Moisture Sorption Properties of Modified Porous Clays for Roof Evaporative Cooling Applications

This research concentrates on evaporative cooling, a sustainable and alternative way to cool a roof surface by taking advantage of the properties of porous materials. During periods of rain or high humidity nights, water sorbents store moisture in their small pores inside their particles. During a warm sunny day, the latent heat released due to evaporation of moisture, maintains the surface temperature at low level. Lower roof temperatures contribute to smaller heat flow inside the building while reducing the cooling load. In this work, materials consisting of ordinary soil, montmorillonite and modified clays were used. Prior to moisture sorption experiments, materials were characterized by techniques including X-ray diffraction, X-ray fluorescence, thermogravimetric analysis and porosimetry. In order to determine the sorption isotherms, dry specimens were placed initially in desiccators above four different saturated salts in water solutions (32.8% to 93.6%). The modified clay was found to have the highest equilibrium state (10% after almost 4 days of sorption at high relative humidity). Also the moisture sorption rate of the modified clay was faster than the rest of the materials and equilibrium was attained in less than 12 hours. Moreover, a specific environment chamber was developed and tested for the evaporative cooling properties of the materials. The lower observed surface temperatures under simulating radiation of the modified clays in comparison to ordinary soil, indicated their significant potential for evaporative cooling applications.