Indagine numerica sulle caratteristiche termofluidodinamiche di un tetto ventilato

One of the European Directive priorities is the development of new strategies for “very low energy buildings”. In regions with high level of solar radiation, ventilation allows the cooling load during summer period and contributes to the reduction of the energy needs of buildings. The most important advantages are the reduction of the heat fluxes transmitted by the structures exposed to solar radiation, thanks to the combined effect of shading surfaces and heat removed by the air flow rate within the ventilated air gap. This work illustrates a numerical investigation on a prototypal ventilated roof for residential use. The physical domain under investigation is two-dimensional and its configuration is geometrically and thermally symmetry, so a single side of the roof is considered. The computational domain has finite dimensions and it is composed by the ventilated channel and two storages located at the inlet and the outlet of the channel. The two storages are useful to know what happens near the region of the thermal disturbance caused by the heat applied on the upper layer of the cavity to simulate the free-stream condition of the flow. The roof is long 6.0 m, inclined from the horizontal of 30° and the ventilated channel, under the roof, has a height of 10 cm. Inlet storage dimensions are Lx = Ly = 3m, equal to the average height of a floor. Outlet storage is characterized by the exit section of the channel and the height of the ridge, h, is equal to 0.10 m. The analysis is carried out on a two-dimensional model in air flow and the governing equations are given in terms of k-ε turbulence model. At first, the influence of the ridge is analyzed, considering different types of outlet reservoirs. Then, the investigation is performed in order to evaluate thermofluidodynamic behaviors of the ventilated roof as a function of the different conditions applied on the top wall and the bottom wall of the ventilated cavity in summer and winter regimes. Different values of heat fluxes are applied on the top wall of the ventilated cavity to simulate typical summer and winter days conditions, whereas the bottom wall is assumed isothermal and different values of wall temperature are considered. The problem is solved by means of the commercial code Ansys-Fluent. Results are given in terms of temperature and velocity distributions, air velocity and temperature profiles along different longitudinal and cross sections of the ventilated layer in order to estimate differences between analyzed conditions.