Experimental Investigation Of The Thermal Insulation And Evaporative Cooling Effects Of Different Shallow-Water-Reserved Roofs

Passive evaporative water-retaining roof has good performance in thermal insulation and ecological benefits, which becomes the hot research topic of the investigation on the ecological insulation roof. However, experimental data of water-retaining roof for different structures is still on the lacking stage, which will affect their applications in actual engineering projects.In this paper, seven different water-retaining roof modules that have the same water-retaining height but different structure are built on the same roof, and the thermal insulation and evaporative cooling performance of the water-retaining roof are experimentally investigated in detail under the real weather. The thermal insulation characteristics and evaluation for water-retaining module of different structure modes are analyzed and derived from the experimental data, and the variations of dynamic evaporative cooling characteristics are investigated and found on the basis of the tests. All these conclusions will be benefit for optimizing the structure of water-retaining roof and conducting the application of water-retaining roof in actual engineering process.Experimental test platform was built in Civil and Transportation Engineering Building Environment and Equipment Engineering Laboratory roof of Guangdong University of Technology. The test time began at2013July22ended at September1. Selecting the continuous sunny days’data to analysis the thermal insulation performance and evaporation and cooling characteristics of modules. Establishing the heat balance equation of different storage modules, discussing and analysis the characteristics of the different modules each heat distribution, access to the equivalent thermal resistance of different modules.The results showed that compared with the open storage module cover water storage module has good thermal insulation effect. The average water temperature of underside of the module in the daytime period (08:00-18:00) lower than the open reservoir. The average low temperature water module underside3.3℃～5.5℃. The open storage module underside volatility and peak temperature difference are the largest, were4.5℃and7.9℃. Different modules’water temperature attenuation ratio was0.41～0.53. Underside of each module maximum temperature than the outdoor air temperature appears moment the maximum time delay occurs, the shortest delay time for open storage module (80min), the longest delay was thick brick module (460min). On the bottom surface of open water module temperature and outdoor meteorological parameters (outdoor air temperature, outdoor relative humidity, solar radiation) correlation analyzes, the regression equation coefficients of determination were0.94,0.96and0.82, reflecting that the open-type water temperature module underside outdoor meteorological parameters affected significantly; Evaporation characteristics: average floating vegetation water evaporation in the daytime module maximum, its value3.41kg/day, evaporation absorbs heat flux ratio of the total38.8%, evaporation heat storage module is highly reflective plate of its total absorption heat ratio of83.7%. The open storage module maximum heat flux values for12.7W/m2, floating vegetation heat flux minimum storage module for4.77W/m2. Thermal performance:equivalent thermal resistance of each module are:thick brick storage module was2.51(m2·K)/W, thin brick storage module came to2.43(m2·K)/W, highly reflective plate storage module came to4.02(m2·K)/W; low reflection plate storage module came to3.90(m2·K)/W, perforated reflector plate storage module came to3.09(m2·K)/W, floating vegetation storage module came to3.50(m2·K)/W, open storage module came to2.01(m2·K)/W.Through comparative analysis of these experimental tests, we can see that there is a big difference between the different modes of storage module structure of its thermal performance characteristics. In the heat of performance:average insulation performance of the best low-reflection plate module, the bottom surface average temperature30.6℃, the average thermal performance open module worst, the bottom surface average temperature was the highest33.2℃; permeable brick module (modules1and2) delay performance of the best outdoor temperature wave, open the module underside highest temperature of about13:00time, while the underside permeable brick module highest temperature than the open time delay of about300min; float vegetation module wave attenuation performance outdoor temperature is best, the bottom surface temperature difference between peak (3.2℃) is the smallest of the modules, each module underside temperature difference between the maximum peak is open module is7.9℃, the temperature of the bottom surface of the remaining modules worse than the open module valley low3.7℃-4.7℃. In the evaporation characteristics:average daytime maximum daily water evaporation time is floating vegetation module for6.25kg/day, followed by open modules for4.69kg/day, the smallest for low reflection plate module for3.18kg/day. In terms of thermal performance:the equivalent thermal resistance is highly reflective plate largest module is4.02(m2·K)/W. The minimum thermal resistance equivalent to open the module was2.01(m2·K)/W, the equivalent thermal resistance than the rest of the module large open from0.50(m2·K)/W to2.01(m2·K)/W.