What is the correct type of pressure (static or total) used in the compressibility factor, K(adsbygoogle = window.adsbygoogle || []).push({}); _{P}, when calculating fan power? Howden's Fan Engineering book seems to indicate total pressures should be used, but I also have a PDF from Howden that indicates static pressures should be used. Online searching has shown mixed answers. For my calculation, I did it both ways and the difference was small enough to be considered negligible by engineering judgement, however, I would still like to know the correct calculation.

The equations I am using are:

H = (Q*P_{T}*K_{P}) / (6356*N_{T})

Where,

H = fan shaft power [hp]

N_{T}= fan total efficiency [%]

Q = fan inlet volumetric flow [acfm]

P_{T}= fan total pressure [in. w.c.]

6356 is a conversion factor

K_{P}= compressibility factor [dimensionless]

K_{P}= [itex]\gamma[/itex]/([itex]\gamma[/itex]-1) * [(p_{2}/p_{1})^(([itex]\gamma[/itex]-1)/[itex]\gamma)[/itex]-1] / ((p_{2}/p_{1})-1)

Where,

p_{2}= total or static pressure at the fan outlet [in. w.c.]

p_{1}= total or static pressure at the fan inlet [in. w.c.]

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# Compressibility Factor Pressure For Calculating Fan Power

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