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Airflow through lightweight wall assemblies - influence of size and location of leakages

: Kölsch, Philipp; Zirkelbach, Daniel; Nusser, Bernd; Wagner, Ralf; Zegowitz, Andreas; Künzel, Hartwig

American Society of Heating, Refrigerating and Air-Conditioning Engineers -ASHRAE-, Atlanta/Ga.:
Buildings XIII Conference. Thermal Performance of the Exterior Envelopes of Whole Buildings XIII International Conference 2016 : December 4-8, 2016, Clearwater Beach, Florida
Atlanta, GA: ASHRAE, 2016
International Conference "Thermal Performance of the Exterior Envelopes of Whole Buildings" <13, 2016, Clearwater Beach/Fla.>
Buildings Conference <13, 2016, Clearwater Beach/Fla.>
Fraunhofer IBP ()

Compared to the overall building envelope airtightness concerning energetic aspects, the condensation caused by air exfiltration is still a challenge today. For a better understanding of the processes inside lightweight constructions, hot-and cold-box experiments and airflow measurements on 14 different full-scale wall assemblies under realistic climatic conditions were performed. The influences of different mineral wool airflow permeabilities and leak configurations, as well as different pressure differences were analyzed. Despite a certain level of uncertainty, the results show some interesting aspects about the influencing factors of the convective moisture entry. The distributions of the water content between sheathing and insulation samples show that more water remains inside the mineral wool with low air permeability, while in case of the more air permeable mineral wool, more water accumulates in the sheathing. Moreover, the findings indicate that the moisture distribution over the height of the sheathing is more influenced by the pressure difference level than by insulation air permeability or arrangements of the small openings. For the tested configurations, a lateral flow due to openings near the studs shows the highest total moisture contents inside the assemblies. In contrast, we could not observe significant differences concerning the moisture content for the different leak arrangements and diameters with the same total leakage area under humidification test conditions, although differences in the flow behavior are clearly detected. However, another important finding of these experiments is that, despite good workmanship, a small amount of air and moisture seams to penetrate the sealing tape joints.