Air intake velocity sizing

[KGBaker]

Discounting the duct velocity, is there an upper air intake velocity for outside air intakes that should be avoided.

I have heard very low numbers to reduce the possiblity of the intake collecting leaves or dragging in rain snow?

Also would intake angle:- vertical,inclined 45 facing down and horizontal have any effect on max velocity?

 

[macmet]

Try this thread,

http://eng-tips.com/viewthread.cfm?qid=103874

or

http://www.energysolutionscenter.org/BoilerBurner/Eff_Improve/Operations/Air_Supply.asp

See if they help.

 

[marcoh]

Weather louvres have a very high pressure drop if air is drawn through at typical duct velocities. Depending on the application I typically design for max 20Pa pressure drop through a louvre which generally equates to about 1.4m/s face velocity.

Different manufactures/louvres will have different pressure drops, open areas, and weather proofing and louvre manufactures will give advice on pressure drops and water ingress vs velocities.

 

[PatBethea]

The ASHRAE Fundamentals handbook has suggested intake face velocities - I generally use 400 fpm as my upper limit. Once the air is inside the building, I treat it like return air (in regards to velocity).

 

[walkes]

Check out the manufacturer's websites on their louver product like ruskin:

http://www.ruskin.com/catalog/servefile.aspx?id=318

They will have the information regarding face velocity, free area, pressure drop, velocity where moisture penetration occurs etc.


If you are just doing a weather hood with a screen then I would agree with PatBethea

 

[hvacinsider]

KGBaker,

Could you be more clear on the application? From your posting it appears that your bringing in outside air thru a gooseneck on the roof? Is this the case?