IBC and ventilation

[DouginMB]

I am facing a frustrating situation and would like some insight from some other folks. Three years ago I designed an HVAC system for a church school. It was a two phase job: classrooms and gymnasium/cafeteria. The first phase was built immediately and the second was deferred until more funds were raised. Back then we were designing under the Southern Building Code (SBC). The SBC referred to ASHRAE for ventilation rates. Under ASHRAE I could reduce ventilation amounts based on time of occupancy. This in turn allowed me to lower the cooling tonnage.

Now the church wants to move forward with the second phase. Since we have switched to the International Code, the architect asked me to research how the job will be impacted by the new code. When i reviewed the ventilation requirements, I found that IBC doesn't reference ASHRAE at all. Nor does it allow for the reduced ventilation for transient occupancy. I found that the cooling load will approximately double - just for the ventilation load. As the original design was the basis for the budget, I don't see how the church can affrod the added tonnage.

Has anyone else run into this problem? Why doens't IBC leave the ventilation requirements up to ASHRAE guidelines?Any advice would be appreciated.

 

[ChasBean1]

It's likely that only life safety issues will be policed by the local authority having jurisdiction - egress, sprinkler application/coverage, exit signage, boilers, fuel, etc. It sounds like to you have strong argument to maintain the original HVAC design intent. Who's stopping you? If you have the dated, original design development drawings that at least roughly depict Phase 2 systems I would think any changes in HVAC ventilation rates could be grandfathered.

What does God say about all this?

What are some of your parameters (unit size, sq. footage, etc.)?

 

[DouginMB]

The "multi-purpose" room floor area is 100'x70'. Originally the architect said to figure on 466 people in assembly occupancy. I figured 15cfm/per and took the full 50% reduction allowed by ASHRAE, giving me 3500 cfm OA. This made the total cooling load about 40 tons. I used two 20 ton split heat pumps to conditon the space and provided full economizer louvers (8000 cfm total).

Under the IBC I would have to design for the full 15cfm/person. This brings the cooling load to 75 tons.

I talked to the architect this morning and he brought up the point you did in regards to life safety. The entire job was reviewed by the city when it was originally designed and approved. We're hanging our hat on that and hope it gets passed. But it will have to get reviewed again since the permit for the multipurpose room expired.

 

[ChasBean1]

What is the 466 people based on? The ASHRAE estimate for classrooms is 50/1,000 ft2 - so about 350 total. Do you realistically think 466 people will be there on a regular basis? You're over 1 cfm per ft2 right now for a space that I would guess will be extremely diverse in occupancy. Oversizing a DX system can also be a killer with respect to humidity problems. I believe in adherence to standards, but for this application (with a typical church-type hall in mind), ~.8 cfm square foot with about 40% minimum outside air, and economizer should suffice, with timed and occupancy setbacks.
Good luck w/this project, -CB

 

[DouginMB]

The 466 number was provided by the architect (not sure how he came up with it.) And no, I don't feel that 466 people will be there on a regular basis; but that's the number the code official will use when he adds up ventilation airflow.

The heat pumps are each two-stage, so that helps.

What I'll probably end up doing is the show the ability to bring in the code minimum of 7000 and provide a CO2 sensor to modulate the outside air.

 

[quark]

What does God say about all this?. That was the brightest expression I have read ever.Great CB.

Next time perhaps God will be kept out of his home for safety reasons and statutory rules.

 

[ChasBean1]

DouginMB, the CO2 idea I think is good for this application. If your code official has time to add up airflows, tax money could be saved by reducing your local government to a core group that focuses on life safety (sarcasm - sorry).

(Quark, had to get that in! -my first response to a church post..)