I have 2 questions re: solar – the first on window glazing for a passive solar room and the second re the best choice for a solar panel.
1. I’m building a passive solar room and want to know what glazing we should put on the south facing windows. One big window manufacturer representative told me to go with Low E and and gave me another web-site backing up his recommendation. He asked me to be sure to call back if I didn’t see what I needed. The info pointed to the efficacy of Low E glazing especially for hot climates in reducing cooling costs. I want winter light to warm the room here in New England. When I called back, I got another technical representative who told to me to go with non-glazed windows on the south facing windows. Who’s right and why?
2. Another (New England) customer is going to push out his attic with a dormer and wants some kind of solar panels installed. He’s not picky about what type other than they should pay for themselves at some point. The recent article on solar panels in “Fine Home Building” was informative but I read a more recent letter to the editor who said that the system discussed in the article was expensive and not the best/most efficient available. Any suggestions?
Thanks,
Don Westwater
Westwater Design and Build Inc.
Replies
"I got another technical representative who told to me to go with non-glazed windows on the south facing windows. Who's right and why?"
Isn't an UNGLAZED WINDOW just a fancy name for a hole in the wall?
Off hand I can't tell you where to look for which combinations are best, but there are several different parameters that are juggled for both heat gains and loses. One is the solar shading.
You might want to start here.
http://www.nfrc.org/
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Bill,
I did check the National Fenestration Council's web site and didn't find an answer tho it could well be there and I just haven't found it.
THanks,
Don
Readers.
I earlier wrote, "unglazed," when I should have written uncoated. I'm intending to use double glazed but am not sure about the coating.
Thanks,
Don
http://www.builditsolar.com/
Everything you ever wanted to know and more.
Joe H
Build It Solar's certainly an ambitious site, even listed our place halfway down their Plans for Solar Homes & Example Solar Home Designs page.
Donni, good question, but the best glazing answer is climate and owner specific. For instance, we don't bother with any window treatment and without low e would have a less comfortable house. If we used well-insulated window shutters, the increased transmittance this time of year would be better.
As it is, there's a noticeable difference between our low e windows and the uncoated sliding door glazing I used in our hinged doors. Very much less comfortable by the uncoated glass if the sun isn't full, or if it's particularly cold outside.
Probably doesn't exactly answer your question, but you need to consider your climate (filling in your profile would help) and the design of the room. Will it overheat?
Our own junkhound once posted that he had a spread sheet showing how low e was worse than double-glazed in his Washington location. Surprised me, as I'd guess that nearly everybody would do better with low e and less transmittance. He agreed.
Not particularly difficult to perform heat loss/gain calculations both ways if you're inclined. Allows you to factor in things such as insulating shutters. Another factor, important to us, is UV degradation of furnishings, greatly reduced with low e.PAHS Designer/Builder- Bury it!
Thank you all.
I'm much more informed now. I'll order windows with as high a SHGC as possible, probably probably in the order .6. I called 2 Canadian fiberglass window manufacturers and hope they'll call back.It's likely that the room will overheat on sunny days in the winter because there's a lot of glass per square feet of floor. The customer is aware of this and is willing to open windows when necessary. The room is only 8' wide and I think I'll install brick halfway up the north wall. I'm hoping that the brick will absorb heat during the day in the winter and release it at night. The brick will not, however, amount to 6 times the square footage of the south facing windows that exceeds 7% of the floor space. The door between the solar room and the main house can also be left open to help disperse excess heat to the rest of the house. We're going to try to minimize window treatments tho, in order to preserve the lake view. Maybe the customer will want UV shades. As for the summer, I'm glad to learn that any glass will deflect light that hits the glass at a steep angle. I'd also seen literature on a coating that worked like a polarizing lens to deflect angled sun rays and admit direct (i.e. winter) sun. I haven't been able to remember or locate it again tho. I'll also build an overhang that will help block light in the summer.Regarding the solar panels. The customer said he wasn't wed to anything in particular. His wife simply wants solar, regardless of cost effectiveness. He's similarly inclined but wants the project to make sence (as in $ and cents). He initially wanted to have his approximtely 30'shed dormer to face north and install solar panels (possibly photovoltaic) south. I told him that it may make more sense to face the dormer south in order to pick up passive solar sun but I didn't know. I'll certainly check the web-site that was recommended which was very helpful re: the windows.
