[Equest-users] Slab extending through wall
David Reddy
david at 360-analytics.com
Tue Nov 5 14:47:54 PST 2013
My guess is that the 3-D thermal model uses a pretty simple surface
convection/radiation assumption, like an air film. To properly model
the fin effects, the thermal model would need to be coupled with CFD and
a radiation model to account for the more complex heat transfer effects
associated with "fins".
On 11/5/2013 2:25 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. 114F: (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>
>
> Copy of ETC_LogoOnly2_rgb_sm.png
>
> *Energy Engineering for a Sustainable Future*
>
> 1997 South 1100 East, Salt Lake City, UT 84106-4471
>
> -------------------------------------------------------------------------------------------------------------------
>
> CONFIDENTIALITY NOTICE This e-mail transmission, and any
> documents, files or previous e-mail messages attached to it may
> contain confidential information that is legally privileged. If
> you are not the intended recipient or the person responsible for
> delivering it to the intended recipient, you are hereby notified
> that any disclosure, copying, distribution or use of any of the
> information contained in or attached to this transmission is
> strictly prohibited. If you have received this transmission in
> error, please immediately notify us by telephone at (801) 278-1927
> <tel:%28801%29%20278-1927> and destroy the original transmission
> and its attachments without reading them. Thank you.
>
> *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**
>
>
> _______________________________________________
> Equest-users mailing list
> http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
> To unsubscribe from this mailing list send a blank message to
> EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG
> <mailto:EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG>
>
>
>
>
> _______________________________________________
> Equest-users mailing list
> http://lists.onebuilding.org/listinfo.cgi/equest-users-onebuilding.org
> To unsubscribe from this mailing list send a blank message to EQUEST-USERS-UNSUBSCRIBE at ONEBUILDING.ORG
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20131105/9cd14724/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/png
Size: 161932 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20131105/9cd14724/attachment-0004.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/png
Size: 130868 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20131105/9cd14724/attachment-0005.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/jpeg
Size: 3124 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20131105/9cd14724/attachment-0004.jpeg>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: image/jpeg
Size: 1559 bytes
Desc: not available
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20131105/9cd14724/attachment-0005.jpeg>
More information about the Equest-users
mailing list