| There are many advantages of building ecological roof, including increasing green area around building, reducing building energy consumption, easing the urban heat island effect, and improving micro climate around building. Besides, building ecological roof can also reduce the pressure of municipal rainwater pipe. More and more advantages will be found after building the roof. Ecological roof is one of the main measures to stop the heat which comes from the the top of building from getting in upper rooms by its small modulation mode with plants covered to stop solar radiation from radiating the top of building directly and with transpiration of plants and evaporation happened in soil layer. Heat can be reduced to get indoor either by small modulation mode of ecological roof with reservoir. In this way, the temperature of the roof surface will be reduced by water in the reservoir evaporated. Consequently, ecological roof can improve the thermal environment in buildingIn this paper, comparative testing platform used to comtrast insulation of water-storage planting roof with insulation of planting one and bare one is built on the top of the building. In addition, parameters and evaluation index of insulation properties were tested. In the meanwhile, indoor comparative experiments studying the impact of the thickness of soil layer and initial height of water on insulation and evaporation performance of water-storage planting roof. The design of the module is optimized after analyzing the result of test, which is used for experimental basis of engineering application.Outdoor test is located on the top of a second-floor teaching building in higher education mega center, Guangzhou. Five modules are built,three of which are water-storage planting modules. The thickness of soil layer of the three modules with planting Chinese chives is 180mm,120mm and 60mm and is with the 35cm height of water in reservoir.The rest of two modules is planting roof with the 60mm thickness of soil layer and planting sedum lineare. Both of two set filter layer in which of one there are ceramic grain and in which of other there are cylindrical activated carbon. In addition, the bare module is also set on the top of building used as comparison. The test lasts forty days, from 7th July to 15 th August,2015. Testing data in clear days is kept track to analyzing the insulation of modules. Parameters of insulation performance of each modules will be obtained after analyzing including analyzing the relevance between the bottom temperature of modules and meteorological parameters, calculating diurnal change of heat flux and equivalent thermal resistance.Outdoor experimental results show that in continuous clear days, water-storage planting module has better insulation performance in high-temperature area. The bottom temperature of module A to C is 5.0℃,4.7℃ and 3.7℃ lower than the surface temperature of bare module, but 1.8℃,2.1 ℃ and 3.1℃ higher than module E. Peak valley difference of water-storage planting modules are 3.3℃,4.2℃ and 4.5℃,2.9℃, 2.0℃,1.7℃ lower than the module E. Furthermore, the temperature amplitude of these three modules are 1.5℃,1.8℃ and 1.8℃.Attenuation performance of water-storage planting modules are much better than the planting modules’.The relative attenuation rate of modules are 0.16,0.21,0.22,0.31 and 0.35. Comprehensive attenuation rate are 15.7,12.7,12.4,8.3,6.9. To water-storage planting module, soil layer of which the attenuation rate are 7.3,4.6,2.2 plays a main role in attenuation. When redusing the thickness of soil layer, the thinner the thickness of soil layer is, the more important role in attenuation the air layer plays. And the attenuation rate of air layer of water-storage planting modules are 1.4,2.6,2.4.Outdoor climate parameters impact on the insulation of water-storage planting module. The relevance between the bottom temperature of modules and the outdoor meteorological parameters in rank from height to low is:outdoor air temperature, intensity of solar radiation, relative humidity and wind speed. In addition, the relevance between each structural layer of module and meteorological parameters in rank from height to low is:the surface temperature of soil layer, the bottom temperature of soil layer, the bottom temperature of water-drainage layer, the surface temperature of water and the bottom temperature of module.Indoor experimental test with simulated radiation is located in the same building. The system of the test is consist of holder, test modules and data acquisition instrument.There are totally four test modules, three of which are water-storage planting module marked as module 1, module 2, and module 3. Module 1 is the same structure as Module A outside,2 is the same as B, and 3 is the same as C. So the thickness of soil layer of these three modules is 180mm,120mm and 60mm. Module 4 is mapping module without soil layer and drainage layer, used to compare with water-storage planting module.Results of indoor test with simulated radiation show that Under 35cm height of water in reservoir, the difference between the maximum of temperature and the minimum of one is 0.2℃,0.2℃ and 0.4℃; Under 25cm, the difference is 0.3℃,0.4℃and 0.8℃; Under 15cm, the difference is 0.2℃,0.4℃ and 0.8℃.Rate of moisture evaporation happened in soil layer changes rapidly at the beginning, after that the change becomes slowly. In addition, the thickness of soil layer impacts on the rate. At the beginning, the rank in descending order of the decline velocity of volume percentage of moisture in soil layer is:module 3(60mm), module 2(120mm), module 1(180mm). And the rank in descending order of the evaporation rate of moisture in soil layer is:module 2(120mm), module 3(60mm), module 1(180mm). Besides, the rank does not changes if it is considered in whole day. According to the regression relationship between soil layer thickness and the rate of evaporation, the thickness of soil layer with the maximum of evaporation rate can be found,which is 114.4mm.Evaporation is influenced by module soil layer thickness and initial water level at the same time, the change of the initial water level of pool water evaporation affect the essence of the module for the change of the thickness of air layer. When the initial water level height is 35 cm, modules 1～3 of the daily average rate of evaporation is 0.066, 0.083,0.21;When the initial water level height is 25 cm, the average daily evaporation rate is 0.011,0.011 and 0.029 respectively;When the initial water level height is 15 cm, due to the evaporation capacity is not obvious, lead to the rate of evaporation is 0. Regression relationship among the thickness of air and soil, and evaporation rate can be obtained by using matlab.In the meanwhile, evaporation rate of moisture in reservoir without air layer under the maximum of evaporation rate of soil moisture can also be found, which is 0.199. |
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