Thermal resistance of an innovative prefabricated wall: in-situ measurements

Thermal transmittance and resistance are common indicators of the thermal performance of building elements and products. Moreover, these parameters represent key factors for the correct definition of simulation models used to evaluate energy and thermal comfort performance of existing buildings within energy audit and certification procedures. Hence, it is important to collect information on the thermal performance of building envelopes in order to optimize the energy performance of existing buildings or verify the “post operam” performances achieved by new constructions. ISO 9869-1:2014 rules the in-situ measurement by means of a heat flow meter and two surface temperature sensors. When applied to walls with high thermal conductance and high thermal resistance, this procedure suffers the energy storage effect coupled with not steady-state condition due to the changing climatic condition. A long period measurement has been performed on a full-scale wall prototype with very high thermal capacity and resistance. A test facility, located in Pisa, has been set up. Measurements were carried on in January 2015 using the instrumentation required by ISO 9869-1:2014, coupled with thermocouple sensors posed on both side of the wall and inside it in order to monitor the wall thermal storage during the test. Post-processing of the collected data was made by the average and dynamic methods proposed by ISO 9869-1:2014, in order to verify their applicability. Results show that both methods can catch reliable values of the wall thermal conductance. The average method needs a long period of measurements and is a slightly less reliable than the dynamic method. Thermal mass correction proposed in ISO 9869-1:2014 for the average method has been also performed in the post processing of the measured data set, but in our opinion it is not able to manage the case of walls with very high thermal conductance and high thermal resistance if the measurement time is not long enough.