Temperature and moisture storage in crop-based materials: Modelling a straw bale wall subject to a thermal shock

Modelling the hygrothermal behaviour of crop-based insulation products 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 sorp-
tion behaviour is known to be temperature dependent. This paper investigates this par-
ticular effect for crop-based materials and uses a refinement of standard mathematical
representations. For this purpose, the effects of a thermal shock on the evolution of
hygrothermal conditions inside a straw-bale wall are studied with several versions of a
flexible research model. The latter is capable of incorporating the temperature depen-
dency of the sorption curve with both a physically-based and an empirical description.
A large climate chamber is used to gather experimental data and is able to host a full-
size straw bale prefabricated panel. Internal conditions of straw bales are obtained with
proper sensors bars. Results show that when large temperature gradients occur in a
crop-based material, a model that considers temperature effect on moisture storage
enhances greatly the prediction of internal conditions.