Study On The Influence Of Plant Planting On The Thermal Performance Of Green Roof

With the development of social economy,the urbanization process is accelerating and urban buildings are becoming more and more dense.As urbanization has changed the underlying surface of the city,and the population in the city is dense,the artificial heat production is increasing,which intensifies the urban heat island effect and the building energy consumption is also growing.Green roofs have a positive impact on urban heat islands and reducing building loads.The green roof utilizes a large amount of unutilized roof area in the city,does not occupy the urban land area,and can also strengthen rainwater management,reduce rainwater runoff,and extend the life of the roof.Green plants have good cooling and humidifying effects,which can weaken the amount of solar radiation reaching the city and improve the urban air environment.There have been some studies on green roofs mainly focusing on theoretical model research and thermal insulation cooling experiments on green roofs.However,there are few studies on the effects of plants on roof thermal performance.This paper mainly uses the combination of theoretical analysis,experimental observation and numerical simulation to study the effects of plants on the thermal performance of green roofs:(1)Based on the principle of green roof insulation and heat insulation,establish a simplified mathematical model for green roof and conduct theoretical analysis.According to the plant leaf energy balance equation,the leaf temperature of plants under different environments was calculated and compared with the experimental values,the results were in good agreement.(2)Establish a comparative experimental platform for green roof and ordinary roof,and conduct a 6-day observation experiment to record the full cycle temperature,heat flux density,thermal resistance and observation temperature of different plants of green roof and ordinary roof.The results show that under the same thermal environment,the green roof has lower overall temperature than the ordinary roof,and the temperature fluctuation is small,and the variation range is only 14% of the ordinary roof;the solar radiation intensity has a greater influence on the ordinary roof heat flux and the effect on the green roof;the average thermal resistance of the plant layer during the 6 days of the experiment was 0.56 W/(m·K).(3)Based on the numerical calculation software CFD,a simplified model of the green roof is established from the microscopic scale of the plant,and the temperature value of the plant leaf theory is used as the first type of boundary condition,and the solar radiation model is used to carry out the flow field and temperature field of the green roof.Study and analyze the relationship between solar radiation intensity(I),wind speed(v)and plant leaf area index(LAI)on various parameters of green roof.The results show that the plant layer plays a role in heat insulation and cooling.When the leaf area index of the covered plant is small,the heat insulation cooling performance increases rapidly with the increase of the leaf area index,and then the growth rate slows down and eventually stabilizes.According to the numerical results,the relationship between the lower surface temperature of the roof,the average temperature of the plant canopy and the heat absorption of the plant on the solar radiation intensity,wind speed and plant leaf area index are given by multiple regression.