High performance thermal insulation materials for buildings - Nanotechnology in Eco-efficient Construction - page 203

use and may also slow down aging of the panels. Also aerogels require
protection due to their intrinsic vulnerability, i.e., low tensile strength. At
material level this is solved by fi brous reinforcement in aerogel blankets,
but this increases the effective thermal conductivity and results in non-
translucent aerogel solutions. Also here, a proper best practice for aerogel
insulation in new constructions requires a shift of application toward pre-
fabricated construction elements, i.e., window fabrication, sandwich ele-
ments or as core material of vacuum insulation panels. Finally, due to their
very low thermal conductivity k and as they are generally applied in thin
layers, thermal bridging in constructions insulated with aerogel or vacuum
insulation panels becomes more important.
Besides using current state-of-the-art thermal insulators the best possible
way, one can envision the development of a thermal insulator combining
the positive properties of aerogels and vacuum insulation panels but solving
their specifi c drawbacks.
The basic required material properties could be stated based on the
properties of the known nanoporous thermal insulators and the partial
vacuum thermal insulators. First, a pore size distribution f ( ) completely

below the mean free path of air at ambient conditions, i.e., 70 nm, which
can be achieved based on aerogel synthesis technology. Secondly, an inner
vacuum is desired without the need for a material envelope. As such, the
thermal conductivity k of the material can be reduced further to the solid
and radiative conductivity of 0.004 W/(mK) without the restriction of not
being able to cut the material on site and without possible damage by
puncture. This could be achieved by a closed porous structure instead of
the classic open porous structure. However, the open porous solid structure
is required in current vacuum insulation panels to enable a vacuum inside
the material. As such, the vacuum pore structure must be created during
the synthesis process of the material. One way to accomplish this is to envi-
sion a solid state material blowing itself up from within during the forma-
tion and subsequent expansion of an inner pore structure, or to create a
grid structure which will effi ciently and completely absorb the pore gas
molecules, e.g., by a chemical reaction process.

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9.6 References

Alam, M., Singh, H., & Limbachiya, M. C. (2011). Vacuum insulation panels (VIPs)
for building construction industry - a review of the contemporary developments
and future directions. Applied Energy , 88(11), 3592-3600.
Baetens, R., Jelle, B. P., Thue, J. V., Tenpierik, M. J., Grynning, S., Uvsløkk, S., &
Gustavsen, A. (2010a). Vacuum insulation panels for building applications: a
review and beyond. Energy and Buildings , 42(2), 147-172.
Baetens, R., Jelle, B. P., Gustavsen, A., & Roels, S. (2010b). Long-term thermal per-
formance of vacuum insulation panels by dynamic climate simulations. In D.