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

Nathan Miller nathanm at rushingco.com
Mon Sep 30 09:04:24 PDT 2013


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:
[cid:image002.png at 01CEBDBC.188EDC00]

ASHRAE 90.1-2004 Appendix G:
[cid:image006.jpg at 01CEBDBC.188EDC00]
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(r)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<http://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<mailto:sherif.sabr at gmail.com> | Skype ID: sherif.farag9


-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130930/d43c29a7/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image002.png
Type: image/png
Size: 103514 bytes
Desc: image002.png
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130930/d43c29a7/attachment-0002.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image006.jpg
Type: image/jpeg
Size: 64314 bytes
Desc: image006.jpg
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20130930/d43c29a7/attachment-0002.jpg>


More information about the Bldg-sim mailing list