Research On Thermal Performance Of The Whole Year And Thermal Effect Of Green Roof

Green roofs can greatly improve green coverage rate of the city. It is the effective method to solve the various comprehensive problem of modern city. Many studies for green roofs’ thermal performance proved that the green roof has obvious effect of heat insulation and cooling in the summer. But It cannot fully describe the performance only through the temperature lower value and heat loss of of green roofs; For theoretical study of the heat and mass transfer of green roof, heat storage and the changes of thermal and physical properties are not considered; So this paper from the perspective of thermal effect will be heat transfer process of decomposition and quantitative analysis. It will has a comprehensive insight into the thermal performance through the analysis of the heat flow throughout the year of green roof.The green roof in this paper is suitable for air- canopy- air within canopysubstrate model. The calculation formula of thermal effect in the previous research is Summarized. The affected factors and the various heat calculation formula of the assumptions are compared. According to the applicability of different formulas, and gives out the suitable for chongqing grass green module component heat calculation formula and parameter.In this paper, through the appropriate assumptions, the heat transfer model of heat transfer in the substrate layer is built. The model accurately describe the stromal layer moisture evaporation and transpiration influence each other by setting the boundary condition. an example is used to calculate and the applicability of the model the was verified. It also calculated temperature distribution and heat by different nodes of substrate layer, and found that the substrate layer of heat storage is not to be ignored.In this paper, the green roof module was tested on winter, spring and summer from the point of view of the annual evaluation of the heating effect of the green roof and it explains the causes of thermal effect by heat flow analysis. On sunny winter day, green canopy has adverse influence on roofing heat gain, the reason is that between the canopy and the sky long wave radiation, latent heat in heat and convective heat consumption of the canopy of the heat gain, have to burn for part of the substrate layer is save storage. On winter and spring green cloudy day, thermal performance is not obvious and the thermal effects are relatively small. On spring sunny day, green roof obviously reduce the effect of solar radiation. long wave radiation and convection heat transfer in the morning make the main heat dissipation effect. In the afternoon, latent heat, longwave radiation, make the main heat dissipation effect. Green roof in the summer have obvious heat insulation cooling effect, because the canopy of the latent heat, photosynthesis and long wave radiation heat transfer plays a main heat dissipation effect.This paper gets heat effect in the primary and secondary relations in the process of heat transfer by comparing the average heat flux of 9:00~17:00 during the day. This paper also studied the dynamic thermal effect. It is presented according to the thermal effect of the evaluation of green roof canopy of three parameters: shading coefficient, canopy temperature and surface temperature of substrate.By theory, simulation and experimental study, this paper established a research method to study thermal performance and give the the change laws of heat effect on green roof module. Although this paper analyzed a particular instance, the method of studying green roof heat transfer can be applied to other green roofing. At the same time, the research of heat transfer of green roofing module can be used as a reference in practical engineering.