differential pressure to cfm airflow measurement devices

Neither of these are anything close to typical or can really be arrived at based on a room volume without known net open crack area. By this equation, a typical 20 ft x 20 ft room (10 foot ceiling) with 600 cfm in and 300 cfm out would calculate to 7.4 x 10^-7 Pa (or 7,600 Pa if the bracket was in the wrong place). I think there might be an assumption built into it that elimintes it from applying to this application. Sauters' equation as given above can't be true in any application I've seen unless the room volume is not in cubic feet. The same would occur in a hypothetically leak-free Boeing plant, although it would take longer to reach that point as such a large volume of air would need to be compressed to the equilibrium fan outlet pressure. Whether you supply a net 100 cfm greater amount than the air exhausted from an office or the Boeing factory out in Everett, WA, your space pressure is a function of the net open crack area.Īssuming (to simplify, for airflow inward only) the office were completely leak free, the space would reach equilibrium with the fan discharge static pressure. RE: Calculate Differential pressure ChasBean1 (Mechanical) 11 Sep 02 22:54 Finally, items to consider with static pressure are: Will the exit doors still open when the room is positive or negative to adjacent space? Will the room pressure cause moist air to enter wall cavities and cause ice or mold problems? In order to maintain the pressure you will need an automatic control to measure the pressure and adjust the supply air or exhaust.ĥ. Ultimately a field balance will set the extra outside air flow or exhaust air flow to obtain the differential pressure your trying to obtain. If you want a space that is slightly negative, make sure the supply air is slightly less than air removed from the space.Ĥ. Though this is variable based on the 'tightness' of the room shell.ģ. My company usually designs at 0.5 cfm/sq ft of extra supply air to give about 0.04' wg static pressure. Second, if you want a space slightly positive to another space, make sure the supply air flow is greater than the air removed from the space (this includes return and exhaust air).

If the reference spot is indoors, keep it away from doors or other spots where the pressure can change easily.Ģ. If the reference point is outside, try adding a dampner to it and try to have it equalize for wind loads by tying-in multiple spots around the building. First, choose a stable reference point to measure your static pressure to. Also, the reference point for checking the diffential pressure probably fluctuates.īut there are still some basic rules-of-thumb to follow:ġ. The reason for this is that all rooms are 'leaky', meaning some air leaks out of door jambs, window sills, wall joints, ceiling tile, etc. My experience says no, there is no way to accurately pre-determine the differential pressure of a space based on supply and exhaust flows.

Differential pressure to cfm airflow measurement devices