CFD analysis and experimental comparison of novel roof tile shapes

In tiled pitched roofs, a ventilated layer reduces the heat transfer between tiles and roof structure by means of natural and forced convection, thereby also reducing the cooling energy requirement. This effect could be enhanced by increasing the air permeability between the tiles by means of novel tile shapes, as proposed by the HEROTILE European project (LIFE14 CCA/IT/000939), of which this work presents the preliminary analysis supporting the new tile designs. Using an experimental rig, the air pressure difference and the volumetric flow rate between tiles have been measured for an existing Portoghese tile design over a range of pressures. Then, in order to understand the air flows under different conditions, a three-dimensional CFD model has been implemented to recreate the full geometry of the rig. The model was calibrated against the aforementioned experimental results, and run with boundary conditions simulating different wind directions. Even in the low velocities typical of average local wind patterns, the fluid dynamic problem remains complex because of the geometry of the gaps between the tiles. However, it has been possible to assess the coefficient of local head loss and then apply it in an analytical relationship between pressure drop and flow rate, taking into account the open area. The results have shown how the wind direction affects the air permeability and, therefore, important insights have been gathered for the design of novel tiles.