Who still makes high solar heat gain windows?

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#31 Post by Oberon »

Great discussion!

Wayside, I have a feeling from reading your posts (and I could certainly be wrong) that you are asking why the window manufacturers introduced U-factor (or value) when R-value already existed? Why mess with a good thing?

You make a very good point concerning the intuitiveness of using an R-value versus U-value for comparison...going "up" as an improvement just "feels better". In fact, I have used that in discussions myself when people have asked why to use one over the other.

What most people don't realize, I think, is that U-value was around as a calculation long before R-value made its appearance. I am not certain when U-value first was used to calculate energy losses (I believe it was in the 1930's - but don't quote me), but R-value was actually developed in the late 1960's / early 70's by the fiberglass insulation folks. So the question of "which came first the chicken or the egg", at least in the case of R vs U, turns out to be the U-value. This surprises many people since they have grown up seeing R-value measurements everywhere when dealing with home energy products.

Really the only advantage of using R-value over U-value is that R-value is easier to visualize. But, that can be a very important consideration when dealing with folks who live in a world of "sound-bites" and fast food.

When a window company salesman starts bragging that the units he is selling have this "great R-value" he is often (always?) simply giving the center-of-glass reading of the unit. The warmest spot on any window is the center of the glass. This is a very real number, but it doesn't say a thing about overall performance of the unit and is thus misleading.

Ultimately, as generally used, R-value is really just a theoretical number...unless it is derived directly from U-value measurements of a specific circumstance. U-value, on the other hand, is an actual physical measurement. A very common assumption is that since R and U are inverse they are simply two different ways to say the same thing, but I think that FenEx did a great job of explaining why that that isn't necessarily true, in his post.

R-value is based on the assumption that the materials used in an application will actually achieve the results that the materials are capable of achieving. In other words, if a certain thickness of material has an R-value of 19 (remembering that this value was developed using U-value measurements on a limited size sample), then filling an entire wall cavity with that thickness of the material will result in a wall with an R-19 insulating value.

Again, I would point out that FenEx's post easily proved that that idea isn't correct and even worse while a homeowner may believe that they have a certain level of insulation value in their wall, they really don't. In fact, they can be significantly below that level of value without realizing it...despite what they believe or what they were told they would have.

A given R-value only takes into account insulating against conduction...neither radiation nor convection is included when dealing with R-values. So, while filling a wall cavity with 3 feet of fiberglass insulation might give that wall an enormous R-value reading, if that wall is full of holes that allow air movement within that wall cavity, the R-value number is meaningless.

In the case of a window, and as we have been discussing throughout this thread, radiation is a very significant part of a window systems insulating equation. We can know the overall R-value of a window by knowing the actual U-value, and calculating the R-value inverse, but we cannot calculate the R-value by using only R-value numbers.

Wayside, all this verbiage does nothing to discredit your central idea that U-value is simply not as easy to intuitively picture as is R-value. But, the point being that R-value is not necessarily the best way to compare apples to oranges and that there really are, at times, very valid reasons for using one system over another.

ColoJohn, good morning!

Although “insulatingâ€Â￾ shades and blinds sound like a good idea, I would suggest checking out this and other sites for questions concerning condensation on window surfaces. One of the biggest contributors to window condensation issues is using shades or blinds that block interior warmth from window surfaces. One of the quickest and easiest fixes for window condensation problems is to open said blinds and shades and allowing room air to circulate over the window.

The folks that sell insulating shades and blinds never seem to mention that possible shortfall.

Your analogy of an electrical circuit really is a good one. Ultimately, a conductor is a conductor and the laws of physics tend to be very consistent when dealing with fluid motion. Nature wants balance. Doesn’t matter if the unbalance is warm and cold, wet and dry, air and argon, high voltage and low voltage – nature wants them equal. Consider a tub of water as “potentialâ€Â￾ and the hose from the tub as the conductor…or a room full of warm air as potential and the window (path of least resistance is the perfect analogy as well) as the conductor.

In both of those cases you can calculate resistance to flow just as you can with a circuit…

P = I * E and R = E / I is true even when dealing with the insulating value of windows... :idea:

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Re: more

#32 Post by tru_blue »

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#33 Post by FenEx »

I agree... great thread. This thread in itself kind of explains why several different forms of measurement are given for a window's performance. Windows are by far the most complex part of a buidling envelope and over-simplifying their classifications down to an R-value and region would be a mistake. The specific requirements of coloJ are a great example and could not be accurately met by getting a single number stamp.

If you really want the inside story, when a house is performance tested and rated, the wall/ceiling/floor insulation R-values and window U-factors are often downgraded based on their installation. The window performance numbers are also adjusted based on not only the region, but their exposure and any shading provided by trees, overhangs, etc. Once the heating and cooling load calculations are completed for the entire shell... they are adjusted even further when the house is tested for air infiltration. A house built with all the best performing building products on the market will fail to meet the Energy Star performance requirements if a few key areas were missed by the installers allowing too many air changes per hour. Once again, the energy takes the easy road.

