Applications of Coupled Heat and Moisture Transfer Simulations in Buildings

The uncontrolled presence of moisture in building envelopes and structures could be the cause of several typologies of damages (for example freeze-thaw cycles damage or corrosion of metal reinforcements) and health and safety hazard for the occupants (mould and fungi growth). Several heat and moisture transfer models could be used to simulate the phenomenon and, using the damage criteria, to predict the failure of the building envelopes or structures. Some commercial software tools are available to the practitioners but, not all the material producers provide the advanced hygrothermal material parameters necessary to perform the simulations. Moreover, the proper weather files that should be used to calculate the boundary conditions for the simulations are rarely available. In this thesis, the models implemented in the commercial software tools are presented and some of the limits met in the simulation process, mostly regarding material parameters and the weather files, have been studied and analysed. First, a practical comparison between the widespread Glaser method, a simplified stationary method for the evaluation of the interstitial condensation, and a transient coupled heat and moisture transfer model is presented, underlining the limitations of the simplified method. With respect to the hygrothermal material parameters limitations, two simple experimental procedures for the evaluation of the material properties are presented. The obtained values are found to be consistent with the experimental results by a comparison with the simulation. Then, the influence of hysteresis on the transient hygrothermal behaviour of a cross-laminated timber wall is presented, showing that by considering the hysteresis in the model, the quantity of moisture retained in the structures during a year changes. Regarding the boundary conditions, the procedures for the statistical selection of representative weather files - used to model the typical weather of a location - and the reference weather files - designed to represent the critical weather conditions of a location - are presented. The study has been undertaken on the typical building envelopes for different locations of Northern Italy.