Window U-Value

Oberon

The very best energy-performing triple pane windows on the market today with a triple silver softcoat LowE coating applied to surfaces 2 and 5 and a krypton infill can reach U.1 or R-10. This is an overall rating and not just center-of-glass.

This also includes a warm-edge spacer system with the the IG slightly recessed into the sash glazing reglet to minimize heat loss thru the edge of the glass, and a foam-filled insulated vinyl or fiberglass sash/frame system.

This would be exceptional energy perfromance.

U-.19 would be considered excellent energy performance in a triple pane and really exceptional performance in a dual pane - and it is possible to get U-.19 in a dual pane using current technology - but difficult and expensive.

There is an IG system on the market that claims a U-.05 for their top performing system (R-20), and I while I personally accept their numbers, there have been significant longevity and performance problems with this particular system in the past. Since window companies don't like those sorts of problems, that particular system is available thru relatively few window companies.

There are two primary types of LowE coatings available - pyrolitic or hard coat - and sputter or soft coat.

Pyrolitic coatings are primarily tin oxide and are applied to the upper surface of the glass in a process called Chemical Vapor Deposition or CVD. In the CVD process, vapor directed to the hot glass surface reacts to form a ceramic coating while the glass is still semi-molten in the tin bath portion of the float process.

Sputter coats are applied to the glass surface as multiple layers of metals and metal oxides in a series of plasma-filled vacuum chambers in a process called Magnetron Sputtering Vacuum Deposition or MSVD.

Coatings are often referred to as LowE, LowE2, LowE3...While LowE is used generically to indicate either a hardcoat or single-silver softcoat, LowE2 or LowE3 is used generically to indictae the number of layers of silver in the coating.

It is not uncommon for folks interpret LowE2 as two separate sputter coatings applied to surfaces 2 and 3 of a dual pane IG unit, but that is actually not the case. Coating both surfaces 2 and 3 in any IGU configuration is almost a guarantee of broken glass or seal failure because of heat trapped in the airspace between the two lites. Dual pane windows (with some very rare exceptions) do not have LowE coatings on both lites.

In fact, when dealing with triple pane IGU’s and having LowE coatings applied to two different lites the coatings are almost always applied to surfaces 2 and 5 in order to avoid excessive heat buildup in the IG airspace - if for example the coating was placed anywhere on the inner lite rather than the two outboards.

Dual or triple silver sputter coats (low solar heat gain products) are generally built to surface #2 of a dual pane IG unit, while a single silver (high solar heat gain) or a pyrolitic coating is often built to surface #3.

In a heating dominated climate, the two reasons for placing the LowE coating on the #3 surface of the IGU is to allow for solar heat gain in the winter and to block the transference of the heat from inside the home to the outside.

High Solar Heat Gain (or HSHG) coatings and Low Solar Heat Gain (or LSHG) coatings are all designed to block far - or longwave - infrared energy. This is the range that includes typical household-produced heat. This is also the frequency range of heat that is produced when the sun warms an object – the heat you feel "reflected" from a hot wall or sidewalk on a hot, sunny summer day. While direct solar energy is shortwave IR, the heat released by a sun-warmed object is longwave IR…and hopefully that made sense.

A typical hardcoat or single-silver layer softcoat works in this application since all types of LowE coatings block the far infrared energy - thus keeping winter heat indoors - but neither is designed to be effective at blocking shortwave infrared - thus "allowing" solar heat access to the home - winter or summer.

Placing a high solar gain coating on surface #3 maximizes the level of solar heat gain thru the IG unit which can be an advantage in winter and can also be a disadvantage in summer.

A Low Solar Heat Gain product, on the other hand, is designed to block both near and far infrared energy. It will keep heat - including direct solar gain – from passing thru the window in both summer and winter.

These coatings are placed on surface #2 to maximize effectiveness against direct solar gain by blocking solar heat before it can pass into the airspace in the IG unit – and into the home.

