Experimental assessment of thermal performance of three passive cooling techniques for roofs in a semi-arid climate

Three passive techniques for air cooling in buildings are tested in the real conditions of Marrakech (Morocco) whose climate is hot semi-arid (BSh type according to the Köppen-Geiger climate classification). The passive techniques, that are white painting, shading and thermal insulation, are applied to the roofs of three outdoor test cells. Thermal performance of these techniques are assessed simultaneously via a 29 summer days monitoring of four test cells, including a reference cell with bare roof. Measurements concerned the cells indoor air temperature, the roof slab inside (ceiling) and outside surface temperature, as well as the heat flux through the roof slab. Moreover, all the local climate parameters were recorded by means of a weather station installed near the test cells. The results show that the studied passive techniques have a significant impact on the heat flux through the roof and consequently on the cells ceiling and indoor air temperature. The white painted roof has the highest thermal performance as it lowers the ceiling temperature by up to 13.0 °C relatively to the reference cell; while this temperature reduction was always less than 9.9 °C and 8.9 °C respectively for the thermally insulated and the shaded roofs. Moreover, the white painted roof reduced the heat flux through the roof slab by up to 66%.