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Sizing of ceiling exhaust fan for storm shelters

Sizing of ceiling exhaust fan for storm shelters

Sizing of ceiling exhaust fan for storm shelters

Hi everyone!

I'm new here at Eng-tips.

A ventilation system will be put up on a storm shelter. (please see attahced)

Can I apply the formula P1V1/T1=P2V2/T2 in sizing the ceiling exhaust fan?

RE: Sizing of ceiling exhaust fan for storm shelters

Can I apply the formula P1V1/T1=P2V2/T2 in sizing the ceiling exhaust fan? ----> What I mean here is that can I get the required static pressure of the fan using the formula P1V1/T1=P2V2/T2?

RE: Sizing of ceiling exhaust fan for storm shelters

First get the manufacturer's fan curve; then calcuate your system curve which will be a parabolic curve; plot both of them on same graph paper(pressure vs. cfm); whre both of the curves intersect will be the fan requirement.
Better yet get an engineering handbook which will show you how to do it.

RE: Sizing of ceiling exhaust fan for storm shelters

Im confused.

Wouldnt the static pressure, be the minimal ductwork, back draft damper, and SP of the roof vent?

Then the cfm would be whatever the cfm required for internal loads or a rule of thumb air change.  (I would guess between 6 and 10).

Im embarrassed to say I dont know how to draw a system curve, but if I plug in the SP and cfm into a manufacturer software program like Greenheck, it will do it for me.

Are we saying the same thing chicopee, your way being the "correct" way but considered old school?

RE: Sizing of ceiling exhaust fan for storm shelters

The old school( the fundamentals) is what you need to understand the results that you want. The static pressure that you seek is actually calculated (via Bernoulli's equation) or measured; in many cases, the initial static pressure will be atmospheric,ie,at the intake of the exhaust fan and ducting system.

The equation that you originally presented is not really applicable for an exhaust system because it is more applicable to static condition where there is no gas flow but just expanding boudaries, pressure and temperature changes. However, having said that, you will find derivations involving Bernoulli's equation( modified first law of thermo)and equation of state (PV=mRT). Bernoulli's equation would be the right choice but must include a term for energy lost along the system length.

My first post is the way to go however you must have an idea on the CFM that you want to exhaust. If you search the web sites you will probably get an illustration on how to proceed with system curves and fan curves.

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