Maintain a minimum outward velocity in a room with 2 doors open?
Maintain a minimum outward velocity in a room with 2 doors open?
(OP)
I am trying to calculate how to maintain a 0.305m/sec(60 FPM) outward velocity in a room with 2 doors. The 2 doors in the room must be considered open simultaneously. So I guess my question is: Given the nature of this problem, what rule of thumb, model, or equation could I use to figure this out?
Room dimensions 29'x11'x8.5'
Door Dimensions 33.5"x77"
Thanks in advance!
Room dimensions 29'x11'x8.5'
Door Dimensions 33.5"x77"
Thanks in advance!





RE: Maintain a minimum outward velocity in a room with 2 doors open?
( Area of Door 1 + Area of Door 2) x 60 = cfm of air that must be pumped into the room continously
RE: Maintain a minimum outward velocity in a room with 2 doors open?
within domian of ventilation and air distribution, specifying velocity is not so simple. what is certain is that there is no way you can have uniform flow through open door.
RE: Maintain a minimum outward velocity in a room with 2 doors open?
Drazen - Thank you for your input! I should have said that a minimum of 0.305m/sec(60 FPM) outward velocity must be maintained. It does not need to be kept at that exact measurement.
RE: Maintain a minimum outward velocity in a room with 2 doors open?
Drazen is correct in terms of uniformity of flow etc , but that is not what you asked
RE: Maintain a minimum outward velocity in a room with 2 doors open?
RE: Maintain a minimum outward velocity in a room with 2 doors open?
RE: Maintain a minimum outward velocity in a room with 2 doors open?
One more that can be a problem: If your two doors are not on the same wall, there could possibly be a pressure difference between the two corridors that those doors open into. One door could be getting inflow while the other has more outflow than expected. This will be especially pronounced of one of the doors opens into the outdoors (bad) or both of them do (worse), even if they are on the same wall. Mother Nature can overcome whatever fan you might have blowing in there...
Best to you,
Goober Dave
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RE: Maintain a minimum outward velocity in a room with 2 doors open?
Interlock the doors so that only one can be opened at a time. Weatherstrip the heck out of any outside doors.
Best to you,
Goober Dave
Haven't see the forum policies? Do so now: Forum Policies
RE: Maintain a minimum outward velocity in a room with 2 doors open?
hypothetically, core zone should cover whole door opening at zero distance from door opening, but that is not of use in practice. what can you do with air in one fixed, two-dimensional plane?
that is why i tried to understand what comes behind your request, to rephrase my question: for what purpose you need to maintain minimum air velocity at door?
RE: Maintain a minimum outward velocity in a room with 2 doors open?
I think you need to review why you need 60 fpm across two open doors. The following are the points of concern:
- This means you would need 2,150 cfm more supply than exhaust.
- Assuming there is no exhaust, the room air exchange rate is 48 air changes per hour. A typical lab is 6-12 ACH (with exceptions for clean rooms and labs with hoods in smaller rooms, etc.).
- Assuming there is no exhaust, you have 6.7 cfm per square foot of supply air to the room. The typical value for space air conditioning is 1 cfm per square foot. Laboratories might see on the order of 2-3 cfm per square foot.
- If you have a hood in the room, it could have difficulty passing certification due to the amount of air being supplied, resulting in high drafts at the hood face.
- One of the two doors will never close, even with the closer set to its strongest closing force – unless there is a large alternate leakage pathway.
When you have a chance, please clarify why there is a design criterion of 60 fpm across two open doors.
RE: Maintain a minimum outward velocity in a room with 2 doors open?
RE: Maintain a minimum outward velocity in a room with 2 doors open?
He asked a bunch of us to try to figure out how much he would have to pump into the room to meet that requirement. Well we were all trying to figure it out, but nobody could agree on the procedure and what not. I was doing some research online and I happened across this forum.
Thanks Again!
Sal.