Barometric Relief Idea

[xac33ncsu]

Currently working on laying out a 1 story office building with a mezzanine. The office building is to be built within an existing warehouse with 2 sides facing the warehouse space. 1st floor return will be through a plenum space while mezzanine return will be ducted. In order to control building over pressurization im considering just ducting from lay-in grilles in the ceiling of each space to barometric relief dampers, set to open @ 0.05" w.g., placed on the warehouse side walls of the office space.

Was wondering if anyone had tried anything similar and their results, or just any general critiques of the situation. Thanks in advance.

Zack

[hvacpope]

over pressurization, why ? design flaw? if its just a bit, I wouldn worry about.

[xac33ncsu]

hvacpope, concerned about overpress. since 25% of the supply air flow will be outside air brought in by make-up air fans via return duct plenum and only other means of exhaust are small bathroom rans.

[hvacpope]

Without knowing more about the particular building condition (tight or leaky structure, geographical location etc) is hard to tell whether the 25% unbalance between intake and return will result on excessive net positive pressure, in the cooling season is desirable to be on the positive side 0.05wg to 0.10, if the expected positive pressure ranges whiting those numbers I wouldn’t worry about, I don’t like gravity relief dampers.

[xac33ncsu]

hvacpope, I don't care for gravity relief dampers either in most applications where they exhaust into an outdoor space. However in this application their should be zero interference from wind on their performance since they will exhaust into a warehouse space.

Also the 25% OA flow concerns me since the office space will have very few windows and only 1 door leading to the building exterior. The warehouse is of concrete panel construction with well sealed seems. Thus not many areas for the air to leak out. Also Id be concerned with building pressures much greater than 0.05" w.g, since the most frequently used doors would be at the end of narrow halways leading to the warehouse space, wouldn't want the air quickly channeling through these hallways.

How do you typically predict natural leakage through cracks, doors and windows?

[hvacpope]

Originally posted by xac33ncsu


How do you typically predict natural leakage through cracks, doors and windows?

you dont, wild guess,good luck and plan"B" in the back pocket just in case.... :D

[just_opinion]

xac33ncsu


Seems to me you got everything under control.

[mardoman]

Packaged RTU with barometric relief dampner purchased as an accessory would be an idea.

[ralphtheplumber]

Originally posted by xac33ncsu
1st floor return will be through a plenum space while mezzanine return will be ducted. In order to control building over pressurization im considering just ducting from lay-in grilles in the ceiling of each space to barometric relief dampers, set to open @ 0.05" w.g., placed on the warehouse side walls of the office space.
Why not just install the relief damper somewhere in the plenum? If you're using it for return, it sort of has to be open to the office spaces.


Originally posted by xac33ncsu
25% of the supply air flow will be outside air brought in by make-up air fans via return duct plenum .
I'm not really crazy about this idea. If you pump a bunch of humid oa into a cool space between floors, you might have a big mess on your hands. Condition it, then pump it in.

Is there some reason you're not using some kind of packaged unit with an economizer built in?

[xac33ncsu]

Ralph, you're right I could just install the relief damper in the plenum. But considering the fact that the plenum will be at slightly lower pressure than the office space, due to return grille pressure drops, and the fact that the exhaust air will empty into an occupied area I felt making a short duct run to directly duct the relief air from the office space to the warehouse was justified.

Also I think i wasnt took clear about brining in the MUA, the outside air will be brought in by a rooftop fan which will be ducted to a return sheet metal plenum built over the return opening of the air handler, it won't be dumped into the office plenum space.

I did consider a packaged roof top but the architect had allowed us no good area for a duct chase from floor to floor, and the first floor is split between two areas with very different loads. Thus I felt like split systems for each zone was a better bet.

Thanks for all the input.