Kitchen Exhaust fan duct sizing

[marthab]

How do I size the duct for an exhaust fan with 1450 cfm and 1,324 rpm.

 

[MECHJAMIECTA]

Are you talking residential kitchen or commercial kitchen?

 

[marthab]

Mechanical

 

[MintJulep]

Fans have a performance curve that defines cfm vs. external pressure drop.

Step 1: Find this curve for your fan.

Step 2: Decide how many cfm you need, and use the curve to identify the corresponding allowed external pressure drop.

Step 3: Size the duct for that pressure drop at the required cfm.

 

[DRWeig]

marthab,

This isn't an exhaust hood over a cooking appliance, is it? If so, you'll have to also consider keeping the velocity of the air high enough to entrain the particulates and grease. If not a kitchen application, listen to MintJulep.

Good on ya,

Goober Dave

 

[berkshire]

Marthab
I do not know where you live, but here is a PDF of the code guidelines where I live. Most states are not that much different.
Pay attention to page 10.

B.E.

http://www.sdcounty.ca.gov/deh/food/pdf/publications_ventilationguideline.pdf

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor

 

[willard3]

Find and employ a Mechanical engineer and don't try to bootstrap this.

 

[cry22]

Berkshire
I am surprised that NFPA 96 is not part of the listed standards governing the design and installation of kitchen exhaust systems in your neck of the wood.

Also: NFPA 96 allows lower velocities as low as 500 FPM nowadays for some specific applications such as Melink control systems.

 

[berkshire]

It is and the guidelines mention it.
B.E.

The good engineer does not need to memorize every formula; he just needs to know where he can find them when he needs them. Old professor