Condensation in double-glazedAcrylic glass windows
Acrylic glass windows occasional condensation in caravan | motorhome windows often leads the entire leisure vehicle industry to believe that the window pane is leaking and needs to be replaced.
With all due respect for your justified concerns, in almost all cases of complaint the window in question is far from being defective if condensation forms between the panes in certain weather conditions.
Don't worry: Over time, especially in better weather conditions, the water evaporates again without a trace.
Why does water vapour or condensation actually form in the window?
We humans live in two climates, so to speak; one inside and one outside. In the case of a double-glazed window, however, one can speak of a third climate, namely that between the panes. Climate-determining factors are temperature and humidity, and sometimes also the wind. If the temperature drops, the relative humidity increases. If warm, humid air is cooled, the moisture condenses on cold surfaces - for example on the inside window pane surfaces.
Double glazing for windows is made of high-quality acrylic glass. The discs are permanently glued together. In between is "normal" ambient air, which serves as an insulator. Acrylic glass is an organic material and therefore not diffusion-proof. This means that moisture and/or gases can penetrate the pane. It can be assumed that at +14°C air temperature and 70% relative humidity, 0.3 g of water will diffuse or pass through a 3 mm thick acrylic glass pane (surface area 1 square metre) in 24 hours, provided that a lower humidity prevails on the other side. The quantity of 0.3 g does not appear large at first glance. However, if we consider that 1 m³ at 20°C can absorb a maximum of 17 g of water, an increase of 0.3 g in relation to the relatively small amount of air between the panes means a lot.
In simplified and possibly more understandable terms, the cause of condensation can be explained by the fact that acrylic glass - like almost all organic materials - can absorb water in molecular form. Assuming an originally completely water-free window, the panes will initially absorb water from the air on the surface. The water molecules then gradually penetrate the inside of the material by diffusion and finally reach the inside of the pane. Here they are absorbed by the air trapped between the panes. If the water vapour content around the window is high enough, this process continues until the air in the window is completely saturated with moisture.
Since the amount of water vapour that a volume of air can absorb decreases as the temperature falls, water is released at the coldest points of the window as the temperature drops, where it becomes visible in the form of small droplets. If the disc then warms up again, the water evaporates again and appears to have disappeared. However, it is actually invisible - as water vapour - in the air between the panes, which is also heated. If the air in the vicinity of the window becomes very dry, the diffusion process through the acrylic glass starts in the opposite direction. The moisture finally disappears from the window as far as possible.
Tips for preventing or reducing condensation:
Steady air circulation is still the best way to prevent condensation from forming on the inside of the double glazing. Circulating air absorbs the humidity, especially when the cold air is heated. Unfortunately, formation and shrinkage can only be influenced within certain limits. The only controllable factor here is the interior temperature in the caravan through the heating. The external environmental factors such as warm-cold, damp-dry, sun-clouds, etc., on the other hand, cannot be influenced by humans.
In extreme cases, the plastic plugs on the window can be removed and the two panes carefully pressed together and released again. This pumping process accelerates the exchange of air between the panes via the open ventilation holes. For discs without plastic plugs, a twist lock can be removed and the pumping process can be carried out.