Lighting Power Density

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Good Afternoon All,

Hopefully this is a simple question. I recently got comments back from LEED
questioning the lighting power density for some of the areas in my Appendix
G model. The comments asked me to provide floor plans for the areas in
question. I am using the space by space method which says area should be
calculated from the center of partition walls. For the areas in question
some of the walls have a chase for plumbing, some have structural columns,
etc. My question is this, in my model I did not create separate zones are
anything for this non habitable area, I just have an interior wall. Should
the LPD be calculated to the center of the chase? To the center of the
column? The center of the wall surrounding the chase? None of these will
make a significant impact on my savings, however, I don't want the reviewer
to reject my number saying something such as "your floor plan included the
chase when it should have stopped at the center of the wall surrounding the
chase"

Thanks for any opinions or experience getting something like this passed by
LEED.

____________________________
Michael Shields

M. Shields's picture
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Joined: 2011-09-30
Reputation: 0

Hey Michael,

For perspective, if that's the only thing your reviewer can find to pick
on, then it's a sign you're doing well overall ;).

LPD calcs for prescriptive compliance strictly speaking should go to the
"center of the partition wall" (Re: section 9.6). I would generally
draw a line through the center of a typical tight plumbing chase and
call the chase space part of the partition.

If it is the sort of deep accessible chase with a door that you are
lighting with separate fixtures (or if I were really concerned about a
nitpicky reviewer) then I'd call it its own space (electrical/mechanical
- 1.5 W/SF, if it is a lit space) and draw centerlines in the
surrounding walls.

~Nick

NICK CATON, E.I.T.

Nick-Caton's picture
Offline
Joined: 2011-09-30
Reputation: 605

Reading between the lines a bit, I believe the reviewer is probably more
worried about using proposed lighting kW for the model while the baseline is
using LPD that include areas of shafts or chases which could penalize the
baseline unfairly. (Maybe airflow too, although you don?t mention this.)

Clearly it is intended by 90.1 to be the center of the partition between two
occupied spaces, however I guess the question here is whether the definition
of the surface around the chase or column is a partion or not?so personally
I?d use the center of that enclosing surface around the shaft/chase/column.
There seems to be some concern by the reviewer about a noticeable area
over-contributing to the baseline energy usage, so I wouldn?t use the option
for ?center of the chase? or ?center of the column? as a possibility if you
agree that this is the concern.

David

*
*

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

*
*

*From:* equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] *On Behalf Of *M. Shields
*Sent:* Thursday, May 19, 2011 4:19 PM
*To:* equest-users at lists.onebuilding.org
*Subject:* [Equest-users] Lighting Power Density

Good Afternoon All,

Hopefully this is a simple question. I recently got comments back from LEED
questioning the lighting power density for some of the areas in my Appendix
G model. The comments asked me to provide floor plans for the areas in
question. I am using the space by space method which says area should be
calculated from the center of partition walls. For the areas in question
some of the walls have a chase for plumbing, some have structural columns,
etc. My question is this, in my model I did not create separate zones are
anything for this non habitable area, I just have an interior wall. Should
the LPD be calculated to the center of the chase? To the center of the
column? The center of the wall surrounding the chase? None of these will
make a significant impact on my savings, however, I don?t want the reviewer
to reject my number saying something such as ?your floor plan included the
chase when it should have stopped at the center of the wall surrounding the
chase?

Thanks for any opinions or experience getting something like this passed by
LEED.

____________________________
Michael Shields

David S Eldridge's picture
Joined: 2011-09-30
Reputation: 2000

I wish this was my only concern. My reviewer also interpreted my wall to
window ratio and a percentage and thought it the value was questionable.

The issue is that if I don't include the chase in the LPD calc then it will
over estimate the lighting because that area is included in the area for the
model. Also I am concerned that they will say "well zone x is 100 sqft
where your LPD calculation says that area is only 98 sqft". I am fine with
overestimating it, I just wondered if anyone has experience about how strict
the reviewer might be for this.

Thanks for the feedback.

M. Shields's picture
Offline
Joined: 2011-09-30
Reputation: 0

Overestimated proposed design will result only if the proposed case also
used a lighting power density. But if the proposed model is using design
values for fixtures, then the proposed airflows and lighting power (not
density) are based on the net occupied area. Therefore the baseline power
(kW) should also be based on the ?real? occupied area and not including the
chases, even if they are lumped in to simplify geometry. So I?d say the
opposite ? by including the chase area in the baseline the total kW is too
high compared to a proposed case that uses an actual kW.

If I?m understanding, the GBCI actually DOES want you to calculate lighting
power in terms of kW per occupied space and allocate it over the same
modeled area as your proposed lighting kW ? in this way both cases will have
a modeled LPD that is lower than if only the occupied areas were used for
those spaces.

You do need a section in your narrative to explain the process of
determining LPD, equipment power density, occupancy per area, etc in the
context of the design documents that don?t include the chases. If I have
it backwards and the proposed design is not using actual values, then you
need to explain this to the reviewer in the narrative as to why the area
basis for power calculations does need to be the same as the zone area.

One possible course of action is to e-mail your reviewer for a clarification
on what they are looking for to make sure things are square, outlining your
understanding of the comments and proposed procedure. (Don?t ask open ended
questions, provide the solution.)

Overall it sounds like the comment is clear, and as you mentioned originally
if the change to the results are negligible, then just do it according to
the comment and close the project out.

David

*
*

David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP

*
*

*From:* equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] *On Behalf Of *M. Shields
*Sent:* Thursday, May 19, 2011 5:27 PM
*To:* 'equest-users'
*Subject:* Re: [Equest-users] Lighting Power Density

The issue is that if I don?t include the chase in the LPD calc then it will
over estimate the lighting because that area is included in the area for the
model. Also I am concerned that they will say ?well zone x is 100 sqft
where your LPD calculation says that area is only 98 sqft?. I am fine with
overestimating it, I just wondered if anyone has experience about how strict
the reviewer might be for this.

Thanks for the feedback.

David S Eldridge's picture
Joined: 2011-09-30
Reputation: 2000