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Air intake velocity sizing

Air intake velocity sizing

Air intake velocity sizing

(OP)
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?

RE: Air intake velocity sizing

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.

RE: Air intake velocity sizing

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).

RE: Air intake velocity sizing

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

RE: Air intake velocity sizing

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?
   

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