[Equest-users] LEED Review Comment on U-Value Input Method

[Eric O'Neill]

Robby, 

 

I see your point. However, I'm curious how many wall assembly types you
can think of that meet the criteria they discuss in that section (and
whether their different themal delay properties would impact the
project):

 

*         Lightweight (I assume this means no brick exteriors)

*         Common

*         Steel Framed

*         R-13 + R-7.5ci (for instance, depending on climate zone)

 

Now, I'm not saying they couldn't be more explicit. You're absolutely
right that they could be. However, I could fairly easily justify steel
siding, 1.5 inches of polystyrene, steel framed wall with batt
insulation and a gyp board finish. Maybe small changes like vinyl siding
or an equivalent level of spray foam insulation would have marginally
different time delay properties, but I'm guessing they would be
negligible based on the information found in the chapter I previously
cited.

 

Eric

 

From: Robby Oylear [mailto:robbyoylear at gmail.com] 
Sent: Tuesday, June 21, 2011 10:12 AM
To: Eric O'Neill; Bishop, Bill; Carol Gardner; Bruce Easterbrook; eQUEST
Users List
Subject: Re: [Equest-users] LEED Review Comment on U-Value Input Method

 

While I agree that modeling the baseline with some level of light mass
should be done to get more accurate results, it's difficult to
understand why 90.1 would not specify a mass value to model. The
definition of a baseline is a minimum value for comparison.  How can
LEED reviewers judge whether or not you're taking the appropriate credit
for thermal mass when the baseline building done by one modeler will
have a different mass value than one done by another modeler?

 

Values that are vague and undefined (process loads or lighting plug
loads in residential for example) are typically left the same between
both models.  This allows for the factor to be accounted for, but
provides no credit to the proposed model.  The same could be done for
thermal mass, to account for it in both models, but not provide credit.
Without a defined baseline, I don't see how one can justify whether or
not they've modeled the correct "lightweight" assembly mass value.

 

-Robby

On Mon, Jun 20, 2011 at 9:47 AM, Eric O'Neill <ELO at michaelsenergy.com>
wrote:

I think some confusion stems from the definition of "lightweight". The
fundamentals book discusses light and heavy constructions in the radiant
time series, and defines a few examples in table 22, ch 30 (2005
handbook - NonRes Cooling and Heating Load Calcs, Radiant Time Series
Method). Light constructions are steel sidings, 2 inches of insulation,
an airspace, and gyp board. It also defines medium and heavy, with brick
and heavyweight concrete, respectively. 

 

So when they say lightweight, I believe they're referring to something
similar. I don't believe "lightweight" is intended to mean "no-weight"
for the reasons Bruce described. It seems to me they're giving design
teams the opportunity to take advantage of a heavy exterior construction
if it reduces the peaks. They do ask that they conform with the
lightweight assemblies, which, in my opinion, just a U-value does not.

 

Eric

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop,
Bill
Sent: Monday, June 20, 2011 11:01 AM
To: Carol Gardner; Bruce Easterbrook
Cc: eQUEST Users List


Subject: Re: [Equest-users] LEED Review Comment on U-Value Input Method

 

Carol,

As we noted earlier in this thread, we can't find an explicit
requirement that layer-by-layer be used. It is strongly implied for at
least the proposed in Appendix G, and it is good practice for several
reasons as Bruce describes below. From the 90.1 User's Manual - "The
general rule for the baseline building run is that all inputs must be
identical to the proposed design run, except for those features that are
allowed to differ." It seems logical to extend this general rule to
input methods as well as inputs. Would you accept the modeling results
if the proposed building was done in TRACE while the baseline was done
in eQUEST?

Bilbo

 

 

From: Carol Gardner [mailto:cmg750 at gmail.com] 
Sent: Monday, June 20, 2011 11:30 AM
To: Bruce Easterbrook
Cc: Bishop, Bill; Pasha Korber-Gonzalez; eQUEST Users List
Subject: Re: [Equest-users] LEED Review Comment on U-Value Input Method

 

I guess we'll have to agree to disagree. 

 

Bilizebub: could you point out the section in LEED or Std 90 that says
that walls must both be layer by layer. Thanks.

