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14 | ZEB Zero Emission Buildings | Final Report 2017

Nano Insulation

Materials for

High-Performance

Building Envelopes

Bjørn Petter Jelle Tao Gao
Professor and Chief Scientist, NTNU and Researcher, NTNU
SINTEF, Work Package Leader, ZEB

The concept of nano insulation materials (NIM) is introduced to make a thermal
insulation material with thermal conductivity as low as that of a vacuum insulation

panel (VIP) in its pristine condition, but without the disadvantages of a VIP.

In a NIM, the pore size within the material is packing of the HSNS in the bulk condition is also an issue to address.
decreased below a certain level at nanoscale. This is Currently, attempts are being made to lower thermal conductivity by a
in order to achieve an overall thermal conductivity parameter variation and by optimizing the inner diameter and wall (shell)
(also including the gas and pore wall interaction) of thickness of the hollow silica sphere.
less than 4 mW/(mK) when in pristine condition, by
utilizing the Knudsen effect in nanosized pores.
Various experimental pathways have been tried
out in the quest to make thermal superinsulation
materials. At the present time, most of these are
based on fabricating hollow silica nanospheres
(HSNS) using a sacrificial template method (Gao
et al. 2015, Jelle et al. 2014). However, it should be
noted that manufacturing a bulk material directly FIGURE 1. Illustration of the sacriicial template method for HSNS fabrication
with nanopores, may be regarded as a more ideal (Jelle et al. 2014).
and efficient way of producing a superinsulation
material. Nevertheless, the HSNS may currently
represent an experimentally feasible method for
actually obtaining a thermal superinsulation
material. The principle of the sacrificial template
method for HSNS fabrication is illustrated in
Fig.1, whereas actual synthesized polystyrene (PS)
templates, PS templates covered with silica, and FIGURE 2. Left, a SEM image of spherical PS templates; centre, small silica
HSNS, are depicted as scanning electron microscope particles coated around a spherical PS template; right, HSNS after removal of PS
(SEM) images in Fig.2. (Jelle et al. 2014).
Thermal conductivity has been measured
for various powder samples of HSNS, where the References: B.P. Jelle, T. Gao, L.I.C. Sandbr, B.G. Tilset, M. Grandcolas and A.
conductivity values are typically in the range 20 Gustavsen, "Thermal Superinsulation for Building Applications - From Concepts to
to 90 mW/(mK), though some uncertainties in the Experimental Investigations", International Journal of Structural Analysis and Design
1, 43-50, 2014.
Hot Disk apparatus measurement method must be T. Gao, B. P. Jelle, L. I. C. Sandberg and A. Gustavsen, ”Thermal Conductivity of
further clarified. In this respect, the specific powder Monodisperse Silica Nanospheres”, Journal of Porous Media, 18, 941-947, 2015.