[Equest-users] LEED Review Comment on U-Value Input Method
Carol Gardner
cmg750 at gmail.com
Tue Jun 21 12:45:32 PDT 2011
First of all, as a former energy code reviewer, 2 years for Oregon and about
5 for the City of Portland, it was my responsibility to interpret the intent
of the code when the language or application was unclear. That explains why
I respond to the word "shall" so strongly.
When I read "shall conform with the following common, lightweight assembly
type" which for walls is stated to be steel framed walls, and "shall match
the appropriate assembly maximum U-factors in Tables 5.5-1 through 5.5-8", I
assume I am being directed to use the Prescriptive assembly U-factor
provided on the Building Energy Requirements table for my climate zone in
Chapter 5.
I did a bit of research to see if there was information in the past versions
of the standard and in the User's Manuals. What I found was that prior to
the adoption of Appendix G, the requirement was to model with the
Prescriptive assembly U-factors as well as to match the heat capacity in
each case: proposed and design. This meant that if the proposed wall was
steel framed then the baseline must be too and credit could not be taken for
added mass or changes in framing.
After the adoption of Appendix G and the Energy Cost Budget Method in 2004
things changed a bit. At that point the direction in the User's Manual
states that the baseline building is assumed to be steel framed no matter
what the construction of the proposed building. If the proposed building
uses added mass, or wood framing or beneficial constructions it is credited
to the building. The baseline building *shall* comply with the applicable
prescriptive requirements for steel-framed walls, i.e the Prescriptive
assembly U-factor for steel framed walls on Table 5 for your climate zone..
So, I do not see a mandate, or an implication even, to specify the baseline
building walls using layers. Rather I see a clear instruction to use the
Prescriptive Path U-value for the baseline and to take credit for any
improvements in the proposed building walls. I don't think this is "gaming
the system" at all. It is sad but true that many buildings being built today
just meet the minimum prescriptive requirement. I have even seen some that
didn't. If a building owner is willing to lay out the extra money for a
better wall, why shouldn't he/she get credit for it?
Stepping off my soap box,
Carol
On Tue, Jun 21, 2011 at 8:55 AM, Eric O'Neill <ELO at michaelsenergy.com>wrote:
> 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<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® AP BD+C
> > Sustainable Building Analyst
> > Stantec
> > 1932 First Avenue Suite 307
> > Seattle WA 98101
> > Ph: (206) 770-7779
> > Fx: (206) 770-5941
> > Gaurav.Mehta at stantec.com
> > 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
> >
> >
> > -----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.
> >
> >
> > _______________________________________________
> > Equest-users mailing list
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> >****
>
> —
> Daniel Knapp, PhD, LEED® AP O+M
> danielk at arborus.ca
>
> Arborus Consulting
> Energy Strategies for the Built Environment
> www.arborus.ca
> 76 Chamberlain Avenue
> Ottawa, ON, K1S 1V9
> Phone: (613) 234-7178 ext. 113
> Fax: (613) 234-0740****
>
>
>
>
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>
>
>
> --
> Carol Gardner PE****
>
>
>
> ****
>
> --
> Carol Gardner PE****
>
>
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> ****
>
> _______________________________________________****
>
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>
> ** **
>
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>
> ** **
>
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>
>
> --
> Carol Gardner PE****
>
>
> _______________________________________________
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> ** **
>
--
Carol Gardner PE
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