Abstract
Vegetation cover provides shading and protects the soil beneath them from warming. Vegetation can be used as passive cooling technique that reduces the thermal load of a building. A numerical study has been carried out on laminar double-diffusive mixed convection in a green roof enclosure. The model is equipped with inlet and outlet openings for air removal while the left vertical wall is heated and partially saturated with water for indoor air humidification. The mathematical model is governed by the two-dimensional continuity, momentum, energy and concentration equations. Transfer equations are solved using a finite difference scheme and Thomas algorithm. The model was applied for the simulation of a building with green roof in Togolese climate conditions. Results showed that, the flow structure is a mixed convection type, but the isotherms et iso-concentration distributions reveal a vertical stratification of the temperatures and the relative humidity.To predict heat transfers inside the cavity, a correlation has been established for the estimation of the average Nusselt number as a function of the Leaf Area Index and Reynolds number under solar heat flux of 350 W.m-2, the average in case of Togo. It was found that a larger Leaf Area Index reduces the solar flux penetration and therefore, reduces significantly heat transfer inside the enclosure and then stabilizes it temperature. For the LAI equal to 3, the indoor air fluctuates around 26°C and the relative humidity range is found to be 50% - 60% under solar heat flux of 350 W.m-2.
Highlights
Natural cooling techniques have been used over the centuries and their application has started to spread throughout the world, in tropical regions where inside temperatures in buildings are far beyond the comfortable conditions
Particular attention is paid to the effects of this governing parameter Leaf Area Index (LAI) on the indoor air mixed convection
The objective of this study is to examine the heat transfer and the fluid flow characteristics due to mixed convection inside a square vented enclosure with a constant heat source on the top wall which represents the planted roof
Summary
Natural cooling techniques have been used over the centuries and their application has started to spread throughout the world, in tropical regions where inside temperatures in buildings are far beyond the comfortable conditions. The introduction of mechanical air conditioning systems into the building, with their great energy expenditure, has become the standard alternative used to natural cooling. Many studies regarding this problematic are developed as ROOFSOL research project [1,2,3,4], which focused on the theoretical and experimental analysis of different roof solutions for cooling in arid region, mainly based on evaporative and radiative cooling principles. A high concentration of buildings raises many environmental issues, such as the Urban
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