Questions about 9.6.2 Additional Interior Lighting Power

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Dear All equest-users,
I have a question about the interpretation of ASHRAE 90.1-2007 9.6.2.
Though it's not about eQuest, I think I could get useful information here because many of you are familiar with 90.1.

9.6.2 presents that the additional lighting power shall not exceed 10.8W/m2. For example if a lift lobby has a general LPD is 10W/sqm and decorative LPD is 14W/sqm.
The additional LPD is exceed 14W/sqm and whether is complied with LEED EA Pr2 and how to do in the ASHRAE energy models?

Following is my understanding:

1. Item a.in 9.6.2 states that: the additional lighting power shall not exceed 10.8 W/sqm, but this is not included in 9.4. A project with additional LPD 14w/sqm could also achieve EA Pr2 & Cr1.

2. For energy models: 1)baseline: the additional LPD should be 10.8W/sqm in this space while 14W/sqm should be 14W/sqm as design.

3. For spaces with additional LPD lower than 10.8W/sqm, both the baseline model and proposed model should be with additional LPD the same with design.

Am I correct?
Thanks for your attentions.

Jie Zhang

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Jenny Zhang's picture
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Hi Jie!

This is certainly a great forum for general 90.1 questions, though you will reach a broader audience I think with the [bldg-sim] mailing list. [bldg-rate] is a less active list that I've used in the past to reach an audience better suited for more technical interpretations, as well.

Note well: italicized phrases in 90.1 have definitions you can refer to for clarification.

1. 9.6.1.d addresses your concern about exceeding the space-by-space LPD. "Trade-offs" are permitted for the space-by-space method, permitting some spaces to exceed the prescribed level (with or without additional lighting power per 9.6.2.a) so long as the building total installed lighting power does not exceed the total allowance. LEED EAp2/EAc1 does not change any of these rules to my understanding.

2. Yes. Proposed model should reflect actual design, and Baseline model should reflect prescribed levels, inclusive of additional lighting power credits for applicable spaces.

3. Interesting question! Your interpretation is probably defensible, but in my opinion overly conservative. I would not limit the prescribed additional 1.0W/ft2 (108.W/m2) to a lesser calculated value to match the installed "decorative LPD." LEED has some extra rules found in the footnotes of the EAp2 modeling spreadsheet along these lines to match exterior non-tradable totals between models, but I haven't encountered any similar restrictions along these lines for interior LPD calculations.

That said, I can't recall using these additional allowances heavily on a submitted LEED project, so perhaps/hopefully someone else can chime in with such experience!

~Nick

Nick-Caton's picture
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Jie, another good forum for that type of question is LEEDuser.

In the spirit of full disclosure, YR&G is the primary author for the forum, but guidance is posted by hundreds of LEED experts from a variety of firms.

Arpan Bakshi, BD+C, PQP

NYCCTgreen's picture
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I believe the answer lies in the text directly part of 9.6.2 before the
subpargraphs on the specific allowances. Note that all lighting that is
installed using the additional allowance must be on automatic controls to
turn off during non-business hours. Right after that, I find this to be
the best answer the what the additional lighting allowance is good for:
"This additional power shall be used only for the specified luminaires and
shall not be used for any other purpose."

Just like the site lighting allowance, this is a non-tradable allowance
only good for the space the lighting is installed in and even more
specifically, only for the lighting that meets the definition. This means
you can't use the additional allowance to make up for an overage in this
space or an overage in the total results of the space-by-space method
caused by non-qualifying fixtures. This has been a LEED review comment in
the past as well.

The math is also explained in the 90.1-2007 compliance forms. They are
optional for LEED purposes, but worth a review, especially for complicated
lighting calculations. They are attached for reference and can be found on
the ASHRAE website.

Jeremy R. Poling, PE, LEED AP+BDC

Jeremy Poling3's picture
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I stand corrected!

Funny, I looked for this language in my print copy of the user's manual before responding, and the same section is worded differently in my copy (perhaps an older printing)... but what you've attached makes this point much more clearly:

"If the installed power is smaller than the allowance, the surplus power may not be allocated to another portion of the building. This type of allowance is often called a "use-it-or-lose-it" allowance."

I think this language specifically calling out "surplus power" is as direct as anything else I've come across.

~Nick

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