And, as usual, I got carried away and I used way too many electrons describing LowE coatings (and ended up a bit off-topic as well)!

dougchips

Oberon, I enjoy reading your posts on the window forums (you get around) but I fail to see how you can get a .19 out of a double pane. If it is possible then the same technology should produce a .10 or .14 when it comes to triple panes. Glass can only be so thin before it breaks, Argon and Krypton have their limits, frames can only be filled with so much foam, spacers.............. I must be missing something, maybe IGU thickness? I know some people are playing around with a 1" IGU for their triple panes.

__________________
To get the best replacement windows, or sun rooms contact the replacement windows experts at FHI Vinyl Window Company.

Walker1

Oberon,
What do you think of Cardinals LoĒ³-366 with its triple layer of silver? The numbers seem impressive.

easy sider

Low emisity coatings and argon gas were developed to reduce air-conditioning costs in the sun belt states. The insulating values of these insulated glass units in colder climates is insignificant as there is not much energy savings with units lower than U .39 and as high as U.50.

The type of of window frame and the style of window have more to do with energy savings than the seal unit.

Home Serve

Easy rider, If this is so than why does the research say otherwise? See below information from a COLD climate.

On same subject it does say that testing done on a single story home in International Falls, MN with a basement, gas furnace, A/C and 300 sq ft of window area resulted in the following determination:

Every .01 U-value improvement in the windows resulted in a reduction of approx. 400 lbs of CO2 and an energy savings of approx. 50.00 annually.

Over next 20 years with 5% annual increase in utility rates:

Comparing U-value of .19 versus .32
period savings
5 years 3,591.66
10 years 8,175.63
15 years 14,026.07
20 years 21,492.87

Research source: by Tru-Seal Technologies using RESFEN 5.0, a computer program which is the industry standard for calculating the heating and cooling energy performance of windows.

Thanks,
Dave

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Missouri Remodeling Company with services for Replacement Windows Vinyl Siding and Entry Doors

easy sider

A sealed unit with a low u value in an aluminum frame, with out a thermal barrier, would negate the energy saving of the low u value of the ig unit. Most test results are not actual results as there is no such thing as a model home environment. There are many variables when it comes to a persons family size and living habits that would influence real energy savings.

In an office building with a controlled environment the energy savings could be achieved.

A sealed unit with a low u value in a vinyl xo slider frame in reality would be less energy efficient than a vinyl framed picture window with a higher u value because of air infiltration.

Energy Star rated windows will get a home owner their rebate and tax credit and every upgrade above Energy Star is over kill in a home environment.

dougchips

Support this statement, it is weak and false.

__________________
To get the best replacement windows, or sun rooms contact the replacement windows experts at FHI Vinyl Window Company.

easy sider

Most homeowners in the USA would not see a benefit equal to the cost of the purchase of these upgrades as the above schedule indicates. The science behind this schedule is only theory as it was one or a few structures tested under optimal conditions. When a home owner upgrades the windows in their house its usually because the existing windows are worn out. The window frame is the real energy problem in most older homes, not the sealed unit. The metal frames conduct heat and cold into the house. Switching to a vinyl frame solves this problem.

These upgrades are useful in a controlled environment such as large office buildings but not as useful in a home environment. The Federal Government has listed Energy Star windows as a product that qualifies for a tax credit. Many electric companies offer rebates for energy star products including windows.

Home owners building new homes in extreme climates would benefit from upgrades that exceed energy star minimums, however, most of the population in the USA living in moderate climates would not see much of a difference.

The upgrades would increase the cost of the window by 30 to 200 percent depending on who is selling them. The upgrades are a useful way of adding value to a window to sell them to people who want more from their window. The upgrades and the above information on return on investment feel more like a sales pitch in a brochure than real science.

The statement that upgrades beyond energy star minimums is overkill for most home owners is more believable than the dollar amounts saved by upgrading in the energy saving schedule posted in thread 25.

