[Equest-users] Window Assembly U, SC Values

[Alex Krickx]

Hi Jason,

I really can't comment on the LEED process - but you can input frame conductance separately from a glass package in eQUEST - which allows the software to calculate full-frame values. Although you won't be using NFRC certified numbers (as you point out- for your glass/frame combo they don't exist) - but I would say that inputting frame conductance and glass performance separately and letting the software area-weight them to get full-frame performance gets you pretty close to a hypothetical NFRC number.

Here's what I think the process looks like:
You need to use Window5 to determine what the frame conductance is - I would expect that the frame conductance doesn't vary too much in different sized windows. From an energy modeling standpoint (not sure what LEED/NFRC would say) I would pick a typical size window and model that in Window5 - making the assumption that the calculated frame conductance is valid for the other sizes in your building.

Going back to eQUEST- I would think that you have your baseline (say double pane low-E in an aluminum frame). To set up your "improved windows" case, create a parametric run that first changes the glass to your better glass, and then changes the frame conductance to match what Window5 outputs.

This approach would let eQUEST take care of calculating full-frame performance, and area-weighting the glass and frame. The only problem with this approach is that you ignore the Edge-Of-Glass performance that Window5 calculates, and eQUEST doesn't take into account. Not sure a way around that one yet.

Just an idea- good luck!

Cheers,
Alex

Alex Krickx
Building Energy Specialist
[cid:image001.jpg at 01CB5EED.10EF00F0]
1250 Elko Dr, Sunnyvale, CA 94089
(t) 408.541.8124

Warning: The information contained in this e-mail may be privileged attorney-client communications or attorney work product and/or proprietary and confidential.  If the reader of this message is not the intended recipient then you have received it in error and any review, distribution or copying of this message is prohibited and you are to notify us immediately by reply e-mail and delete the original message immediately.



From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Jason Wendel
Sent: Tuesday, September 28, 2010 7:35 AM
To: 'equest-users at lists.onebuilding.org'
Subject: [Equest-users] Window Assembly U, SC Values

I got the review comment back from LEED that I needed to use the window assembly U-Value and SC Value, not the center of glass.  Unfortunately we have the problem, and it sounds like others do too on this forum, that the glass manufacturer gives values for the center of glass values, and then sells their glass to the frame guys to get the frames that the owner and architect want.  Neither one is willing to NFRC certify their product.  So, my options are to use the values in ASHRAE 90.1-2007 Table A8.2 which are horrible, or model the windows on LBNL Window5.
There are lots of windows and lots of different sizes of windows in the model, so my plan is to find the area (square feet) of each window, and then run Window5 on typical windows in 5 square foot increments (5, 10, 15, 20, etc. square foot windows) so that I can run 10 windows instead of 150, and then put it all in a spreadsheet and solve for the weighted averages.
If I put the weighted average of the window values into Equest, will they accept that?  Has anyone ever tried it?  I'm in the process of doing another LEED certification that will be using the same technique if it works, but I won't know if it was accepted in the first instance before I submit the second project.

Thanks,

-Jason

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20100928/9ae92b4d/attachment-0002.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 5602 bytes
Desc: image001.jpg
URL: <http://lists.onebuilding.org/pipermail/equest-users-onebuilding.org/attachments/20100928/9ae92b4d/attachment-0002.jpg>