Window U-Value

dougchips

Oberon, I'm trying to figure out the payback on triple over double. I like the chart on efficientwindows but it does not tell me what the difference is with our current oil prices.

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easy sider

Oberon
Thanks for the calculations. It would be interesting to know how enegy savings can be calculated into dollar amounts.
Thanks

Oberon

I think that efficientwindows.org probably is the best source on the web for getting basic cost information when dealing with windows, but it is pretty much impossible to keep it updated with the way fuel prices are changing. So, in the interest of playing with even more numbers...

R-value measures the thermal resistance of a material while U-factor measures thermal transference thru a material (preaching to the choir here).

The formula for computing U-value is: Btu / (hr x degrees F x sqft)

The formula for computing R-value is: (hr x degrees F x sqft) / Btu

The formula for computing heat transfer is: (BTU/hr) = (area / R) * ΔT
With ΔT = the temperature difference between what is inside and what is outside.

Converting U .35 and U .19 to R = R 2.86 and R 5.26 and still using our 10 square foot window:


If ΔT = 10°, then (10 sqft / R 2.86) = 3.5 * 10° = 35 BTU/hr
If ΔT = 10°, then (10 sqft / R 5.26) = 1.9 * 10° = 19 BTU/hr

Notice the relationship between BTU/hr and U factor in this first example? This relationship is simply the result of laziness on my part (from the very beginning) in picking numbers that I can do in my head because of the inverse connection...)

However, considering a more robust temperature differential:

If ΔT = 40°, then (10 sqft / R 2.86) * 40° = 140 BTU/hr
If ΔT = 40°, then (10 sqft / R 5.26) * 40° = 76 BTU/hr

Again, notice the relationship between BTU/hr and U factor? Using a 10 sqft window makes the rest of the calculations really easy because of R = 1/U and U = 1/R....

And finally, if we happen to have a mind-numbing ΔT of 100° (which does happen where I live), then:

(10 sqft / R 2.86) * 100° = 350 BTU/hr
(10 sqft / R 5.26) * 100° = 190 BTU/hr

And remember that is from a single, small window.

When building a new house, a builder can control many of the variables involved with calculating costs and ROI, but when remodeling and adding new windows the overall calculations (unless the home has an energy audit) can be difficult. There are many different variables to consider.

I would agree with easy sider that in most parts of the country the performance advantage of a good triple pane over a good double pane will not result in a significant enough payback to make up for the cost difference. But, in a harsh environment, more insulative value, whether window, wall, ceiling, etc. can result in some significant energy and cost savings.

Ed the Roofer

This is one of the most informative threads I have ever read on this site, both in regards to questions and answers.

Thank you all for the education.

Oberon, how did you get that triangle symbol keyed in? Do you have a better keyboard with math formula keys?

Ed

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Oberon

Ed,

Go to start;
all programs;
accessories;
system tools;
Character map

and you will find pretty much any symbol that you might want to use.

° Σ ¿ ψ Ф Ω Δ etc

easy sider

An old dog like me seldom learns any thing new. This info on this thread was one of those occasions.

Thanks

Oberon

This is a good thread, thanks as well.

Another interesting keyboard "trick" is Alt codes.

While typing here, hold down the Alt key while typing specific number sequences on the keypad (not the numbers on the alpha-numeric keys, must be keypad keys), release the Alt key and you get the same sort of symbols, letters, etc that you find in the character map.

For example, typing the numbers 0123 while holding the alt key down will result in (when the alt key is released) a { when the alt key is released.

Google Alt codes and you will be able to find several lists of such codes.

Enjoy!

dougchips

Search for his post on other forums as well, Oberon knows a thing or two about windows.

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Ed the Roofer

I will definitely do that.

Thanks for the suggestion.

Ed

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Oberon

Dougchips, thank you. I enjoy participating in interesting discussions and can't help but put my two-cents in...I get paid to do some of this stuff in my day job, so what the heck!

Dougchips and Easy sider, did the BTU calcs help any with cost analysis?

Ed, did you try the Alt key and "accessories" for finding symbols?

Ed the Roofer

Not yet. Didn't have the need for it right now, but I will save the method.

Thanks.

So far, their are too many Oberons on the internet.

Gaming

Plutos Moon

But I did find you one on a home and garden site.

