[Bldg-sim] Above Grade External Wall Area Weighted U-value Calculation

Jeremiah Crossett jcrossett at phasechange.com
Mon Sep 30 09:13:25 PDT 2013


You might find the report by morrison hershfield useful for researching
methodologies.
http://www.morrisonhershfield.com/ashrae1365research/Pages/Insights-Publications.aspx

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*Jeremiah D. Crossett  | Senior Analyst  |  Phase Change Energy Solutions*
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120 E. Pritchard St.  | Asheboro, NC 27203  | Mobile 503-688-8951
www.phasechange.com
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On Mon, Sep 30, 2013 at 9:04 AM, Nathan Miller <nathanm at rushingco.com>wrote:

>  It isn’t like the reviewer is making things up, I think it is pretty
> clear from the language of 90.1 Appendix G that you have to account for
> these exposed slab edges. Frankly 90.1-2007 is a little more forgiving,
> allowing for area-weighted U-factors for the entire wall, I believe
> previous versions of Appendix G (2004 for example) actually specifically
> required that you model uninsulated assemblies as their own discrete wall
> types. See excerpts below:****
>
> ** **
>
> ASHARE 90.1-2007 Appendix G:
> ****
>
> ** **
>
> ASHRAE 90.1-2004 Appendix G:****
>
> ****
>
> We usually model the slab edges as separate walls (only about 1 foot high)
> and make the other walls “shorter” when you take out this area. If you
> don’t do this in the wizard, you can set up a macro in the .inp to to it,
> but it takes a bit of work. Frankly if you already have the model set up
> without slab areas, it seems much easier to to do the weighted U-factor
> calculation. ****
>
> ** **
>
> *Nathan Miller **-** **PE, LEED®AP BD+C, CEM*
>
> *Mechanical Engineer/Senior Energy Analyst *
>
> *RUSHING* | *D* 206-788-4577 | *O* 206-285-7100****
>
> *Our new web site:** **www.rushingco.com***
>
> ** **
>
> *From:* bldg-sim-bounces at lists.onebuilding.org [mailto:
> bldg-sim-bounces at lists.onebuilding.org] *On Behalf Of *Sherif Farag
> *Sent:* Sunday, September 29, 2013 9:32 AM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] Above Grade External Wall Area Weighted U-value
> Calculation****
>
> ** **
>
> Dear All,****
>
> I have submitted a project for review and received a comment requesting me
> to include the concrete slabs between floors (Not drop beams) in the
> External Wall' area weighted U-value calculation, the reviewer believes
> that concrete slabs acts as a thermal bridge and should be insulated from
> the outer side (The slab thickness), my understanding that concrete slab
> shouldn't be regarded as a part of the occupied area and therefore
> shouldn't be included in the area weighted U-value calculation.****
>
> I would appreciate if you can advise on the above query!****
>
> Thanks & Best Regards,****
>
> ** **
>
> *Sherif Farag*
>
> *Senior Sustainability Consultant*
>
> P.O. Box: 127842****
>
> Abu Dhabi, UAE****
>
> M: +971 55 199 0022 | E: sherif.sabr at gmail.com | Skype ID: sherif.farag9**
> **
>
> ** **
>
>
>
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