Behaviour of a lightweight external wall under Mediterranean climatic conditions

The increasing development and use of new lightweight building technologies makes more urgent the evaluation of their energy performance. It is even more necessary in climatic contexts, like the Mediterranean basin, in which the effect of the solar irradiation during the summer period could not be sufficiently lessened by low mass. In Sardinian region, for example, the average irradiance value on a horizontal plane is higher than of 290W/m2. In that case Italian legislation requires the use of an opaque envelope with a areal density bigger than 230 kg/m2 for all orientations with the exception of NW-N-NE or, a periodic thermal transmittance Yie<0,12 W/m2K for external walls and Yie<0,20W/m2K for horizontal or sloped roofs. The study here presented deals with the assessment of thermal performance of an opaque envelope designed and built in Sardinia in 2013. The building is aimed at maximizing the energy saving and the use of natural materials. The study is focused on the measurement of the steady state thermal transmittance and the dynamic parameters of prebuilt wall, made of OSB panels and cellulose. The measurement is compared with the minimum requirements of Italian national standards. The analysis was carried out using a climatic chamber settled in the DICAAR (Department of Civil and Environmental Engineering and Architecture) laboratories of the University of Cagliari. The chamber consist of two shells that create on both faces of a full scale wall different hygro-thermal conditions. One of the shell simulates the external conditions while the other recreates internal ones. A first set of data was collected in steady state conditions measuring the heat trough the specimen by means of flux meters and RTD sensors. A second set of data was acquired to measure the heat storage capacity of the specimen, and then the dynamic parameters are calculated according to the UNI EN 13786:2007