Assessment of the thermal emissivity value of building materials using an infrared thermovision technique emissometer

Following international standards concerning energy performance of buildings, in absence of reliable data on the envelope characteristics, thermal transmittance of building elements should be measured in situ. The method commonly used, based on ISO recommendations, is the heat flow meter measurement method. An alternative approach is based on the infrared thermovision technique (ITT). In this case, actual thermal emissivity value of the surface finishing material is paramount to obtain the true value of the surface temperature. Several methods and instrumentations are available for laboratory measurement of emissivity of materials, whose values can be even retrieved in databases. In this study a novel method for a direct evaluation of the emissivity of common building finishing materials by means of ITT is presented, using a portable instrument affording a comparatively fast but still quite accurate procedure. The laboratory experimental results, referring to six different building materials, provide promising indications on the possibility of applying the methodology to on site tests, so taking into account real material conditions, like environmental pollution, aging, laying mode.