Air Change Calculation

Dear all,

I want to qualify my cleanroom, especially air change parameter. Now, I’ve qualified air change and calculate from velocity of diffuse grill. But, my supplier told that the air change must be calculated from return grill’s velocity. Does anyone have any information about it? Should I qualify air change from diffuse grill velocity or return grill velocity or both of them?
Any information or related article is really helpfull.




You have to calculate air changes from Supply Grill (Diffuse Grill). Refer ISO-14644.


You have to calculate air changes from Supply Grill (Diffuse Grill). Refer ISO-14644.[/quote]

ACH formula

ACH = Total actual air supply in CFM X 60 min
Room volume (Cu ft)

Hi Felisia

Tell your supplier to go away.

The room air change rate is exactly what it states – the air coming into the room is going out (or the room is growing). It does not matter how the air is leaving. The air can be leaving around doors or through doors (when they are open), down extract systems (if you have them), through product transfer hatches (if you have them). If your flow into the room is correct and you room differentials are correct, you are correct.

Inlet filters are lines scanned and the total flow can be measured quite accurately. Out filters are not line scanned, and because of access problems are often difficult to measure accurately. When you come to high class rooms then laminar flow is usually required, but there again your only interested in your room differentials, your room air change rate, and your flow pattern.

Alex Kennedy

Dear all,
Thanks for your attention. Your information is really helpfull.
Now, I can be sure to my qualification method.
For Alex, I’ve told to my supplier about your messages and they’ve gone away now. :stuck_out_tongue:



Do some one explain me how to interprit this formula for calculating the air changes according to room type.
Please give an example to make it clear.

v = g/(x-s)


Hi. Try this site. it contains some interesting facts wrt your question.


If you are still in doubt, ask away. :slight_smile: