Experimental and numerical evaluation of the hygrothermal performance of a hemp-lime building
Hemp-lime concrete (HLC) is a bio-based material which is currently undergoing a growing development. HLC is a low embodied energy material and an excellent hygrothermal regulator. Its thermal, hygric and mechanical properties are well known, and its capacity to reduce energy needs and to improve hygrothermal comfort was demonstrated across many laboratory and numerical studies. However, there are few works about its hygrothermal performance in real climatic conditions on the scale of a building. A French HLC individual dwelling-house was monitored during 2 years. Its envelope is made of 300mm thick sprayed HLC associated with a timber frame structure. Air temperature and relative humidity of each room were measured. Temperature and relative humidity of North and West facing walls were measured at their surfaces and inside the walls at two different depths. Besides heat flux is measured at the inside surface of the north wall. This paper presents the results collected in the framework of a field study to determine the transient hygrothermal behavior of HLC in real conditions. In-situ monitoring of walls temperatures shows the ability of HLC to almost completely dampen variations of external temperature with 11 hours time-shift. The evolution of indoor relative humidity confirms that HLC has an excellent moisture buffer performance. The analysis of the hygrothermal behavior of a wall is achieved by comparing measurements and numerical simulations results. In this study, two simulation tools are used and compared. The first tool is based on the well-known Wufi software and doesn’t take into account the hysteresis effect. In the second simulation tool, numerical simulations are performed with a hysteresis model implemented in a heat and moisture transfer model. Comparisons between numerical and experimental results highlight some influent parameters in the simulation of the hygrothermal response of a HLC wall in real climatic conditions.