Air Change Calculator, Air Change Per Hour Calculator

Calculate air change per hour using calculator

Hello engpocket friends! How are you? In this post we will talk about air change per hour.

Maintaining good indoor air quality (IAQ) is not just keeping a room cool. It is about how often the air inside the room is completely replaced with fresh, filtered air. This can be measured by calculating air changes per hour or ACH. If some of you are HVAC engineer or contractor, this must be your daily lunch :).

What is air change per hour?

Air change per hour tells you how many times the total volume of air in a room is replaced with fresh air within one hour. In the modern HVAC design, calculating the correct ACH is vital for removing contaminations, odors, and airborne pathogens, ensuring a healthy environment in the projects.

Why we must calculate air change per hour?

High ACH rates are required in cleanrooms to prevent the spread of infections.
Meeting ASHRAE standards for ventilation.
Removing stale air and humidity from offices and residential spaces.

Air change per hour formula

This is the formula of ACH

$ACH = \frac{CFM \times 60}{Volume_{room}}$

CFM = Airflow rate in cubic Feet per minute.
60 = Conversion factor (minutes to hours).
Volume = Length X Width X Height (in cubic feet).

Case of calculating air change per hour

My office room is 20 ft long, 15 ft wide, and 10 ft tall ceiling. The Aircon unit provides an airflow of 250 CFM. Can engpocket help me calculate the ACH?

$Volume = 20 \times 15 \times 10 = 3,000 \text{ ft}^3$

$ACH = \frac{250 \times 60}{3,000}$

$ACH = \frac{15,000}{3,000}$

$ACH = \mathbf{5.0}$

Answer: The room has an ACH of 5.0, which is enough for standard office. I do not have to add anything. All good

Alright, are engpocket friends understand about ACH now? Wrote your taughts on the comment section.

We also have a free calculator to calculate BTU to PK for room. Check the calculator on this link.