Experimental validation of an approach to reduce uncertainties in the in-situ estimation of straw bales' thermal conductivity

The energy consumption of a structure is largely determined by the thermo-physical properties of its envelope. The thermal conductivity of the materials composing the envelopes is among the most important properties to be determined. However, this value has not been precisely defined in-situ for the straw material. Despite the fact that several studies have been conducted to quantify this value, yet disparate findings have been reported. For a more in-depth understanding of the thermal behavior of building components, experimental measurements are essential. Therefore, a protracted experimental campaign was carried out on a newly built structure in northern France under real weather and occupation conditions. Temperature, relative humidity and flux sensors were implanted through the wall and wheat straw bale thickness to understand hygrothermal behavior transfers and heat flow profiles changes along the whole monitored period. The instrumentation and data processing were compliant with the heat flow meter extended average method, a modified version of the ISO 9869-1 standardized approach. The experiment's results are satisfactory; when comparing the measured values using the extended average method with the theoretically calculated value, a good agreement was obtained, with a deviation of 4.66 %. The extended average method has proven to be an accurate and reliable in-situ measuring approach for determining the effective thermal conductivity of wheat straw bales at various temperatures and moisture levels. • Review on the straw bales thermal conductivities values and correlations. • Outlining the experimental campaign's procedures and values assessment. • Monitoring of temperature humidity and heat flux in a straw wall for 41 months. • Comparison of the measured values at different temperature and moisture levels. • A reliable measurement technique for estimating the effective thermal conductivity.