12 ACH and operating rooms higher, around 15–20 ACH. Other terms, like air pressure differential, describe pressure differences between spaces, not how quickly air is exchanged.