TEMPERATURE AND MOISTURE STORAGE IN CROP-BASED MATERIALS: MODELLING A STRAW BALES WALL SUBJECT TO A THERMAL SHOCK

Among insulation products, crop-based materials present a porous structure which results in high moisture storage and transfer capacities associated with dynamic phase changes phenomena. Modelling their hygrothermal behaviour is essential to assess their impact on the energy performance of the building, predict indoor climate conditions and prevent any risk of unexpected degradation. Traditionally, transient numerical models that predict internal conditions of construction materials consider that the variation of moisture storage with temperature is negligible although the sorption behaviour is known to be temperature dependent. This paper investigates this particular effect for crop-based materials and offers a refinement of standard mathematical representations. For this purpose, the effects of a thermal shock on the evolution of internal conditions of a straw-bale wall are studied with several versions of a flexible research model. The latter is capable of incorporating the temperature dependency of the sorption curve with both a physicallybased and an empirical description. A large climate chamber is used to gather experimental data and is able to host a full-size straw bales prefabricated panel. Internal conditions of straw bales are obtained with proper sensors bars, which answer the need of reliable temperature/humidity data at different depth inside high thickness porous wall. Results show that when large temperature gradients occur in a crop-based material a model that consider temperature effect on moisture storage enhances greatly the prediction of internal conditions. A one-parameter description of this particular effect succeeds in improving drastically the model efficiency and a complex physically-based approach only offers little additional improvement. This analysis also illustrates the upgrading potential of a heat and moisture transfer model developed in a general computational tool