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Participant

Join Date: Aug 2008
Posts: 2

Selecting Fans for an Air Duct System

08/17/2008 5:51 AM

Good day. I just want to ask, what are the things to be considered in fan selection for an air duct system aside from air flowrate? sorry for the noob question. I'm currently taking BS in Mechanical Engineering and designing a centralized airconditioning system is one of our projects. I would gladly appreciate it if you could help me.

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Pathfinder Tags: airconditioning system HVAC
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Guru

Join Date: Jul 2008
Posts: 927
Good Answers: 56
#1

Re: Selecting Fans for an Air Duct System

08/18/2008 12:16 AM

I won't attempt to make specific suggestions as I do not know enougth about moving air thru ductwork.

Over the years however, those system I have experience with were friendlier to end users when they had large diameter fans moving slowly as opposed to smaller fans spinning faster. Air volume was the same, but the big fans were lots quieter and apparently needed less power.

The other trick the HVAC guys mentioned was to size the ductwork as the air moved downstream so the air velocty remained constant.

Perhaps others with a better understanding of this environment can explain why.

L. J.

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Associate

Join Date: Dec 2006
Location: Silverdale, Washington
Posts: 29
#2

Re: Selecting Fans for an Air Duct System

08/18/2008 10:59 PM

You need lots of data - look over the attached site it should be of good use to you.

http://www.greenheck.com/pdf/fans/FanFundamentalsMay2005.pdf

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Anonymous Poster
#3

Re: Selecting Fans for an Air Duct System

08/18/2008 11:59 PM

Go to the Library and get a copy of ASHRAE handbook (There are 4 of them but I cannot remember whether it is Fundamental or System).

You just need to calculate the total pressure drop of the ductwork and the air flow rate folllowign the step in the handbook. Then find a fan to suit.

Good Luck.

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Anonymous Poster
#4

Re: Selecting Fans for an Air Duct System

08/19/2008 12:05 AM

My last comment did not go through.

Just go to the Library and get a copy of ASHRAE handbook (ther are 4 of them but I forget whether it is Fundamental or System). Follow the step and calculate the total pressure drop (static and velocity). Together with the air flow rate, select a fan form the catalogue to suit.

Good Luck.

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Participant

Join Date: Aug 2008
Posts: 2
#5

Re: Selecting Fans for an Air Duct System

08/19/2008 8:24 AM

thanks everyone. ok i'll do that.

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