POSTED BY aurita | Nov, 12, 2019 |
, Condensation on windows – how to prevent it?

The formation of steam is a completely natural phenomenon. Produced during everyday activities such as cooking, washing, drying or washing. It is also excreted when we breathe. So how do you deal with frequently steaming windows? Whether it’s old or brand new windows, there is one problem that comes up in conversations with homeowners planning a replacement: condensation on windows. If you have older windows that aren’t as efficient as modern vinyl windows, they are more likely to fog-up, accumulate moisture around the sill, or even freeze. But does this necessarily mean the window has to be replaced? What if the window has just been replaced and the condensation seems to be even worse than with the old windows?

What causes steam on the glass?

The condensation of water vapour on the outer surface of the glass unit is usually caused by very good thermal insulation of the glass. Most often, the problem occurs in the case of panes whose heat transfer coefficient Ug is very low. The result of such good window insulation is the formation of a large temperature difference between the panes, where the outside remains cold (around 9-10ºC). It is on this glass that moisture begins to condense, taking the form of water vapour.

Condensation occurs when warm moist air comes in contact with cooler air or surfaces. As the warmer air cools, it can’t hold as much moisture. Excessive moisture in a room can be the result of various sources: steam from cooking, showers, clothes dryers, un-flued gas heaters, washing machines, indoor plants, even evaporation from your body and breathing.

The good: condensation on the outside of windows

Atmospheric air, and such air is filled in the rooms in our homes, is a mixture that always contains a certain amount of water vapor. The content of water vapor in the atmospheric air changes, and its behavior is different from other gases, because water vapor can easily change its physical state and change from volatile to liquid phase. Therefore, the amount of water vapor contained in a unit of air volume should not exceed a certain maximum value, which depends on the temperature. If we have not thought about the possibility of window evaporation before buying them and we have no clue about the temperature and humidity conditions prevailing in our house or apartment at certain times of the day, our possibilities to influence its occurrence and intensity are very limited.

This does not mean, however, that we are completely defenseless. How can you keep your windows from steaming? In principle, two ways of proceeding can be adopted. The first can lead to a decrease in the thermal transmittance of windows, and thus an increase in temperature on their surface, and thus, an increase in dew point temperature. In this way, under given standard temperature and relative humidity conditions, the phenomenon of evaporation can be prevented or its intensity significantly reduced. How can we reduce the value of the window heat transfer coefficient after the purchase? One option is to install additional devices, e.g. blinds or facade blinds, on the outside. The second way should lead to greater impact on controlling the level of indoor air humidity. Practice shows that sometimes it is enough not to close the door to the rooms at night, and the intensity of the phenomenon of condensation on the windows decreases and even disappears, thanks to the improvement of air circulation in the house or apartment.

When this does not help, care should be taken to increase air exchange throughout the building, and in particular in rooms more exposed to the phenomenon of window evaporation. For this purpose, you do not need to install outside air inlet windows. The simplest solution for natural ventilation is … ventilation. It is worth remembering not only about daily airing the apartment several times, but also about increasing the air exchange in each case of activities that contribute to increasing humidity, such as cooking, washing or bathing. When the simplest measures to combat excess moisture fail, you can use easily available professional or home air dryers.

The bad: condensation inside windows

At the end of the 20th century, in a conventional insulated glass, the space between the glass panes was filled with air. In the 21st century, inert gases were introduced into the inter-pane space, most often argon or krypton. In this way, the space between the glass of the combined package is filled with a mixture of air and noble gases, which significantly contributes to the change of its performance in terms of heat permeability. Due to the fact that from 30% to 50% of heat transfer through the insulating glass takes place by means of thermal conductivity and convective movements of gases in the inter-pane space, replacing the air with gas of lower thermal conductivity, one can achieve the effect of a significant reduction of heat transfer for the entire insulated glass.  A prerequisite for obtaining a lower heat transfer coefficient for the insulating glass is filling the space between the panes with a mixture in which the inert gas constitutes at least 85% of the content. Good quality standard glazing should maintain its insulation properties for a minimum of 10 years.

Hermetic sealing of the glass edges prevents gas exchange with the environment. Misted windows between panes are a sign of condensation in the space between panes. If the misting of the window between the panes occurs shortly after purchasing new windows, this is a typical symptom of unsealing the insulated glass packet and loss of airtightness of the connection. In this case, unsealing the package should be considered a significant defect in the glass, which should be replaced by the seller or guarantor. It also happens that the natural loss of inert gas from the inter-pane space and its replacement by atmospheric air will cause evaporation between the panes in windows used for a long time. The gradual loss of gas from the space between panes is not a disadvantage, so despite the loss of functional properties of the insulating glass, the glass cannot be considered faulty.

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