The Influence Of Green Roof On Building Energy Saving

China’s economy has developed rapidly since the reform and opening up,however,it also brought a series of problems,such as the over-exploitation of natural resources and the resulting damage to the natural ecology,and the waste of resources caused by low energy utilization.Nowadays,the economic development has turned to a new model with the opening of the new era,economic development no longer be done at the expense of environmental damage,and energy conservation and environmental protection economy should be advocated as well.In order to study the heat transfer characteristics of leaves,dozens of plants are selected to determine the thermal conductivity of plant leaves.The correlation equation between thermal conductivity resistance（TCR）and water content of leaves was fitted through plate heat conduction experiment.And then wind tunnel experiment was used to study the heat characteristic in convective heat transfer process between leaves and surrounding air.The relationship between sensible heat resistance（convective heat transfer resistance）and leaf area index(L_ai),as well as latent heat resistance（transpiration heat transfer resistance）and L_ai was determined by the wind tunnel experiment,and the correlation expression between sensible heat resistance and L_ai was proposed.The final research results showed that the TCR of leaves varied less with leaves’temperature from5℃to 30℃,the thermal conductivity of leaves decreased with the increase of leaves’water content when the leaves’temperature is at 25℃;The sensible heat resistance had a nonlinear relationship with L_ai and decreased with increasing of L_ai,and latent heat resistance showed different variation patterns with the change of L_ai according to the different transpiration capacity of different leaves.In order to conduct heat transfer study of the whole green layer system on the roof,the roof green layer is divided into different energy levels according to different energy conversion forms and the steady heat transfer resistance model of roof is established,and then the calculation expressions of heat transfer resistance and heat flux of each energy level in the model are deduced according to the related formulas proposed by predecessors based on the heat balance relation.The following conclusions are obtained by using the derived calculation expressions above:The leaves’sensible heat resistance decreases with the increase of wind speed and increases with the increase of solar radiation intensity;The latent heat resistance of leaves does not change significantly with the increase of wind speed,but decreases with the increase of solar radiation intensity;Soil sensible heat resistance decreases with the increase of wind speed and increases with the increase of solar radiation intensity;The latent heat resistance of soil decreases not only with the increase of wind speed but also with the increase of solar radiation intensity.In order to verify the computational expression derived above,the general applicability of the expression is proved by monitoring the relevant parameters of ten plants planted on the ground,and then the expression’s applicability in a particular environment on roofs is proved by monitoring various parameters of green plants on the roof.According to comparing green roof with ordinary roof and numerical calculation,it is found that:In summer,the daily heat flux through the green roof fluctuates little,the heat flows from the indoor to the outdoor in most of the time,and only in the afternoon between 1:00 and 3:00,the heat flux flows from the outdoor to the indoor,which result in much less heat load than the ordinary roof at the same time.In a day,compared with ordinary roof,the energy saving efficiency of green roof is about 184.85%at most,and 91.13%at least,and the average value can reach 108.06%,which is nearly consistent with the research results in the literature.