  The double-skin roofs investigated in this paper are formed by adding a
metallic screen on an existing sheet metal roof. The system enhances passive
cooling of dwellings and can help diminishing power costs for air conditioning
in summer or in tropical and arid countries. In this work, radiation,
convection and conduction heat transfers are investigated. Depending on its
surface properties, the screen reflects a large amount of oncoming solar
radiation. Natural convection in the channel underneath drives off the residual
heat. The bi-dimensional numerical simulation of the heat transfers through the
double skin reveals the most important parameters for the system's efficiency.
They are, by order of importance, the sheet metal surface emissivity, the
screen internal and external surface emissivity, the insulation thickness and
the inclination angle for a channel width over 6 cm. The influence of those
parameters on Rayleigh and Nusselt numbers is also investigated. Temperature
and air velocity profiles on several channel cross-sections are plotted and
discussed.
