Experimental Investigation Of The Thermal Insulation Performance Of Composite Planting Roof Module

The process of urbanization has spawned a series of environmental and energy problems.Planting roofs,pond roofs and ventilation roofs are effective passive roof insulation technologies,which can improve such problems.Through the investigation of literature,the existing research focuses on the influence of structural parameters on the thermal insulation performance,lacking of discussion and innovation on structural.This paper proposes to combine the planting roof with pond and ventilation layer respectively to design four kinds of composite planting roof with different structures,and a photovoltaic fan is set to enhance the heat dissipation effect.The thermal insulation performance of each test module under three different test phases(summer,transitional season,winter)were analyzed.The influence of each module structures on thermal insulation performance were concluded,and the heat transfer process is analyzed and the heat balance equation is established.By comparing calculated values with the experimental values,the main reson for the error is obtained,which provides a basic theoretical basis for further research.The results of thermal insulation performance:the average temperature at the bottom of each planting roof module from low to high:module D<module B<module A<module C<module E.In summer,the average temperature at the bottom of module D is 28.8℃,the amplitude of the bottom temperature is only 0.2℃,which can reduced60.7%of the heat that transfer into the room.The insulation performance is optimal.In winter,the average temperature at the bottom of module C is 18.4℃,which is the maximum value in the planting roof modules,and the temperature amplitude is maintained at 0.2℃.Under the indoor air conditional temperature is 18℃in winter,it can reduce the heat loss about 39.2W/m~2,so the heat preservation performance is optimal.The difference in module structure influence the thermal insulation performance:(1)Compared with module B,the average temperature of the bottom temperature of module A under different test phases is 0.9℃,0.5℃and 0.6℃higher,and the temperature attenuation rate of the ventilation layer is 7.6%,13.6%and 3.0%lower.Setting the photovoltaic fan in the ventilation layer does not improve the thermal insulation performance.(2)The planting soil temperature attenuation multiple of module D is higher than other planting module,and the average of the bottom temperature of module D is 3.1℃,2.4℃and 2.0℃lower than the average of the bottom temperature of module C,which mean that setting the photovoltaic fan in the planting soil can improve the attenuation ability.(3)Compared with module C,the average of the bottom of module B is 2.6℃,1.4℃and 0.9℃lower,and the bottom temperature amplitude is about 0.9℃,1.4℃and 1.6℃higher.The temperature attenuation rate and temperature attenuation multiples of the ventilation layer is lower than that of the water pond.This may due to the specific heat capacity of the water,which can storage or release the heat to adjusted the bottom temperature,but lacking of heat dissipation lead to increase the bottom temperature.The heat balance equation of each planting roof module is numerically solved,and the error between the calculated value and the measured value is affected by the change of the outdoor temperature.Under different test stages,the minimum average relative error of each planting module was 3.4%,and the maximum average relative error was11.2%.By comparing the error of each planting roof module,the fitting degree of module A and module D is better,and module B and module C is worse.The main reasons of this relative errors are:(1)neglecting the difference of vegetation growth and leaf area index.(2)The convective heat transfer in the ventilation layer is regarded as steady-state heat transfer.(3)Ignoring the influence of water evaporation on the moisture content of the planting soil and the water level of the water pond.