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Duct Construction and Uses
Discussion in fabricating and use of products that move air including spiral pipe, duct board and typical sheet metal work.
       


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  #1  
Old 06-27-2015, 10:54 AM
Bradleyc1982 Bradleyc1982 is offline
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Default Fan selection process????

Can anyone help?? I want to know how to work out what pressures etc are created by different fittings in a duct run, e.g. 90/45 degree elbows, offsets and straight runs?!? Also duct sizings and fan selection processes? I make extractor hoods and duct for commercial kitchens and use a technician where we get the fans from to size them accordingly at the moment but would like to know how to do it myself!!

I (think) i know how to work out what air needs to be moved by the extractor hood itself (length x depth x .5), for example if the extractor hood was 2m x 1.2 m it would need to move 1.2m3/s, but what I would like to know is how the elbows and duct runs affect the performance of the fan?? So I can size the fans correctly!

Any help much appreciated, thanks and can't wait for responses

P.s not sure this is posted in the right section?!?!
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Old 09-23-2016, 09:53 AM
ductworker ductworker is offline
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Quote:
Originally Posted by Bradleyc1982 View Post
Can anyone help?? I want to know how to work out what pressures etc are created by different fittings in a duct run, e.g. 90/45 degree elbows, offsets and straight runs?!? Also duct sizings and fan selection processes? I make extractor hoods and duct for commercial kitchens and use a technician where we get the fans from to size them accordingly at the moment but would like to know how to do it myself!!

I (think) i know how to work out what air needs to be moved by the extractor hood itself (length x depth x .5), for example if the extractor hood was 2m x 1.2 m it would need to move 1.2m3/s, but what I would like to know is how the elbows and duct runs affect the performance of the fan?? So I can size the fans correctly!

Any help much appreciated, thanks and can't wait for responses

P.s not sure this is posted in the right section?!?!
BRADLEY, the correct fan selection is probably more important than the actual design of hood and extract duct, the fan must have enough power to overcome total resistance of duct fittings, length of duct, filters etc. If the velocity design is fast then additional resistance is incurred. Please google for ASHRAE duct fitting database, it will help you immensely.
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  #3  
Old 09-23-2016, 12:58 PM
Bradleyc1982 Bradleyc1982 is offline
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Thanks mate, since posting this I have been acquired lots of data on duct pressures etc, I will be sure to check the ashrae data out though!! Thanks
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