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In fact their windows are generally so much better, that the problem of external condensation is more widely known and understood…
I had to think about that for a moment - how could you get external condensation!? So, I figure that this is most likely to happen early in the day, the external glazing has cooled overnight, the external air is warming up and increasing its moisture capacity, but comes into contact with the cooler glazing (which is warming more slowly than the air, and isn't being warmed from internal sources because it is more efficiently insulated).
Would that be the scenario?
excerpt from Pilkingtons
The following is an explanation by Pilkington of the phenomenon of External Condensation.
Other Information:
Condensation Explained
External Condensation
Internal Condensation
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Condensation on external glass surfaces
External condensation (dew) can occasionally occur on highly insulating glass units in temperate climates. Such occurrences will only happen on cloud-free nights when there is little or no wind and usually when a warm front follows a dry spell.
The combination of several factors, namely external air temperature, localised microclimate and the thermal transmittance of the glazing itself may all contribute to the formation of external condensation. As a consequence of variable temperatures and localised conditions, it is possible to experience a situation whereby both clear and ‘misted’ windows exist at the same time in the same development.
This phenomenon is influenced by the thermal insulation of the glazing. Single glazing offers poor thermal insulation therefore heat escaping from inside a room readily passes through the glass to the outside environment. Consequently, the external surface temperature of single glazing is generally higher than the‘ dew-point’ temperature of the outside air, thus prohibiting the formation of condensation on that surface.
With conventional double glazing the thermal insulation is improved, but sufficient heat still escapes through the glass so as to warm the external surface of the outermost glass, thereby precluding the formation of condensation in most circumstances.
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In common with other low emissivity glasses, Pilkington K Glass reflects heat back into the room and as such the quantity of heat passing through the glazing is reduced. Consequently the external pane of low emissivity double glazing is not warmed by escaping heat (which instead is retained within the room) and therefore presents a colder surface to the outside environment.
In such cases, and in situations where the external glass surface temperature is lower than the ‘dew-point’ of the air, (and when weather conditions are comparable to those mentioned previously) condensation can form on the external glass surface.
However, the combination of these contributing factors is largely unpredictable and therefore it is not possible to quantify the number of occasions when external condensation will occur.
Instances of external condensation are relatively rare and in all cases it will be a transient effect. Upon any one of the climatalogical variables changing, the condensation on the glazing will usually dissipate within a short period of time in much the same way as morning dew.
I felt this was the easiest way of explaining this , by copying one of the manufacturers of the glasses information....