Air movement in egress elements

[PatBethea]

Can somebody help me with some code interpretation? I'm designing the mechanical systems for a daycare facility in Florida. There is a corridor that runs east-west through the middle of the building (100 feet long). The corridor opens up on each end to a lobby with a lot of glass. I've calculated the load in the lobbies and corridor to be just under 1.5 tons. To meet the load, I'm supplying 680 cfm. I planned on removing a large portion (~600 cfm) through 2 equally spaced return grilles and ductwork located in the corridor. The architect I'm working for says that RA take-offs in the corridor violate the FL Building Code. The code states, "Exit access corridors shall not serve as supply, return, exhaust, relief or ventilation air ducts." Simply stated, I have taken that to mean that you can't take out of a corridor more than you put in. The architect is saying that you can't take anything out directly (regardless of what you put in).

Opinions?

 

[PatBethea]

Rephrase - In a corridor, at what point does it go from circulating air within a conditioned space to using said space as a 'duct'?

 

[MintJulep]

The code provides a list of five items, comma separated, except for the last item separated by "or". This implies that each of the items in the list must also be "or"s, so each must be considered one at a time.

Supply duct: a duct that supplies conditioned air to an occupied space. Is your corridor the source of conditioned air to any other space?

Return duct: A duct that removes air from a conditioned space and transports it back to a piece of HVAC equipment. Does your corridor connect directly to some equipment?

Exhaust duct: A duct that transports air to the outside. Does your corridor open to the outside?

And so on...

The architect's interpretation can't be correct. If you can't take any air out of the corridor, then the air that you put in must be going someplace, hence it would be a supply duct.

 

[redgdon]

Hi,

Would agree with you there MintJulep.

I would ask your architect if all of the internal doors which lead off of this corridor are air tight, since natural leakage around the door would then imply that the corridor is a supply duct.

I’ve only just moved to North America (Canada), but I’ve been on this forum for some time. This is merely a question and is in no way meant to offend anybody.

One thing I’ve never understood is why, rather than asking for someone’s opinion on here, don’t you ask the person who is going to give you the completion certificate for the building on matter such as this, preferably in writing.

That way you have a definitive answer and not the opinion of someone who may be from the other side of the world and has never set foot in the US.

 

[PatBethea]

Can't speak for everyone. I made my case with the architect and I know it will pass muster. I was interested in opinions, though.

I think it is an interesting question, but I may be alone in that. When can a corridor be considered a duct? Consider this hypothetical situation - a long corridor (150' long). On one end of the corridor a diffuser supplies 1000 cfm. On the other end, a return grille pulls 1000 cfm back out. I think it could be argued, in this case, that the corridor was acting as a duct. When does circulating air through a corridor cross the line and turn into using the corridor as a duct? How is it quantified? Or, does it fall into the gray area of "engineering experience and judgement"? I lean towards the latter, but am interested to hear what others think.

 

[RossABQ]

As long as the return air for the corridor doesn't mix with other return air, I don't see a problem. But if the SA/RA systems are common to other areas, I see why the Archie is concerned. The concept is that an "exit passageway" or "egress corridor" is an area that is separated from the adjoining occupancies so that it is not affected by a fire in another area (from an HVAC perspective).

I've never done a daycare facility, but I'd assume it's got some requirements that go beyond the typical "B" occupancy. I also don't know what BOCA says specifically about this type of facility. I would goo over it with the AHJ as suggested.

 

[atlas06]

See IMC section 602 of IMC 2006, duct systems.
One cannot use a room as a return air plenum.

The architect is right.

 

[PatBethea]

RossABQ,

You said, As long as the return air for the corridor doesn't mix with other return air, I don't see a problem. But if the SA/RA systems are common to other areas, I see why the Archie is concerned.

If I interpret your statement correctly, you and I are on the same page in that I'm only taking air out of the corridor that I'm putting in (minus the minimal infiltration and mixing when doors are opened into the corridor). If on the other hand you mean to say that the RA coming out of the corridor should not mix with other RA anywhere in the system, then I'm in trouble. I.e. this latter interpretation would necessitate a separate system serving only the corridor and lobby areas. Will you clarify your position?

 

[PatBethea]

To clarify the design, there are three split system heat pumps and an energy wheel being used (I was limited to single phase equipment). One system serves the nurseries. One serves the classrooms for the older kids. The third system is serving the common areas - the corridor, an office, the kitchen, staff lounge, and a computer room. The return airs for the various systems do not mix (in any meaningful way).

 

[redgdon]

From what I've read above I would think that if the return air ducts from the rooms are branched into the return air duct in the corridor, then provided you install the appropreate fire dampers where fire barriers are breached there wouldn't be a problem.

If however the return air ducts from the rooms spilled air into the corridor before being pulled through the grille to exhaust then that would be a problem.

I don't understand why it would be a problem, again if the ducts were installed with the correct fire dampers, but there is probably something I'm missing.

 

[PatBethea]

In this case, an exit door is located in each classroom (and nursery room). This allows the corridor walls to be fire-rated for just 1-hour. One-hour rated walls do not require fire dampers at penetrations.

 

[atlas06]

One hour rated walls require fire dampers per IBC. NFPA does not not require fire dampers, but NFPA 90A is NOT a code. In NFPA, only transfer ducts require fire dampers. Unless your local code say otherwise. What you need is to tell your architect that he does not need rated walls if you building is fully sprinklered.

Some jurisdictions allow penetrations no larger than 96 square inches without fire dampers through one-hour rated corridors.

The RA plenum thing is that if you transfer air form one room to another room before returning it to the system, then your are in violation of the code, i.e you are using the room as RA plenum, not the ceiling.

It is OK to transfer the air from ceiling to ceiling using fire dampers and then return the air from the corridor ceiling, but NOT from the corridor itself.

If you serve the corridor and return that supplied air from the corridor, then you are OK.

Hope it helps, good luck.

 

[PatBethea]

Atlas,

You are correct. Reading what I last wrote, I see that I did not lay it out clearly or properly. The walls are rated at one-hour. Due to the fact that the classrooms have exterior doors, the IBC does not require a fire-rating (section 1016, I believe). So, the one-hour rating is "above-and-beyond" the requirements of the IBC. With the IBC requirements satisfied, NFPA 90 is the next thing to comply with and it says fire dampers are not needed.