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40
ZEB
annual report 2015
To overcome the low thermal resistance
of transparent surfaces, different types of
multi-glazed windows have been developed,
of which a wide variety are available on
the market today. Triple-low-energy-glass
windows with low-emissivity coatings and
argon gas filling, for instance, represent an
effective energy-saving solution. However,
these technologies have the drawback that
they drastically reduce the amount of solar
radiation that passes through the glass due
to the use of several coated layers. This
condition can be disadvantageous at northern
latitudes (such as in Scandinavian countries)
where solar radiation in winter is low in terms
of both hourly availability and quantity. Glazing
with an aerogel filling has been proposed as
a technology capable of providing daylight,
with the benefit of an insulation value higher
than that of classic triple and quadruple
glazing solutions. The results presented here
compare and assess the greenhouse gas
(GHG) emissions of three different glazing
technologies applied as part of the energy
retrofitting of a housing complex located
near Oslo, Norway. The triple-glazing units
with argon were partially substituted with
double-glazing units with either monolithic
aerogel or granular aerogel. Building energy
use and GHG emissions were calculated and
compared for the cases with different windows
technologies.
Aerogels are extremely innovative materials
that, among several applications in a variety of
different fields, show very interesting insulation
properties in both opaque and transparent
building components. Aerogels have the
special characteristic of being highly porous
materials. The porous structure, constituting
the skeleton of the aerogel, is called gel. The
gel is a three-dimensional sponge-like network
of particles made by condensing particles that
are dispersed in a liquid solution, called sol.
To obtain the final product from this sol-gel
compound, the liquid part is substituted with
air through various processes and the final
product can take the form of powder (granular
aerogel) or be a monolith (monolithic aerogel).
Almost all metal or semimetal oxides, such as
silica (SiO
2
), aluminium oxide (Al
2
O
3
), titanium
oxide (TiO
2
), and zirconium oxide (ZrO
2
) can
contribute to a gel formation. Among these,
the SiO
2
-gel is the one that has found the
widest application. SiO
2
aerogels, like the
other metal oxides-based aerogels, also
have interesting optical properties. Since the
pores forming the gel networks are smaller
than the visible light wavelength (380-740
nm), aerogels can be partially transparent.
For this reason, aerogels represent the
most promising solution for achieving very
low insulation values in transparent and
translucent surfaces without compromising the
daylighting conditions.
A multi-glazed window with low-energy coating
and gas filling has an insulation value of 0,5
W/m
2
K-1 and a g-value of 0,50. On the other
AEROGEL AND ARGON INSULATION IN WINDOWS
AEROGEL OG ARGONISOLASJON I VINDUER
Nicola Lolli (NTNU/SINTEF)