Environmental Engineering Reference
In-Depth Information
Along with the insulation of the walls, the structure of the windows is also an
important element. Compared to conventional thermal double glazing, triple glazing
can reduce heat loss from windows by over 40%. Vacuum glazing is a new technol-
ogy on the market in which air is evacuated from the gap in the double glazing to
create a vacuum. A perfectly sealed edge prevents any penetration of air. Small
spacers between the layers of glass provide the necessary stability so that the exterior
air pressure does not crush the two glass panels together. Spacers made of glass are
hardly noticeable.
In addition to the type of glazing selected, the type of window frame is also impor-
tant. The frame of a window can cause further heat loss. Therefore, for the U-value
a differentiation is made between a U
G
value (g for glass) for the actual glass panel
and the lesser U
W
value (w for window) for the complete window, including the
frame. Some manufacturers only provide a general U-value. In most cases, they
mean the U
G
value.
Windows are not just sources of heat loss. They also let in sunlight, which in the
winter helps to heat rooms. For an optimization of solar energy gain, south-facing
windows in colder climates in the Northern hemisphere should be as large as pos-
sible, whereas those facing north should be smaller. Exterior shutters or blinds on
the sunny side are important to prevent well-insulated buildings from becoming too
hot in the summer.
Buildings with optimal insulation are comparatively airtight. For good air quality
in the winter fresh air should be let into rooms frequently. But airing rooms also
causes considerable heat loss. This is remedied through the use of controlled build-
ing ventilation systems (Figure 3.8). Ventilators blow fresh air into living areas and
Figure 3.8
Principle of controlled ventilation with heat gain.
