Roof cooling by direct evaporation from a porous layer

As the world continues to urbanise, significant challenges are arising to environment, energy and water sustainability in cities. One of the most challenging consequences of increased urbanisation is increased energy consumption adversely affecting the quality of life, environment and public health. This motivated many researchers to find innovative methods to reduce energy consumption in buildings for cooling practices. In this paper, a series of experiments was conducted to investigate the performance of an evaporative layer of porous media and the effects of its particle size on reducing the roof surface temperature. To do so, customized rectangular Plexiglas columns were packed with three types of sand with well-defined particle size distribution saturated with water with all boundaries closed except the top, which was exposed to air for evaporation. The obtained results revealed the great potential of drying porous media to reduce the heat flux through roof via utilizing a part of the energy for liquid vaporization. As particle size decreased the temperature of roof remained lower than the bare roof for a longer time as a result of the presence of more liquid pathways connecting the receding drying front to the evaporation surface, which kept the surface wet for a longer time. Our results present new insights about the physical mechanisms controlling the performance of drying porous media to regulate roof surface temperature.