[Equest-users] Slab extending through wall
Bruce Easterbrook
bruce5 at bellnet.ca
Wed Nov 6 09:40:26 PST 2013
True. I was thinking more on the comparison of insulation efficiency.
These buildings as modelled and designed have R-18.5 of insulation and
the net effect to the envelope is R-10 or less. Comparing this type of a
building and our current housing code in Canada where glass is limited
to 17% of the wall area, R-4+ glass, wall insulation of R-28 and roof
insulation of R-60 and intense scrutiny of thermal breaks, well lets
just say they are energy pigs. When you have an R-2 or 3 glass wall a
little bit of R-2 concrete in there doesn't make much difference. Even
if you stick a fin out 8' is still doesn't make much difference.
The research is interesting and quantifies the effect. It also shows
current modelling does a reasonable job of reflecting what is going on.
But for the building as a whole and the model it can have a small impact
if it isn't efficiently designed. The impact of how it is modelled has
an even smaller impact. 60% of R-20 is significant, 60% of R-2 is
meaningless and a 3% error in that is nothing.
The big picture is getting lost in all this work. We are using a
modelling technique in which a 10% error is considered very accurate, a
good model. Many of the early LEED buildings, as built, deviated from
the models by 100% brand new. Many others that did ok on day one were
way out by year 5. The models weren't the main problem, it was
application. Modelling is expensive. It seems to me that sometimes too
much time, effort and money is spent chasing less than a percentage
point of gain. There is a science to keeping the model efficient as
well. Also, the main way a model is used is as a "what if" test
platform. Holding most things constant and trying variations. This
reduces error as well. But if the sealing contractor does a poor job
and the building takes a 15% hit a little bit of R-2 concrete on the
envelope doesn't matter very much.
The science is great, this type of research is very illuminating and
will drive better design. The application of our technology, the tools
we use and how we use them is the biggest variable affecting the
efficiencies we are trying to achieve.
Bruce Easterbrook P.Eng.
Abode Engineering
On 06/11/2013 10:57 AM, Nathan Miller wrote:
>
> I wasn't saying the effect of exposed slab edges and balconies is
> insignificant. What I was saying is that I don't see much difference
> in using the thermal performance for those assemblies modeled in the
> report vs. using typical practice of just calling balconies and
> exposed slab edges "uninsulated concrete walls" and assigning that
> default U-factor to them (hence you would have about a 1' high
> uninsulated concrete wall and an 8-9' high typical opaque wall).
>
> *Nathan Miller **-****PE, LEED^® AP BD+C, CEM*
>
> /Mechanical Engineer/Senior Energy Analyst /
>
> *RUSHING*| *D*206-788-4577 |*O*206-285-7100
>
> *www.rushingco.com <http://www.rushingco.com/>***
>
> *From:*Bruce Easterbrook [mailto:bruce5 at bellnet.ca]
> *Sent:* Wednesday, November 06, 2013 5:45 AM
> *To:* Robby Oylear; Nathan Miller
> *Cc:* David Griffin; Kapil Upadhyaya; equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] Slab extending through wall
>
> I would think the effect of the balconies would increase the thickness
> of the exterior laminar layer on the building. The air flow is
> perpendicular to the fins. In calm conditions the main driver is
> going to be stack effect. The exposed edges are on a flat surface and
> would have a normal boundary layer. Without a projection they would
> offer little resistance to the airflow from the stack effect.
> A 60% reduction in effective R-value for a building is quite a
> significant effect depending on where you are starting from. A high
> ratio glass building is a low starting point.
> Bruce Easterbrook P.Eng.
> Abode Engineering
>
> On 05/11/2013 05:25 PM, Robby Oylear wrote:
>
> It surprises me that the report indicates a better R-value for the
> fin effect of a concrete balcony vs. the simplified exposed slab
> edge approach. Seems to violate the basic teachings heat transfer
> 101. I can't think of a logical explanation of how that could be
> the case and would chalk it up to intricacies of the modeling
> tool. However I agree with Nathan that since the report doesn't
> show nearly any difference between the fin effect vs. the exposed
> slab edge that it's not necessarily worth the complication in
> modeling unless the balcony slabs are the focus of the study.
>
> On Tue, Nov 5, 2013 at 2:00 PM, Nathan Miller
> <nathanm at rushingco.com <mailto:nathanm at rushingco.com>> wrote:
>
> Kapil,
>
> No, I am only accounting for the "face" of the balcony, as if
> you sheared it off at the plane of the wall.
>
> That is my point, the fancy thermal modeling in the report,
> which is supposed to account multi-dimensional fin-effects
> doesn't come out with much different result than if you just
> take a simplified approach like a typical UA-trade-off
> calculation (one directional heat transfer, no fin effects
> accounted for). So by that line of reasoning, you would likely
> be OVER ESTIMATING heat loss if you throw in all three
> heat-exchanger surfaces that you mention in your methodology.
> I'd be interested if you compared your calculation results to
> the thermal modeling in the report if you feel like a little
> intellectual exercise.
