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 Posted by: constrictor ® 10/12/2004, 19:32:27 Author Profile Mail author Edit hello there, im new to this forum. I would like to ask anyone who has the knowledge in duct design. Here are some of my questions. 1) how do you compute static pressure? 2) how do you compute the losses of air volume on a duct run? 3) Do you know any site which teaches you techniques for a good duct design? Thanks guys!

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 Re: duct friction Re: duct design -- constrictor Post Reply Top of thread Forum
Posted by: vsenbe2000 ®

10/13/2004, 04:24:48

Author Profile Mail author Edit

# Duct Friction Calculation Formula

## A duct friction - major loss - calculation formula of rectangular and circular ducts

### Circular Ducts

Major loss - friction - in circular ducts may be expressed as:

Pd = (0.109136  q1.9) / d5.02        (1)

where

Pd = friction (head or pressure loss) (inches water gauge/100 ft of duct)

d = equivalent duct diameter (inches)

q = air volume flow - (CFM - Cubic Feet per Minute)

### Rectangular Ducts

For rectangular ducts the diameter - d - may be calculated as:

d = 1.30 x ((a x b)0.625) / (a + b)0.25)       (1)

where

a = length of one side (inches)

b = length of the other side (inches)