Designing Supply-only Pressure Differential

[AJKue]

Hello all,

I am a new-grad from mechanical engineering beginning work on designing a supply-only positive-pressure "booth" with a single blower at the inlet.
Starting with the ASHRAE eqn. for pressure differential (in PA) based off of differential flow rate given a leakage area;

Q=165.5*A*√∆P

This works fine when a reasonable estimate for the supply and exhaust flow are known, but if there is a simple damper on the exhaust, I'm wondering whether this equation is still usable, or if the equilibrium point of the space is governed by some other logic.

Additionally, this booth will be very small and well sealed (like this sound booth)

so I think it's somewhat reasonable that the leakage area will be negligibly small.

I hope to maintain a target pressure differential range without controls or an active damper on the exhaust.

Thanks very much in advance for any experience / insights / ASHRAE guidelines you might have

 

[GT-EGR]

The crack area method is part of the equation, but only gets you a ballpark estimate on how much air would leak out through other locations if there was no damper. The exhaust damper has published values of how much pressure it takes to flow a certain CFM through it. Having the damper gives you flexibility to make adjustments that you can’t make by changing the cracks.

If you have a positive pressure target in mind, do your crack area method calc to see how much air you need to pump in to keep the pressure in the room. You want to overestimate that value for your fan sizing. And then once you turn the oversized fan on and see what positive pressure it actually creates, you can then slowly open the damper until you lower the interior pressure to get the value you want.