Abstract
Heat and Moisture Transfer (HMT) simulations are used to evaluate moisture related damage risks in building envelopes. HMT simulations are commonly performed accepting the hypothesis of not considering the moisture hysteresis of materials. The results of HMT simulation of a timber wall with hysteresis are presented, and compared to the results of three simplified models, showing the effects of hysteresis on the simulation results and on the assessment of the risk of decay. Moisture content is the most influenced variable, while temperature and relative humidity are slightly affected. The wood decay risk analysis is performed using the simplified 20% moisture content rule. Similar temperature values and relative humidity values are calculated as simplified models, while the moisture content annual average values have differences up to 2.3%. The wood decay risk obtained with the simplified models could be overestimated if the simulation is performed using the desorption curve, while it could be underestimated with the adsorption curve. The best approximation is obtained with the mean sorption curve, while the desorption curve and the adsorption curve could be used to calculate the upper and lower boundary of the moisture contents respectively.
Highlights
To reduce the carbon footprint and energy consumption of buildings it is possible to produce high performance envelopes using sustainable materials
From the results presented in literature [15], temperatures and relative humidity (RH) are expected to be not influenced by hysteresis while moisture content (MC) is expected to have the larger differences between the different sorption curves
The damage rate is evaluated with a simplified model, as the number of hours of the year with moisture content values over 20%
Summary
To reduce the carbon footprint and energy consumption of buildings it is possible to produce high performance envelopes using sustainable materials. Moisture related damages could affect bio-based materials causing health hazards and structural damages. These could be avoided with careful design procedure and risk assessment. The adsorption property of the porous media is described by the sorption function, which associates to every value of relative humidity (RH) a single value of moisture content (MC) and vice-versa. This is an accepted simplification of the moisture accumulation behaviour, but as experience shows, several materials (especially bio-based materials such as wood) can reach
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