Experimental correlation of thermal conductivity with dielectric properties of wood and wood-based materials: Possibilities for rapid in-situ building energy evaluation

In-situ measurement of thermal transmittance properties of building envelopes is important yet remains elusive. Several studies have pointed to the discrepancy between assumed and actual thermal transmittance of building envelope components; however, the measurement is not usually carried out because the available methods are time-consuming and have restrictive boundary conditions. Nonetheless, this measurement is crucial as it is a key predictor of building performance and energy consumption. This paper proposes an approach to predict thermal conductivity using dielectric properties. The objective of our study is to find a correlation between thermal conductivity and dielectric properties of wood and wood-based materials with the intent of facilitating in-situ measurement of thermal transmittance properties of building envelopes in the future. These two material properties are each proportional to the density of the medium, thereby making any interrelationship highly likely. To verify this correlation, 30 solid wood and 17 wood-based materials were tested. The coefficient of determination between thermal conductivity and relative dielectric constant for the aggregate was found to be 0.87, which is stronger than its correlation with density. 72% of the data points were found to be within 10% of the regression line, revealing the strength of the correlation. Both wood and wood-based materials were found to fall within the same regression line. This correlation is the first step towards inferring thermal transmittance of wood-based materials using devices that can quickly measure dielectric properties. Future studies are needed to determine whether this correlation persists for insulations and wall assemblies.