Numerical analysis of passive cooling using a porous sandy roof

A mathematical model to simulate an unsaturated sandy roof is considered in order to predict its effects on building passive cooling. The present methodology is based on the theory of Philip and De Vries, using the hygrothermal properties for different types of building envelope porous materials. The governing equations have been discretized using the finite-volume method for modeling the physical phenomena of heat and mass transfer in unsaturated porous media and they have been solved by using the MultiTriDiagonal-Matrix Algorithm (MTDMA), avoiding numerical instability related problems due to the strong coupling between the mass and energy conservation equations. In order to predict the room air temperature and relative humidity, a lumped transient approach for a building room has been considered. Comparisons of the sand layer effect on the heat flux through a horizontal roof and on the indoor psychrometrics conditions are discussed.