Baseline System For Semi-Heated Space for LEED

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Hi,

I have a space that meets the requirements of a "semi-heated" space.
Question is - how do I model the baseline system? I have found no
information in AppG, LEED, or any other resources.

Thanks,

--
Karen

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Karen,

A "semi-heated" space is not a "conditioned space" per ASHRAE 90.1. For a LEED/Appendix G model, the baseline system type is based on conditioned floor area, and the requirement for modeling heating and cooling applies to conditioned spaces only. You could model the space as unconditioned in the baseline and proposed models, and capture the semi-heating as neutral process energy.

Alternatively, you could use System Type 9 or 10 from ASHRAE 90.1-2010. Systems 9 and 10 apply to "thermal zones designed with heating only systems in the proposed design, serving storage rooms, stairwells, vestibules, electrical/mechanical rooms, and restrooms not exhausting or transferring air from mechanically cooled thermal zones in the proposed design" per G3.1.1 Exception e. The ASHRAE definition for "zone, HVAC" is "a space or group of spaces...", not "a conditioned space...". So I think you could apply System 9 or 10 to a semi-heated space, if the space type is one of those listed.

Either of these options should be easy enough to change/undo if a LEED reviewer disagrees with your approach.

Regards,
Bill

[Senior Energy Engineer 28Jun2012]

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Thanks Bill. I didn't realize 90.1-2010 gave a little more info on this
topic. The space is actually pretty large, and doesn't fall under one of
the types you listed in ASHRAE 90.1-2010. It's a maintenance/garage area
and has less than the required btu/sf for space heating (but some
additional capacity to to temper ventilation air). There is additional
capacity to make up for outdoor ventilation air, so not modeling the energy
use would be a mistake, I think. What do you think about modeling the HVAC
systems for the spaces identically in the baseline and proposed?

--
Karen

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Joined: 2011-09-30
Reputation: 200

Karen,

I'm not convinced it makes sense to break out the heating capacity into ventilation and non-ventilation. I would include the total heating capacity of all units serving the garage to determine if it falls under the 3.4 Btu/h-ft2 threshold per the semiheated space definition. If you still think it is a semiheated space then I think you could model the baseline and proposed with identical HVAC systems and consider it process energy. Garage ventilation should probably be considered process energy either way, as it is not just for meeting minimum occupant-based ventilation. If it ends up being a conditioned space, you should be able to apply a System 3 or 4 to the baseline per the other G3.1.1 exceptions (different process loads or schedules, code-required minimum circulation rates, etc.).

Bill

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Karen and Bill,

One interesting caveat to this discussion is that ASHRAE definitions for
conditioned, unconditioned, and semi-heated spaces all apply only to
enclosed spaces, but definition of unconditional space included in 90.1
Section 3 suggests that garages should not be considered enclosed:

unconditioned space: an enclosed space within a building

that is not a conditioned space or a semiheated space.

Crawlspaces, attics, and parking garages with natural or

mechanical ventilation are not considered enclosed spaces.

I like Karen's idea of modeling the same system type in the baseline and
proposed model for the garage. I would also look into using exceptional
calculations to claim credit for improvement in equipment efficiency, demand
control ventilation, and fan power relative to allowances in Table
6.5.3.1.1A/B.

Maria

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