Comparative Experimental Study On Thermal Insulation Performance Of Composite Water Storage Planting Roof With Ventilation Coupling

With the rapid development of society,developing ecological buildings,reducing energy consumption in the whole life cycle of buildings,and improving the comfort of the building environment have become the mainstream directions for the current construction industry to adapt to the "dual carbon" goal and sustainable development.The southern part of China belongs to the subtropical climate zone,and the outdoor weather conditions in summer are characterized by long sunshine hours,large solar radiation,high outdoor air temperature,and high relative humidity.Buildings in the southern region mostly adopt the form of ventilation and heat dissipation to cool the buildings.The thermal insulation performance of the envelope structure is relatively general,and the roof of low-rise buildings in this area accounts for more than 30%of the total surface area of the building envelope.Due to direct sunlight,the heat transferred into the room through the roof of the building is relatively large.This thesis designs and builds three new types of roofs,namely composite water storage planting roof,ventilated planting roof and water storage and ventilation planting roof.The thermal insulation performance of each module is studied through tests,and a related heat transfer model is established.At the same time,the dynamic heat balance heat transfer mechanism of the composite planting roof is discussed.In summer,the use of composite overhead ventilation planting roofs is more conducive to lowering the roof temperature and the heat transferred from the roof to the interior,but it cannot solve the problem of reverse heat transfer at night;the use of composite water storage planting roofs in winter is more beneficial Insulation to reduce the impact of outdoor temperature on the roof.During the test time,the module A,Module B,Module C,Module E,Module F,Module G,and Module H The average bottom temperature is 7.9℃,8.9℃,7.9℃,7.5℃,9.7℃,10.0℃,7.2℃ and 7.9℃lower than the bare roof modules,respectively.℃.The total heat flow of module F is the smallest,which is 65 W/m2,which is 189.2W/m2 lower than that of the exposed roof;the setting of through-type ventilation is beneficial to improve the heat dissipation of the module,which can be reduced by 0.9℃～1℃;the ventilation of the aquifer alone cannot effectively reduce the bottom temperature.The temperature at the bottom of module D（unventilated state）was higher than that of module J for more than 22 hours a day,which indicated that increasing the thickness of the soil layer could not reduce the temperature of the module,but weakened the heat dissipation capacity at night.When the wind speed in the module D is 2.2m/s,the average temperature at the bottom of 0m/s and lm/s drops by 1.7℃ and 0.9℃,indicating that ventilation is beneficial to reduce soil temperature and heat storage,and improve the thermal insulation performance of the module.The maximum temperature at the bottom of module G is 2.5℃ lower than that of module I,indicating that the soil layer above the water storage can be used as a shading to reduce the impact of solar radiation on the roof.The minimum temperature at the bottom of module G was 2.7℃ higher than that of module I,indicating that the soil layer also inhibited the heat dissipation capacity of water storage at night.In the transition season,the maximum temperature of the composite planting modules was lower than the average outdoor air temperature（26.8℃）.During winter,the average temperature at the bottom of the composite water storage planting ventilation module（module H）is the highest（18.4℃）,and the heat transfer direction of module H is the heat transfer from outdoor to indoor throughout the day,and the total heat transfer heat flow is 7.2 W/m2,It shows that its thermal insulation performance is the best.Among all roof modules,only the heat transfer direction of module H is from outdoor to indoor heat transfer throughout the day.In this thesis,the heat balance equation is established,and the heat flow of each part is calculated to calculate the hourly average temperature of the soil layer.Test values and calculate theoretical values through summer experiments.The results show that the model numerical trend of each module is the same as the experimental test temperature trend,the maximum relative error of all modules is less than 10%,and the fitting degree is high.The economic advantage of the composite overhead natural ventilation planting roof（module F）is the most obvious.The initial investment cost is 70.6 yuan/m2,and the energy saving effect is the best.The total annual income is 14～18 yuan/m2,and the investment return period is 3.9～5 years.All in all,the composite planting roof structure combined with ventilation,water storage and planting can achieve the purpose of reducing roof heat flow and roof temperature in summer,reducing the role of building energy consumption,and improving indoor comfort,in the field of building energy saving and green building.It has certain application prospects.