LEED Review Comment for Appendix A constructions

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Hi -- hopefully others have run into this before. We have a review
comment that suggests that we need to revise our Proposed Construction
performance values by reference of Appendix A constructions from 90.1
standard.

This is a new comment which I have not experienced LEED Reviewers
addressing on past projects, and it seems to be in line with the release of
the new Table 1.4 that is so interactive and also requires reference to
Appendix A tables for proposed construction performance values.

I have re-read Appendix G and cannot find any required reference to using
Appendix A performance values for proposed construction except for
Fenestration that is Not NFRC rated. Where does it state the
requirement to use Appendix A values for all of the proposed envelope
construction values?? Why is GBCI implementing this now, and it was never
a factor before?

I need some education on this one please, I couldn't find any specific
references on my own.

Thanks!

Pasha

Pasha Korber-Gonzalez's picture
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Good morning, Pasha,

Appendix G primarily provides very specific guidance for building the
appropriate Baseline model to use as a benchmark to calculate the projected
energy savings for your Proposed building as designed. Most of the guidance
in Table G3.1 for the Proposed model indicates it must be modeled as
designed. This is where appendix A comes in for the Proposed constructions.
U-values may only be calculated using the inverse of the sum of the
R-values if each layer is continuous (e.g. uninterrupted by other materials
such as steel studs or joists). Appendix A provides tables with the
effective U-values for various common heterogeneous constructions. Depending
on the construction, the overall U-value for the assembly can vary
significantly from the U-value calculated by summing the U-value of the
major components. The Appendix A assembly performance must be used for the
Proposed constructions to accurately reflect performance of the building
envelope. Hope this helps.

Have a great day!

Cam Fitzgerald

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Thanks Cam, I couldn't find where it reads this in Table g3.1, Could you give me a page reference please? I need to provide my client with this reference info for their future projects.

Also can you explain why this hasn't been addressed on LEED projects in the past? This is the first time I have received this comment on any of my LEED submissions.

Thanks,
Pasha

Sent from my iPhone

Pasha Korber-Gonzalez's picture
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I think he's referring to Table G3.1, No. 1.a for the Proposed model where it states that the simulation model of the proposed design shall be consistent with the design documents, including proper accounting of fenestration and opaque envelope types and areas.

I can't speak to the inconsistency on GBCI reviews. Was the U-value in this case particularly low? As for the comment itself, I think it simply speaks to the need to include the effects of thermal bridging in determining the overall U-value for the assembly. Maybe you've already done this, in which case I would suggest you simply document your approach in your response.

I highly recommend checking out this paper published in 2011 which uses 3D heat flow modelling to calculate thermal transmittance through steel-framing, parapets, balconies, spandrels, etc.

http://www.morrisonhershfield.com/ashrae1365research/Documents/MH_1365RP_Final_%20small.pdf

All the best,
Dan

?
Daniel Knapp, PhD, P Phys, LEED? AP O+M

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The new LEED Section 1 4 Table (Dec 2012) requires the use of Appendix A for
calculating assembly u-values.

Filling out this form adds considerable time onto modeling projects, so you
might want to take a look before you bid you next job.

Regards,

Paul Diglio, CEM, CBCP

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Pasha,

You are right that Table G3.1#4 does not specifically cite Appendix A, it simply says the Proposed model must be modeled as shown on the drawings or as built for existing envelopes. Since the envelope performance listed in Tables 5.5-x are prescriptive requirements, the reference you seek is in Section 5.5.3 which defines how to determine if the envelope meets the prescriptive requirement.

I cannot address your second question as to why you have not encountered this issue in previous LEED submissions, but it is not related to the new Table 1.4 form. This issue has been questioned since well before LEED 2009 was released.

Good luck,

Cam

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Good morning,

Just some thoughts?

My understanding is that the new Section 1.4 Tables are a tool provided to project teams which should be used during design development and before doing a final model for submission to LEED. The spreadsheets are designed to highlight many of the common errors made in modeling both the Proposed and Baseline buildings.

If modelers are aware of these common issues during design development AND pay attention to them, the end result would be a more accurate model for informing design decisions as well as a reduced number of comments needing to be addressed and fewer revisions required between review phases. It should also increase the chances of having a Preliminary model awarded in the Preliminary Review. That in the long run should result in savings for the modeling budget, not cost more time and money just to fill out the form?

