Hygrothermal performance of highly insulated external walls subjected to indoor air exfiltration

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Journal Title
Journal ISSN
Volume Title
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
2022-09
Major/Subject
Mcode
Degree programme
Language
en
Pages
55
967-1021
Series
Journal of Building Physics, Volume 46, issue 2
Abstract
The study comprises three laboratory tests in which typical Finnish highly insulated (HI) walls were exposed to concentrated leakages of indoor air under steady outdoor temperatures of 1–5°C. Airflows with a relative humidity of 50% and at rates of 1–3 L/min were directed close to the wooden frames inside the walls. The thermal resistance ratios between the exterior sheathing(s) and the whole wall (Γ) were 20%–22% and 1%–10% for the HI and baseline (BL) walls. The HI walls that presented Γ values of at least 20% were observed to be resistant to air exfiltration, and their durability was not affected by the addition of a gypsum sheathing outside the wooden frame or a more permeable vapor retarder. This is related to the negative linear correlation that exists between the moisture accumulation rate in wood-based material and the dew point depression (DPD) value. The developed approach, called the DPD method, shows that a significant degree of moisture accumulation does not occur even for DPD values of as low as−2°C if the exterior sheathing is vapor permeable. The airflow does not penetrate into the rigid mineral wool sheathing, which helps to avoid interstitial condensation. Regardless of thermal transmittance, the HI and BL walls with maximum Γ values of 1% were exposed to a high relative humidity and even interstitial condensation because the DPD values were often below −2°C. For these walls, the mold index analysis and visual observations confirmed the local risk for mold growth on the opposite side of the leakage point. In practice, long-term mold growth may be limited if the seasonal periods during which the outdoor temperature is 1–5°C last for a maximum of about 1 month every year.
Description
Keywords
Exfiltration, air leakage, moisture convection, highly insulated, dew point, mold growth risk, MOISTURE CONDITIONS, MOLD GROWTH, WOOD, PERMEABILITY, ASSEMBLIES, PRODUCTS, LEAKAGE, MODEL
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Citation
Viljanen , K , Puttonen , J & Lu , X 2022 , ' Hygrothermal performance of highly insulated external walls subjected to indoor air exfiltration ' , Journal of Building Physics , vol. 46 , no. 2 , pp. 967-1021 . https://doi.org/10.1177/17442591221109956