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: 4741

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

Videos

  • Add Videos
  • View All

Twitter

Latest Activity

Michael Wenzel is now a member of Home Energy Pros
4 hours ago
Stan Harbuck added a discussion to the group Energy Auditing Equipment for Sale, Trade or to Purchase
Thumbnail

4 Fans, Doors, Gauges, etc. for Sale - 4 Q4E 3300 Retrotec Fans, Doors, Drivers, etc.

4 Rarely used Q4E 3300 Retrotec fan sets (2010/2011) and all related equipment for sale, including…See More
7 hours ago
Stan Harbuck joined allen p tanner's group
Thumbnail

Energy Auditing Equipment for Sale, Trade or to Purchase

Discuss the pros and cons of the equipment you are interested in prior to purchase. Post equipment…See More
8 hours ago
Amber Vignieri posted a blog post
yesterday
Barbara Smith's video was featured

Weatherization: Crawl Spaces

Crawl Spaces - Training for Weatherization Installers. Re-posted from Seventhwave.org
yesterday
Kelly replied to Colin Genge's discussion What is the value of using a pressure pan to test outlets?
"Hi Colin, I like using the pressure pans at outlets to guide my inspections once I'm in the…"
Thursday
Leo Klisch commented on Home Energy Magazine's blog post Natural Gas is Becoming Less Attractive
"It seems a bit wasteful to use NG for such a low temperature application as space heat. If a heat…"
Thursday
HomeWiz posted photos
Thursday

© 2016   Created by Lawrence Berkeley National Laboratory.   Powered by

Badges  |  Report an Issue  |  Terms of Service