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: 1712

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

Glen Gallo replied to Tom Conlon's discussion Whole House Fans - Love 'Em or Not?
"Title 24 requires whole house fans in zones 8-14 in the prescriptive path only. With many…"
14 minutes ago
Jenn Saunders replied to Jenn Saunders's discussion iEnergyApp: Quickly generate professional reports for homeowners and get more contracts!
"Hey Tom, You are most welcome.  iEnergyApp is not free, but it is reasonable and pays for…"
27 minutes ago
Jenn Saunders posted a photo

Automatically Generate Clean Simple Reports for Homeowners

Stop spending hours cropping and resizing images, formatting and reformatting a Word document to…
34 minutes ago
Eric Sperline added a discussion to the group Energy Auditing Equipment for Sale, Trade or to Purchase
Thumbnail

Beware ebay seller "supermomofps"

I bought a blower door system on Ebay from "supermomofps"  The item was never sent and…See More
1 hour ago
Larry Nissman replied to John Shillito's discussion Fixing a water heater?
"I have to agree with Kurt. 2000 ppm is exceedingly high. I have tested hundreds of hot water heater…"
1 hour ago
Tom White's video was featured

Passive House Revolution - Film Trailer

Looking for energy-efficiency in buildings? There's no need to wait for new technology - Passive House buildings use 80-90% less heating and cooling energy.
1 hour ago
Diane Chojnowski joined Hal Skinner's group
Thumbnail

Radiant Control Coatings

A group where people who work with radiant barrier coatings can let others know all of their uses.See More
1 hour ago
Richard Beyer replied to Shawna Henderson's discussion High Density Foam -- Any Incidents of Cracking in Frame Walls as Studs Dry/Twist?
"Shawna foam pulling away from the studs due to over application will cause spontaneous…"
2 hours ago
Hal Skinner posted a group
Thumbnail

Radiant Control Coatings and their many uses.

A group where people who work with radiant barrier coatings can let others know all of their uses.See More
2 hours ago
Profile IconAlex Burnham and Annika Brink joined Home Energy Pros
2 hours ago
Kurt Shafer replied to Tom Conlon's discussion Whole House Fans - Love 'Em or Not?
"Reading the Invisco description you will find that it is designed to be surrounded by cellulose to…"
yesterday
Glen Gallo replied to Tom Conlon's discussion Whole House Fans - Love 'Em or Not?
"Kurt, I think cost of operation is always a factor but I am not sure I would leave it just cfm.…"
yesterday

© 2014   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service