Natural Aging Processes Of Reflective Roofs And Its Effects On Energy Consumption

With the accelerating process of urbanization and increasing heat island effect in recent years, the living environment and building energy saving has been widely received greater attention. In residential buildings, the roof, as one of the main components of the building envelope, has a larger heat flow compared to the exterior wall and the ground under the sun. By applying high-reflective coatings on the roof, which can reflect more solar radiation, the urban micro-climate can be improved and building surface temperatures as well as ambient temperatures could be decreased. In order to study the durability of high-reflective coatings and the impacts of high-reflective roofs on buildings, research was carried out on natural aging performance of high-reflective coatings, energy saving effects and indoor thermal environment after the application of reflective roof in a dormitory building.In this dissertation, heat-insulation mechanism, heat transfer theory, natural aging principle and thermal comfort theory of high-reflective roofs were presented. Meanwhile, air-conditioners selection of households and roof reflectance of existed buildings in Xiamen were investigated through a questionnaire and filed surveys. The results showed that 59.8% of the surveyed families cannot use air conditioners for heating in winter and the solar reflectance of most aged roof materials was lower than 0.4.A dormitory building located in Tongan, Xiamen, was selected to set-up coatings' natural aging platform and black baseline roof(with initial solar reflectance of 5.0%), white reflective roof(with initial solar reflectance of 78.8%) and yellow reflective roof platform(with initial solar reflectance of 56.6%). The solar reflectance and thermal emissivity of coatings, thermal parameters, and electricity consumption of air conditioners of coating rooms were measured at regular intervals. The results showed that after 14 months of natural aging, solar reflectance of white and yellow reflective coatings remained stable(white coatings with aged solar reflectance of 51%, yellow coatings with aged solar reflectance of 42%), and for black coatings it increased slightly, while thermal emissivity of the three coatings had small variations. Compared with black baseline roof, reflective roofs significantly improved indoor thermal environment in summer and transient seasons, and its negative effects on indoor thermal environment were limited in winter. For the whole-day air conditioning state, the electricity saving rate of white and yellow coatings room were 28.2% and 23.7% respectively, while at nighttime air conditioning state the rate were 22.7% and 13.7% respectively.The last section of the dissertation deals with the energy simulation using DesignBuilderV3.4 software to build prototype with the same geometry dimension of the measured building. After model verification, the building envelope parameters were assigned compliant with prescriptive requirements or recommended design values in Design Standard for Energy Efficiency of Residential Buildings in Hot Summer and Warm Winter Zones(JGJ 75). Meanwhile, typical meteorological year of Xiamen was assigned to simulate annual air conditioning cooling and heating loads, and electricity consumption of baseline and reflective coatings room. Also, equivalent thermal resistance of roofs with different solar reflectance was simulated and calculated.In conclusion, three research methods, field survey, case study and energy simulation, were used to analyze natural aging processes of reflective roofs, and its effects on energy consumption and indoor thermal environment of coatings room. Research results provided a theoretical basis for engineering application of reflective roofs in Xiamen.