Development of a standard laboratory testing method for thermal diffusivity measurements of building walls: Combined use of Infrared thermography and guarded hot box

Abstract

The thermal diffusivity value of a building wall can be calculated theoretically by using the thermophysical properties of its materials listed in standards and literature. In these lists, building materials in the same category can be defined by different thermal properties; therefore, the theoretically-calculated thermal diffusivity values can be misleading. In this study, an experimental setup was developed that can directly measure the thermal diffusivity (α, m2/s) value of building walls by the combined use of infrared thermography and guarded hot box methods. A 19cm-thick wall sample made of lightweight concrete block with pumice aggregate and mortar was prepared; this wall is positioned between a controlled warm ambient on its one side and a cold ambient on the other side, where its surfaces were monitored by sequential IR imaging. The thermal diffusivity value of the sample wall was calculated by using the data showing temperature change versus time and the relevant theoretical equation. The reference thermal diffusivity value (αREF) of the sample wall, calculated by using thermal properties measured by standard laboratory tests, is 3.40x10-7 m2/s. The thermal diffusivity (αIRT) of the same wall, measured with the proposed IRT-GHB experimental setup, is 3.38x10-7 m2/s. The value measured with that new setup is similar to the reference thermal diffusivity value. The results show that the new experimental setup can directly measure the thermal diffusivity of a wall. Compared to the existing ones, the proposed experimental setup presents a measurement technique that saves time and sets the basis of a scientific, practical, and more economical analytical method.