I like to look at it as a three sided scale with conduction, convection and radiation. It's impossible to perfectly balance the three equally for any circumstance. Addressing one, shifts the others.

Good Luck to you coloJ... don't drive yourself too crazy trying to get it perfect. Your obvious research and understanding puts you well ahead of the curve already.

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#34 Post by ColoJ »

The windows have been ordered from Milgard, hardcoat for the solarium south and east sides, softcoat for the rest.

Thank you again for your help and encouragement. The research and the project have been interesting. To me, the insight that heat loss through windows is similar to parallel electrical circuits was worth the price of admission in itself.

For anyone interested in researching windows, I found a book in the public library that was especially useful. The book is entitled, Residential Windows, A guide to new technologies and energy performance by J. Carmody, S. Selkowitz, and L. Heschong; W.W. Norton & Company; New York, 1996. ISBN 0-393-73004-2.

I have experienced the problems with insulating shades, wood windows, and condensation first hand. Even here, in what was before irrigation the great American desert, the windows behind the cellular shades condense water on nights when temperatures drop into the teens, and ice forms when temperatures fall into the single digits. This has been bad for the windows over the years, and was one of the reasons for researching fiberglass and vinyl replacement windows. In the end, price drove the choice, but my preference would have been for fiberglass had the bids been closer.

The fact that lowE windows condense water behind cellular shades is good and bad. The condensation is bad, of course, but it indicates that the shades are sufficiently reflective to help prevent the loss of heat by radiation, I think. It still is not clear to me how the R-values listed for cellular shades are determined.

Is there a concern with vinyl or fiberglass windows being exposed to the condensate, or does the problem of condensation mostly affect wood windows?

Is there any danger that ice formation from condensate could damage the spacer seals or separate the frame from the glazing?

Some shade manufacturers make side rails that provide an improved seal around the shade. Do these products reduce condensation?

Stephen Thwaites
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Location: Ottawa, Ontario, Canada

Canadian Energy Rating (ER)

#35 Post by Stephen Thwaites »

In a recent thread on "Who makes high solar heat gain windows?" there were some comments about the Energy Rating or ER, a rating system develped in Canada.

As a member of sub-commitee responsible for this part of the Canadian Window Standard i thought i should add my perspective to these comments. In the interests of full disclosure i work for a small manufacturer of fiberglass framed windows.

By way of background the ER was developed for a climate where the heating load is significantly larger than the cooling load. It includes the effects of solar gain as a positive and the effects of conduction and air leakage as negative.

So, one of the comments was:

" My understanding from the Canadian sites is that the hardcoat will give a positive ER rating, meaning that the window will provide a net gain of heat during the winter months. This would be particularly impressive if they get a net gain in Toronto where much of the winter is cloudy. A good description of the Canadian rating system can be found at http://www.thermotechwindows.com/NRC6.htm

I think that I remember reading someplace that the Europeans were also considering inclusion of solar heat gain in their window ratings systems, but I can’t recall the reference. "

Not sure about the other Europeans, but the UK also has a one number system based on solar gains being positive and heat losses being negative
See http://www.bfrc.orgfor more info.

Stephen Thwaites
Technical Director
Thermotech Fiberglass Fenestration
Ottawa, Ontario, Canada

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#36 Post by solarmax »

It appears that the high SHGC combined with a low U value may be the Holy Grail. I had been looking for such a creature before coming to this forum. Environment becomes all important in choosing the right product. Briefly, high heating and cooling demands lead to a soft coat answer for most of the house. Living in Granby Colorado at 8400 feet, the context is only one of high heating demands with lots of wind and up to -40 F in the winter (not a chill factor, folks!) After using the low e soft coat in the upper part of a two story, south facing sunroom, and clear glass in the lower part, the obvious performer is the clear for the south facing application. The floors are isolated from each other, and the sunspaces can be shut off from the house at night.

Would a hard coat help retain more energy at night? I am sure it would, but I am also sure that the added expense of that panel could well be put toward the purchase of insulating shades. A top down/bottom up cellular shade could be used to further cool the sunroom in the summer. Solar intrusion, however, is minimal with just a two foot overhang. Cross ventilation, provided by high end windows also helps to keep the temperatures moderate. High temps here in Granby (Home of the infamous Bulldozer/Tank attack) never exceed the high 80's in the summer, and cool nights with open windows keep that house very comfortable without the added expense of AC.

The low sun in the winter at this 40 degree latitude floods the sunspace, hitting the rock wall on the back side of the sunspace, water barrels, and tile floor to store heat and moderate the sunroom temperature. Again, these sunspaces can be closed off from the rest of the house, but during the day, provide a lot of heat to the interior. Tomato plants growing in the lower sunspace through the winter provide proof of heat retention of the system of gain and storage. Solar is the only heat source for the sunspaces. Again, the addition of something as simple as cellular shades hinders convection currents, and helps the window to minimize heat loss.

