Hi, We our working in a CS2009 project where ca 20% of the total gross area of the building is existing construction and the rest is new contrustion. Of the existing part, ca 17% is renovated and the rest 3% is unrenovated. As part of the renovation, the cooling system of the new building will cover as well some part of the existing building but the existing cooling system remains as the main one for the existing part. The building envelope, fenestration and lighting remains as it was. According to LEED Reference Guide, an existing building can be modeled using its existing building envelope thermal parameters for the Baseline case. And according to LEED user FAQs here, there is no need for rotating the existing building for the Baseline case. What about the HVAC system, fenestration and lighting system then? How should we model the existing part of the Baseline case? Keep the existing part is it is was for both the Proposed and Baseline cases and claim no savings for this part, or keep the building envelope the same and use ASHRAE for the rest of the requirements (lighting, fenestatrion, HVAC system)?

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Wed, 05/29/2013 - 20:17

The fenestration is covered under the envelop provision in Table G3.1-5 Baseline (f). There is some debate about the HVAC and lighting. In our opinion if there is an existing system which is not being replaced or modified then it should be identical to what exists and the same in both models. You can make a case for this position with the User's Manual and the fundamental premise of the standard that is only covers what you are changing. Others would argue that the Baseline should always be Appendix G unless Appendix G says otherwise (like for the envelop). Whichever method you use the one most likely to be accepted without question would be the one that yields the most conservative savings. If you make the case that your results are conservative they should be accepted.

Therese Malm

WSP Environmental

LEEDuser Basic Member

6 thumbs up

Wed, 05/29/2013 - 21:46

Thanks for the answer Marcus. I was thinking in the same way, that since there is not a clear guidance to follow a case that lead to less savings, that would be of course keeping the existing part identical for both the Proposed and Baseline cases. I guess that a better guidance should be demonstrated though, otherwise one can interprate appendix G in different ways (except to the envelope case).

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Existing renovated and no renovated as part of a CS2009

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