Air conditioning restrooms

[tikitime]

What do you do when there is a big difference between your calculated supply air and calculated exhaust air? I know you want to maintain a negative pressure in restrooms, usually 110 to 120% of supply air, but you also don't want too high of a negative pressure.

It seems that you could either install a transfer duct or increase the supply air amount, but neither really appeals to me. Both options would rely on the exhaust fan running continuously so that odors would flow out of the restroom and you wouldn't be freezing people out.

Any ideas?

 

[KenRad]

csaskie,

If this is a public restroom, then I believe that the code says that the fan needs to be running continuously whenever the building is occupied. Either way, the ONLY way to ensure that objectionable odors don't make their way out is to run the fan continuously during occupied hours.

If this restroom is adjacent to a conditioned space, I would install a grille in the door to provide the majority of your makeup air. It's cheap, and it doesn't freeze people out with supply air. You may not get precise temperature control, but people shouldn't be spending a large part of their day in there anyway.

--KenRad

 

[stevenw]

KenRad is correct.
by the time a t-stat see a load in the restroom the people have left and the space over cools.

 

[ChasBean1]

I third the motion. Restrooms are very often draw-through ventilation, no supply. Use a grille on the door or an above-ceiling transfer duct. Just have at least 75 cfm of exhaust air per urinal or crapper and if you have supply, make sure the volume is less than the total exhaust volume.

As KenRad says, run exhaust continuously during occupied hours, unless this is a smaller commercial application where it can be rigged with the light switch. Either way, the exhaust flow volume should meet code (75 cfm of ventilation air per w.c.)...

 

[Vicsidhu]

I usually design my restrooms with draw-through ventilation. Depending on the fixtures intstalled in the restroom, I would put in a door grille or undercut the door. The code calls for 50 cfm of exhaust per fixture (except wash basin/lavatry).

When there is a rrestroom with more than 3-4 fixtures, I would put in supply air 90% of Exhaust needed. Reason being - undercuts, transfer air grilels might not let in enough air.

 

[pmarty]

Where do you find in the code that negative pressurization is required for a restroom? Which code is it?

 

[tikitime]

The Florida Mechanical Code, Uniform Building Code, and International Mechanical Code all call for restrooms to have a certain level of exhaust typically 50 cfm per water closet or 2 cfm per square foot. This is not the same as a "negative pressure" requirement - my mistake, but it is inferred - I think - by the exhaust requirement, lack of equivalent supply air requirement, and good engineering judgement to have odors flow into the restroom and not out.