Ed

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dougchips

I've been busy this week installing your (?) glass. Early next week I am going to spend some time with the numbers.


Is it true that Argon leaks form a IGU faster than Krypton? On the same note, the "Krypton gas shortage", truth or myth?

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Oberon

Krypton is harder to keep in an IG than is argon. The better IG systems can maintain argon loss at 1% per year, and there are a number of ways to measure argon in an IG (easy sider mentioned a couple in one of his posts).

Argon is plentiful, at about 1% of the atmosphere, and cheap. Krypton is rare at about .00011% of the atmosphere and it is not cheap.

There is not enough krypton "produced" annually to fill any meaningful percentage of the IG units manufactured in the US in one year, we would run out.

Ed the Roofer

I wanted to bump this thread up, because there was so much good practical knowledgeable information contained within it.

Also,

Would providing an Energy Audit be a feasable approach to showing clients their existing Heating and Cooling Loss spots, particularly regarding the Windows, to be able to provide a visual incentive, by using a FLIR IR Camera set up and showing the energy loss spots.

Yes, it would be feasable, but what is required to be able to conduct an Energy Audit, or at least a minimal Energy Loss study on their home and windows?

What is involved in becoming an Energy Audit Contractor???

Ed

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Home Serve

Good questions Ed, I am waiting to see some comments as you are.
Dave

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Ed the Roofer

I have a call in to the guy from this company in my area. He seems to have taken the step from just contracting to adding this to his arsenal of services.

http://www.performance-exteriors.com/homeowner.htm

Here are other links I discovered last night when I was thinking about this ad on to services available:

http://www.bpi.org/

http://www.eere.energy.gov/weatherization/apply.cfm

http://www.aceee.org/consumerguide/envelope.htm

http://hes.lbl.gov/

http://www.bpi.org/documents/BPI_Rec..._Providers.pdf

http://www.bpi.org/documents/BPI_Sma...Procedures.pdf

http://www.bpi.org/documents/BPI_Sta...e_Schedule.pdf

http://www.nachi.org/forum/showthread.php?t=30474

Ed

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davinci

i have been researching windows(various) for the past few months and have found that most of the so-called upgrades do not increase their effectiveness in real world settings. however, a few window companies that i have researched do. i just looked at a window that was 7/8 i.g. with argon/low-e with a u-value of 32 and another window with a 3/4 I.G /argon low-e with a u-value of 31. in theory the 7/8 should provide a better u-value. that is where quality comes into play. also,KRYPTON performs better in triple pane windows with smaller spacing whereas argon is more effective in wider spacing.another factor is the spacer that is used; most use a PPG intercept warm edge spacer and then some use a super spacer. as i posted in another thread,i think Gorell is one of the best windows out there that have all the specs we have been talking about. what separates them is that their claims are true and they are of the utmost quality. expensive but very good.

john haddad

I found this site that makes it easy to find your savings with windows. just convert the U value to the r value and plug and chug. the here is a link to the site: http://www.builditsolar.com/Referenc...sulUpgrade.htm

TyD

Pretty much a dead issue seeing how well everyone has covered this but the key points. The only window that can be in that "U" value range are triple pane w/kypton. Frankly, i've never seen a triple pane without it, doesnt work.
2nd, our frame and sash components are of a commercial caliber vs. lets say, Republic. Or when empire was doing windows, they too had triple pane windows wrapped in poop. Cadillac paint job on a yugo?
But it costs $100 bucks less per unit than mine do and if you can get the customer to only focus on that one aspect, good for you.
Just like SilverLine Windows by Anderson. What a joke, SilverLine was failing, Anderson bought them to compete with Pella's ThermaStar. Both products are terrible but people shop by name so what can you do?
I just cant sell garbage no matter what the cost.

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DuPontOne.com

Some customers just aren't worth it, thank you crapcustomers.com

enforcer

triple pane has a smaller spacing than double and that is why krypton is best used . krypton loses its effectiveness as as a space gets wider. for exapmle a 13/16 I'G is MUCH better off with argon than krypton. my defense against another window company is the quality of the pvc,the hardware,and all the cool features. i then say a competitors window may look good today but call me in 5 years......i also say you can buy a counterfeit POLO shirt in china town for 5 bucks instead of buying a real one for 75 bucks;they look and feel the same but after you wash them both,one falls apart in 2 weeks.