Thermal stress reduction in cool roof membranes using phase change materials (PCM)

A considerable amount of energy is used in the building sector for air conditioning purposes. Additionally, the building sector contributes to the urban heat island (UHI) phenomenon which causes temperature rise in urban areas. Cool roof is an emerging passive cooling technology that can contribute to reduce the cooling energy use in buildings and to mitigate the UHI effects in the urban area. Cool roofs and reflective coatings, despite of being effective in terms of reducing the cooling thermal loads in buildings and decrease the UHI, can suffer from extreme thermal stress which negatively influences their lifespan and performance. Thermal energy storage (TES) is a promising technology which can be applied together with cool roof technology to decrease the extreme thermal stress due to solar radiation as well as providing thermal inertia to the building. In this study, simulation-based optimization will be used to optimize the PCM melting temperature when integrated into a polyurethane-based cool roof membrane to reduce the thermal stress of the cool roof and also to improve the annual energy performance of the building. The optimization results showed that the application of PCM and cool roof technologies together can reduce the severe thermal stress of the cool roof membrane when the optimization objective is the annual thermal stress of the cool roof. On the other hand, when PCM melting temperature is optimized to reduce the annual energy needs, higher annual energy savings could be achieved with acceptable reductions in the cool roof membrane thermal stress.The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 657466 (INPATH-TES). The work is partially funded by the Spanish government (ENE2015-64117-C5-1-R (MINECO/FEDER) and ENE2015-64117-C5-3-R (MINECO/FEDER)). The authors would like to thank the Catalan Government for the quality accreditation given to their research group GREA (2014 SGR 123). GREA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This project has received funding from the European Commission Seventh Framework Program (FP/2007-2013) under Grant agreement Nº PIRSES-GA-2013-610692 (INNOSTORAGE). Alvaro de Gracia would like to thank Ministerio de Economia y Competitividad de España for Grant Juan de la Cierva, FJCI-2014-19940. A.L. Pisello’s acknowledgments are due to the UNESCO Chair “Water Resources Management and Culture”, for supporting her research