城市街区形态及冷却屋顶对冠层内辐射热通量的影响

在当前中国城市化进程愈演愈烈的情形下，城市热岛冷却效应的研究对于确立城市生态环境可持续化发展的正确途径等有重要意义。采用离线城市冠层模型分析了城市冠层中街区形态和屋顶材料的变化对辐射热量、表面温度及冠层内气温的影响。研究发现:建筑物高度、宽度以及街道宽度等参数的改变对冠层各表面温度的影响较大，当街道宽度增加3 m时，地面温度升高约3.5 K。但是街道宽度增加，多重反射导致的辐射截陷效应减弱，墙面上更多的热量释放出去，各墙面温度降低约1.5 K；冠层气温先增加，日出后降低约0.4 K。屋顶材料的改变对辐射及热通量和表面温度也有较大影响，与灰色水泥屋顶相比，采用高反照率白色涂料冷却屋顶后，屋顶净辐射热量损失约380 W m-2，屋顶表面温度降低约10 K。冠层内街区形态和屋顶材料对城市辐射热环境产生直接的影响。

A Preliminary Analysis of the Influence of Block Morphology and Cool Roof on the Radiation Heat Flux in Urban Canopy

With the rapid urbanization in China, the study of the cooling effect of urban heat island is of great significance to promote the sustainable development of urban ecological environment. In this paper, the influence of block morphology and roof materials on radiant heat and surface temperature are analyzed by using an offline urban canopy model. The results show that the height and the width of the building and the width of the street have great influences on the surface temperature of the urban canopy. When the street width is increased by 3 m, the ground temperature would rise about 3.5 K. However, if the street width increases, the radiation cutoff effect caused by the multiple reflections would be weakened. Thereby, the wall will release more energy, which can lower its temperature by 1.5 K. The canopy temperature increases first, and then decreases by about 0.4 K after sunrise. The change in roof materials also has great impacts on radiation, heat flux and surface temperature. Compared with the gray cement roof, the cooling roof with high-albedo white paint can reduce the net radiation by about 380 W m^-2 and the roof surface temperature would reduce by about 10 K. The block morphology and the roof material have a direct impact on the urban radiant heat environment.