Thanks again all.
Don
Nice site Joe. I don't know if Donni will use it, but I sure will.Tigger
Nice site Joe. I don't know if Donni will use it, but I sure will.
Tigger
The post above yours is the site owner, Gary.
Fascinating stuff hidden there.
Joe H
Don,
1. You want insulated glazing with a high-solar-gain low-e coating. Glass manufacturers make the stuff, but almost all window manufacturers are too ignorant to know how to order it. You want windows with a hard-coat (pyrolytic) low-e coating, not a soft-coat (sputtered) coating. If US window distributors continue to act stupid when you ask for high-solar-gain insulated glazing, buy your windows from a Canadian supplier. Most Canadians distributors understand these issues better than American suppliers.
2. "Some kind of solar panels" is pretty vague. Solar hot water collectors? Photovoltaic modules? You probably need to read up on these technologies a little bit so that your questions are more focused.
Are you and I talking about the same thing?
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Piffin,
You refer to something "that is designed so that solar rays hitting it at an extremely high angle from summer sun get reflected off again, but when the solar rays are more direct from winter sun low in the sky, they pass thru and add heat energy." The thing you are thinking of -- the thing you forgot the name of -- is called a roof overhang. If you design your south overhang properly, it will shade the south windows during the summer, while allowing the winter sun to hit your windows and enter your home.
No _do keep elevation and latitude in mind but this is something they wer pushing back in the early eighties. Coulda been a farce for all I kow,but remember being introduced to the concept in a class.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
I was under that idea when we built our place. Low angle-sun energy in/hi angle-refection.
Used the deep overhang and didn't clear cut the deciduous woods.
Something seemed to have worked. No overheating in the summer, good passive solar in the spring and late fall. Added heat in the winter.
Lucky break I guess.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
I'm not sure what the name is, but some manufacturers have a low E coating that is designed so that solar rays hitting it at an extremely high angle from summer sun get reflected off again, but when the solar rays are more direct from winter sun low in the sky, they pass thru and add heat energy.
At least it used to be that way
Welcome to the
Taunton University of Knowledge FHB Campus at Breaktime.
where ...
Excellence is its own reward!
"I'm not sure what the name is, but some manufacturers have a low E coating that is designed so that solar rays hitting it at an extremely high angle from summer sun get reflected off again, but when the solar rays are more direct from winter sun low in the sky, they pass thru and add heat energy."
Yes, it's called glass. All glass, regardless of coatings, will reflect more incident sunlight the steeper the angle of incidence.
<!----><!----> Solar Transmission (single glazing - deviation from 90°):<!----><!----><!---->
0-30o deviation = 87%<!----><!---->
45o deviation = 85%<!----><!---->
60o deviation = 79%<!----><!---->
75o deviation = 42%<!----><!---->
90o deviation = 0%<!---->Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
No, it is not called glass. It is a coating I was referring to that was once marketed as increasing the effects you try to chart for plain bare glass.Maybe it didn't sell.
Maybe it was only available in limited markets.
Maybe they pulled it off the market as ineffective or not effective enough to be worthwhile.
Maybe they still do it and it is just one more thing that you don't know about.But I can remember sitting in a lecture on passive solar techniques back then and being shown the drawings and charts on how it worked. It did exist!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
"No, it is not called glass. It is a coating I was referring to that was once marketed as increasing the effects you try to chart for plain bare glass."