 

 

On Mon, Jun 20, 2011 at 7:01 AM, Bruce Easterbrook <bruce5 at bellnet.ca>
wrote:

I think what is being forgotten is "intent", and the accuracy of your
model.  So for intent the desire of the powers that be is that smart
design be used to reduce the energy consumption of buildings.  You
should not be manipulating the "system" to take credit for something
which is not really a credit.  Your model should be as accurate as you
can possibly make it with reasonable effort.  U-value construction is
not accurate, all buildings have mass.  Mass serves to shave peaks.
When you have a building modelled with no mass as soon as the sun hits
it you will have a cooling load.  With U-value construction the heat
hitting the building is immediately loaded on to the cooling system at
100%.  This doesn't happen in reality and you will oversize your cooling
system.  Therefore you have designed an inefficient system, you are
costing your client money because they have to buy and operate a bigger
cooling system than required.  Logic and good modelling dictate you
account for mass.  The baseline is a "standard" building construction in
use at this time and that is defined, "lightweight steel construction".
You don't get credit for the mass of this building.  However if you
start adding mass strategically to further load shift your peaks you
should be able to take credit for that.  Besides U-value construction is
the old school, brute force technique when energy was cheap and we used
spread sheets and calculators.  eQuest allows us to accurately predict
the mass effect of a building and we have the computing power to run
this program sitting on our desk.  A good modeller is required to use
all the tools at their disposal to create the best base model they can
so that the project people can assess different techniques to reduce the
energy usage of the building and the economic costs of doing this.  I
think it is pretty obvious the evaluator will reject a model not done
layer by layer.  They can't easily check the base construction, the
U-value method is not accurate and they are overloaded.  So it's file 13
and on to the next project.
Bruce Easterbrook P.Eng.
Abode Engineering 


On 20/06/2011 09:03 AM, Bishop, Bill wrote: 

Like Pasha mentioned, if you use layer-by-layer method in the proposed,
you should use the same method in the baseline, unless you want to argue
that "lightweight" requires the use of the U-value construction method.
I don't see what advantage that serves, other than helping you avoid the
time of creating baseline envelope constructions. While "lightweight" is
not defined in 90.1, the baseline layer materials and thicknesses are
described in A3, so if you use the layer-by-layer method for both
baseline and proposed, and if there is a difference in the overall mass
of each wall construction, the modeling output will reflect that
difference. Both baseline and proposed constructions will have "mass",
and if the proposed construction is optimized, there will be energy
savings.

 

The eQUEST help menu item for "EXTERIOR-WALL  and ROOF" states that
using LAYERS rather than U-VALUE can result in greater computational
time, but gives more accurate results. Computational time is at the
bottom of my eQUEST concerns. I have not compared modeling results of
LAYERS vs. U-VALUE. Delayed construction appears to be required by
Appendix G, is supposedly more accurate, and I don't see a good reason
not to use it.

 

Billzebub

 

Error! Filename not specified.

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Pasha
Korber-Gonzalez
Sent: Saturday, June 18, 2011 4:39 PM
To: eQUEST Users List
Subject: Re: [Equest-users] LEED Review Comment on U-Value Input Method

 

Following the other comments on this, I am confused and worried too that
if they are requiring to simulate mass in the baseline, then how could
we use Mass constructions as "passive" design strategies and take credit
for this type of ECM?

 

Directly from what I was reading in the 2007 code: Table G3.1.5-Baseline
Building Enevelope

Opaque Assemblies.  Opaque assemblies used for new building or additions
shall conform with the following common, lightweight assembly types and
shall match the appropriate assembly maximum U-factors in Tables 5.5-1
through 5.5-8:

 

Doesn't the reference to "lightweight" assemblies mean that you don't
have to account for thermal lags (massing)?   This has always been my
interpretation.  Therefore, when it comes to modeling the U-values for
the assemblies with the U-value method versus the layer method would be
acceptable for your baseline simulations.  Where there is no requirement
to show any type of massing effects it shouldn't matter if you choose to
use the U-value input method or the layer-by-layer method.

 

But--it is important for the simulator to understand that when using
eQuest (I can't speak for other simulation tools); the input method has
to be matched in both the baseline and proposed.  You can't choose
U-value input for the baseline and layer-by-layer for the proposed, you
have to use the "apples-to-apples" approach for both models.

 

It will be a big issue if GBCI mandates that we have to use only
layer-by-layer inputs for compliance where Appendix G is clearly stating
that there is no need to account for thermal lag in the baseline
building as it states "lightweight" construction.  Any type of thermal
lag characteristics in lightweight construction are negligible to the
performance of such constructions as required by Appendix G baseline
inputs.

