So you don't have them because you've not seen anyone else with them? That seems like a very odd reason.
I can't give you one off the top of my head but if you're really interested (and I bet you're not) I suggest you ask a supplier, such as these:
John Weston submitted this idea :
My thinking behind negative pressure (vacuum) was that any sealant smeared around the edge would be pulled into any leaks, rather than being blown out.
I'm not sure about modern seals being better than the ways they used to do it. Our DG is 35 years old and no leaks as yet. A pub just down the road from here had a conservatory built 5 years ago with DG and that is forever misted up.
I'm also fairly sure some DG has been built with a partial vacuum, because if you look at some of the reflections on panels, they appear to bow in. I would also suggest that a partial vacuum is easier to maintain than a slight positive pressure because it will help tighten the seals.
Germans tend not to have net curtains, as houses are often much further back from the road anyway. In Holland people just don't care whether passers-by look in or not. My relatives near Hamburg don't have net curtains anywhere. They do have heavy curtains in the sitting room they pull across in winter, but that is more to keep heat in.
MM
Or they where made further up a hill than the installation and the increased air pressure is causing them to bow in.
If I take an empty but sealed old plastic pop bottle down to sea level the increase in pressure is enough to partially crush the bottle. Similary bring a sealed one up and it'll go phsst when you open it. I'm only talking about just over 1000' of height difference as well. Make them on top of hill when a depession is passing over...
I would expect temperature to have even more effect.
DG of that age probably has an external waterproof seal between the frame and the glass to prevent moisture getting in to the frame and to the edge of the sealed units. That will prevent any danger of the units sitting in a puddle in the frame, which is the common cause for failure of the glass unit's seal. I had aluminium DG units which got to 25 years old with no failed glass units, again with properly waterproof seals. (Unfortunately, they were fixed to the old sash boxes and those went rotten, so they had to be replaced.)
That's not been done for years now because it required much more skilled installation than is available and it took longer, making the installation more expensive. Modern DG just has a rubber strip to limit the amount of water getting into the frame, and if properly installed, has drainage channels in the frame to collect the water which gets in and discharge it. If that doesn't work, the units end up sitting in a puddle and this causes quick failure.
There's no reason to do this.
A dutch collegue told me this was about neighbours being able to look in, to prove you weren't up to anything you shouldn't be.
I installed the windows on my old house myself. In the winter they would always fog up on the OUTSIDE! only, not in the cavity. I was extra careful to make sure the K-glass double glazed panels were installed the right way round (there was a label on each one saying which side 'out' should be). I never quite figured out why they should do this. Everyone else's windows in the street were perfectly clear at the same time.
My next door neighbour's parents have them (in North East England).
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