HEAT-TRANSFER BEHAVIORS OF A SLIGHTLY HORIZONTAL VENTILATED ROOF UNDER VARIABLE CLIMATIC CONDITIONS

Abstract

This paper illustrates a numerical study to evaluate thermal and fluid dynamic behaviors of natural convection inside a slightly inclined ventilated roof for residential building in the Mediterranean area. The system is studied considering a roof with a length equal to 6.0 m and three different inclinations with respect to the horizontal plane (0◦, 2◦, 5◦). The ventilated channel, under the roof, has a distance between the flat plates equal to 10 cm. A two-dimensional natural convection with surface radiation model is considered assuming a turbulent air flow. Different conditions are applied on the top wall and the bottom wall of the roof to simulate summer and winter conditions. Different values of solar heat fluxes are applied on the top wall of the ventilated cavity together with heat transfer with the external ambient. Along the bottom wall there is a heat transfer toward an internal ambient by means of a thermal conductance. The problem is solved by means of the commercial code Ansys-Fluent. Results are given in terms of temperature and pressure distributions, air velocity, and temperature profiles. The increase in inclination of the pitched roof determines a better performance of the component. In fact, during the summer, the efficiency of the system improves because the high heat flux produces an optimal air-convective condition into the ventilated channel. In the winter, the effect of the ventilated layer is more significant to fulfill optimal thermal and hygrometric conditions.