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absorption peak in the near infrared, which yields a much enhanced modu-
lation of solar energy transmittance and a higher luminous transmittance
(Li
et al.
, 2010). The next and obvious step, which has not yet been taken
(in 2012), will be to explore the infl uence of Mg doping on VO
2
nanopar-
ticles. Well crystallized VO
2
-based nanoparticles - produced by some effi -
cient high-temperature process - may be possible to embed in polymer foils
and laminates (Ji
et al.
, 2011; Lu
et al.
, 2011), which opens interesting
avenues towards low-cost implementation of thermochromic fenestration.
The recent advances in electrochromics and thermochromics make it
interesting and timely to consider possibilities to develop 'super fenestra-
tion' in multiple-pane constructions with an electrochromic functionality
on the outer panes - which may be dark or transparent depending on tem-
perature or user preferences (Azens and Granqvist, 2003) - and thermo-
chromic functionality on the inner panes which tends to follow the room
temperature. The electrochromic and thermochromic components should
be thermally decoupled, which can be done by vacuum insulation to cut
down on conductive and convective heat transfer and a low-emittance
coating to minimize radiative heat transfer (Baetens
et al.
, 2010b; Smith and
Granqvist, 2010). The vacuum gap needs some spacer, such as tiny glass rods
or silica aerogel. Figure 11.12 illustrates such 'super fenestration' with an
electrochromic outer pane according to Fig. 11.2 and a thermochromic inner
OUTSIDE
INSIDE
Electro-
chromic
foil in outer
pane
Thermochromic
laminate in inner
pane
Low-e coating
on the inside
of the outer pane
Thermo-
chromic foil
Electrochromic
foil
Low-e coating
on the outside
prevents
condensation
in cold climate
Spacers
(glass rods)
Vacuum insulation
between panes
11.12
Conceptual sketch of 'super fenestration' combining
electrochromic and thermochromic functionalities.
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