Our Campus Application CS mixed use/office project uses a common HVAC (district energy) system. The Owner's program required 100 s.f. per ton for the retail areas and 300 s.f. per ton for offices. Our problem is that the energy model outputs roughly 300 s.f. per ton for retail and 400-500 s.f. per ton for office. Therefore our numbers for energy efficiency do not look too good ,especially for the quality equipment we have ordered. The designs use two chillers. And, it appears that some of the time only one chiller will be operating to meet loads. Our question is: Is there some way to factor the discrepancy? Is there an exception that we are missing?

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Marcus Sheffer

LEED Fellow

7group / Energy Opportunities

LEEDuser Expert

4454 thumbs up

Wed, 12/12/2012 - 21:57

Love it - a modeling issue instead of an Appendix G question!! Wow right-sizing should be a fundamental green building principle. So it sounds like your proposed equipment is grossly over-sized by a factor of 1.5 to 3! The baseline equipment can only be over-sized by 25% and 15%. So I think you are stuck with that discrepancy. You have to model what you have designed, no exceptions. Are you following the DES guidance for the baseline? Might want to check the equipment curves to make sure they are accurate. Your chiller which does not operate should not affect the energy use so in effect the cooling plant size is cut in half right? Is it a bigger problem on the heating or cooling side? Have you tried to isolate this issue (i.e. eliminate other energy saving strategies) to see what it's effect really is vs your other energy saving strategies?

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