High performance thermal insulation materials for buildings - Nanotechnology in Eco-efficient Construction - page 201

building applications may be divided into several groups, i.e., for building
envelope retrofi tting, as main building envelope insulator, in sandwich ele-
ments, and in domestic appliances.
Retrofi t insulation of the existing building envelope is an obvious applica-
tion of vacuum insulation panels as this is the domain where its main
advantage has most value, i.e., its highly limited thickness. As installing
additional insulation on the inside results in a great loss of fl oor space,
vacuum insulation panels are of great interest for renovations. However,
special attention has to be paid to low surface temperatures and possible
condensation damage at connections to surrounding compounds.
The use of vacuum insulation panels as main building envelope insulation
for new buildings differs from retrofi t solutions as the thickness is of less
importance, i.e., the structure can be adapted for thicker insulation layers
without loss of space. In such applications, it is always studied whether or
not the complete envelope building components should be pre-assembled
in advance, to ensure the proper handling of the vacuum insulation panels.
As such, sandwich elements applying vacuum insulation panels as vacuum
insulated sandwich elements in door frames, window frames, curtain walls
(see Fig. 9.4) and in non-load bearing walls form a major part of this
application.
Thermal insulation of household appliances, such as pipe insulation, insu-
lation of thermal storage tank, insulation for underfl oor heating, but also
refrigerators form a last area of application. The strong reduction in required
thickness is the main benefi t with these cases, where the restriction of pos-
sible envelope damage forms a lower risk due to the possible protection of
the panels.

9.5 Future trends

For further development and application of high performance thermal insu-
lators based on nanotechnology, further progress is required in two domains:
product and application development of the current products toward more
durable solutions, and further exploitation of the (theoretical) physics of
inhibited heat transfer, including radiation and solid conduction.
The reduced thermal conductivity k in the Knudsen regime is exploited
in the nanoporous thermal insulators based on its f (

￿ ￿ ￿ ￿ ￿ ￿

) as well as in partial
vacuum thermal insulators based on their reduced p . Neither silica aerogels
nor vacuum insulation panels, however, form a durable solution for high
performance thermal insulators (based on the Knudsen effect) due to
their drawbacks, i.e., the very low pristine thermal conductivity k of
0.004 W/(mK) of vacuum insulation panels must be weighed against their
strong aging through time and limited application possibilities, whereas the
combination of a rather low thermal conductivity k of 0.014 W/(mK) with

Λ