Oberon

Dougchips,

In my original post I stated that it was "theoretically possible to get U-.19 in a dual pane using current technology - but difficult and expensive". Then I removed theoretically while editing the thing. On hindsight I should have left it in. The comment really was meant as an "in general" reply to the .19 in the original post and it wasn't meant to suggest that such units are available; it was more of a "thinking-out-loud" comment and under the circumstances I should have been more clear.

Although I know of no dual panes that are in the .19 range, there are some in the low/mid .20's as there are triples in the .12 range, and there are folks out there claiming that their windows can achieve .10 or even a bit better. There are a few companies even offering quad panes...

A dual pane window with a softcoat dual or triple layer silver coating and argon gas will slightly outperform a triple pane window made with clear glass. The real advantage of a triple pane is that since there is that extra glass layer the manufacturer now has the ability to coat two different surfaces with the coating.

As a general rule, triple panes come in two varieties – one version has a relatively narrow space between the lites – consider a 1" overall dual pane and dropping another lite between the first two; then there is a triple pane with a wider spacing between the lites - kind of like taking two "standard" dual panes and removing a lite from one and slapping the remaining parts together.

Both work, but there are some differences worth considering.

The narrow airspace version works best when surfaces are dual or triple silver softcoat LowE coated and krypton gas is used between the lites. Krypton gas performs at its energy-saving best in a narrow space of about 3/16" or so. In this configuration it is possible to achieve a U factor in the .1 range, although that is something of an ideal. Still, this configuration is very energy efficient and works really well.

The wider triple pane version should generally have an airspace of about 7/16" between each lite plus or minus a little. Again, the advantage is in having the coating on two separate lites. In this case, argon gas would be the most cost effective fill, rather than krypton, simply because argon is cheap and plentiful and at the 7/16" spacing it is almost as good as krypton in performance numbers – not quite as good – but the slight insulating advantage of krypton in this configuration doesn't offset the additional cost of the gas.

The biggest disadvantage of the wider triple pane is the physical size of the IGU – or more precisely the width of the glass package.

While manufacturers who use a wider airspace IG must build their sash to accommodate the depth, not all companies can or will do so, so not all companies can offer a triple pane package in this configuration. And while the wider-spaced glass package (with argon fill) version may have slightly higher U-factor when compared with the narrower version (with krypton fill) IG, the wider glass package requires a thicker sash/frame as well so that the slight energy advantage of the narrow air-space triple pane (again, thinking krypton gas) may be offset by the potential R-value advantage of the deeper sash/frame package using the wider air-space unit.

Oberon

Walker1,

Cardinal's LoE³-366 has the best energy performance numbers of any LowE currently on the market.

As you say, the numbers are very impressive. It is truly amazing that a nearly-invisible, microscopically thin coating on the glass surface can increase the performance of the glass/window to such a degree over clear glass.


The original LowE coatings were hardcoats and they were introduced in the north, in heating dominated climates, in order to improve window performance during the heating season. Hardcoats offer virtually no advantage over clear glass during summer cooling season or in the south where cooling was/is the primary consideration.

The first softcoats were developed in Europe and were later introduced into North America (by Cardinal as a matter of fact), in the early 80's.

The original softcoats, like the hardcoats, were introduced into heating dominated climates to improve window performance in winter. Like the hard coats, the single-silver softcoats have excellent longwave heat-blocking ability, but relatively poor short-wave or solar-heat blocking. Thus they worked great in the North, but were not always considered for southern applications even though single-silver softcoats have about a 12-14% lower U-factor than hardcoats and they block about 12-14% more direct solar heat gain than do hardcoats.

In the early 90's, the dual-silver or LoE² (Cardinal specific) or LowE2 (generic) softcoat was introduced. The dual-silver coating resulted in improved U-factor versus the hardcoats or single-silver softcoats, as well as having significantly better Solar Heat Gain Coefficient (SHGC) numbers than either predecessor. This was the first coating that was applicable to cooling dominated climates as well as heating dominated climates.

