Measurement of the environmental temperature using the sol-air thermometer

Abstract

Heat flow measurement with a heat flow meter is a standardized method (ISO 9869-1) to estimate thermal transmittance (U-value) of a building element. The heat flow meter is a thin plate mounted on top of the surface of the element, and measures the heat flux q through the plate. The measured q is the product of the difference in temperatures between exterior and interior environment, and the U-value. The heat transferred from the element is based on the radiant and the convective heat transfer.ISO 9869-1 specifies that the environment temperature Te “is a notional temperature" and it "cannot be measured directly” (section A.3.1). The air temperature Ta is proposed as a reasonable approximation for the indoor environment, while overcast conditions and absence of significant solar radiation are specified conditions for replacing Te with Ta for the exterior environment.The sol-air thermometer (SAT) measures the sol-air temperature Tsa, i.e. the equivalent temperature of the convective and the radiative environment. In the absence of solar radiation, Te = Tsa. SAT is a sensor consisting of a thin flat solid plate, of high thermal conductivity. The front side of the sensor is exposed to the environment, whose Tsa is to be measured, and the backside is thermally insulated. The temperature of the SAT-plate equals Tsa.In this work we propose introduction of the measured Te in the existing standard (ISO 9869-1). The method for measurement of Tsa, using the SAT, has been demonstrated experimentally for different periods, without solar radiation present and under stable climatic conditions.