This could really boost the efficiency potential of buildings
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That's very good news. I hope we hear something similar from others in the field, soon.
reinvent,
Bring it on! it can't arrive too soon..
But what is the visible light transmittance and the solar heat gain coefficient for passive solar applications?
As windows get more energy-efficient they look more and more like a blank wall, which can have a much higher R-value.
Solar & Super-Insulated Healthy Homes
What are you saying riversong? Sometimes I just don't get your posts.
I'm glad someone else didn't understand the post, besides me.
I'm saying that if the goal is just to reduce window heat loss, then it's easier to eliminate the windows and have more wall.
Every time we add R-value to a window, we reduce the amount of natural daylight and the amount of solar gain that comes in. We also tend to add considerably to the cost.
From my perspective, the only place that "super-windows", or even triple-glazed windows for that matter, are justified is on the north. But we still have to be willing to accept the tradeoff of less natural light, which is important to make a space more livable and more healthy (reduces seasonal affective disorder and increases vitamin D synthesis) as well as reducing artificial lighting costs.
For the superinsulated, passive solar homes I design and build, I've found that annual heating costs are LESS with high solar heat gain double-glazed lowE windows than with anything more insulating. This is because the decrease in heat loss with high-efficiency windows is more than offset by the decrease in free solar heat, if properly designed.
In other words, the annual heating season net gain of (free) energy through a double-glazed lowE window is a good deal more than the annual heat loss. This, of course, holds true only in a heating dominated climate zone. And it holds true even here in New England where we have solar availability of only about 50%.
If I spend more money on "better" windows, it costs more to heat these houses.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 3/17/2008 3:33 pm ET by Riversong
Good posts. Is their any data on the phenomenon you describe in superinsulated homes?
Expensive window technologies have certainly become the quick fix for homeowners who routinely ignore the whole equation in conditioning their homes.
Is their any data on the phenomenon you describe in superinsulated homes?
Yeah. Every heat loss/heat gain analysis I've ever done.
Each house is a special case and has to be analyzed individually, but I have generic thumb rule data from 30 years ago showing that a clear double-glazed window facing south offers a net gain in New England of about 1.2 therms per square foot per year. Southeast and southwest windows offer about 0.8 therms per sf. and east and west windows about 0.2 therms per sf.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I would undoubtedly be a candidate for a high R window if they make them at a reasonable price. I am planning on building in the Columbia River Gorge with a 2200 foot hill (I guess in the east they would call that a "mountain") rising at about a 45 degree angle about a hundred yards behind my property line. I get no direct sun during much of December and part of January, and limited sun for several weeks each side of that period. I do get lots of direct sun in July and August, however, when it can get up to 115 F for a short period.
Thanks for esplaining riversong! I see how windows facing the right way with a shade for the summer and dirrect sun for the winter would work.
The problem I have is that windows are in the wrong place most of the time. The house wasn't designed for solar gain in the first place. People are stuck with houses that were designed with cheap energy in mind.
Edited 3/17/2008 5:36 pm ET by popawheelie
A vacuum space is not going to eliminate solar gain. Low E coatings, depending on which side of the glass they are applied to will have a greater impact on solar gain. And the largest potential for solar gain has to do with the design of the building and where it is located.The added cost of these windows vs the savings has yet to be determined but it sounds very promising. Also look at the benefit of this in retrofit apps not just new construction.Here is some more info I found:http://spie.org/x8586.xml
A vacuum space is not going to eliminate solar gain.
No, but double, soft-coat (lowE²) plus "a large number of small support pillars" will signficantly reduce the SHGC.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
I wouldn't bite on these until they'd been in service quite a while. Glass and window manufacturers took a long time to figure out how to seal gas filled windows properly so holding a vacuum over time in a window subjected to seasonal temperature changes, vibration and wind is a tall order.
I'm trying to imagine the sound when they break. Must be a nice pop. :-)
I agree. Unless they're made like the old Anderson IG units, with welded glass, then they're going to lose vacuum over time.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
The vacuum space is only .25mm across thats about half the thickness of a business card. Here is some info on how they are constructed:http://www.physics.usyd.edu.au/app/research/vacuumglazing/index.html
Reinvent
Thanks for the link. As I am sure you know, the concept of vacuum glazing has been around for about a century or so.
The use of pillars for supporting the panes under vacuum has long been the sticking point as complex manufacturing is one issue, while delamination, visual clarity and light transmission are others.
Given that Spacia glass (commercial vacuum glass with pillars) is only warranted for 10 years and has other associated warnings, I don't think it's ready for a double hung window being slammed down by a kid in the great white north just yet. So far, it's only been used in a limited number of commercial buildings in Japan right?
http://www.nsg-spacia.co.jp/tech/warranty.html
Sounds interesting, but I think we'll have to wait and see on this one.
Edited 3/18/2008 5:12 pm ET by WindowsGuy
R12 is bad for the ozone. DUUH!
??? was that the propelent that was banned?
Yeah. R134A windows are the green ones!
reinvent,
Here's a brief article giving a condensed version of current window technology. They know nothing about the sealed units you refer to, though.
I have been especially interested in progress in aerogels. R5 - R7 per inch thickness in a window!
Ron
Wow that was brief.
Try again
I must have forgotten the link.
http://shttp://irc.nrc-cnrc.gc.ca/pubs/cp/win1_e.html