If the vacuum fails, as it will eventually, perhaps we could arrange to pump out the gas and restore it?

Fail safe is the way to go and a terrestrial vacuum is definitely going to fail. the second it does you will have condensation between the glass.

Then the plug will let air in for sure -- its a non starter in my book.

I like the sound of the supply air windows also. Combined with passive ventilation, they seem to offer a viable alternative to very expensive, high performance triple glazing and ventilation systems for low energy houses.

Chuckey: The panes are held apart by stainless steel spacers on a 20mm grid.

Biff: It's ok. The U value isn't particularly amazing. I think it's about 1.5 centre of pane. The edge effect will be massive if you just stick it in a wooden frame, as the edge is made of solder glass.

There are some big problems with their manufacturing technique, in my view. For example, they don't make the stuff in an evacuated environment, so they have to have a pump-out tube, which I imagine is really ugly, and must be delicate despite their claims.

They have to heat the glass during manufacture to off-gas it. This has two bad effects. Firstly, you can't have toughened glass. That probably rules it out for sash windows (the main potential market in the UK I imagine) unless you get some sort of dispensation. I'm sure you could get one, but would it be worth the effort?

In addition, the high temperatures would destroy the coatings on soft-coat glass, hence they have to use hard-coat. This severely limits the insulation potential. Incidentally, somebody mentioned supply air windows. These can't use soft-coats either, giving rise to the same problem.

One futher gripe is that the spacers are stainless steel. That's not very conductive for a metal, but some sort of high-strength glass would surely be much better.

I imagine evacuated glazing probably is the future, but the first generation product isn't all that great.

I'm sure other people would do a lot better with the idea. They know very little about insulation products in Japan - the main competition for this product is single-glazing. But of course, they hold the patents...

There is a Dutch joinery manufacturer using this glass. Maybe you could talk to them: http://www.vanruysdael.com/en/glas/glassoorten.html

Posted By: Peter Clark

That's why I like the idea of supply air windows (http://www.biffvernon.freeserve.co.uk/air_flow_windows.htm" >http://www.biffvernon.freeserve.co.uk/air_flow_windows.htm) - if you make them with two single panes there is no sealed unit to fail. Therefore they may last for centuries, all the while giving effective u values as good as sealed units.

The only UK manufacturer - Howarth Windows - has stopped making them. Problems with unwanted draughts I believe. Experimenting with a new vent and unlikely to be avilable until next year at the earliest.

Monty

I've finally seen this in the flesh, here:

http://www.superhomes.org.uk/events/london-camden-bertram-street-3/
http://www.superhomes.org.uk/superhomes/london-camden-bertram-street/

It is great. The spacers are almost invisible even from close up, but the pump out tube is very visible even from the outside. So if you're going to use this in a retrofit, you might want to get the spacers located toward the edges of the window (I assume this is something you can specify, although how you say it in Japanese I don't know...)

The windows of the house I saw are 3-over-3 and 2-over-2 (with true divided panes, which apparently were mandated by the conservation department). On this job the pump out caps were all in the bottom left as viewed from the inside (IIRC) which made them more visible in the upper sash and unpleasantly asymmetrical from the outside. If they had been in the margins, they would have been more of an attractive feature than a problem.

The glass was being used in the lower sash of the windows, apparently without any building regulations safety issues, even though its annealed.

I don't actually gives a better u-value than would single glazing with secondary gazing made of double glazed units, though, but I suppose it transmits more light.

In this situation I can only foresee the vacuum breaking down short, medium and long term and air getting in, leaks or diffusion, were moisture to get in then we all see the results.

I built quadruple glazed 20 years ago with 2 dg units 300mm apart, no problems yet in the big gap, it was basically for sound insulation but saves a lot in heat losses too

I did no ventilating!

Posted By: RobinBtwo sets of inexpensive DG windows

Posted By: RobinBsingle 3G window at five times the price

That's not right - there's little price difference now between 2G and 3G, from the right sources - some say 2G actually costs more because non-standard in Europe (where the best deals come from).

Posted By: fostertomThat's not right - there's little price difference now between 2G and 3G, from the right sources - some say 2G actually costs more because non-standard in Europe (where the best deals come from).

Hopefully I'm out of date - sorry if I misled. Be interesting to see results of your latest "price survey"
thanks
RobinB

Very interesting , not sure what he means by or uses as a 'Desiccant'
thanks

and for some reason the "Do Not Eat" is always in quotes.

I did not see SteamyTea's post.

That forum thread explains it well.