Public restroom Exhaust-Fresh air?

[texanman]

I am trying to confirm whether the the new 75 cfm exhaust per fixture mandated by code (ASHRAE 62 or IMC 2006) means 100%fresh air or can this be air from adjcent areas pulled in. This could be supply conditioned air (has a % of fresh air ) or just infiltration from areas adjacent to the restroom. Any comments?
Thanks,

 

[Dan1978]

Hey Texanman,
The air that gets drawn into the space your exhausting from adjacent area does not have to be 100% fresh air. As long as it is free of contaminents or is not itself polluted you can use it. ASHRAE 62.1 goes over the classifications of air within a building and what types of air you can re-use.

Good Luck

 

[Cachuca]

texanman:

If you mean, will you provide supply air along with exhaust, then the room should be negative (actually it should always be negative). The air that you pull out can come from adajacent rooms (not 100% OA), but keep in mind the effect this will have in adajcent systems too (S=R+OA).

Typically, I provide cooling or heating to Toilet rooms that are either too large, or have major heat loss'/gains thru them. Most times I only provide exhaust.



Cachuca

 

[HVAC68]

Whatever air you are exhausting through the toilets, will either get drawn from the adjoining areas or by a positive supply of cool air into the toilet itself. Obviously, no return please.

This air that is being exhausted through the toilet will have to made up as fresh air in the AHU.

HVAC68

 

[willard3]

Don't forget that the building is a control volume and, if you take 75cfm out, you will have to put 75cfm in somewhere or the building will be nagative.

 

[texanman]

Thanks for your comments. It is undestood that any air exhausted from will have to be brought in through the fresh air component of the many AHU's that this building has.
regards,

 

[HVAC68]

In fact, if you want to have a positive pressure in the building, then you should bring in slightly more fresh air than what is being exhausted. This additional air will find its way out through door gaps, cracks, crevices, etc.

HVAC68