On the Effects of Variation of Thermal Conductivity in Buildings in the Italian Construction Sector

Stationary and dynamic heat and mass transfer analyses of building components are an essential part of energy efficient design of new and retrofitted buildings. Generally, a single constant thermal conductivity value is assumed for each material layer in construction components. However, the variability of thermal conductivity may depend on many factors; temperature and moisture content are among the most relevant ones. A linear temperature dependence of thermal conductivity has been found experimentally for materials made by inorganic fibres such as rockwool or fiberglass, showing lower thermal conductivities at lower temperatures. On the contrary, a nonlinear temperature dependence has been found for foamed insulation materials like polyisocyanurate, with a significant deviation from linear behaviour. For this reason, thermal conductivity assumptions used in thermal calculations of construction components and in whole building performance simulation have to be critically questioned. This study aims at evaluating how temperature affects thermal conductivity of materials in building components such as exterior walls and flat roofs in different climate conditions. Therefore, experimental conductivities measured for four common insulation materials have been used as a basis to simulate the behaviour of typical construction components in three different Italian climate conditions, corresponding to the cities of Turin, Rome and Palermo.