R-VALUE ESTIMATION BY LOCAL THERMOGRAPHIC ANALYSIS

IR thermography applied in a proper way is able to detect very accurately temperature difference between air and surfaces. By means of this tool is now possible to analyse the local instantaneous heat flux through the surface of a building. In case of steady thermal state, this gives the thermal performance evaluation of the building envelope. In case of a transient condition an averaging process or a system identification algorithm must be applied on time-series of such a data. In any case, it is demonstrated that a standard technique based on thermal flux meter for the thermal resistance (R-value) measurements is more affected by errors than thermographic measurements using this new approach. The method is illustrated with experimental results obtained into a residential building. A dedicated thermographic apparatus is used to map the temperature of the indoor surface of an internal wall and to measure in same positions the air temperature at 10 cm from the surface. From these data the local heat flux is detected at any point of the internal surface. A conventional thermogram of the corresponding outside surface or the outdoor air temperature history allows an easy way to achieve both thermal conductance and transmittance of the investigated wall. In this way it is possible the evaluation of both radiative and convective heat flux on a local basis with a space resolution of 1 cm. The results are here presented within a comparison with the local measurement with a thermal flux-meter device. These results are important in order to enhance energy efficiency and comfort in buildings.