Wood and bio-based materials are easily fouled by microfungi (molds) if they are exposed to relative humidities as low as 70 or 75%. This is very low compared to the humidity demands of other types of organisms, and that is why microfungi is the main biofouling problem in buildings.
It is of interest to model if a certain construction part will be fouled by mold or not. Such models usually take time series of temperature and relative humidity from building physics simulations as inputs and calculate some type of mold index. If this index exceeds a certain threshold value the model predicts that mold will have developed to a certain degree. There are today several such mold models published that are used in the construction industry.
The core part of any mold model is the growth rate as a function of temperature and relative humidity, but a more complicated issue is how to model fluctuations of these abiotic factors or to model dry periods (a period outside the fungus activity range). Some measurements have been made in which the time to get mold growth has been studied when the relative humidity has been switched between two levels, for example 90 and 60%, but the information is quite limited considering that the relative humidity (and temperature) can vary in many different ways. We study the effect of drying events on fungal activity by measuring the thermal power from growing fungi before and after these events. The measurements are made in isothermal calorimeters, and the thermal power is proportional to the fungus’ respiration rate. Our hope is that this is a quick method to map the effect of dry periods on the growth of microfungi, and that this can be used to improve the mold models.
Keywords: Bio based materials, fungi, mold, temperature, relative humidity
Authors
Wadsö L.
Lund University, Lund, Sweden
Johansson S.
Lund University, Lund, Sweden
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