I didn't "try to chart" the effect of incident angle on glass, I DID chart it. You seem to have trouble accepting clear and unabiguous presentations of simple physics while you continue to offer vague recollections and a long list of hypotheticals in order to bolster your claim:
Maybe it didn't sell.Maybe it was only available in limited markets.Maybe they pulled it off the market as ineffective or not effective enough to be worthwhile.Maybe they still do it and it is just one more thing that you don't know about.
But I can remember sitting in a lecture on passive solar techniques back then and being shown the drawings and charts on how it worked. It did exist!
You offer no trade name, no manufacturer, no source of this information - but continue to assert that "it did exist". And then you accuse me of ignorance!Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Well, I'm sure that lead won't help you, but it might help the OP if he follows it up.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
MartinHolladay is correct, except that US window manufacturers aren't stupid. They've moved to more insulative windows since that's what customers are demanding (very few homes are built to include passive solar design), and with a double low-E coating (surfaces 2 & 3), they can sell the same window in a heating climate or a cooling climate. Smart for them, but a problem for us solar builders.
As far as solar gain, the most important NFRC number is the "solar heat gain coefficient" which is the percent of incident solar energy that will pass through the window at 90° angle of incidence. So, for a passive solar application, you want a window with .60 to .70 SHGC.
You will almost always come out ahead by using a single-surface pyrolitic low-E glazing unit. This offers the best balance of visible light transmittance, solar heat gain, UV reduction, and insulative quality. But you might have to hunt around for a window in the 70% SHGC range.
Beyond glazing choices, you also have to consider amount of glazing, overhangs or other shading to prevent overheating in the summer, ventilation, daylighting and views, and thermal mass.
If you use more than 7% of the floor area of a space in solar glazing, then you need to add thermal mass at the rate of 6 sf of sun-swept mass for each additional 1 sf of south glazing.
Solar & Super-Insulated Healthy Homes
Good solid common sense advice in this thread!
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Soneone, I think that it was 3M, had a plastic material with a bunch of fine dividers in it so that light would only pass through it if it was straing on. I saw it used on LED displays to keep them from being washed out by the sun. The same technology is used on traffic lights, so that you can only see the light straight on. Except that it is a bunch of tubes. I think at the time they where being suggested for use on windows, but I don't know if they ever where..
.
A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Riversong,
It is not uncommon for folks interpret LowE2 as two separate sputter coatings applied to surfaces 2 and 3 of an IG unit - that is actually not the case. LowE2 refers to the number of layers of silver (or in some cases titanium) in the coating that is applied to a single surface within the IGU – generally surface 2. <!----><!----><!---->
<!----> <!---->
Coating both surfaces 2 and 3 in any IGU configuration is almost a guarantee of broken glass because of heat trapped in the airspace between the two 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. <!----><!---->
<!----> <!---->
While a single surface pyrolitic coating is excellent for both solar heat gain and heat retention, a single silver sputter coat applied to surface 3 will have close to the pyrolitic solar heat gain property as well as equal or better heat retention capability (U-value) often with better visibility and UV blocking numbers. While either coating can be effective in a solar heat gain situation, as was previously pointed out, both are much better than using uncoated glass in any event. <!----><!---->
<!----> <!---->
Piffen,
All LowE coatings (as well as clear glass) will tend to deflect solar rays at a high angle of incidence. I am guessing that what you may be remembering is that there was some advertising and articles written that discussed the ability of high solar heat gain LowE coatings (drawings, illustrations, and such) to deflect low angle solar rays in relation to solar heat gain in summer versus winter – and it does work that way for the most part.
