Air Density Correction for Altitude and Temperature (ACFM/SCFM)
Density factor DF = (1 - 6.73e-6 elev)^5.258 x 530/(460+T), converting ACFM to SCFM = ACFM x DF and correcting the 1.08 sensible constant and the rated fan static. 5,000 ft is ~16% thinner; 120 F rooftop air ~9% thinner at sea level. A correction factor; the fan curve governs.
Formula and source
alt = (1 - 6.73e-6 elev)^5.258; temp = 530/(460 + T_F); DF = alt x temp; SCFM = ACFM x DF; const = 1.08 x DF; sp = rated_sp x DF.
The air density correction for altitude and temperature from the ASHRAE Handbook - Fundamentals, by name.
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