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: 2408

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.  Home Energy Pros is sponsored by the Better Buildings Residential Network.

Latest Activity

Bijou Lulla posted a blog post

ENERGY EFFICIENCY RETROFITS.....IN NUMBERS WE TRUST

There has been much ado about the recent paper published by E2e; Do Energy Efficiency Investments…See More
5 hours ago
Mariusz Chorazy posted a blog post

Here are a few tips to keep your air conditioning bill low

TAKE GOOD CARE OF YOUR AIR CONDITIONER – Like any major appliance, your AC requires regular…See More
yesterday
Dale Pickard replied to Rod Fox's discussion Does altitude affect AFUE? or just the input/output BTUs?
"Morgan, I got this below from the Knight installation manual. I note a few things, -These…"
yesterday
Dale Pickard replied to Rod Fox's discussion Does altitude affect AFUE? or just the input/output BTUs?
"Hans, The car manufacturer's are doing it with mass flow sensors and oxygen sensors…"
Saturday
Dale Pickard replied to Rod Fox's discussion Does altitude affect AFUE? or just the input/output BTUs?
"I was trying to avoid naming manufacturers, but I was going by the published information for the…"
Saturday
Eric Kjelshus replied to Rod Fox's discussion Does altitude affect AFUE? or just the input/output BTUs?
"I look at this not about AFUE,  but flue gas dewpoint.  If your burn rate is rotting the…"
Saturday
Bob Blanchette replied to Kirsten Richnavsky's discussion Crawl spaces and attics: OSHA to implement new rule on confined spaces
"Keeping HVAC equipment out of attics should be part of the new code. "
Saturday
Linda Wigington replied to Linda Wigington's discussion Weigh in - Honorable Mention? 2nd Base? Half-Way There? 50% Better? On the Path? in the group 1000 Home Challenge
"Nickie -  Good points. I think it is easy enough to flag or designate projects that achieve…"
Friday

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service