[Greenbuilding] Thermal insulation through double windows

[Reuben Deumling]

In my quest to achieve high whole wall R-values in the 115 yr old house I
live in, I'm now contemplating window configurations. We experience roughly
4,500 HDD in Portland, OR annually. Because I am exceedingly fond of
(simulated) divided lites and I am having a hard time imagining how that
could work with triple or quadruple pane windows, I'm now thinking I could
design two sets of double-pane windows with the outer set being removable
tight-fitting "storm" windows. My questions are
(1) How much of an air gap between the two panes in the thermopane windows?
(2) How much of an air gap between the two sets of thermopane windows?
  I am planning a roughly 12" thick wall, and expect to bevel the jambs on
the inside to let in more light, but I can still achieve a several inch gap
if this will make a big thermal difference.
(3) I'd like to use a lot of wood for the sashes and the jambs. The windows
are roughly 70" tall x 28" wide. What sort of a thermal penalty should I
expect from slightly thicker than standard frames with this sort of setup?
Are there tricks for minimizing this?
(4) For the interior (permanent) set I'm leaning toward inward opening
casements. Does anyone custom build these in the Western US? In Germany
these are the standard, and the requisite hardware is both ubiquitous and
(if you want) very sophisticated. But I want to use local wood (CVG fir most
likely) and my local wood window maker doesn't do inward opening casements.
I'll probably make my own storm windows.
(5) Finally, are there any guides, books, websites where such matters are
discussed well?


Thanks.

Reuben Deumling