[Equest-users] Modeling Windows: Center of Glass vs Assembly

[Alex Krickx]

I've had some looks, nothing too deep, but I don't think I've ever seen a reference to edge-of-glass (EOG) performance, only COG and frame conductance... And I would also guess that when looking at COG values of U-0.3 (typical double pane low-E) and frame value U-1 (TB aluminum) that the edge of glass performance is not that good and would noticeably affect building energy use.

I don't know of any way of taking this into account. One option would be to figure out the area-weighted average conductance of the COG and EOG (1 U-factor that takes both components into account), the problem is that in order to input that into eQUEST, you would need to do it as a "simplified input" which I know people on this list-serv dislike doing.

I can't think of another way to account for EOG performance.

Alex

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Carol Gardner
Sent: Thursday, September 16, 2010 4:21 PM
To: STEVE SAMENSKI
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Modeling Windows: Center of Glass vs Assembly

Happy reading. I'm not sure exactly how eQUEST handles all of this but I would assume, oooh, dangerous, that if you put in your glass type carefully and take care to specify the width and type of frame you have, all of which are in the Wizards, you should be good. You could test the output by comparing it to a Win5 calculation of your COG U value and frame, or just import the Win5 data into the model.

Carol
On Thu, Sep 16, 2010 at 2:38 PM, STEVE SAMENSKI <steve at thespinnakergroupinc.com<mailto:steve at thespinnakergroupinc.com>> wrote:
Does anyone know definitively if eQuest calculates window assembly U-values based on user input?

As many have pointed out, the USGBC is now being careful about the distinction between center-of-glass U values and assembly U values.  I've been entering center-of-glass U-values and precise window geometry, counting on eQuest to do the heavy lifting for me.  Report LV-D says "U-VALUE INCLUDES OUTSIDE AIR FILM; WINDOW INCLUDES FRAME, IF DEFINED".  However, combing through several posts to this forum, some say eQuest doesn't really calculate an assembly's U-value, because it ignores the edge-of-glass effects due to the frame.  (Not to be confused with the thermal conductance of the frame itself, which I'm sure eQuest uses in its calcs.)  I'm hoping that one of the programmers can answer this, or maybe someone who got the story from a programmer.

I plan to read the ASHRAE Fundamentals Chapter on Fenestration this weekend.  Wish me luck.

Steve Samenski, PE, LEED AP, BEMP
Vice President - Sustainable Technologies
The Spinnaker Group, Inc.
http://equest-diary.livejournal.com/
www.thespinnakergroupinc.com<http://www.thespinnakergroupinc.com> <http://www.thespinnakergroupinc.com>
Become the solution... Join the USGBC!

_______________________________________________
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>



--
Carol Gardner PE
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20100916/5100cb0e/attachment-0002.htm>