Flexible Air Duct Pressure Drop Calculation.
We use flexible air duct in almost all building construction application.
•EXAMPLE:
Airflow, Q = 1200cmh
Terminal duct/ flexible dia. 350 mm
Flexible bend r= 0.5d
Installation length 1.5m.
By using above chart
Linear pressure loss 0.7Pa/m
(by using galvanized duct chart 1.55 x 0.4 = 0.62)
Assumed that at actual installation flexible is compression to 85% of its fully extended length
By using Ashrae compression ratio chart 0.7Pa/m x 2.7 = 1.9Pa/m
à bend loss r=0.5d, à 4.4Pa
Total pressure loss on flexible is 1.9Pa/m x 1.5m + 4.4Pa = 7.25 Pa
