LIGHTWEIGHT WINDOWS | LETTE VINDUER

Life is nothing without a view
LIGHTWEIGHT WINDOWS | LETTE VINDUER
Steinar Grynning (NTNU)
Windows are key elements in buildings that
have a goal of reducing their energy demands
and carbon footprint. Previous studies shows
that a large part of the net energy demand
of an office building is related to window
heat loss and cooling demands induced by
solar irradiance. It is therefore crucial that
the combined effects of solar heat gains and
thermal losses are optimized Large window
areas will in general be beneficial in terms
of increasing daylight availability, whereas
smaller window areas are desirable in terms of
heat loss reductions.
to the interior. The combination of high
thermal insulation levels and a high daylight
transmission is traditionally difficult to achieve.
We have therefore looked at solutions
for improvement of the thermal insulation
properties of the glazing units.
both mounting and operating the windows will
become cumbersome. A solution to this is to
use glazing units with thin, intermittent layers.
Here, the structural stability is maintained by
using tradition glass layers, typically 4-6 mm
thick, in the outer panes. The intermittent
layers can then be replaced by polymer layers
There are several parameters which can be
or glass layers with thicknesses down to 0.1
improved in order to improve the insulation
mm. By doing this replacement, the weight of
properties of a glazing unit and hence improve a multilayer glazing unit can be kept close to
the entire window. The three factors most
that of a double- or triple pane glazing unit.
prone to improvement are the following: the
number of glass panes in the glazing unit,
It must be kept in mind that improving the
the emissivity of the glazing surfaces and the thermal insulation of a glazing unit only is one
Windows which have good insulation
thermal conductivity of the gas fillings in the
piece of the puzzle. Improving the thermal
capacities and, at the same time, let a
cavities.
resistance will in general deteriorate other
suitable portion of the solar heat gains into the
properties, such as the solar energy and
It has been found that increasing the number visible light transmittance of the glazing unit.
buildings are important to ensure low energy
of glass panes in the insulating glazing
demands. At the same time it is important
In addition to the thermal performance, optical
units
(IGU)
is,
by
far,
the
most
efficient
way
to keep in mind that the windows are the
properties and aesthetics, ageing properties
elements that provide communication between of improving thermal resistance. However,
and robustness must be maintained at
adding more glazing layers to the glazing unit adequate levels. One of the findings in this
the interior and exterior of the buildings
will increase the weight substantially, and
and thus must provide sufficient daylight
work was that the thermal stresses to the
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ZEB annual report 2014