Sizing of a linear slot diffuser & calculating its area factor

[mohsinrkhan86]

Hi everyone,

Can anyone explain me about sizing of a linear slot diffuser. I do size it but i am still uncertain about it.
Please help me with an example. Say, 500CFM of air for a reception lobby. What shall be the slot diffuser size for it & how to analyse it?

Expecting experts view here.

Thanks

[hvacker]

Morning. Some of this I'm sure you know. The K factor is from the manufactures engineering publications. It's the free area of a grill/diffuser. So if your diffuser was 6 x 30, and the K factor was .75 the actual area would be 6x30 = 180 sq in. /144 = 1.25 sqft, *.75= .94sqft free area.
If you require 500 cfm you will need 500 cfm/.94 area = 531.9 fpm velocity.
Most grill applications consider cfm required for the load and velocity based on noise levels and on how the room is being used. The recommended velocities are published in a number of books.
Of course the air has to be there so it begins at the equipment and duct design stage. So with your problem the size will depend on cfm required and the noise level desired.
Cfm=area x velocity velocity = cfm /area area = cfm/ velocity

[madhat]

Every time I talk to a PE, I beg him not to use these, unless it's higher than ten feet for a horizontal throw. Fourteen feet for a vertical throw. I absolutely hate them in any office environment.

[hvacker]

Every time I talk to a PE, I beg him not to use these, unless it's higher than ten feet for a horizontal throw. Fourteen feet for a vertical throw. I absolutely hate them in any office environment.

Usually used to wash the parameter windows. They look good and a lot of architects like looks over performance. I think architects invented perforated diffusers.