Question in PRESSURE ROOM

[ALKURDI]

PRESSURE ROOM

HOW TO CALCULATE PRESSURE ROOM IN PASCAL ??
i have ROOM SIZE : 4m * 4m * 3m (height)
how many cfm i need to make this room 1 pascal (positive pressure)

pls

 

[willard3]

There is going to have to be way more information given to answer this question.

 

[BronYrAur]

As long as this thread is here, let me ask a followup while we wait for more information from the originator. By the way ALKURIDI, the construction of the room is most important missing information. You can't hold pressure in a leaky room. Cracks, openings, etc. all need to be known.

Let's say the room above was in feet to keep the units simple, so 4ft x 4ft x 3ft or 48 cubic feet. In a perfect scenario with absolutely no leakage, would it not be true that adding 48 cubic feet of air to this room would increase the pressure by a factor of 1 atmosphere or 14.7 psi? I know this is way outside the realm of room pressurization, but just thinking it out to an extreme. Every time you fill the volume with air, the pressure should increase by 1 atmosphere, correct?

 

[pocketengineer]

General form of equation across the opening is
Q = C*A*sqrt(2*dP/rho)
where
C = discharge coefficient for opening, dimensionless
A = Flow opening area or leakage area, m2
dP = pressure difference across opening, Pa
Q = airflow rate, m3/s
rho = air density, kg/m3

From the above equation, you will see the parameters required in room pressurization concept.

Hope this help you.

 

[ALKURDI]

i am sorry for late

okay
1. i have gap in tow doors ( 1 cm*0.90 cm)
2. gypsum board for selling is sealed
3. 4 led panel light (60*60) 48 watt
4. the important things i have safety cabinet in one room
5. the safety cabinet is class 2 type B2 that mean is Exhaust all air out side building (800cfm)
6. no cracks no windows no another leakage

and thanks for your response .

 

[willard3]

I guarantee you have air leakage other than what you have enumerated.

 

[pocketengineer]

As mentioned earlier, to determine the airflow offset or differential airflow required to attain a specific room differential pressure in relation to the adjacent space, follow the formula given earlier. A room's differential pressurization value with respect to an adjacent area is totally dependent upon the room's differential airflow (offset) and its leakage area. You need to map out the pressure regime for each space. Estimate the leakage area to the best of your knowledge (ASHRAE or NFPA has some guides on wall/floor construction leakages). Indicate the directional airflow on plan, and balance the airflow.

Apart from performing design calculations, to maintain a room differential pressure at the level desired is NOT EASY in practice. Your control strategy is crucial and upmost important. Is your safety cabinet with VAV control? Is achieving a proper directional airflow (inward for a -ve room) good enough for your project? Just to throw some, all these will affect your decision on control strategy.

Good luck.

 

[BronYrAur]

can anyone offer comments on my little sidebar question?

 

[willard3]

That would be true if air were incompressable, byron; it's not.

 

[VerneE]

I've always used the idea that at an opening, the pressure of the high side is used to create a velocity through the opening based on the differential pressure of the two sides. Area times velocity is CFM of flow to maintain the pressure in the space. This has worked for me over the years.

 

[lilliput1]

The room should be negative, not positive because of the Class II Type B2 biosafety hood. We design negative isolation rooms with 400 CFM differential to be above the minimum 0.001 in. wg pressure required for isolation rooms. The room/hood exhaust must be at least 400 CFM more than the room supply air. 1 pascal is 0.00401865 in. wg.

If you really want to operate at negative .0040865 in wg, Exh minus Supply CFM differential would need to be about 800 CFM instead of 400

 

[lilliput1]

Room should be negative instead of positive because of the Class II type B2 biosafety cabinet. With sealed isolation rooms we have found that 400 CFM should be the design CFM differential to hold minimum 0.001 in. wg pressure differential. 1 pascal is 0.0040865 in wg. If you really want to operate at negative 1 pascal CFM differential would need to be 800 CFM instead of 400. Since the biosafety cabinet is already exhausting 800 CFM you need to exhaust additional air from the room equal to the room supply air.