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NC-2009 EAc1:Optimize Energy Performance

ABSL-3 Baseline vs. Proposed Fan Energy for RTU

I've recently come across a deblitating problem as it pertains to the energy modeling of an ABSL-3 space. The sensitive, high-containment nature of these spaces predicates an essentially CAV, 100% OA unit coupled with a dedicated exhaust fan system. The particular building I'm analyzing is small enough square footage wise (7,000 SF) to dictate a Type 3-PSZ arrangement, aka unitary air conditioners. The problem that I'm encountering by the intepretation of Appendix G is that I'm unable to credit a realistic exhaust air fan energy into the baseline unitary air conditioner. There are credits allowed for various other system components, i.e. sound traps, fully ducted exhaust, filtration, etc., but this amounts to only a fraction of actual exhaust fan operation. In the end, I'm eating up to half of the amount of year round energy for a 22 BHP exhaust fan. Has anyone been involved with efforts by LEED to rectify this? On a side note, I also noticed that a question was answered regarding lab spaces in reference to "laboratory spaces that exceed 5,000 CFM" are to have "System 5 or 7 centralized units w/ VAV". I interpretted this portion of Appendix G as a reference to any solitary lab space that exceeds 5,000 CFM as opposed to "lab spaces" meaning "lab building". Has there been any clarification issued for this wording because it seems as though it could be interpretted either way. Regardless, although it would seem to help me for my case by allowing me to baseline a combo supply/exhaust fan AHU, it also calls for a 50% turndown, which again, I am unable to do because of the highly sensitive nature of these spaces. What is the take on approaching this problem? We often times design buildings that are similar to these spaces and I would hope a CIR could aid in a reasonable precedent being set. Thank you, all.

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Tue, 02/14/2012 - 15:57

Check all of the credits under Table 6.5.3.1.1B. For example any exhaust treatment in the proposed allows the same pressure drop to be used in the baseline. If this is an issue it needs to be resolved by the ASHRAE 90.1 committee, not LEED. Section G3.1.1(d) - For interpretations of 90.1 we look to the User's Manual and sometimes 90.1-2010. The 2007 User's Manual is not any help. The same provision in 2010 seems to imply all the lab spaces, not just one. Do not assume that the Baseline system will be designed and function properly from an mechanical design perspective. Quite often the baseline system does not make sense from this perspective.

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