Abstract
Mould growth in buildings is a complex process, affected by moisture and temperature, the properties of the building material as well as characteristics of the mould fungi. The complexity poses challenges when assessing the risk of mould growth in buildings. Mathematical models are often used to predict whether mould will grow in a part of building with expected RH and temperature conditions. The models can be described as static or dynamic. In a previous round-robin study, comparing results from models with observations from field studies, the outcome of the dynamic models evaluated depended on the user of the model. Also, the models often underestimated the risk of mould growth. A better agreement was found for static models, especially for the PJ-model. It is a part of a standardised technical specification (SIS-TS 41:2014) and has not previously been described as a model. The critical moisture level (RHcrit), determined by tests according to the method, is used as input. Thus, the subjectivity in the predictions is reduced. RHcritis the lowest moisture level at which mould can grow and is temperature-dependent. The PJ-model provides an equation to estimate RHcritat typical temperatures in buildings. If RH in a building section exceeds the limit values at the current temperature, growth is predicted. This paper describes the PJ-model version 1.0, some of the extensive work performed during the development and validation of the model and the ongoing work to refine the model to include considering transient conditions and measurement uncertainties.
Highlights
Different materials vary in their susceptibility for mould growth
One way to describe this is by critical moisture level/limit, RHcrit, the lowest RH at which mould can grow on a specific material
Mould growth is expected to occur on a building material if the RH conditions exceed the critical limit for mould growth at the current temperature
Summary
Different materials vary in their susceptibility for mould growth. One way to describe this is by critical moisture level/limit, RHcrit, the lowest RH at which mould can grow on a specific material. Mould growth is expected to occur on a building material if the RH conditions exceed the critical limit for mould growth at the current temperature. The study showed that different end-users make different choices of input parameters for the same product for example, to which material class a specific product belongs and this affected the outcome of the comparisons between predicted and found mould growth. The model is described in Annex C of a test method for determining the critical moisture level for mould growth on building materials [9], published as a standardised technical specification [10]. It has not, previously been described as a model. It is expected that extended results from the development of the model will be presented at the NSB conference in September 2020
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