Airflow Based on SP and Duct Size
Airflow Based on SP and Duct Size
(OP)
It's been years since I've done any fluid analysis in depth. Is there a quick and dirty method to estimating SCFM when you have the SP and the duct size? I'm dealing with SP's in the range of 15-50 inches of water and duct sizes from 4-18 inches round.
Barring a quick estimate, about how close can you come if you neglect compressibility effects?
Barring a quick estimate, about how close can you come if you neglect compressibility effects?





RE: Airflow Based on SP and Duct Size
Pd in inches wg/100 ft of duct = (0.109136 x (CFM)^1.9)/ (d)^5.02
Where d = equivalent duct diameter in inches
For rectangular duct with side 1 = a & side 2 = b
d = 1.30 x ((a x b)^0.625) / (a + b)^0.25)
Thus for 2000 CFM in 24" x 12" duct:
d = 18.2805
Pd = 0.0944 in wg /100 ft of duct
This formula is a bit different from that in the Carrier manual but it fits the Chart values in SMACNA better.