In general,<!----><!---->
<!----> <!---->
There are two primary types of LowE coatings available - pyrolitic or hard coat - and soft or sputter coat.Softcoats are multi-layered coatings consisting of several different metallic oxides with silver as the primary heat-blocking ingredient. Softcoats are applied in vacuum chambers to finished glass.Hardcoats or pyrolitic coatings are applied to the glass while the glass is still semi-molten in the tin bath portion of the float process. Basically, the bottom side of the glass will have a coating of tin from floating in the bath (as does all float glass), but the topside will also have the layer of (primarily) tin oxide - which is the LowE coating.So in one sense, glass with a pyrolitic coating has two "tin-sides", but one - the LowE side - of them is much thicker than the other. Often, the pyrolitic coating is applied to the #3 surface of an IG unit if the unit is intended for use in a heating-dominated climate - but not always since there are also solar-reflective pyrolitic LowE coatings that are applied to the #1 or #2 surface of an IG unit to reflect solar heat gain in cooling dominated climates.Sputter LowE coatings are also applied to the air-side of the glass, primarily because the metallic layers tend to adhere better to the air-side, but also because it is possible for the slight metallic (tin) layer on the tin-side to affect the performance of the coating.A sputter coat is applied in multiple layers, typically about 7 to 11 layers depending on the coating. People really don't realize, or can appreciate, how thin a typical sputter LowE coating is. Sputter coat folks measure the thickness of each metal oxide layer, as well as the finished coating, by how many atoms thick it is. A typical softcoat LowE coating is somewhere in the neighborhood of 500 to 1000 atoms thick.<!----><!---->
Dual or triple silver (or titanium) sputter coats (low solar heat gain products) are generally applied to surface #2 of an IG unit, while single silver (high solar heat gain) is often applied 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 when you touch the 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.<!----><!---->
<!----> <!---->
<!----> <!---->
Edited 1/25/2008 8:21 pm ET by Oberon
Edited 1/26/2008 10:47 am ET by Oberon
"It is not uncommon for folks interpret LowE2 as two separate sputter coatings applied to surfaces 2 and 3 of an IG unit - that is actually not the case."
Thanks for the clarification. I believe it was Pella Corp. that told me that their lowE² units had both #2 and #3 surfaces coated, but I might have misunderstood.
lowE² is a trademark of Cardinal IG, though other glass manufacturers also use similar multiple sputter coats.
I though that it was soft coat lowE that used to have a bluish tint and, for that reason, manufacturers moved to hard coat. It seems that they've been able to make soft coat transparent now.
But I still don't understand why companies like Pella (in their ProLine) offer only lowE² low solar heat gain glass, even in severe heating climates. They could at least use surface #3 (instead of #2) coatings to make the units more appropriate for heating climates.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/25/2008 9:12 pm ET by Riversong
No problem. It is a very common misconception and I have heard window folks say the same thing on occasion – particularly marketing folks.
<!----><!----> <!---->
You are correct that LoE2 (rather than LowE2) is Cardinal’s trademark for the dual-silver coating. LowE2 (rather than LowE2) has become something of a generic term for this particular coating – and all of the LowE manufacturers have some version of the coating, as you also mentioned.
<!----> <!---->
The first coatings on the market were pyrolitic. Sputter coats came later. It is actually the pyrolitic coatings that tend to have noticeable tint – sputter coatings are generally more neutral in color – but there are variations between various coatings and also variations between applied surfaces.
<!----> <!---->
For example if someone were to install side-by-side windows in a home and one window has a surface 3 coating and one a surface 2 coating it is very possible that there would be a noticeable difference in the color. Yet if both were surface 2 or both surface 3, it is likely that no one would even notice that there was a coating at all. Our eyes can see very subtle differences.
<!----> <!---->
Most of the sputter manufacturers have four primary categories of coatings (and potentially variations within each category) - single silver high solar gain, dual silver low solar gain, tinted dual silver for lower solar gain, and the newest is triple silver for even better low solar gain.
<!----> <!---->
The low solar gain products do tend to have better U-factor figures which can cause difficulties when dealing with solar gain in heating-dominated climates – as you are very aware – since lower U-factor equates to higher insulating value and Energy Star isn’t designed with variations in mind.
