Coupling of Solar Reflective Cool Roofing Solutions with Sub-Surface Phase Change Materials (PCM) to Avoid Condensation and Biological Growth

Abstract

Cool roofs are effective solutions to counter the overheating of building roofs, inhabited spaces below and urban areas in which buildings are located thanks to their capability of reflecting solar radiation. Nonetheless, the relatively low surface temperatures that they induce can cause condensation of humidity and leave the surface wetted for large part of the day, thus promoting the growth of bacteria, algae and other biological fouling; this can cause a quick decay of the solar reflective performance. Biological growth is countered by surface treatments, which, however, may be toxic and forbidden in many countries and may also vanish quickly. It can also be countered by lowering the thermal emittance and thus decreasing heat transfer by infrared radiation to the sky and the consequent night undercooling, but this can decrease the performance of cool roofs. An alternative approach, which is analyzed in this work, is to embed in the first layer below the cool roof surface a phase change material (PCM) that absorbs heat during the daytime and then releases it in the nighttime. This can increase the minimum surface temperatures, thus reducing the occurrence humidity condensation and also the biological growth. In this work, preliminary results on the coupling of a cool roof surface with a PCM sublayer are presented, being obtained by theoretical investigation on commercial materials and taking into account the time evolution pattern of the environmental conditions.