Building passive cooling through unsaturated capacitive porous medium on roof

A mathematical model to simulate an unsaturated highly capacitive porous medium on roof (sand) 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 thermophysical properties for different types of porous medium (building envelope) with different chemical composition and porous size distribution. The governing equations were discretized using the finite-volume method for describing the physical phenomena of heat and mass transfer in unsaturated porous medium. The robust MultiTriDiagonal-Matrix Algorithm (MTDMA) was used to solve this strongly-coupled problem, allowing the use of large time steps for long-term simulations. In order to precisely predict room air temperature and humidity, a lumped transient approach for a building room is considered. Comparisons of the sand layer effect in terms of heat fluxes through a horizontal roof, indoor conditions and thermal comfort (PMV – Predicted Mean Vote) are presented.