The need for an accurate indoor humidity model for building envelope performance analysis

Tariku, Fitsum (Fitsum Tariku (Fitsum_Tariku)) (author)
Kumaran, Mavinkal, K. (author)
Fazio, Paul (author)
(editor)
(translator)

© 2009, Tariku, F., Kumaran, M. K., Fazio, P.

Proceedings of the Fourth International Building Physics Conference: Energy Efficiency and New Approaches: 15 June 2009, Istanbul, Turkey. The performance of a building envelope component is usually assessed based on the moisture analysis of individual components (such as cladding, sheathing board and/or drywall) for their drying potentials and likelihood of occurrence of problems associated with high moisture accumulation. In the current building envelope simulation practice, the indoor and outdoor boundary conditions are predefined in the context of the local weather data. The indoor boundary conditions are usually assumed to be constant throughout the simulation period, or two sets of values for the summer and winter periods are assumed. Although the outdoor boundary condition (weather data) is independent of the hygrothermal condition of the envelope, the indoor condition is highly influenced by the building enclosure and occupants? activities. Consequently, simplistic assumptions of indoor humidity profiles, which ignore the dynamic coupling of the indoor environment and building enclosure and represented with a set of empirical values, may lead to inaccurate conclusion about the moisture performance of the building enclosure. In this paper, the effects of indoor humidity profiles that are assumed during moisture performance evaluation of exterior building envelope component are analyzed. The indoor humidity profiles, which are considered in the study, are based on measured and simulated data of a real house. Indoor humidity models including a whole building hygrothermal model are used to generate four indoor humidity profiles. The hygrothermal dynamic responses of the building envelope component with respect to the various cases of indoor humidity assumptions are simulated and analyzed. The simulation results suggest that it is important to have more accurate indoor boundary conditions data, which are based on measurement or whole building hygrothermal modelling, to satisfactorily asses the moisture performance of a building enclosure and potential occupants health problems related to mould growth.

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