Improved Thermal Transmittance Measurement with HFM Technique on Building Envelopes in the Mediterranean Area

Although the designed theoretical value of U can be derived from the thermal parameters of layers composing an opaque element, according to ISO 6946:2007, measurements are necessary to confirm the expected behaviour. Currently, the measurements of thermal transmittance based on Heat Flow Meter method (HFM) and according to standard ISO 9869-1:2014 are widely accepted. Anyway, some issues related to difficulties in measurements are present: the roughness of wall surfaces, the proper contact between the heat flow plate and the temperature probes with wall surfaces, undesired changes in weather conditions. This work presents the results obtained in thermal transmittance measurements with a modified HFM method, widely described in this paper. Differences between U-values obtained with the modified HFM method and theoretical ones were in the range 0.6 - 6.5 %. Moreover, the modified HFM method provided a result closer to the theoretical one, when compared to that obtained with standard HFM method (discrepancy with theoretical value were 0.6% and 16.4%, respectively).