[Bldg-sim] 90.1 appendix G Baseline System interpretation

Fri Aug 26 15:17:44 PDT 2016

I agree with Rut:  extra caution to consider baseline system types #1 and #2 if you are handling a residential vs. non-residential split.  

If this is for LEED also consider whether baseline system types #9 and #10 and the associated new exceptions to G3.1.1 might help clarify your situation (permissible under LEED v3 if you look to the EAp2 documentation workbook).

Also I’d think twice before considering your parking garage for either occupancy type, in this particular context.  Carefully review the definitions for “conditioned floor area” à “gross conditioned floor area” à “space” à “unconditioned space” in that order, and you might agree with me that parking garages are not meant to be counted for “conditioned area.”

Bear in mind, once you have made a successful justification for multiple baseline system types, it doesn’t particularly matter which one was the “predominant” case.  It sounds as though you could claim a residential system type as your predominant occupancy (by area), and still invoke the same exception to apply a non-residential baseline type to the non-residential areas.

It still will come to pass however where it totally makes sense to have multiple baseline system types, but the rigid language permitting a distinction only by 20,000sf of conditioned floor area does not capture these realities.  When this happens, the best advice I can give is to proactively reach out to the AHJ/reviewer/GBCI to explain your concerns and make your case.  I have been both successful and unsuccessful in convincing my past reviewers that the language on the books does not always align with the intent.  It comes down to interpretation, but I’d consider including the following when making your case:

1.       Illustrate/demonstrate how the usage/EUI/operations/ventilation rates/whatever is substantially different

2.       Detail other by-the-book reasons the shoe fits for a different baseline case (i.e. different heating source, residential vs. non-residential).

3.       Show why the interpretation to this exception is important in the end results.  If it’s ultimately a big deal to the final numbers, and you convey the gravity of the decision, it may help motivate an otherwise overworked/tired/ready-for-the-weekend reviewer to sharpen their pencils and give your case due consideration.

4.       It also never hurts to offer a direct meeting/conversation… and to say please and thank you.

Best of luck!

~Nick

Nick Caton, P.E.

  Senior Energy Engineer
  Energy and Sustainability Services
  Schneider Electric

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From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Rut Wattanasak via Bldg-sim
Sent: Friday, August 26, 2016 1:21 PM
To: David BRADLEY
Cc: Building Simulation
Subject: Re: [Bldg-sim] 90.1 appendix G Baseline System interpretation

David,

I was just looking into a very similar scenario this morning in fact. I have one question and some follow-up comments as well. 

You stated that exception G3.1.1a can be applied, does the non-predominant conditioned space total to be at least 20,000 sf?  If so, shouldn't the residential baseline (system #1) be used for all residential units (according to Table G3.1.1A), and not system #3 as you stated? Also in this case, the whole baseline building should be fossil fuel heat source - check LI 10132 that discusses baseline heat source selection, if you're doing this for LEED. 

The next step would be to determine the commercial space baseline, based on the floor areas of the first two levels. You might end up with System #3 or #5 depending on the total area of the commercial space. At least that's how I read "ASHRAE Interpretation IC 90.1-2007-05", you can search the quote to find the document. I'm not sure if there's anything else that supercedes that interpretation since.

To put it simply, if exception a applies, then I'd personally model the upper 3 floors using system #1 and the lower 2 floors with either #3 or #5 based on total commercial space area. That's how I interpreted those two referenced resources. 

Thanks,

On Fri, Aug 26, 2016 at 1:35 PM, David BRADLEY via Bldg-sim <bldg-sim at lists.onebuilding.org> wrote:

Colleagues,

  I am working on a 90.1 Appendix G model of a 5-story mixed-use building. The bottom two floors are commercial spaces, the top 3 floors are residential. There is an underground parking garage as well, which I have considered to be part of the residential use). The building is heated by a combination of gas and electricity; gas use predominates. By floor area the building is predominantly residential. However, about 62% of the building's total energy use is associated with the commercial parts. Because of the way that energy use breaks down I am leaning toward considering the building to be non residential, using System 5 as the baseline and taking exception G3.1.1 a (system 3) for the residential spaces. If anyone has experience with such buildings and could share their thoughts on the validity of my interpretation, I would greatly appreciate it.

kind regards and my thanks in advance

 David

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