High performance thermal insulation materials for buildings - Nanotechnology in Eco-efficient Construction - page 186

9
High performance thermal insulation
materials for buildings

R. BAETENS, KU Leuven, Belgium

DOI : 10.1533/9780857098832.2.188

Abstract : Recent developments in high performance thermal
insulators based on nanotechnology have enabled a strong drop in the
effective thermal conductivity of insulation materials, down to
0.004-0.014 W/(mK). The reductions are achieved using the Knudsen
effect, which describes the effect of pore size distributions and partial
gas pressure in materials on the gaseous heat transfer. The resulting
thermal insulation materials have specifi c properties of importance for
the building industry, which should be considered in each project.
Further exploitation and a similar approach to solid conduction may
result in the next-generation high performance thermal insulators.

Key words : Knudsen, vacuum insulation, fumed silica, aerogel.

9.1 Introduction

The true origins of thermal insulation are diffi cult to identify. Prehistoric
humans clothed themselves with wool and animal skin and built homes of
wood, stone and earth, whereas the Romans as well as early inhabitants of
Spain already used cork as an insulating material for roofs. Mineral fi bers
from volcanic deposits were fi rst used by the Hawaiian natives to blanket
their huts, but it was not until the fi rst industrial revolution that commercial
application of thermal insulation became common with Cabot's Quilt in
1891 as the earliest example. Since then, rock wool, fi berglass and extruded
polystyrene have appeared commercially as thermal insulators in commer-
cial and residential buildings (Close, 1947; Jester, 1995).
Recent progress in the development of high performance thermal insula-
tors is due to progress in nanotechonolgy and material sciences, allowing the
adaptation of known theoretical principles of thermal physics in practice.
High performance thermal insulators (HPTIs) strongly differ from tradi-
tional insulators on base principles considering heat transfer. Traditional
thermal isolators are distinguished by how they trap a gaseous material, i.e.,
in a fi brous material, in a cellular material, or in a granular material. These
insulators have a thermal conductivity in the range of 0.025-0.040 W/(mK)
and show a lower limit for their thermal conductivity close to the thermal
conductivity of the trapped gas. As such, high performance thermal

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