Passive houses need windows

logo_smallA reader commented on our suggestion to use cellular glass for a catenary house. If we would work with a catenary tunnel, we could use 100% glass for the side walls, because the catenary tunnel is self supporting.

But in that case, we have to use the best thermally insulating glass possible. This particular reader focused my attention on double pane  low emissivity glass with one or more transparent polymer layers between the two panes. In that way, we obtain the thermal equivalent of triple or quad pane glass but with the weight of standard double pane glass. Versions filled with Krypton are even possible.

As a consequence, the window frames can be lighter than for triple pane glass and I guess that a polymer film instead of a glass pane is also a lot more ecologic. In the extreme case of quad glass with Kr filling, we obtain  U=0.4 W/(m2K), which we have to compare with the 0.15 W/m2K for the catenary wall. The extreme U=0.4 W/(m2K) can also be reached with triple glass with special coating and gas filling.

More information can be found in the following files:

In fact, the window industry made a nice evolution in W/(m2K)

  • single pane: 6.2
  • double pane: 2.7
  • double pane with low E coating : 1.66
  • triple lowE coating with Ar: 0.90
  • triple lowE coating with Kr: 0.61
  • quad (polymer film) low E coating with Ar: 0.49
  • quad (polymer film) low E coating with Kr: 0.40

The window industry improved with a factor 15 but the above values have to be compared with the 0.15 W/(m2K) for a passive housing wall in Belgium and 0.1 W/(m2K) in Sweden. In fact, windows have to be oriented and installed in such a way that also solar heating can be absorbed in winter without over heating in summer.

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