Clean Room Pressurization
Clean Room Pressurization
(OP)
I am designing the HCAC system for a small clean room (~200ft^2 w/ 8ft ceiling, Class 10,000). The client wants 60 air changes per hour with 0.05 in WG positive pressure (relative to building).
How do I calculate the amount of exhaust air to provide positive room pressurization?
How do I calculate the amount of exhaust air to provide positive room pressurization?





RE: Clean Room Pressurization
Thread403-31557. I still stick to my stand in that post for if you provide enough air to compensate for leakages there is no pressure built up in the room. However, is your system ciculatory type or once through?
Regards,
RE: Clean Room Pressurization
Supply Air = 1400 cfm (from 60 ach) + 2 ach exfiltration = 1453 cfm. Where, ach is the air changes per hour.
Exhaust Air = 1400 cfm
This should maintain a slightly positive room pressure because SA > EA.
RE: Clean Room Pressurization
Leakage through (closed!) doors (m3/second) at stated pressure difference (Pa) across door (m3/second@Pa):
Single Door:
0.03@5, 0.05@10, 0.06@15, 0.06@20, 0.07@25, 0.07@30, 0.08@40
Double Door:
0.04@5, 0.08@10, 0.10@15, 0.11@25, 0.11@20, 0.12@30, 0.13@40
So, for instance, if the room is reasonably well sealed and the bulk of the air leakage is through the standard gaps (4mm along bottom, 3mm along top and sides, 2mm between double leaves) at doors, then:
If it is a single door and the room pressure is 15 Pa above that on the other side of the (only) single door, the leakage out of the room will be 0.06 m3/sec. If the supply air is in excess of the extract air by that amount, then the room pressure will be about 15 Pa above the pressure outside the door.
Beware, it is often the case that other "unexpected" leakage paths, etc occur during construction; these must be catered for as well as the doors.
Regards,
Brian
RE: Clean Room Pressurization
Brian!
As per your calculation the 120 cfm extra air is leaking out of the room. So how the pressure is being maintained?
Or, if I pass only 120 cfm to the room and not taking anything through return (that is cfm in return ducting is zero) still can we be able to maintain the pressure inside?
Note: This is in continuation to my discussion in the other thread I already mentioned. Perhaps I may have some misconception.
Regards,
RE: Clean Room Pressurization
You may consider using the requation Q = 2610 x A x dp, where Q = Differential air quantity etween supply & exhaust in cfm / A is the net leakage area in sq ft / dp is pressure differential between room and outside in inches of water column. This equation is from the ASHRAE handbook. Only problem is how to estimate or quantify A. I reckon a close examination of the space and an educated guesstimate are the answers, which will yield a ball park figure.
Anyone having a more accurate method, please help.