<!----> <!---->
Energy Star recognizes U-value requirements in heating dominated climates without regard to SHGC considerations. <!----><!----><!---->Canada<!----><!---->, on the other hand, does recognize the possible advantages of a high solar gain product in combination with (unavoidable – to date) higher U-factor (remembering that “higher U-factor” means less insulating value).
<!----> <!---->
And of course there are excellent studies that indicate that factoring in high solar gain windows with higher U-factor in heating dominated climates is an advantage over low solar gain windows with lower (better) U-factors – and of course there are just as many, and just as excellent, studies that indicate that high solar gain in winter does not offset energy losses due to lower overall efficiency associated with high solar heat gain windows…it is a controversial subject to say the least. And honestly, I believe that the folks involved on both sides of the controversy truly believe that they have the best solution.
<!----> <!---->
Window companies see these studies and they see the results of test houses that exist to compare the differences with different products and different applications. Those results often become the basis of what they decide they are going to offer to the public.
<!----> <!---->
Now imagine that you are the owner of a very large company that supplies a particular product to many different geographical areas.
You do your best to supply a quality product; but it is still a production rather than custom product. You have a limited mark-up on this product so that getting it out quickly and correctly is very important to keeping this product affordable (within the price range that you have established) – consistency in your operation is supremely important and is ultimately is a huge part of your potential success or failure.
As part of your product, and potentially affecting consistency, you offer a particular upgrade to your product. In 2/3’s of the geographical locations that you supply, this upgrade is the best version available for your product. But in 1/3 of the locations that you supply there is some controversy about this upgrade and whether or not it is the most appropriate to be used since it may not be the best version of this particular upgrade to use in those locations – or it may be – depending on who you believe because there are valid arguments that it is and valid arguments that it isn’t.
<!----> <!---->
And, although geographically 1/3 of your market area might be considered as “controversial” in regards to best available product, in reality you sell 75% or more of your product in the 2/3’s area – the market coverage is not consistent.
<!----> <!---->
So you, as the owner, have to make a decision to whether or not to adjust your process to take advantage of producing a slight variation (which arguably is not even a more appropriate or better version) on your product for a small portion of your total consumer base, or to maintain consistency with the product over the entire consumer base – which also has arguments as being the better application - and keeping in mind that offering any version of this upgrade already has had an effect on the consistency of your manufacturing process. What would you do?
<!----> <!---->
But, you are now the owner of a small company with limited geographical coverage and less dependence on consistency, so that you can produce a more custom product thus satisfying the requirements of your customers – you can give them exactly what they want.
<!----> <!---->
Given that the consumer may pay more for this flexibility in your manufacturing process (or not depending on a few other factors); you have filled a particular niche which benefits you and your customer base.
<!----> <!---->
You, as the owner of the niche company, will certainly highlight the advantages of different variations of the product that you produce, saying that your product may be more suited for the area that you service than is the product of the larger company. Whereas the large company will tend towards the less “controversial” or more mainstream version of the product, you will offer a “better” or more specific variation of the product – for your location – and you will grab on to the reports and studies that support your position.
<!----> <!---->
You, as the owner of the smaller and more niche company, will aggressively share any data that you have that supports your position – both as a marketing tool and because you truly believe it – whereas the larger company may simply “file away” the information supporting their position along with all the other information that a large company invariably accumulates.
<!----> <!---->
Who is correct? Ultimately, it is the consumer who benefits from the different options available. Is one option “better” than the other? Again, this largely depends on an informed consumer who has the opportunity to choose.
<!----> <!---->
<!----> <!---->
<!----> <!---->
<!----> <!---->
Edited 1/26/2008 10:25 am ET by Oberon
And of course there are excellent studies that indicate that factoring in high solar gain windows with higher U-factor in heating dominated climates is an advantage over low solar gain windows with lower (better) U-factors – and of course there are just as many, and just as excellent, studies that indicate that high solar gain in winter does not offset energy losses due to lower overall efficiency associated with high solar heat gain windows…it is a controversial subject to say the least.
