Why can glass mist up from the outside?
Have you had this too? You've had UNIGLAS® | TOP
Energy-saving glass put into your house to save on
heating energy. But on mornings after clear cold nights,
the new panes are misted up on the outside - and that
never happened with the old glass. So now you
justifiably ask why this is so and whether this is a
product defect.
If the warm interior doesn't keep supplying enough heat,
then the temperature of the glass surface drops below
the air temperature.
As soon as the dew point
(= air saturation) is
undershot, the water
contained in the air
condenses, and misting
results on the outside. This
misting happens particularly
in the case of panes in
unprotected positions, with
a free view to the sky.
But is this condensation a product defect?
Quite the contrary! With older insulating glass, this
effect doesn't occur because it has poorer thermal
insulation. Heat from the building is lost through the
window glass. The outer pane is thus unwittingly heated
– at the expense of indoor comfort and lost heating
energy.
Components or objects can mist up when they're colder
than the air around them and when this air contains a lot
of moisture. Because air can only absorb a certain
amount of water vapour - and the warmer it is the more it
can do so. If the air temperature drops during the night,
the relative humidity increases.
The picture shows on the
left how heat is lost in the
lower windows. The red
colouring shows the heat
radiated to the outside
through the glazing.
Following the laws of nature, the result is always a
temperature equalization from warm to cold. On clear
nights, the glass surface loses heat to the colder sky and
ground in the form of radiated heat.
UNIGLAS GmbH & Co. KG
Robert-Bosch-Straße 10
D-56410 Montabaur
Telephone: +49 (0)26 02/9 49 29-0
Fax:
+49 (0)26 02/9 49 29-299
e-mail:
Internet:
[email protected]
www.uniglas.net
The better the thermal insulation of the insulating glass,
the more likely the formation of outside condensate. This
is an indicator of the high quality of your windows.
Thanks to excellent insulation from modern thermal
insulation glazing, its heat transmittance is very low. This
means that heat stays inside the room, and hardly any of
it passes to the outside. So the outer pane has a lower
surface temperature than the outside air on clear, cold
and windless nights.
With correspondingly high relative humidity in the
outside air, the dew point on the glass pane is not
reached, and so condensate forms on the pane surface.
UNIGLAS® | TOP Energy-saving glass by contrast
uncompromisingly keeps the radiated heat inside the
room. The outstanding thermal insulation function of
UNIGLAS® | TOP Energy-saving glass permits hardly
any heating up of the outer pane. This is why
condensation can temporarily occur.
This dew water on the outside is in no way a defect. On
the contrary, it is a sign of excellent thermal insulation.
Condensation takes place on your car and everywhere
else in nature, following the same physical laws.
If you have any further questions, your personal
UNIGLAS experts will be glad to help.
______________________________________________
The condensate formed in this way disappears as soon
as the glass surface gets warmer again, for example due
to sunlight.
Our information is provided to the best of our knowledge and belief,
but rules out any warranty. Right to printing errors, mistakes and
changes reserved. (Date: August 2012)
UNIGLAS GmbH & Co. KG
Robert-Bosch-Straße 10
D-56410 Montabaur
Telephone: +49 (0)26 02/9 49 29-0
Fax:
+49 (0)26 02/9 49 29-299
e-mail:
Internet:
[email protected]
www.uniglas.net