External Condensation On Windows
External condensation on windows appears mainly during clear nights with no wind and high relative humidity. The better the heat insulation (lower U-value) and the more exposed to the sky the window is, the more frequently condensation is formed.
“The choice is between some condensation now and then
… ..or higher heating costs, a higher environmental load and poorer Indoor comfort”
External Condensation On Windows Is A Natural Phenomenon
External condensation on windows is a natural phenomenon, which can appear on all surfaces as soon as the surface temperature falls below the dew point of the surrounding air*. A familiar example is when
condensation has to be cleared away from the wind-screen and rear window of cars
in the morning after a clear night. The same thing can happen on the windows
when the cooling effect from the clear sky is not balanced by heat losses through the
window. Modern double- or triple-glazed insulated glass units have such good heat insulation (low U-values) that this can happen during clear and calm nights. If external condensation appears on your windows, it is proof of a high-performance window. For external condensation to appear on a high-performance window not only a clear and calm night is needed, but also high relative humidity, a relatively low temperature and free exposure to the clear sky. For certain air pressure and humidity, the dew point is the temperature when water vapour in the air condenses and forms water drops on cold surfaces or as mist in the air.
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