Ventilation Exhaust Air under Door?

[jdmz]

For offices, the requirement for OA is very small (10-30 cfm per office). I can't find in the code whether I can supply ventilation to the office using a diffuser and pull it under the door to the corridor where it is exhausted. The system is VRF with dedicated ERV providing ventilation to spaces.

 

[willard3]

This is a code violation. The corridor is an exit during a fire and you don't want to pull smoke from an office and put it in the corridor.

 

[EnergyProfessional]

I often see designs (even in VAV systems) where the corridor is used as a return plenum. I agree with willard3 that it is wrong and violates code. IBC and IMC both independently prohibit egress paths to be used as plenums. You'll need to duct the air from the offices (or use plenum above ceiling).

Ducted VRF units may make your life easier. They also will work better meeting ASHRAE 15 requirements. I'm just saying that since un-ducted ceiling and wall VRF units most likely exceed the allowable refrigerant discharge amount in small offices. For most commercial systems you need ducted units just for that reason and ducted units may help with your original problem.

 

[moideen]

If you have under cut door to toilet and wash room, then the air can be pulled by toilet extract fan. The total fresh air is the quantity of toilet ventilation air +supply air for maintaining positive pressure inside the office.

 

[EnergyProfessional]

My understanding is the OP wants to feed outside air into the office, and not directly return or exhaust it from there. Return or exhaust would go from office through the door to the corridor (and then to some sort of exhaust or return fan). At least this is how I read the OP. And that is illegal.

What moideen describes is drawing air from corridor to a bathroom for exhaust. That is allowed by most codes under certain conditions. YMMV

Note that code uses "Outside Air"(OA) for air from outside and "Exhaust Air"(EA) that has to be exhausted from the building (and can't be re-circulated). Return air comes from a space and can be re-circulated. Supply air to a space from an AHU could be OA, or a mixture of return air (never exhaust air!) and OA. Best to use terms consistent with code so we all know what type of air is being talked about.

 

[jdmz]

EnergyProfessional - Yes, that is what I am asking.

I am reading IMC 2021 and 601.2.1 mentions that the corridor can be used as "return air" plenum if 1 of the 5 conditions are met. However, in this case the air is not "return air", but "exhaust air" so I agree that this is probably illegal and safer just to duct an exhaust into the room.

 

[EnergyProfessional]

You forgot to highlight the important term "above". What they allow under those conditions is the space between the ceiling and floor (or roof structure) ABOVE. Not the floor of the level in question.
So they basically allow the space ABOVE the ceiling to be used a plenum if you meet one of the conditions listed.