Study On Impact Prediction Of Green Roofs On The Regional Thermal Environment

With expansion of the cities, urban ecological environment is deteriorating and urban heat island effect is strengthening. By growing plants on buildings’ roofs, green roof technology adds greening to land-tension built-up urban areas and effectively improves the thermo-physical properties of the underlying surface area. It is considered ro be one of the effective ways to solve comprehensive problems in modern cities. In view of the green roof application in urban regions, this paper studied systematically the influence of different types of green roofs and the green roof design factors on regional thermal environment.This paper comprehensively reviewed the research status on green roofs at home and abroad from three aspects: heat and mass transfer mechanism, cooling and energy saving effect and ecological and environmental benefits. The problem frontier was learned through the summary and analysis of existing research. A research method which combines field measurement and numerical simulation was adopted. The main research contents of this article was then defined.Green roof projects in Chongqing were selected as the field test objects. Outdoor thermal environment of extensive and intensive green roofs were measured under typical winter, summer and transitional season climatic conditions. Analyzed the impact of different types of green roofs on outdoor thermal environment during different climatic seasons. This measurement supplemented the experimental data about intensive green roofs and seasonal conditions, which were ignored in previous studies. It also got a lot of relevant valid data, which would be useful for further study on green roof energy efficiency coupling the indoor thermal environment and the regional thermal environment.Measured the impact scope of green roofs on thermal environment in the regional scale for the first time. In summer conditions, vertical and horizontal distribution of temperature and humidity around green roofs were found by fixed and mobile observation. Analyzed and classified the factors which contributed to the regional thermal environment. Quantified the impact scope of green roofs on regional thermal environment.Mathematical model of green roofs and regional thermal environment were established based on the heat and mass transfer mechanism of green roofs and the forming principle of regional thermal environment. The coupling and numerical methods were discussed combining with a special simulation software. Analyzed and validated the ENVI-met simulation software and determined the optimal initial conditions, boundary conditions and simulation accuracy. Experimental data were used to verify the applicability of the model in climate of Chongqing for the first time.Variable factors which determined the impact of green roofs on regional thermal environment can be divided into three categories: weather factors, regional planning factors and green roof design factors. The factors values were discussed combining with the design specifications and planning targets. 29 simulation scenarios were established by changing the variables. Evaluated quantitatively the impact of green roof type, coverage and distribution on regional thermal environment and determined the optimal green roof configuration.Finally, the paper carried on the forecast to the follow-up studies.