Performance analysis of a planted roof as a passive cooling technique in hot-humid tropics

Planted roofs are passive cooling techniques that reduce the thermal load of buildings. In this paper, the authors have developed a model for evaluating the cooling potential of green roofs. Transfer equations are solved using a finite difference scheme and Thomas algorithm. The study was conducted taking into account the Togolese climate conditions. The effect of Leaf Area Index (LAI) and Biot (Bi) number on diurnal variation of the Solar Heat gain Factor (SHF) is presented and analysed. A correlation for the estimation of the Solar Heat gain Factor as a function of LAI and Bi has been established. The results presented in terms of evapotranspiration (ET) and Solar Heat gains Factor (SHF) show notably that the foliage density and hence the vegetable canopy type selection influence the thermal efficiency of the bioclimatic insulation screen greatly. It was found that a larger LAI reduces the solar flux penetration, stabilizes the fluctuating values, and reduces the indoor air temperature.

► We model the effect of vegetation screen on the heat gains in buildings.
► Evapotranspiration and soil heat fluxes are deduced from temperature variations.
► We analyse the effects of atmospheric conditions on the evapotranspiration process.
► A larger Leaf Area Index stabilizes reduces the indoor air temperature.
► A correlation of the heat gains in a building across the green roof is established.