Can you offer any links to those who claim that high solar heat gain windows in a cold climated DON'T offer a net heat-load advantage?
I've been designing passive solar homes for a long while (and do my own thermal engineering)and I've found that even a slight increase in solar heat gain is always an advantage over a similar increase in R-value, and this holds true even in superinsulated homes in which the windows are the weakest link in the thermal envelope.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Riversong,
As you obviously know, orientation counts.
A local (Nova Scotia) solar guru, speaking about our solar regime, says that any window oriented south or 45 degrees either side of south is a net heat gain through the year. Any other window is a net heat loss. The same window will give different results depending on the location.
I hadn't been aware that both low solar gain and high solar gain windows were available. I wonder if I could buy a mix of glazing for the next house depending on where the window will be installed? The lower "U" windows would be a worthwhile substitute on the north side or any shaded side.
Ron
"I hadn't been aware that both low solar gain and high solar gain windows were available. I wonder if I could buy a mix of glazing for the next house depending on where the window will be installed?"I tend to doubt you would have much luck on that with most manufacturers and their reps. I knew both types existed because of living in both north and south climates, but I find that even most window reps do not know, and some makers make it hard to buy one or the other depending. Part of the reason is that manufacturing and marketing in a competitive marketplace demand that things be standardized and simplified as much as possible. IN the same way that it is easier and cheaper for you to paint your whole house one colour, it is easier for makers of windows to sell all of them with the same glass. some will and some won't accommodate you. Those that will are going to be charging you a premium as a general rule.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
A local (Nova Scotia) solar guru, speaking about our solar regime, says that any window oriented south or 45 degrees either side of south is a net heat gain through the year. Any other window is a net heat loss. The same window will give different results depending on the location.
It also depends upon the degree-day climate, the annual average insolation, and the solar shading coefficient for the particular building site.
Engineer Charlie Wing calculated 30 years ago that for a Portland ME climate and average solar availability of only 50%, double-glazed windows (this was before lowE coatings) would offer a net gain of 1.2 therms/sf glass for south glazing, 0.8 therms/sf for SW or SE glazing, and 0.2 therms/sf for E or W glazing.
I've found that, in most cases, the only place that glazing more insulating than lowE IG is justified is on the north facade, though low solar heat gain glazing might be appropriate on E or W if overheating might be a problem because shading is impossible.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Can you offer any links to those who claim that high solar heat gain windows in a cold climated DON'T offer a net heat-load advantage?
Not specifically. Do they exist on line? I don't know. But like anyone else I would have to Google to find them. I don't work directly with online data - i.e. internet-based - rather reports that I deal with are much more likely to be either hardcopy or email. <!----><!----><!---->
Thinking about your question, I am not sure that I can recall anything that addresses your question quite as asked. While I have seen reports that compare the advantages of solar gain with lower R-value glazings in northern climates, I can't remember ever seeing any reports that discount solar gain in the same environment (which is obviously not a good plan - free heat is your friend when it is cold outside). In more moderate and hotter climates I have seen those discussions - primarily concerning year-round performance - but nothing comes to mind related specifically to cold climates.
I am preaching to the choir, but the Canadians have done a good bit of work in that area and there is a push to incorporate solar-gain calculations into the next version of Energy Star - which is currently under going an upgrade. One such consideration currently on the table is to breakup the continental US into more heating-cooling zones, for example.
