Anyone ever hear of a window, or unit of insulated glass, as having different winter and summer U values? 

 

This wasn't on an NFRC sticker.  It was on a glass manufacturer's spec sheet. 

 

They listed it like this:

 

Winter - Air / Argon  0.35 / 0.31

Summer - Air / Argon 0.32 / 0.28

 

Our program requires a U value of 0.30 to receive an incentive rebate.  So obviously, homeowners and contractors want to average the summer and winter Argon fill U values to come up with an average of 0.295 and call it good.

 

I think it is just a piece of insulated glass that they want to have installed/retrofitted into their existing wood windows, and get an incentive for that. 

 

Views: 2171

Attachments:

Reply to This

Replies to This Discussion

The winter U-value is what is shown on the NFRC labels, and should be used for code compliance and incentive programs. It is calculated at -18C (about 0F) outside, and 21 C (about 70F), and a roughly 15 mph wind speed. The summer U-value is calculated with conditions where it is warm outside and hardly any wind. This means that the U-value will be a bit better, but it is not a representative condition for heat losss. The Solar Heat Gain Coefficient (SHGC) is more important during periods with solar gain. So think U-value for heating, and SHGC for cooling.

Christian
WIndows and Daylighting Group
Lawrence Berkeley National Laboratory
Adam:

Currently in communication with this gentleman:

Andre Anders, PhD
Leader, Plasma Applications Group
Lawrence Berkeley National Laboratory
1 Cyclotron Road, MS 53, Berkeley, California 94720, USA
Tel. 510-486-6745, Fax 510-486-4374

He's circulating the information among his associates and will be in touch following the holiday. Will probably find it's way Christian at LBNL, who has responded since last I checked in.

BTW, Christian's advice to use the winter number is probably not what you wanted to hear regarding the available incentive. If 0.30 U is a common cut off # for incentives, I would expect manufacturers to work to that figure, although in a manufacturing environment, such changes may be a challenge. Perhaps a bit of latitude from incentive providers is in order...who is going to notice a U difference of 0.01 ?

Thanks for surfacing this mystery.
Steve, Adam,

Andre forwarded your question to me, that is why I responded here. Many manufacturers have products that meet U=0.30, since that was the cut-off for the IRS tax credit.

If you are looking for even better windows, you can take a look at this website, where you can find listing of manufacturers that meet U=0.22 and less.
http://www.windowsvolumepurchase.org/

Christian
Thank you for the replies! Our program does require NFRC stickers, so this guy is going to be out of luck anyways.

But I was curious about the different winter and summer U values anyways. Thanks for the response and clairificaiton!

Adam

RSS

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.

Latest Activity

Hal Skinner replied to Hal Skinner's discussion 'YGRENE' super fund for energy upgrade financing
"Hi again John, If you could directly answer these questions and comment on anything else related,…"
1 hour ago
Gregory Homan commented on Tom White's video
Thumbnail

The Future of Housing - And How Airtightness Can Help

"This is a reposting. The original is out of date due to the URL of the source video having…"
2 hours ago
Profile IconRick Causo, Sean McLoughlin, PAUL JOHNSON and 1 more joined Home Energy Pros
2 hours ago
Chris Dorsi posted a group
Thumbnail

International Home Performance Forum

A group dedicated to international collaboration among home performance practitioners.All topics…See More
2 hours ago
Tom White commented on Tom White's video
Thumbnail

The Future of Housing - And How Airtightness Can Help

"This video link has been deleted.  You can now view and comment on the updated video at…"
2 hours ago
Tom White posted a video

The Future of Housing - And How Airtightness Can Help

http://www.houseplanninghelp.com/80 The search for a new home can be daunting; whether it’s your first purchase, you’re relocating, or your family is increas...
2 hours ago
Corbett Lunsford's 2 videos were featured
3 hours ago
Sean Lintow Sr posted a blog post

http://thehtrc.com/2015/illinois-the-eri-the-iecac-resnet-the-final-push

Monday April 6th (10 AM to noon) will decide whether the ERI aka as the HERS option will be part of…See More
4 hours ago

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service