Free air space - code requirements

[stillfan]

I was hoping soemeone could point me in the direction of where in ASHRAE does it dictate free air space requirment calculations. I ran the calcs for CFM but the client wishes to install a passive system. So the CFM calc means nothing, right?

CFM = Volume *3/60 (3ACH/60min/hr) = 80CFM

 

[willard3]

What is free air space, or, rather, what do you mean by it?

 

[chicopee]

He is probably thinking about natural air circulation which can also be expressed in CFM.

 

[stillfan]

She - and yes, I am speaking of a passive/ natural air system. When I size my intake and exhaust louvers for a passive system it only uses free air specs so I need to calculate my req free area based on the ASHRAE code.

For example, on a residential crawlspace you have to meet a min req free air vent. You also have to meet these requirements in the attic area.

Does anyone know where I would look for these requirements.

 

[MintJulep]

Natural Ventilation is discussed in the ASHRAE Handbook, Fundamentals Volume, Chapter 16.

 

[msquared48]

I believe that old UBC's addressed this requirement, and I'm sure the current IBC or ASCE7 do too.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[KiwiMace]

Do you mean the free, or effective area of the louvre? A natural vent calculation will provide the size of an open hole. When you put a grille in the hole, it blocks a given amount of the space. Any grille/louvre manufacturer will provide the free area of the grille product expressed as a percentage.