All windows are vertical. Tilted glass would have more summer gain, demanding shading or definitely a low E soft coat application. This all applies to a southern orientation in the Northern Hemisphere. Windows on the North side of a home would receive nearly zero solar gain, making the low E soft coat the obvious choice. Because they do not see much winter sun, the East and West sides of the home, should employ low E soft coat also.

Southern exposure in this climate with 320 days of sun, and a decent roof overhang, beg for either a hardcoat or clear with the possibility of shades to retain the solar gain.

Depending on the site application, a combination of different low E glass or low E with clear glass for different aspects of the home would provide the most energy gain and retention. Ordering only low E soft coat inhibits a huge amount of potential solar gain for high degree day homes. The home, of course, has to be situated with decent southern exposure.

The answer to the original topic is PPG makes Sungate 500 with only 7% less heat gaining ability than clear.

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#37 Post by Oberon »

Single silver softcoat LowE products have very comparable solar gain numbers to hardcoats.

When considering different coating types and desireable solar heat gain performance I would compare high solar gain with high solar gain products regardless of whether they are hardcoat or softcoat.

I admit I was using hardcoat to indicate high gain and soft coat to indicate low solar gain somewhat generically at the time.

Ultimately, in most areas low solar heat gain coatings have (often significant) advantage over high gain products in year-around applications.

Even in places where heating considerations are more important than cooling, the heat-blocking ability of low solar gain products will usually outperform high gain products in most instances because of their abilty to keep heat inside where it belongs.

I will certainly agree that the "holy grail" in heating dominated climates would be a coating that would have the direct heat gain of high solar gain coatings and the heat retention ability of low solar gain products.

Stephen Thwaites
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#38 Post by Stephen Thwaites »

Ultimately, in most areas low solar heat gain coatings have (often significant) advantage over high gain products in year-around applications.
Actually, there is a study by Lawrence Berkley National Labs that disagrees with that statement.
Google "Performance Criteria for Residential Zero Energy Windows" for the whole study.

In summary,
they looked at a 'typical' 2,000 ft^2 single story new house with 300ft^2 of windows equally distributed between the north, south, east and west.

Window type #3 was a high solar gain double (U 0.37, SHGC 0.53)
Window type #4 was a low solar gain double (U 0.34, SHGC 0.30)

I'll try to summarize some of the projected annual energy consumption figures below - see the full report for all the results

- #3 high solar gain double; 99.3 MBtu
- #4 low solar gain double; 101.9 MBtu
Salt Lake City,UT
- #3 high solar gain double; 62.3 MBtu
- #4 low solar gain double; 64.0 MBtu
Washington DC
- #3 high solar gain double; 62.8 MBtu
- #4 low solar gain double; 63.5 MBtu
- #3 high solar gain double; 31.5 MBtu
- #4 low solar gain double; 29.8 MBtu
- #3 high solar gain double; 50.0 MBtu
- #4 low solar gain double; 46.7 MBtu

So i think the conclusion should be that high solar gain windows provide lower energy annual energy consumption in northern climates and low solar gain windows provide lower annual energy consumption in southern climates.

An even better solution than picking one type of low e coating or the other is to pick both. Use high solar gain low e on the south and low solar gain low e everywhere else. Unfortunately few manufacturers offer this option....


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Re: Who still makes high solar heat gain windows?

#39 Post by RafaelMorton »

ColoJ wrote:Does anyone have information on who manufactures windows with a high solar heat gain coefficient suitable for a solarium?

I live in northern Colorado and have been looking windows with a high solar heat gain coefficient (SHGC). I am not so sure how well high SHGC windows perform in climates where the sun is not visible from November to April, but in Colorado with about 6000 heating degree-days per year and nearly 300 days of sunshine, they can provide much of the house heat. I would like to say that I have found this discussion board very helpful in making decisions about what windows to purchase, and I would especially like to thank Jscott, Oberon, and Guy for their help.

In searching for windows with a high SHGC I have found that few window manufactures make windows with either a hard coat on the #3 surface or a soft coat on the #3 surface to provide a high
solar panels heat gain. Of the manufacturers that I have contacted Milgard and Gienow use a hardcoat (Milgard uses PPG 500 and Gienow uses AFG). Pella appears to confine hardcoat windows to their Designer line; they are not available in the Impervia line.

Amerimax, Atrium, Simonton, and Jeld Wen do not offer a high SHGC product. Is, as some have suggested, the Energy star rating leading the extinction of high SHGC lowE windows?
Hello friend sorry for old thread reply but were you able to find the right manufacturer? I am searching for one such company producing windows with a high solar heat gain coefficient suitable for a solarium.. Please post suitable reply

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