Thermal transmittance measurements with the hot box method: Calibration, experimental procedures, and uncertainty analyses of three different approaches

A large amount of heat loss through building envelopes takes place via inhomogeneous components suchas windows, doors, and thermal bridges. This loss can be approximated by measuring in lab the actualthermal transmittance of these components with the use of a hot box. The calibration and experimentalprocedures can be performed, taking into account three standards for calibrating hot boxes: the EuropeanEN ISO 8990; the American ASTM C1363-05; and the Russian GOST 26602.1-99. An experimental setupfor testing the accuracy of these standards has recently been created at the University of Perugia; after ameasurement campaign for the validation of the test rig, the differences of the approaches were evaluated.Results showed that although the EN ISO 8990 and ASTM C1363-05 are similar in terms of proceduresdefinition, methodology of thermal transmittance calculation, and level of uncertainty, theGOST26602.1-99 differs from the others since it adds individual measurements of the thermal characteristics of eachsample component. The analysis highlighted that the ideal procedure should include the Russian methodto define the thermal behavior of each component under analysis, with a contemporary validation of theglobal results to be performed with one of the other two approaches.