I do remember one report that compared different coatings (related to advantages of higher R-value coatings) and one particular line that I recall from that report does relate somewhat back to your question - specific that "in areas other than the far north low solar gain will outperform high solar gain coatings in year-round performance" (italics mine - and while this is not a direct quote I think it is reasonably close to the original), I don't recall a specific definition for far north from the report . <!----><!---->
This report also included graphs showing performance of various coatings in different climate areas and potential cost savings (but then every report tends to have at least a couple of graphs - it's a cool feature in word and excel and everyone like graphs!)... And, while I don't remember comparisons to direct solar gain, one would have to assume (a very dirty word) that the reported disadvantage to using higher R-value (necessarily lower solar gain) coatings in that environment had to be due to the advantage of solar gain in winter. <!----><!---->
While I do occasionally work with directly with various coatings (both hardcoats and softcoats) I have never specifically conducted any studies relating directly to solar gain vs U-factor, for example. My involvement with coatings is much more related to durability and performance under various types of high-stress conditions rather than how well they actually do what they are designed to do when installed in someone's windows - and even then it is somewhat limited to a few specific areas. <!----><!---->
Basically, any knowledge that I might have relating to actual environment-specific-energy-saving-performance in this area should be considered peripheral (given the potential that this information may conceivably come from some of the leading experts in the field), but it is not data that I have personally gathered (from direct research), and what information that I do have in this area was certainly never directed towards me personally (unless I happen to ask a particular question simply because I am curious about something - I am lucky enough to be acquainted with some of the right people), but in that case it is simply a matter of being lucky enough to be in the right place on my part.<!----><!---->
And finally, I know that I really missed answering your question directly here, but I hope that my ramblings made some sort of sense....<!----><!---->
<!----><!---->
<!----> <!---->
Edited 1/28/2008 7:24 am ET by Oberon
This is a slight highjack, but I would appreciate your indulgence and if you have any information or insight into this, I would appreciate your assistance. When my site plan for building in the Columbia Gorge Scenic Area was approved, the reviewer added a provision that if the widow area in my proposed house was over a certain percentage of the wall space, that I was required to get windows of a certain reflectance - I think it was 13% or 16%, but don't remember for sure.I have done an Internet search, talked to several window installers, and reviewed the websites of the major window vendors and found only one reference to window reflectance and that was on a film applied to the window rather than the window itself. Do manufacturers actually publish reflectance figures on their windows? Where would I find some information on this? Do windows actually come in different reflectances - and if so, how is this done, through different types of glass, coatings, or films? Is it likely that anyone other than this site plan reviewer gives a whoot about window reflectance?
Casey,
What sort of documentation will the reviewer require after the fact?
Do you own a printer?
Ron
Casey,
As a general rule, low solar gain hard coats tend to be the most reflective coatings on the market. Off the top-of-my-head I couldn't give you numbers associated with specific reflectence of specific coatings, though.
Typically, manufacturers try to control reflectivity in their coatings. For example, the coating that popped immediately into my head when reading your question was Pilkington's Solar-E - which was the first low solar gain pyrolytic coating on the market. But, one of the selling points Pilkington used was that it was a low-reflectivity coating. I am guessing somewhere in the 10% range or so.
I am not certain why the inspector would require high reflectivity, unless it is an attempt to help your new home to blend in with the surrounding area a bit better?
Columbia River Gorge - are you near Hood River? Cardinal has a plant there and perhaps they can offer you a solution?
Sorry I could not offer more...
Ronbudgell -
I have no idea what the planning commission will accept - getting to this point has been a fairly unsuccessful adventure in attempted mind reading... And I do have several printers.Oberon -
The stated requirement is: "All glass areas visible from key viewing areas shall have a 14% or less outdoor reflectance rating."Key viewing areas are places people are likely to be and will be able to see my property. These include the Columbia River, Highway I-84, and Hwy 30 immediately to the north of my property, and a scenic lookout several miles to the west at the top of Rowena Loops. The fear is that someone will possibly catch a glimpse of reflected sunlight from a surface. The regulations also prohibit painted metal roofs for the same fear. I will probably just select a window vendor and then have them contend with the requirement.My building site is in Rowena, OR, which is 14 miles east of Hood River.