Jake Stevens

Anybody thats a contractor can buy the Paradigm window. The cost to the contractor vary on how big the contractor is. The center of glass is a test that they do in house just to get a better tested. With NFRC all companys have the same size window and are based on a whole window. No windows are rated on the R value. To get a R value they would have to insulate by improving the wall space that there install.

When we install windows (replacements) we like to bed in the windows and seal the outside. We use fiberglass insulation aroung the windows. One thing that I find is that a lot of companys screw in the window then insulate. If you do that you can't get in as much insulation in. What we do is bed the window, set it in the hole, use a Awl at the top of the window to hold in the hole, ( you can use a nail) then you can push to one side and insulate and then the other side. This also helps to square the window. We lay insulation under the window and under the cap. This is a little long bu I hope it helps.

Oberon

Easy sider,

You have made a number of definitive statements on this thread that are incorrect or else are opinions that may not be supported by the facts.

With all due respect and regard for other folks' opinions and statements on threads like this one, and in the interest of a well-rounded discussion, I am curious where some of your information comes from....

Low e square or double low e is a hard coating that needs to be applied twice to equal one coat of wet low e.

This statement is simply not correct.

The sealed unit is measured top, center and bottom for argon gas and these measurements are allowed a percentage difference since the argon will settle to the bottom of the sealed unit

Can you please explain how the unit is measured top, center and bottom for argon gas and the process or formulas used to allowed a percentage difference?And who actually does this?

Low emisity coatings and argon gas were developed to reduce air-conditioning costs in the sun belt states. The insulating values of these insulated glass units in colder climates is insignificant as there is not much energy savings with units lower than U .39 and as high as U.50.

This entire statement is incorrect. If you have references to support it, I would certainly want to read them.

Most homeowners in the USA would not see a benefit equal to the cost of the purchase of these upgrades as the above schedule indicates.

sealed unit with a low u value in a vinyl xo slider frame in reality would be less energy efficient than a vinyl framed picture window with a higher u value because of air infiltration

The upgrades would increase the cost of the window by 30 to 200 percent depending on who is selling them

Energy Star rated windows will get a home owner their rebate and tax credit and every upgrade above Energy Star is over kill in a home environment

A sealed unit with a low u value in an aluminum frame, with out a thermal barrier, would negate the energy saving of the low u value of the ig unit

Given that these are simply opinions, I am curious if you have any data to support them?

dougchips

Oberon, the people who make windows tend to give window dealers tainted information. In the past I've been talked into believing all sorts of garbage. These are some of things that dealers tell homeowners about triple pane windows:

1. They are to heavy to open.

2. The 3rd piece of glass can not be supported by the frame, the window will fall apart.

3. The extra Low E coating makes the window so dark you can't even see out of it.

__________________
To get the best replacement windows, or sun rooms contact the replacement windows experts at FHI Vinyl Window Company.

Oberon

I agree. There are many misconceptions concerning triple pane windows. In real life, a well designed and made triple pane window will be no more difficult to operate than any well-made dual pane or even single pane window, although the triple pane IG can be pretty darn heavy! A cheap, poorly made dual pane is going to be much more of a problem than a good triple pane.

Considering that glass weighs 155 lbs per cubic foot, one square foot of 1/8" (or 3mm or double strength) glass weighs about 1-1/2 lbs. So, a nine sqft lite would weigh 13-1/2 lbs. Turn it into a dual pane and you have 27 lbs. Add a third lite and you are looking at a nine sqft IG that weighs 40 lbs - that is without the rest of the window....

easy sider

Oberon
It appears you are correct in the process of making a sealed insulated glass unit. My original statements on Low e are dated and were obtained on the golf course, not the Internet. Atrium and Jeldwen use soft coat Low e , (Cardinal 272) now, but in the past used hard coat.