 

pkg

 

 



 

On Fri, Jun 17, 2011 at 3:23 PM, Carol Gardner <cmg750 at gmail.com> wrote:

I'll bite. What extends it to the baseline? I still see that it just
says to credit it to the proposed building. Wasn't this language created
to guide people to the fact that even if mass was added to a steel
framed building it still fell under the "steel framed" category and not
the mass? 

 

On Fri, Jun 17, 2011 at 2:07 PM, Bishop, Bill
<wbishop at pathfinder-ea.com> wrote:

Another piece of the puzzle. >From the 90.1 User's Manual, section on
Baseline Building Opaque Assemblies (p.G14 in 2004 ed.):

"The baseline building is assumed to be steel framed no matter what the
construction of the proposed building. If the proposed building has
thermal mass in the exterior construction and this is a benefit in a
particular climate, then the mass is credited in the building
performance rating method."

 

So delayed construction is the de facto method for modeling the proposed
envelope, and by extension, the baseline.

 

Bill

 

Error! Filename not specified.

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Carol
Gardner
Sent: Friday, June 17, 2011 4:40 PM
To: Daniel Knapp
Cc: equest-users at lists.onebuilding.org


Subject: Re: [Equest-users] LEED Review Comment on U-Value Input Method

 

But the Simulation General Requirements are for the simulation model
itself and it's capabilities, they do not address the simulation inputs.

I think this section of the code is what governs this issue:

Opaque Assemblies. Opaque assemblies used for new buildings or additions
shall conform with the following common, lightweight assembly types and
shall match the appropriate assembly maximum U-factors in Tables 5.5-1
through 5.5-8:

But I disagree with Guarav's interpretation for these reasons. The use
of the word assemblies might "suggest" the need to model the whole
structure but the use of "lightweight" in the sentence, and it's
location after the word shall, is the key. Those U-values in Tables
5.5-1 through 5.5-8 are for lightweight construction. Lightweight
construction is not delayed construction. The Standard 90 committee even
gave us a variety of wall types to select from on those tables so that
we would have an appropriate assembly maximum U-factor to use.

Anyway, that's my interpretation.

Carol

On Fri, Jun 17, 2011 at 9:24 AM, Daniel Knapp <danielk at arborus.ca>
wrote:


FYI, Simulation General Requirements as laid out in 11.2 of the 90.1
User's Manual specifically call for the treatment of Thermal Mass
Effects in the Minimum Modeling Capabilities.  (see 11.1.2.3 and as
already mentioned G2.2.1.c) and notes that "A building's ability to
absorb and hold heat varies with its *type of construction* and with its
system and ventilation characteristics.  This affects the timing and
magnitude of loads handled by the HVAC system.  Simulation programs must
be able to model these effects".



On 2011-06-16, at 7:15 PM, Mehta, Gaurav wrote:

> Michael,
>
> Agreed, appendix G does not specifically states that one needs to
model delayed construction. However, going by the semantics used in
Appendix G, one can conclude that delayed construction should be used.
Consider the following:
>
> Table G3.1-5 Building Envelope, under Baseline Building Performance,
part (b) Opaque Assemblies: states that Opaque assemblies......shall
confirm with the following common, lightweight assembly types and shall
match the appropriate assembly U-factors.....
>
> **The use of the term 'assemblies' suggests the need to model the
whole assembly rather than only the U-factor**
>
> To answer your other question, how do you know what comprises of the
baseline opaque assembly, I'll suggest use Appendix A. For example, for
steel framed walls, see section A3.3.1 General, you'll find the assembly
layers that you can use to model the baseline above grade walls.
Similarly, you can use respective sections for roof, floor, etc. to
determine the baseline assembly layers.
>
> If I remember correctly, somebody in the past has been kind enough to
post the baseline assemblies that can be copied to the inp file (or
imported into the inp file). Search the archives.
>
> Furthermore, eQUEST has an extensive library of materials that one can
use, which includes the thickens, specific heat and density of the
material. You can create your own materials by using the ASHRAE Handbook
of fundamentals, chapter 26 (2009).
>
>
> Thanks.
>
> Best regards,
>
> Gaurav
>
> Gaurav Mehta, LEED(r) AP BD+C
> Sustainable Building Analyst
> Stantec
> 1932 First Avenue Suite 307
> Seattle WA 98101
> Ph: (206) 770-7779 <tel:%28206%29%20770-7779> 
> Fx:  (206) 770-5941 <tel:%28206%29%20770-5941> 
> Gaurav.Mehta at stantec.com
> www.stantec.com <http://www.stantec.com/> 
>
> The content of this email is the confidential property of Stantec and
should not be copied, modified, retransmitted, or used for any purpose
except with Stantec's written authorization. If you are not the intended
recipient, please delete all copies and notify us immediately.
>
> Please consider the environment before printing this email.
> -----Original Message-----
> From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of James
Hansen
> Sent: Thursday, June 16, 2011 3:09 PM
> To: Bishop, Bill; Michael Mantai; equest-users at lists.onebuilding.org
> Subject: Re: [Equest-users] LEED Review Comment on U-Value Input
Method
>
> Michael, I'd advise that you email the project coordinator (or
whatever GBCI calls the "head" of a project review team).  Usually they
will answer relatively quick and easy questions so that you don't have
to risk improperly addressing a comment.
>
> Ask them where in Appendix G it specifically requires the time delayed
method be used.
>
> GHT Limited
> James Hansen, PE, LEED AP
> Senior Associate
> 1010 N. Glebe Rd, Suite 200
> Arlington, VA  22201-4749
> 703-338-5754 (Cell)
> 703-243-1200 (Office)
> 703-276-1376 (Fax)
> www.ghtltd.com <http://www.ghtltd.com/> 
>
>
> -----Original Message-----
> From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bishop,
Bill
> Sent: Thursday, June 16, 2011 4:22 PM
> To: Michael Mantai; equest-users at lists.onebuilding.org
> Subject: Re: [Equest-users] LEED Review Comment on U-Value Input
Method
>
> Michael,
>
> My understanding has always been that delayed construction should be
> used, though I can't find exact wording in Appendix G that requires it
> other than G2.2.1(c). For other components/layers of steel-framed
walls,
> look to A3.3.1, and to Table A3.3 for assembly U-Factors for different
> stud spacing. You should be pretty close to the required U-Factor if
you
> use the correct materials and thicknesses from A3.3. Yes, you may need
> to tweak a layer or two to get the construction to match the U-Factor
> exactly. As described in other posts, once you create these
> constructions for the baseline, copy them for future models.
>
> Regards,
> Bill
>
> -----Original Message-----
> From: equest-users-bounces at lists.onebuilding.org
> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of
Michael
> Mantai
> Sent: Thursday, June 16, 2011 4:00 PM
> To: equest-users at lists.onebuilding.org
> Subject: [Equest-users] LEED Review Comment on U-Value Input Method
>
> We received the following comment on recent LEED review:
>
> "The simulation input screenshots, provided in the EAc1 modeling
> narrative
> report, indicate that the exterior wall and roof constructions were
> modeled
> as QUICK surface type (U Value Input specification method), which does
> not
> account for the time delayed heat flow through the constructions as
> required
> by Section G2.2.1(c). Revise the Proposed and Baseline models so the
> exterior walls and roof surface types are modeled as DELAYED (Layer
> Input
> specification method) with the thermal mass effects of the
constructions
> taken into consideration. In addition, provide a revised LV I report
for
> each model reflecting the changes."
>
> Section G2.2.1(c) describes modeling software requirements, but I
don't
> see
> anywhere else in Appendix G that specifies that thermal mass effects
> have to
> be included in the baseline model.
>
> Previous review comments on other projects have led me to believe that
> U-value input was the correct method to set up the baseline model.
>
> If I revise the model to input each layer, what layers do I input?
> 90.1-2007 Appendix G states to use steel-framed walls, and the Tables
> provide minimum R-value for insulation and overall assembly U-value.
> But it
> does not appear to provide such other items as stud spacing,
sheathing,
> or
> even what material is on the outside of the building (for exterior
> walls).
> Has anyone else had this type of comment before or are you using the
> layer
> input method for baseline models?  It seems that if I need to specify
> layers, the resultant U-value should equal exactly the minimum U-value
> per
> the 90.1 tables.  That would lead me to believe that there might be
> different combinations of layers that result in the same U-values but
> result
> in different energy use in the baseline, and obviously I would want to
> have
> the highest energy use for LEED purposes.
>
>
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-
Daniel Knapp, PhD, LEED(r) AP O+M
danielk at arborus.ca

Arborus Consulting
Energy Strategies for the Built Environment
www.arborus.ca <http://www.arborus.ca/> 
76 Chamberlain Avenue
Ottawa, ON, K1S 1V9
Phone: (613) 234-7178 ext. 113 <tel:%28613%29%20234-7178%20ext.%20113> 
Fax: (613) 234-0740 <tel:%28613%29%20234-0740> 




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-- 
Carol Gardner PE





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