>
> *Nathan Miller **-****PE, LEED^® AP BD+C, CEM*
>
> /Mechanical Engineer/Senior Energy Analyst /
>
> *RUSHING*| *D*206-788-4577 <tel:206-788-4577> |*O*206-285-7100
> <tel:206-285-7100>
>
> *www.rushingco.com <http://www.rushingco.com/>*
>
> *From:* Kapil Upadhyaya [mailto:KapilU at kirksey.com
> <mailto:KapilU at kirksey.com>]
> *Sent:* Tuesday, November 05, 2013 1:53 PM
> *To:* Nathan Miller; Bishop, Bill; David Griffin; 'Coleman,
> Kevin'; equest-users at lists.onebuilding.org
> <mailto:equest-users at lists.onebuilding.org>
> *Subject:* RE: [Equest-users] Slab extending through wall
>
> Nathan,
>
> In the Balcony calculation, are you accounting for both the
> 'edges' and 'exposed area' of the balcony ?
>
> In my opinion, a concrete balcony should be accounted for as a
> heat exchanger with 3 surfaces (perimeter edges, upper
> surface, lower surface); it looks like you are only accounting
> for the edges.
>
> I had a 'heated' discussion about this with a vendor recently
> and the above is more or less a conclusion of that. Some of
> the structural thermal break products can be too expensive to
> justify based on energy savings, if area of balconies is not
> accounted for; the bigger your balcony, the better your
> payback from thermal breaks.
>
> Best,
>
> *Kapil Upadhyaya, LEED AP*
> Associate
>
> *Kirksey* | Architecture
> 6909 Portwest Drive | Houston Texas 77024 |www.kirksey.com
> <http://www.kirksey.com>
> o 713 426 7508 <tel:713%C2%A0426%C2%A07508> | f 713 850 7308
> <tel:713%C2%A0850%C2%A07308> |kapilu at kirksey.com
> <mailto:kapilu at kirksey.com>
>
> *2012-2013 Firm of the Year *
> Texas Society of Architects
>
> *From:*Nathan Miller [mailto:nathanm at rushingco.com]
> *Sent:* Monday, November 04, 2013 5:27 PM
> *To:* Bishop, Bill; David Griffin; 'Coleman, Kevin';
> equest-users at lists.onebuilding.org
> <mailto:equest-users at lists.onebuilding.org>
> *Subject:* Re: [Equest-users] Slab extending through wall
>
> To me the most interesting part of the report isn't the
> conclusion that thermally broken balconies and slab edges give
> significantly better thermal performance (we all know that
> intuitively). Instead it gives a way of back checking what I
> would consider to be "standard practice" for calculating
> area-weighted U-factor for these same assemblies using default
> ASHRAE U-values to sophisticated thermal model results. Here
> are my thoughts, checking my calcs and comments appreciated.
>
> *Executive summary: It looks like our standard assembly
> performance tables and area-weighted U-factor calculations get
> us "close enough" to the results from this report that it
> doesn't seem to suggest we should switch methodologies. *
>
> **
>
> *Comparison calculation for steel-framed walls (stud
> insulation + exterior rigid):*
>
> For a 16" OC metal stud wall, R-12 Batt cavity insulation and
> R-5 continuous rigid insulation, the report states that the
> Effective R-value for the wall + slab will be R-7.4.This is
> based on 8'8" floor-to-floor, and 8" slab.
>
> Using ASHRAE 90.1-2007 Table A3.3 for steel framed walls, we
> would get an effective U-factor for the wall portion of U =
> 0.0785 (interpolating between the R-13 + R-11 batt values). If
> we use Table A3.1A for the exposed slab edge (assuming 8"
> normal weight solid concrete walls), we get a U-factor of U =
> 0.740 for the slab edge.
>
> Doing an area weighted U-factor calc: U_eff = U_1 *A_1 +U_2
> *A_2 /(A_1 +A_2 ) or in this case, factoring out the Length of
> the wall section we use: U_1 *H_1 +U_2 *H_2 /(H_1 +H_2 ) =
> (0.0785*8 + 0.740*8/12)/(8+8/12) = 0.1294 or an effective
> R-value of 7.73, which is pretty close to the R-7.4 claimed, a
> difference of about 4% in U-value. Maybe I'm cynical, but to
> me that seems close enough.
>
> I only spot checked this assembly, so maybe there is more
> impact with different construction types.
>
> Another interesting tid-bit: Apparently the much vaunted
> fin-effect is actually pretty minimal. If you look at the
> results of the exposed slab-edge condition vs the full balcony
> fin-effect, the balcony scenario actually shows slightly
> BETTER thermal performance. Odd.
