That brings us back full circle to the question that experience tell me that the polyeurethane foam filled aluminium lats do have an insulating property, the question being how much, and the level of accuracy of my calculations (apparently not very).
.............................................width........k value.........r value
glass (thickness m)..................0,005....... 0,9........... 0,0055555556
air gap m.................................0,02...........0,025........0,8
Glass (thickness m)..................0,006........0,9...........0,0066666667
shutter....................................0,004..........0,02.........0,2
air gap m (window/shutter).......0,02..........0,025.......0,8
...............................................................r value.........1,8122222222
...............................................................u value.........0,5518087063
The weakness is that the shutter front is not going to be airtight therefore elevating the final u value for the overall unit.
Regarding costs, again I have to agree with you regarding installation and unit costs, but if we set this against the cost of changing frames and glass from double to triple and a supply of blinds that is considerably cheaper than UK prices, the whole idea now comes into a 10-11 year payback period, which I think you'll agree isn't too bad. We're also looking at it from another point of view and that being that glass is a pretty poor material for windows, ok you can see through it, but that's about it.
In the summer the solar heat gain can can be sufficient that A/c becomes the norm for cooling, I never used A/c when I lived abroad, and also it'll fade fabrics over time (replacing furniture and carpet has a negative cost impact). If you fit a glass that reduces solar heat gain you're going to lose any gains you need in the winter and of course vice versa, anything you choose has pros and cons. Cost factors against for using just glass, I think a combination of materials will improve the situation dramatically.
This is without looking at the security aspects, if we ever see a long hot summer again they will allow me to leave the windows open all night and the shutters down (outward opening windows need not apply) allowing fresh air to enter but not the burglar.
The way we're looking at it is as a supplement to double glazing, and not a replacement, to move things closer to triple but with extra benefits that triple can't offer. As I said earlier I'm comfortable with the look of buildings with shutters and a hidden box gets rid of the idea of ugliness. And I think the correct choice of colour can actually add to the building's look.
I think you'll agree that if I'm looking at having a chunk of the work done anyway as an upgrade from double to triple, then the extra added cost for replacing the lintels and the reduced cost (I'd say i'm looking at 30-40% less) of the shutters combined with what I see as extra benefits kind of adds up. So in my opinion it's far from being barmy, and possibly you'll agree, as I'm writing this it actually seems to be making bloody good sense....
I understand what you're saying about replacing windows and lintels in and existing property is going to increase the payback period and new build would be better, but as said above if some of the work is going to be done anyway and the shutter cost is low.
The key being the u value, I'm British I need facts and figures.
@ JohnD, it's nice to see a real life, positive experience in mid/northern Europe, they appear to be very popular in Germany, Holland and Poland. There must be a reason for this, no?