Experimental on-site measurement of thermal conductance by means of heat flow meter applied to nanocomposite thermal insulating mortar coating

In the energy refurbishment of buildings, the declared thermal conductivity is the key to meet the minimum requirements concerning energy efficiency and tax incentives. Regardless of the assessment method for thermal conductivity, in situ measurements using the heat flow meter technique can be always performed, especially in case of very low and self-declared thermal conductivities. In the present work, the reliability of the heat flow meter approach is validated considering a multilayer wall, with all thermal properties declared by means of technical regulations or CE marking. The measured total conductance of the wall is in very good accordance with the calculated one. Then, the heat flow meter has been applied to a plastered stone masonry wall before and after the application of a nanocomposite, thermal insulating, mortar coating 8 mm thick, with a self-declared thermal conductivity of 0.0019 W/(m K) without CE marking or appropriate laboratory tests. The thermal conductance obtained from the on-site measurements is about five times greater than the expected one. The increase in thermal resistance due to the mortar is comparable to a material with the same thickness, but with the thermal conductivity one order of magnitude greater than the self-declared value.