Best Regards,

Sheila Sagerer

Energy Engineer, EIT, LEED AP

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Pasha,

Appendix A is referenced by 90.1 Section 5.5.3. It is not a new rule, and must be used for determining thermal properties of the proposed designs because many simulation tools including eQUEST cannot capture two-dimensional heat transfer (thermal bridging) of the specified constructions. Thermal bridging is an especially big factor for steel-frame constructions, where calculating overall U-value of wall assembly using weighted average properties of frame and cavity sections (parallel path method) can distort result by factor of 2+ compared to the tables provided in Appendix A (such as Table A3.3 or A9.2B). Note that Thermal bridging is accounted for in Tables 5.5-x which list the baseline constructions. For example, for climate zone 5 (Table 5.5-5) minimum insulation R-value of steel-framed walls in non-residential spaces is R-13 cavity plus R-7.5 continuous. If we do not account for thermal bridging, then the overall R-value of insulation in the cavity portion of the wall is R-20.5, and we?d expect that overall surface U-value (not accounting for gypsum board, siding, air, etc.) would be somewhere around 1/20.5=0.049 because cavity section is very wide compared to frame section. However the equivalent Assembly Maximum for the surface is U-0.064, which is what you?d get if you use tables in Appendix A to calculate thermal properties of frame/cavity portion of the wall assembly instead of parallel path method. There is a nice discussion on that in 90.1 User Manual.

Good luck with your project,

Maria

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Sheila:

I find it takes significant additional time to fill out the form. Additionally
NC-2009 EAp2 requires that we download it, fill it out and upload it.

Paul Diglio, CEM, CBCP

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Maria & Cam---thanks for taking time to offer your guidance.

Maria--I was hoping to hear from your experience & advice. :)
Cam--thanks for confirming that I'm not blind! :)

I don't have issue with the engineering theory of the topic--I understand,
agree and recognize thermal bridging effects and so forth (thanks to my
great engineering mentors in my younger days.)

What I was challenging specifically was that this was the first instance
that this Review Comment & request for Appendix A reference has been
presented on any of my LEED projects reviews---and I only am introduced to
it since the inception of the new Table 1.4 which specifically points out
the use of the Appendix A reference.

--(Thanks Shelia for your input also---I learned of the use of the new
Table 1.4 after I painfully filled it in for a project that was modeled
over a year ago. In the future I will certainly be filling this table out
as I develop my LEED models as a simultaneous action from now on. I like
how it is interactive and determines the correct references for us---agree
with the potential for less mistakes, but I dislike how it does take
significantly more time than the previous Table 1.4 which unfortunately
does eat into the project budget a bit more; however if we complete the
form during model development there may be potential to streamline/average
the additional work from the overall project time...)--

I've now read through Section 5.5.3 and the User's Manual info and have a
better understanding of the nature of the Review comment requirements.
I'm still baffled as to why this issue hadn't been brought up on any of my
previous project submissions as I had not changed my reporting approach
from then until now---I don't discount that it is an existing requirement
from prior to LEED 2009, but again it is frustrating when you think you are
applying 100% compliance to your document submissions and *out of the blue*
GBCI throws a new thing at us!

I respect that everything including LEED is a growing/improving process,
but it has been a painful growing process since the inception of GBCI
reviews.---(I just needed to vent.) If GBCI is such an authoritative
review group then why didn't they have all this in place from the get go??
I'm sure I'm not the only one who dislikes getting a curve ball---As a
LEED modeling veteran I thought that my submissions were closer to perfect
than not---it's the perfectionist-side of me that doesn't like to be
'blind-sided' by something that didn't seem to be a factor in the game
before now.

I guess today is already a productive day since I have learned something
New! Thanks to all of you for sharing your time, experience & advice.
This list-serve is the BEST!!

Cheers,
Pasha

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Shiela:

Sorry if I gave the impression that I was offended. I was not. I am somewhat
curt by nature. Too much time spent growling at my laptop instead of talking
to people!

You did bring up some good points. I usually develop a sort of matrix with all
the baseline and proposed information (i.e. wall u-values, glazing u-values,
etc) and submit that with my LEED model. I just find that the Table 1.4
Dec-2012 is much more involved that the Table 1.4 Sept-2011 and am working on a
project that I priced before this new table became effective, so like Pasha, I
am somewhat taken back. I think filling out this table has added 3-4 days onto
the project. For example, since my space areas and those used by the electrical
engineer differ and I need to add spaces together and apportion the LPD by
percentages.

I can understand the GBCI position that assembly performance rating needs to be
calculated using the 90.1 Appendix A since eQuest does not always calculate
accurate u-values when building an assembly using the materials in the library.

One question that I would like to ask. I sometimes input a wall u-value using
the Specification Method- Layers Input of say .064. Then when I look at the
LV-D simulation report the u-value there does not match my input. For example
on a current project, in order to get the LV-D to report an exterior wall
u-value of .064, I needed to tweak my exterior wall construction layers to be
.066. Have you had this problem? Same for the vertical fenestration.

Is it something I am doing wrong? Perhaps the Specification Method-Resistance
is not correct?

Anyway, you have a great weekend also.

Paul Diglio, CEM, CBCP

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Paul,

I might be wrong, but I have a hunch/vague recollection that the reports do not account for air films ? you might confirm by checking out the detailed sim reports PDF help file!

