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NC-2009 EAp2:Minimum Energy Performance

Baseline PTAC sizing

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April Ambrose
Business Development Manager
Entegrity
LEEDuser Basic Member
154 thumbs up

I have a residential facility seeking LEED v2009 certification with small room loads (approx 2,000 BTU/hr). My understanding of ASHRAE 90.1-2007 is that these spaces need to be modeled with PTACs oversized by 15% (2,300 BTU/ hr). The PTACs scheduled are much larger (approx 8,000 BTU/hr) than the load as a small enough PTAC in this particular line is not available. I've heard a rumor that there is guidance that makes it permissible to model the baseline units with a capacity larger than the 15% oversized specification if such a unit is unavailable. So in this case, an 8,000 BTU/hr unit can be used instead of a 2,300 BTU/hr unit in the baseline. I'm trying to put an end to this rumor with a label as fact or fiction. Can someone help me?

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
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Tue, 03/27/2012 - 17:11

Fiction. The only allowance for going over the 15% is outlined in G3.1.2.2 and is related to reducing the unmet load hours in the Baseline if you are over the limits. The Baseline model's HVAC system design does not need to get designed or installed. It simply gets modeled according to Appendix G. So the availability of PTACs in a certain size range is not applicable to the situation.

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