Argon gas is measured in a sealed unit at our local Atrium with a duel probe sensor to 90% argon in the unit. At our local Jeldwen facility the sealed unit is processed with a similar type of duel probe sensor. These sensors are sniffer type. The reason given for 90% argon in the sealed unit is that argon will expand and damage the ig unit. Jeldwen also uses a hand held unit that emits an electrical charge through the glass to measure argon density and the unit is tested top, center and bottom with the results recorded.

As far as my statements about energy savings, they are correct. A home owner buying replacement windows receives more energy savings from switching to a non-conductive frame than a upgrade on the sealed unit.
u values of .35 = energy star rated window . U.35 divided by 1 = R 2.86. Clear insulated glass u.50 divided by 1 = R-2. The R-.86 difference in the windows will not equal thousands of dollars in energy savings. Even at u.19 divided by 1 = R-5, that's only 3 r values difference from clear insulated glass. It would cost more than what its worth to most home owners to replace with any thing higher than the energy star minimum. At the energy star minimum a home owner receives the tax incentives and rebates to off set the cost of the improvements.

The test house used to calculate energy savings in the above thread is subjected to that house only as test results will vary. Thermal imaging will show were energy loss occurs and although the windows will show up as a point of energy loss because of the lower r value, so will other components of a house. Many things combined can affect energy savings such as air infiltration, heating/cooling equipment, insulation and even building color.

Different businesses sell windows at different prices. The mark ups are all over the place. This is a fact. Go get some bids if you dont believe this.

dougchips

http://www.efficientwindows.org/city...dtype=WN&id=17

I don't care/know how to update these figures based on our current heating costs, if someone cares to please post the correct figures for a .35 compared to a .19.

__________________
To get the best replacement windows, or sun rooms contact the replacement windows experts at FHI Vinyl Window Company.

easy sider

1/u = r ........ 1/r = u

Oberon

Imagine a single wall in a home that is 100sqft. For this example I am going to assume that this wall has an overall R-value of 10 including the effect of studs, outlets, etc (but not windows), and just say that out wall averages R-10 across its total surface.

If I add a 5’x 2’ (10sqft) window to this wall and this window has U factor of .35.

Wall = R10 or U.1
Window = U.35
Window = 10% of wall
Wall = 90sqft, window = 10 sqft, overall 100 sqft
Wall = 90 sqft x U.1 = 9
Window = 10 sqft x U.35 = 3.5
9 + 3.5 = 12.5/100sqft = U.125 or overall wall R value of 8.

Now if we change to a window with a U.19 –

Wall = R10 or U.1
Window = U.19
Window = 10% of wall
Wall = 90sqft, window = 10 sqft, overall 100 sqft
Wall = 90 sqft x U.1 = 9
Window = 10 sqft x U.19 = 1.9
9 + 1.9 = 10.9/100sqft = U.109 or overall R value of 9.17.

So, changing from U.35 to U.19, in this example, results in an improvement of 84% in window performance (also keeping in mind that doubling insulative value doubles performance), but it also results in an improvement of 15% in the entire wall structure – the higher the percentage of window sqft in the wall; the more the overall R-value improvement if using the lower U-factor window.

easy sider

Oberon
Your last thread was very interesting and easy to understand. How did you calculate the the R-1.17 difference to 84% improved window performance. I understand that R-1.17 would be 15% of R-10.

Oberon

No trouble -

If an R-2 is a 100% increase over an R-1, or an R-10 is a 100% increase over R-5 then using the same formula = (x-y)/y*100

(10-5)/5*100 = 100% or 10 is a 100% increase

Or, if gas was $2.00 last week and $4.00 this week, then what is the percentage increase from last week to this week?

(4-2)/2*100 = 100%


Keeping in mind that the 84% was simply the percentage improvement between .35 versus .19 in the window illustration -

(.35 -.19)/.19*100 = 84% increase

The 15% improvement in the overall wall performance is between R-9.17 and R-8.

The wall would have an R-value of 9.17 using the .19 window and R-8 using the .35 window in the example.

(9.17-8)/8*100 = 15%

Dougchips, does this answer at least part of what you meant when you asked for actual performance figures?