I am running into a conundrum for a CS warehouse that will have no HVAC systems installed upon completion of the CS project. The only energy savings to document are for the envelope and lights. The building will have envelope values that exceed the nonresidential requirements of ASHRAE 90.1-2007.
When I calculate the proposed model on its own, the warehouse Btuh/SF would qualify it as semiheated, which would mean I could use the semiheated envelope values from 90.1-2007 in the baseline. However, when I enter those worse envelope values in the baseline model, the calculated capacity of the baseline model would qualify it as heated, which in itself wouldn’t be an issue except for the fact that (per review comments) the CFM in the proposed model must be equal to the baseline. Since deltaT is also the same for the proposed and baseline, overriding the proposed CFM to match baseline will result in the same capacity, therefore the proposed model would also be classified as heated and I can no longer use the semiheated envelope values.
According to the review the only way I can have a lower CFM in the proposed model is to indicate a CFM/fan power limitation in the lease agreement, which the owner doesn’t want to do.
So long story short, it seems like I’m stuck in a code loop. When I start out, my load calculation indicates the warehouse is semiheated. When I enter the semiheated envelope values in the baseline model, there are a series of requirements that make me adjust the proposed model so that it would then be considered heated. So my question is, which envelope values should I use in the baseline? Semiheated or heated?
I would greatly appreciate any advice you might have.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
May 8, 2015 - 4:41 pm
The determination of conditioned or semi-conditioned is based on the Proposed Case, not the Baseline. If the Proposed is semi-heated that use those insulation parameters in the Baseline.
If no HVAC has been designed then the Proposed uses the same system as the Baseline but the supply air cfm does not need to be identical in both models. In fact that and the capacities of the system would be auto-sized in both cases and should be different. The outside air cfm is supposed to be identical. Assuming this would be a heated only space use system 9 or 10 from 90.1-2010 via Adendum dn.
Tony Schafer
24 thumbs up
May 8, 2015 - 5:35 pm
Thanks Marcus - very helpful. I agree 100% with what you're saying about the supply air being autosized in both the baseline and proposed models and that it would be different in each. In fact that is how I modeled it originally. However, I got a review comment back saying very specifically that the fan volume and power must be modeled identically between the proposed and baseline cases. They said the only way they can be different is if I have a fan CFM/power limitation in the lease agreement, but the owner doesn’t want to do that.
I wasn’t able to find anything in 90.1-2007 to substantiate the need to have the fan CFM/power identical for both cases. Table G3.1 does mention that where no HVAC systems exist they need to be identical, but I always took that to mean the system types have to be identical and the actual capacities, CFM, fan power, etc would be autosized based on the loads. Should I just report autosized fan CFM/power in the proposed and say they were autosized based on the loads? Should I question the validity of the comment in my response?
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
May 11, 2015 - 10:07 am
Unless all of the parameters in both models are identical (envelop and lighting) you should have different auto-sizing outcomes. Assuming that is not the case then the reviewer is wrong (it happens to all of us).
You model the systems with the identical methodology, not necessarily the same values.
Rather than just question the comment in the response, I would submit a project team inquiry via the web site - http://www.gbci.org/contact - and make your case there before you submit all of your responses.