friction loss per 150' of duct
friction loss per 150' of duct
(OP)
i'm trying to size ductwork based on a total run of 150'. is there a formula to determine duct sizing or some way to convert the duct sizing on a ductulator to handle the friction loss for 150' vs. the standard 100'?





RE: friction loss per 150' of duct
Scale the pressure down by a ratio of 100/150. 0.1" per 100 ft is the same as 0.067 per 150 ft as an example.
Again that is for straight duct, some use equivalent lengths for fittings and add it to the straight lengths for an equivalent length.
I prefer using the coefficients that make fitting losses proportional to the velocity head myself.
RE: friction loss per 150' of duct
If your actual length is 150 ft and you want the pressure drop to be 0.1", but your ductulator gives the pressure drop for only 100 ft, then calculate the size duct to give you 0.067" over the 100 ft and that should give you 0.1" over the full length of 150 ft.
Katmar Software
Engineering & Risk Analysis Software
http://katmarsoftware.com
RE: friction loss per 150' of duct
RE: friction loss per 150' of duct
RE: friction loss per 150' of duct
The approximate duct size for 1000 cfm and 0.1"/100' will be about 12"x13" and 12"x16" if you use 0.1"/150'. You have to go for 75 sq.ft of extra ducting in this case. However, 0.05" doesn't make much difference with respect to a fan static pressure and subsequent power consumption.
RE: friction loss per 150' of duct
For 1000 cfm - 0.1" per 100' friction corresponds to 950 fpm.
For 10000 cfm - 0.1" per 100' friction corresponds to 1600 fpm
For 50000 cfm - 0.1" per 100' friction corresponds to 2300 fpm
The best way would be to fix the initial velocity based on the application - I use 1250 to 1500 fpm for comfort air-conditioning and 2000 fpm for ventilation.
HVAC68
RE: friction loss per 150' of duct
I find that fitting cost frequently exceeds the cost of keeping the duct the same size.
Balancing is easier with static regain as static is pretty much constant along the duct length.
Fan energy is less with static regain and fan energy is a large fraction of HVAC operating costs
This also decreases velocity downstream of the fan causing less noise in occupied spaces.
RE: friction loss per 150' of duct
lilliput1