Also, to your LPD woes, I haven?t yet been assigned to work through the new spreadsheet so I might be missing some context, but one thing I?ve picked up in the past (with the previous spreadsheet iterations) is that no reviewer has ever given me flak for revising/reworking the spreadsheet to more clearly document things as they?re modeled?

Possibly that has changed with the new spreadsheet (might be worth asking the question through your LEED project manager, time allowing), but if you have some fundamentally different approach in your modeled inputs than what?s assumed by the spreadsheet for documentation ? I might consider whether the spreadsheet is in fact ?requiring? a specific approach or if you can?t simply re-work the spreadsheet to more easily document what you?re actually modeling.

~Nick

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NICK CATON, P.E.

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To chime in with some extra thoughts:

I've actually adopted citing Appendix A quite often for both baseline and proposed construction descriptions, before even seeing the new EAp2 spreadsheet.

If anyone has ever looked hard at the .inp files we've passed around on the lists here for baseline constructions (see attached), you'll find they include quite a few citations to Appendix A.

That particular table for various framing combinations Maria is referencing is super useful for energy modeling studies beyond LEED as well. I recall looking up the math involved to derive how steel studs circumvent batt insulation once, and let's just say I came away happy to know there's a table handy for these things =).

The best of us, modelers and reviewers alike, are learning all the time - so some degree "inconsistency" is to be expected project-to-project, and it's a 2-way street. I would expect a competent reviewer to come up with new ways to analyze and challenge documentation over time, just as I would expect a competent modeler to improve themselves and the quality of their models/documentation. I am often seeing new questions/commentary I've never seen asked before, ranging from thought-provoking to inane, but I think it's to be expected to some degree and nothing to lose sleep over.

Regards,

~NIck

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NICK CATON, P.E.

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Nick:

Thanks for the heads-up on the air films, Sheila also mentioned that.

I tried some edits on the spreadsheet, but there are so many macros that I was
messing it up. If you develop some handy hints, I would be interested to hear.

One of the LPD problems I am having is that the EE did not zone the building as
I did. As you know, we don't always zone every tiny closet separately. In
addition this building has a L shaped corridor with an exit stair at either
end. The EE chose to increase the LPD for the 10' of the corridor in front of
the stairwell doors so I need to apportion the LPD based on areas and
percentages. Table 1.4 does not allow notes in the Lighting table. It would be
so much easier to keep track of combined spaces and averaged LPD's if a note
section, per space, was provided. In the past, I have just sent the engineer's
LPD spreadsheet and it was accepted by the GBCI.

The spreadsheet does have some advantages in the Air Side HVAC tab. It will
calculate the allowed fan power and highlight the cell in red if it is too low
or too high. I find that I need to keep revising the model in order to get the
allowed fan power right, which does effect the system size due to the motor heat
introduced into the air-stream, which in turn slightly alters the allowed fan
power, on and on.

Anyway, I think it will take me some time to become accustomed to this new form.

Have a great weekend.

Paul Diglio, CEM, CBCP

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Paul and others:

In regards to LPD calcs, the spreadsheet I have a copy of does permit typing in the margins (white cells adjacent to and above/below the tables), should you feel compelled to provide extra narrative explanations in big, bold, red text.

Still, as long as USGBC is taking on this degree of prescribing how models are to be documented, I think the onus is implicitly on them to revise/improve the spreadsheet for clarity?s sake ? not us... in that light I wouldn?t spend extra time improving their spreadsheet for them until they call for additional clarification through review commentary. If requested through review commentary, I?ll consider re-working their spreadsheet for them as needed for clarity, but if they have locked it up in some fashion that this is overly difficult for us then they?ve shot themselves in the foot and will just have to deal with long, exhaustive narrative response essays (queue the pipe organ and evil cackling)!

In the meantime, new EAp2 spreadsheet or not, I would not feel compelled to re-zone a developed model to distinguish each and every space with different LPD, unless you intended to do that in the first place (in which case, power to ya!).

You should be able to transpose the same space area and LPD tallies in the EAp2 spreadsheet that the original LPD calculations demonstrate, uploaded as supporting documentation. The zoning pattern you determined appropriate to the models (remember 90.1 explicitly permits flexibility on the modeler?s part here) drives the separate task of applying these LPD?s to the models in a fashion that makes sense. Whatever degree of detail you choose to invest your efforts in this task (there are always multiple right answers), it?s probably more important that you are careful to apply the Proposed & Baseline LPD?s to each model in an identical/consistent fashion.

Regards,

~Nick

PS: Actually, the ?Instructions? tab of the new spreadsheet specifically calls out separately uploaded LPD calcs as something which can theoretically supplant the ?Lighting? tab inputs. I?ve done this in the past with the previous EAp2 spreadsheet, simply making a short reference to the other supporting documentation in the input cells:
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NICK CATON, P.E.

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