Space by Space LPD requirements for 90.1 modeling

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Dear All,

Recently i have received a comment from design team peer reviewer on
applicability of space by space lighting power density for 90.1 appendix G
compliance modeling for manufacturing facility and given as follows:

*"Space by Space" method can only be used if the actual proposed design
meets the space by space requirements for each included space type.*

I found similar discussion happened on *23/5/12- Building Area Method
90.1 *(great
insight from Nick) but didn't noticed any such requirements like mentioned
above. I am clueless on this and can't even verify if this is a valid

I would appreciate if someone could guide me on this.

Thanks in advance,


Javed Iqbal, LEED AP, CEA
Sr. Energy Analyst

javed's picture
Joined: 2011-04-11
Reputation: 0

Dear Javid,

You are right to question this review comment. Interior lighting is tradable
when using energy simulations not the prescriptive 90.1 requirements. I
suggest you send an inquiry to the review team requesting confirmation of
the requirement and further explanation. You should explain your
understanding of the Appendix G requirements and briefly explain how the
lighting is modeled in the baseline and proposed case. Clarifying the issue
before you make any changes to the model and resubmit could save a lot of
headache (and time). Good luck!

Cam Fitzgerald

Energy Opportunities/a 7group company

1200 E Camping Area Rd, Wellsville, PA 17365

Cam Fitzgerald's picture
Joined: 2011-09-30
Reputation: 0

historically this is not correct. see the 90.1 user's manual example
9-J, page 9-17 of the 2007 version (similar location in 2004, i don't
have 2010 or 2013 handy to check page number). the total allowance for
the building is 1.22 w/sf ... compare this to the 1.17 w/sf determined
for the same building example 9-H (building area method).

also on page 9-16, 1st paragraph, "rather than looking up the lighting
power allowance for the entire building, the lighting power allowance is
determined separately for each space within the building and then summed."

so unless you've got multiple occupancy space types (core/shell/tenants)
where you'd want to do trade-offs (you can't trade off between tenant
spaces using building area method & tenant spaces using space-by-space

unless it's changed in 2010/2013 of course ... or there're ashrae
interpretations otherwise but this is how it's been traditionally
enforced by usgbc/local authorities where i'm at.

that being said the last sentence in paragraph 1 of page 9-16 reads
"even though the designer must develop lighting that works in each
space, it may be simpler for code compliance purposes to use the
building area method." so this might be what the reviewer is reading.

Patrick J. O'Leary, Jr.'s picture
Joined: 2011-09-30
Reputation: 0