Toilet Makeup Air for Required Exhaust

[MECHJAMIECTA]

thread403-309881

The older thread was closed, but I have a question regarding transfer air as makeup for toilet exhaust. Someone was stating that it is not allowed by code anymore by saying "transfer of room air to another, i.e use of a room as a return plenum is a code violation."

However, does this not fall into the exception the IMC gives you? 601.2 does state "Corridors shall not serve as supply, return, exhaust, relief, or ventilation air ducts" however it also then says "Use of a corridor as a source of makup for toilets, dressing rooms, janitor closets is permitted." So, they clearly recognize that you aren't using transfer air into these spaces as return and rather as makeup air.

My question is this (pretty common scenario I imagine for the senior engineers here):

I have a bathroom that only requires 35cfm of cooling supply air based on the load calculation (only overhead lights and couple people). However, code requires 150CFM of exhaust air out of the space. In an attempt to not over-cool the space, I would prefer to supply 50 and then exhaust 150 by transferring ~100 CFM through the bathroom door. The bathroom is off of the elevator lobby area and has a buffer vestibule. The vestibule and the bathroom itself each have single 3x7 doors with a specified 0.5" gap. This would keep the bathroom a little chilly, but not terrible since it isn't regularly occupied.

The problem is that transferring the 100CFM through the current opening would be around 330 fpm, and while this keeps the door opening force easily under the 30lb requirement, the velocity is still a little higher than I would prefer so I figure I have a couple options.

1)I could overcool the space further and do something like 75CFM supply and 75CFM transfer. The building is set at 77F so, this would essentially bring the bathroom down to a chilly 67F before mixing the transfer air in, leaving the bathroom around 72F which is not bad.

2) I could put a door grille in to allow me to transfer more air without worrying about velocity or door forces. I didn't see any problem with this until I remembered this thread and it had me second-guessing myself again vs the code requirements.

3)I could potentially utilize a series FP VAV to mix plenum air to prevent it from getting too cold in the bathroom while keeping the set supply air.

Obviously I would really like to avoid using reheat since it is electric and seems to be a waste of energy in an unoccupied space like this.


Any suggestions?

 

[MTES93]

You are correct w/ the exception. check to see if there is a caveat about making sure whatever serves the hallway has sufficient OSA to makeup the rest room(s), can't remember 'zactly but I thought there was something in there about that. Assuming you don't have a fire code separation between the RR and corridor I think a door grille would work.

 

[cdxx139]

I generally take transfer air form the corridor, and not supply bathrooms directly (unless they are much larger than 2 or 3 toilets, as in your case). [Although I have been in some one person bathrooms lately, which were conditioned and it felt great, so I may change my design process in the future].

If the corridor wall is fire rated, a door grille may not be allowed, so transfer duct (sized for 300 fpm) w fire damper will do the trick.

Option 3 seems like an overkill.



knowledge is power

 

[MECHJAMIECTA]

I appreciate the responses.

11241: You are right as far as the code stating something about the outside air, but the only time it mentions OA being greater than the transfer air taken out is in the section on corridors:

"1. Use of a corridor as a source of makeup air for exhaust systems in rooms that open directly onto such
corridors, including toilet rooms, bathrooms, dressing rooms, smoking lounges and janitor closets, shall be
permitted, provided that each such corridor is directly supplied with outdoor air at a rate greater than the rate
of makeup air taken from the corridor."

In the IBC, they define a corridor as an enclosed space.

The other area that talks about transfer air in general is:

"Except where recirculation from such spaces is prohibited by Table 403.3, air transferred from
occupied spaces is not prohibited from serving as makeup air for required exhaust systems in
such spaces as kitchens, baths, toilet rooms, elevators and smoking lounges. The amount of
transfer air and exhaust air shall be sufficient to provide the flow rates as specified in Sections
403.3 and 403.3.1. The required outdoor air rates specified in Table 403.3 shall be introduced
directly into such spaces or into the occupied spaces from which air is transferred or a
combination of both."

In my opinion, something like my situation where I am transferring air from an elevator lobby that is completely open to a large open office area, I really shouldn't have an issue with transferring the air to the toilets since I am supplying the required amount of OA directly to the lobby/open office and then, instead of all of it being returned to the plenum, some of it is just transferring to an adjacent space.

cdxx139: My toilets actually only have 3 fixtures each, but you seemed to indicate that I must have more than that for the 150CFM exhaust rate. It is my understanding based on ASHRAE 62.1 2007 that I would require 50CFM per water closet or urinal. So in my 3 fixture case (1 urinal, 2 water closets for guys and 3 water closets for girls) it looks like I require 150CFM of exhaust. Let me know if I am reading into that incorrectly please. You have me second-guessing myself now haha

 

[cdxx139]

no I meant 2 to 3 as in your case, meaning I would expect you to have 2 or 3, your good.

knowledge is power

 

[MECHJAMIECTA]

ok great, I see what you meant now. Thanks for the clarification.