Edited 1/26/2008 11:14 pm ET by CaseyR
Thank you!
It is amazing how easy this is with some direct knowledge from someone like yourself. I spent an hour trying to digest information I had Googled up with nothing becoming clear enough to post it.Hope it helps the OP in his quest.
Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!
Thanks Piffen. I thoroughly enjoy reading your posts as well and I have learned a much in many different areas from doing so!
Hi,
If the object is to get the maximum solar gain, than (as has been said) you want the highest SHGC you can find. This will likely be a window with no low e at all -- a plain old double glazed window.
This window will have somewhat higher heat loss than than a low e window. So, the best compromise is probably the highest SHGC you can find in a low e window.
If you decide to go with plain double glazed, some areas won't allow this now -- the way around this is to call it a greenhouse.
http://www.EfficientWindows.org is a good site for window selection, and has an explanation for how the various types of coatings work. It also has a window selection tool that will provide you with a list of candidate materials for your climate, including U factors and SHGC for each window.
Windows are good and efficient solar collectors. The only downside is that they lose heat at night -- insulating curtains can fix that. But, even without the curtains, south facing windows are a net gainer in all but the most extreme climates.
If you can provide an overhang above the window, it will shelter it from the high summer sun, while still allowing the low winter sun to enter. This would help prevent overheating in the summer. Some calculators to figure out how large an overhang is needed here:
http://www.builditsolar.com/References/SunChartRS.htm#Overhangs
On the solar collectors.
They need to face south.
Solar heating collectors will have a much shorter payback than solar electric collectors. The heating collectors are about 5 times more efficient, and cost less per sqft -- so much more cost effective.
Solar water heating collectors might be a good choice.
Gary (from BuildItSolar)
If the object is to get the maximum solar gain, than (as has been said) you want the highest SHGC you can find. This will likely be a window with no low e at all -- a plain old double glazed window.
Not necessarily.
You have to balance the advantages of solar heat gain with insulating quality. In all my solar engineering, I've found that in a 7,000-8,500 DD climate with 50% solar availability, double-glazed high solar heat gain lowE (on surface #3) windows come out ahead.Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Hi,You can use the free Resfen program to actually evaluate individual windows with specific locations (cities). If you use the full report option, it gives the net heat gain or loss (solar gain - heat loss) for the each direction of window. It allows various sorts of overhangs and sun blockages, but not thermal shades (which, I think, would make quite a bit of difference). Resfen in a full blown, hour by hour simulation with local weather, so I suppose it should give good answers. Very straight forward to use.In the couple northern cities I tried, the low e window did do better than the double glazed clear, which surprised me a bit. The SHGC they had in the windows that are built into Resfen were only a couple points better for the double clear than the double low e -- I thought there was more difference.http://windows.lbl.gov/software/default.htmGary
You can use the free Resfen program
Yeah, I downloaded that years ago but don't like using a machine whose "gears" I can't see. I don't know how they've set up the program.
So I created my own spreadsheets to do all my thermal and solar engineering, and they've been very accurate compared to actual fuel consumption. My software might not be as sophisticated as the "factory-built units", but at least I know what goes in and what comes out and why.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/27/2008 10:08 pm ET by Riversong
I am resonponding more specifically to Oberon, Riversong and Gary tho others may be interested. Thanks to everyone for adding to my education.After initially hearing from so many people who argued for reducing insulatating performance in favor of increasing solar heat gain, I was taken aback a bit by the 2 most recent responses arguing for the opposite. Oberon's musings were helpful tho I'd be interested to know what northern cities you checked because I haven't run the RESFEN (SP?) because my computer is a MAC an the software only runs on a PC operating system. I'm in Boston. The other consdiration that may tip the balance of whether to go for uncoated or low E is the fact that the winter sun is obscured on this sun room after about 1:30 or 2:00 (just after winter solctice).Thanks again all for the discussion.
Donni