Study On The Energy-saving Effect Of Thermo-chromic Top-Floor Rooms Of Residential Buildings In Chongqing

As the conflicts between global resources,environment and economic development increase,people have been paying more and more attention to the level of building energy consumption every year.The building roof is one of the main factors that affecting the building thermal environment and air-conditioning energy consumption.The top floor of residential buildings has been widely criticized for its poor thermal environment and high energy consumption.The paper studies the energy-saving effect of air conditioning of the thermo-chromic roof of a residential building in Chongqing using the method of combining field measurement and numerical simulation in order to determine the energy-saving roof forms more suitable for residential buildings in Chongqing City.Firstly,on the basis of the principle of roof heat balance,the paper analyzes the energy saving mechanism of the thermo-chromic roof using the evaluation method of indoor thermal comfort of the top-floor room,and clarifies the present situation of air conditioning habits and roof reflectivity of residential building in Chongqing through literature research and field investigation.The roof reflectivity of residential buildings in Chongqing City is relatively low(about 0.25).The frequency of air conditioning in winter is lower than that in summer among residents.In summer,air conditioning is often opened on weekdays and early in the morning,and run all day on the days off,while it’s used at night and early in the morning in winter.Secondly,the paper sets up an experimental platform of natural aging and energy saving effect of thermo-chromic coatings to regularly measure the reflectivity of thermo-chromic coating substrate and monitor the thermal environment parameters and air conditioning power consumption of top-floor rooms with the thermo-chromic roof and common roof at the same time.Under the natural exposure environment,the thermo-chromic coating will fade,and the initial reflectivity of the colored phase is 0.5,which is almost stable at 0.65 after four months while the reflectivity of the colorless phrase is kept at 0.79.In contrast to the common roof,the thermo-chromic roof can significantly improve the thermal environment of the top-floor room in summer and transition seasons,and the thermal environment in winter is slightly less favorable than the common roof.Thermo-chromic roof can reduce the energy consumption of air conditioning in summer and has negative effect in winter.Finally,on the basis of the Design Builder platform,the paper establishes a residential building model with the same size as the measured building.Based on the actual measurement and verification,it simulates and predicts the annual cold/heat load and annual air conditioning power saving rate of the thermo-chromic roof used in the new building in comparison to the common roof and traditional high reflection roof,uses EMS(Energy Management System)module to complete the optimal design of the coloration temperature of the thermo-chromic roof,and evaluate the economic suitability of its application in Chongqing area.The annual electricity saving rate of the thermo-chromic roof is 9.5%.The optimum roof coloration temperature used in Chongqing is 19.6°C,at which the thermo-chromic roof can save another 1.65 k W·h/m~2 per year,which is 1.87k W·h/m~2 more than that of the high reflection roof.Thus,the thermo-chromic roof is suitable for application in Chongqing area.Through the above research,the paper reveals the law of reflectivity of thermo-chromic roof coating in Chongqing area,evaluates the thermal environment of the top-floor room,and quantitatively analyzes the energy saving rate of air conditioning using actual measurement and numerical simulation.It is hoped that the research results will provide theoretical and technical support for the construction of comfortable indoor thermal environment for top-floor rooms in areas with hot summers and cold winters.