>
> *Nathan Miller **-****PE, LEED^® AP BD+C, CEM*
>
> /Mechanical Engineer/Senior Energy Analyst /
>
> *RUSHING*| *D*206-788-4577 <tel:206-788-4577> |*O*206-285-7100
> <tel:206-285-7100>
>
> *www.rushingco.com <http://www.rushingco.com/>*
>
> *From:* equest-users-bounces at lists.onebuilding.org
> <mailto:equest-users-bounces at lists.onebuilding.org>
> [mailto:equest-users-bounces at lists.onebuilding.org] *On Behalf
> Of *Bishop, Bill
> *Sent:* Monday, November 04, 2013 1:42 PM
> *To:* David Griffin; 'Coleman, Kevin';
> equest-users at lists.onebuilding.org
> <mailto:equest-users at lists.onebuilding.org>
> *Subject:* Re: [Equest-users] Slab extending through wall
>
> Here's a timely report on effective R-values of assemblies
> with slab/balcony thermal bridges:
>
> The Importance of Slab Edge and Balcony Thermal Bridges
> <http://www.rdhbe.com/database/files/library/Balcony_and_Slab_Edge_Thermal_Bridges___1___R_values_and_Energy_Code_Canada__Sept_24_13.pdf>
>
> Regards,
>
> Bill
>
> *William Bishop, PE, BEMP, BEAP, LEED AP | Pathfinder
> Engineers & Architects LLP*
>
> *Senior Energy Engineer*
>
>
>
> webCertified_logo_colorRGB72DPI.jpg
>
> 134 South Fitzhugh StreetRochester, NY 14608
>
> T: (585) 325-6004 <tel:%28585%29%20325-6004> Ext. 114 F: (585)
> 325-6005 <tel:%28585%29%20325-6005>
>
> bbishop at pathfinder-ea.com
> <mailto:wbishop at pathfinder-ea.com>www.pathfinder-ea.com
> <http://www.pathfinder-ea.com/>
>
> PSustainability -- the forest AND the trees.P
>
> *From:*equest-users-bounces at lists.onebuilding.org
> <mailto:equest-users-bounces at lists.onebuilding.org>
> [mailto:equest-users-bounces at lists.onebuilding.org] *On Behalf
> Of *David Griffin
> *Sent:* Monday, November 04, 2013 4:20 PM
> *To:* 'Coleman, Kevin'; equest-users at lists.onebuilding.org
> <mailto:equest-users at lists.onebuilding.org>
> *Subject:* Re: [Equest-users] Slab extending through wall
>
> Kevin,
>
> I'm fairly sure eQUEST is not even going to closely
> approximate the heat loss/gain accurately unless you dial the
> loads in manually which means you have to calculate them by
> hand first. I suggest referring to ASHRAE-D-RP-1365 for
> guidance on estimating the loads. The section you are
> interested in starts on page 35.
>
> Thanks,
>
> **
>
> *David W. Griffin II*
>
> Energy Analyst
>
> ETC Group, LLC
>
> 801-278-1927 x 128 <tel:801-278-1927%20x%20128>
>
> Cell 480-736-2945 <tel:480-736-2945>
>
> dgriffin at etcgrp.com <mailto:dgriffin at etcgrp.com>
>
> www.etcgrp.com <http://www.etcgrp.com>
>
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> *From:*Coleman, Kevin [mailto:kcoleman at nexant.com]
> *Sent:* Monday, November 04, 2013 11:56 AM
> *To:* equest-users at lists.onebuilding.org
> <mailto:equest-users at lists.onebuilding.org>
> *Subject:* [Equest-users] Slab extending through wall
>
> I am evaluating a new 10-story hotel design that is proposing
> glass curtain walls and pre-tensioned concrete floors that
> project beyond the walls. On 3 sides the projections are
> minimal (6 inches). However, on one side, the projections
> extend about 3 ft.
>
> For the small projections, I intent to use the following
> method recommended in the thread below. "In screen 4 of 25 of
> the DD shell wizard you can specify "Slab Penetrates Wall
> Plane" (check box)."
>
> I am interested in any tips for modeling the thermal impacts
> of the larger projections. Thoughts? (I plan to use window
> shading for the light/shading impacts.)
>
> I am hopeful that the analysis will help convince the design
> team to incorporate some insulation and thermal breaks!
>
> Thanks in advance!
>
> Kevin
>
> Brian Fountain bfountain at greensim.com <http://greensim.com>
>
> Mon Dec 6 11:45:18 PST 2010
>
> Previous message: [Equest-users] balcony
>
> Next message: [Equest-users] Shading
>
> Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]
>
> In screen 4 of 25 of the DD shell wizard you can specify "Slab
>
> Penetrates Wall Plane" (check box). If you do, eQUEST created
> a new
>
> wall type of height equal to your slab thickness and composed
> of 1' of
>
> concrete plus any slab edge insulation you specify on the same
> wiz
>
> screen. That provides a parallel path for the heat transfer
> from the
>
> balcony or slab edge. Not exactly 2D heat transfer modelling
> -- but at
>
> least you aren't ignoring the effect of the slab edge or balcony.
>
> *Kevin Coleman, CEM, LEED AP*?*Project Manager **?****Nexant,
> Inc.****?** Demand Management *
>
> 1232 Fourier Drive, Suite 125?Madison, WI 53717 ?608.824.1230
> <tel:608.824.1230> ?_kcoleman at nexant.com
> <mailto:kcoleman at nexant.com>_
>
> P Please consider the environment before printing this email**
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