Is it possible to arithmetically prove when mould occurs?
Another important factor where comfort and health are concerned is the avoidance of condensation and mould. As a general rule, moisture gathers at the coldest point in the room – which is frequently around the edge of the glass. Consequently, mould often forms here because the high moisture level provides the best conditions for it to grow. When combined with condensation, structural damage can also occur.
Important to know: Mould starts growing above the dew point temperature. Surface temperatures must therefore be above the so-called mould temperature to effectively protect a building’s structure and the health of its occupants.
That can also be calculated: The so-called temperature factor fRsi has become established as an indicator for the hygiene-related conditions on the edge of the glass. If this value is at least 0.7 in a cool-temperate climate, it can be assumed that no mould will grow at normal levels of indoor humidity. An effective solution for avoiding mould is therefore to increase the temperature on the edge of the glass.
The following table stipulates the comfort and hygiene requirements for the different climatic zones:
What specific examples did the study look at?
It is now clear that the window must always be considered in conjunction with the building’s location. The study therefore looks at, for example, the suitability of different combinations of window profiles, glazing units and spacer bars for five basic climatic conditions, namely Arctic, cold, cool-temperate, warm-temperate and warm climates.
The following table summarises the results of the study. It shows which investigated combinations of window frame, glazing unit and spacer bar are suitable for the various basic climatic conditions in terms of comfort and hygiene.
What conclusion does the study reach?
The PHI study shows that the choice of spacer bar has an important effect on the window’s thermal quality: From the warm-temperate climate and cooler, the general recommendation is to use triple glazing in combination with highly energy-efficient spacer bars such as the Swisspacer Ultimate. The values required for comfort and hygiene could then be achieved even with the uninsulated window frames widely found in these regions. With well insulated window frames, the requirements for warm-temperate and cool-temperate climates can be met both with stainless steel spacer bars and with the premium space bar from Swisspacer. The particular requirements of the Arctic climate necessitate the use of the Swisspacer Ultimate in conjunction with a particularly well insulated frame.
The study was commissioned by Swisspacer. For years, the Passive House Institute in Darmstadt and Swisspacer have been working together on studies that provide fundamental information for the market. Swisspacer started participating in the Passive House Award this year and has announced its own special prize, which will be awarded for the first time in 2021.