If I know the leakage of my building; How do I know the amount of supply air (CFM) to reach a 0.1 in w.c. positive pressure? I have been reading some guidelines from ASHRAE journal and it refers to have a differential capability of 400 cfm to reach 0.01 in w.c. Is there any empirical way to estimate it? They also refers commom leakage through open doors (3'X 7')as 1050 CFM and 150 for closed doors.
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mechanicaldude
Mechanical
- Nov 10, 2006
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Why do you need .1" that seems awefully high. How did you arrive with that number ?
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mechanicaldude
Mechanical
- Nov 10, 2006
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I can't say that I'm an expert in this area but there is an equation found in ASHRAE that might apply to this situation.
DP = (Q/2610*A))^2. Where dp is the diffential pressure (0.1" in this case), Q is the cfm, A is the area of leakage.
You can solve for Q to find the cfm, but you need to know what your Leakage area is. The cfm required to maintain a certain differential pressure is dependent on construction type.
I know when designing negative pressure rooms in hospitals the cfm required to maintain a .05" pressure can range from 100 to 500 cfm difference between exhaust and supply depending on how tightly sealed the doors and ceilings are.
I also believe somewhere in ASHRAE they recommend no larger than about a .03" WC across a door so that it isn't too difficult to push open.
This probably doesn't completely answer your question, but maybe its a start.
DP = (Q/2610*A))^2. Where dp is the diffential pressure (0.1" in this case), Q is the cfm, A is the area of leakage.
You can solve for Q to find the cfm, but you need to know what your Leakage area is. The cfm required to maintain a certain differential pressure is dependent on construction type.
I know when designing negative pressure rooms in hospitals the cfm required to maintain a .05" pressure can range from 100 to 500 cfm difference between exhaust and supply depending on how tightly sealed the doors and ceilings are.
I also believe somewhere in ASHRAE they recommend no larger than about a .03" WC across a door so that it isn't too difficult to push open.
This probably doesn't completely answer your question, but maybe its a start.
1050 cfm for open door (based on 50fpm velocity across the door opening)and 150cfm for closed door are good guidance values. That gives you some relief with the door bottom gap to be as high as 10mm. Oflate, the trend is not to use drop seals and this value can be useful if you plan to do so. If I use drop seals then I go for tighter OA control.
0.1"WC is quite common in pharma industry and you should really worry if the pressure is above 0.12"WC.
The thread403-196510 can be of help to you.
0.1"WC is quite common in pharma industry and you should really worry if the pressure is above 0.12"WC.
The thread403-196510 can be of help to you.
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