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Requirement for Outdoor Air Dispute

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PatBethea

PatBethea

Mechanical
Nov 16, 2006
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I completed the HVAC design for a church in my area a while back. Currently there is a disagreement over the neccessity for outdoor (ventilation) air. I'm in FL and the current Florida code is based upon the 2003 IMC.

Section 403.3 of the 2004 Florida Mechanical Code states, “Ventilation systems for other than Group R-3 (one- and two-family dwellings), shall be designed to have the capacity to supply the minimum outdoor airflow rate determined in accordance with Table 403.3 based on the occupancy of the space and the occupant load or other parameter as stated therein. The occupant load utilized for design of the ventilation system shall not be less than the number determined from the estimated maximum occupant load rate indicated in Table 403.3. Ventilation rates for occupancies not represented in Table 403.3 shall be determined by an approved engineering analysis. . .”

The mechanical contractor on this project has convinced the owner that because Table 403.3 does not explicity list churches, they are exempt from vetilation air requirements. I pointed out to the owner that the table does not list everything and that the paragraph states "Ventilation rates for occupancies not represented in Table 403.3 shall be determined by an approved engineering analysis" which I did. The owner countered that some county official has sided with the contractor in this case.

I believe that counties and municipalities can have their own requirements independent of the state, but this doesn't seem right at all. I have asked the owner to secure a letter from the county office which states that ventilation air is not required. If they are able to get this letter, I will then ask the owner for a letter stating that they have asked me to not include ventilation air in the design and recognize the health risks associated with this decision. At that point, I suppose I will remove the outside air and resize the equipment. Can anybody offer any advice on this situation?

Let me add that I have emailed the state Building Codes and Standards Office looking for their input as well.
 
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Wow... Hard to believe people could take such a radical stand on ventilation. Of all the places ventilation would be desired an assembly type occupancy would be one of the most important.
Couple thoughts... What is driving the contractor and owner's to NOT provide ventilation? Is their motivation just the operating cost? If so, you could tell them they can shut the OA dampers down after install if they want.

Another angle would be to inform them ASHRAE is the leading HVACR industry organization that writes the majority of the standards the codes adopt. The "Applications" handbook Chapter 4 "Places of Assembly" states that OA for Places of Assembly should be provided per ASHRAE 62. ASHRAE 62 doesn't specifically list churches either BUT! It does say in the bottom of Table 6.1 (General Note #6)

Unlisted Occupancies: If the occupancy category for a proposed space or zone is not listed, the requirements for the listed occupancy category that is most similar in terms of occupant density, activities, and building construction shall be used."

This clearly states that at least SOME kind of ventilation is required.
Hope that helps,
RDmac
 
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Does the church have operable window? If so, the contractor may be hanging his hat on this exception of the code - assuming the ratio of openings to floor area meets code requirements. I've only used this exception for condominium projects, never tried it on a commercial installation as I don't think it is appropriate. I would have done the same as AbbyN and classified it as Assembly.

I was taken aback by the code officials leaning this way - especially in the State of Florida. I do tons of work there and if anything, they interpret the codes more stringent than others.

Andy W.
 
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The Engineer has design responsibility and not the contractor/owner/building inspector.

It is common knowledge, good practice and a code requirement that assembly spaces be ventilated.

If there's controversy, you're the man......
 
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Thanks guys. I used the ASHRAE 62.1 option and classified the spaces correspondingly. But, yes, if I were to stick to the IMC's table, I would probably use "Theatres - Auditorium" for the sancuary.

Throughout the building, there are a few operable windows, but not nearly enough to do away with mechanical ventilation.

Andy (Wareagle) - I'm in the rural panhandle - things are typically alot less stringent up here than in the peninsula. ALOT less. But I think this is taking things too far.
 
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Sounds to me like this scenario -
The owner has been told that this will save money and won't make any difference, by the mech contractor.
The owner twists/makes up the story about the code official and only hears what he wants to hear.

Tell the owner that if he pre-cools his Mary and leaves her near a window, not only will she cry a few tears, she will sweat a baptismal font.

 
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you are not going to ventilate a space in humid florida with windows
Click to expand...

I challenge you to find a condominium in FLA that is not ventilated with windows.

No, I Would Never recommend to a commercial client to ventilate in this manner. I'm just making a speculation on the contractor's thought pattern.

PatBethea - I've also done a far amount work in the panhandle - mostly the Destin & P.C. area.

Andy W.
 
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In case anyone wondered, the state agreed with me (and all of you) that churches are not exempt from ventilation requirements. Further they confirmed my belief that local jurisdictions can make building laws/rules more restrictive than the code, but they can not (legally) enact looser requirements.

I passed all of this along to my clinet who indicated they would be in touch after talking to the local officials. That was three or four days ago. Hopefully the issue is closed.
 
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The temptation to ignore ventilation is powered by the prospect of reducing cooling capacity, shrinking the mechanical contractor's equipment cost. It sounds like there could be some politics involved between the church administration and the contractor. Someone once said that being involved in your own church construction project is the unpardonable sin.

Outdoor air ventilation cooling load can be mitigated by using air to air heat exchangers. Also your utility may have off peak ice storage or chilled water storage rebates.

You may need to look at the block load for that short time period when the main sanctuary is occupied, try running the load calcs and allow some deviations from ideal conditions. For a few hours/week this is not eschatological. Also try a pre occupancy cooldown cycle with next to zero outside air. Most dampers leak 5% even when shut. You can measure the CO2 or O2 with a sensor and get by with no extra OA.

Another strategy for churches is to use chilled water, size the sanctuary and fellowship hall air handlers for their respective loads, however the chiller that serves both AHU's will see a load that is less than the sum, because the occupants don't occupy both spaces simultaneously.

There are some legitimate means of reducing the tonnage on a church HVAC system. Eliminating OA ventilation is not one of them. SARs, tuberculosis, influenza B, other airborne infectious diseases make an expenditure for ventilation very necessary.
 
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I would be surprised if an assembly occupancy in Florida, when ventialted to code, would not require reheat or supplimental dehumidification.

Especially when ventilated to an excessive code which anything based on the current ICC code set would be.

Perhaps it is not a Pentacostal Church, those are always as tough as doing a gym :)



Take the "V" out of HVAC and you are left with a HAC(k) job.
 
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could easily end up with an SHR less than 0.6 hard to deal with using standard equipmemnt.

Maybe an ERV preconditions and then feeds the AC with air

Take the "V" out of HVAC and you are left with a HAC(k) job.
 
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PowerPup hit it on the head. I see church after church that was designed and installed per code, but the owner then closes at OA damper (or at least sets it to a minimum). The motivation is operating cost. Since assembly times are limited to a few hours at best followed by a series of doors being opened, I have never heard of any CO2 or other IAQ problems.
 
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As noted in another response, this sounds like a perfect application for demand controlled ventilation and/or an energy recovery ventilator if the budget allows.

You might tell the Church that if the CO2 levels are not controlled, the entire congregation may get sleepy during the service. Of course, that could be caused by CO2 or a boring sermon!!
 
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