Sensor specifications for in-situ measurement of the temperature distribution inside the wall material for evaluating thermal performance of residential buildings

It is important to measure and ensure the thermal insulation performance of newly built or existing residential buildings to promote energy-efficient and comfortable housing throughout society. Among various in-situ measurement methods for this purpose, this study focuses on the probe insertion method, in which a borescope and a temperature sensor are inserted through a tiny hole drilled in the interior side of the wall to visually inspect and measure the temperature distribution inside the wall. In this method, the temperature sensor itself can act as a thermal bridge, which causes a deviation from the original temperature distribution inside the insulation material. In this paper, based on physical considerations and heat conduction simulation, we introduce two dominant dimensionless numbers that determine the temperature deviation: the Biot number and the newly defined N_c value. In addition, we draw schematic charts to find the temperature deviation from the introduced dimensionless numbers, and suggest a procedure to determine the required specifications of a temperature sensor that can accurately measure the temperature distribution.