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< BR> <BR> Introduction <BR> As people more and more attention to environmental pollution, indoor air quality requirements for continuous improvement, constantly stepping up to the implementation of Air conditioning Energy conservation, improve indoor air conditions, while looking for alternative sources of cold, many countries are actively explore the use of natural conditions, the cooling method. Theoretically, to reduce Building Maintenance of structures, the surface temperature of objects for the purpose of use Solar Energy Passive evaporative cooling problem, the mechanism by evaporation can be divided into two categories: free water surface evaporation cooling problems, such problems include roof water storage, water floating debris, shallow water, mobile water film and the complexity of the spray measures; other which is the problem of porous materials, water evaporative cooling. <BR> 1. Category: free water surface evaporation cooling <BR> Earlier building passive evaporative cooling has not been detailed classification, mainly in the roof covered with a layer of water bags on the way to cool the building. Water bags have a layer of removable insulation panels, insulation panels during the day will cover the water bag on it from sunlight, with the water bag, the ceiling temperature is lower, the indoor play the role of the cold source. Night, the water bag exposed to space radiation by convection so that it will lose heat dispersion. In drier areas, summer programs can use evaporative cooling, a raw device set up to increase air humidity, that is, when the outdoor air through the wet and allows cool air humidifier, these two methods can be called passive evaporative cooling of the embryo. <BR> 2. The second category: the problem of porous materials, water evaporative cooling <BR> Such evaporative cooling in buildings with paved surface layer of porous material, such as loose sand or aerated concrete layer, the layer of material to rely on watering or natural rainfall to replenish moisture layer of water. When the material after moisture atmosphere by solar radiation and air convection and long wave radiation heat transfer, internal heat and moisture transfer mechanism of water through the role of migration to the surface and in the evaporation. Porous body moisture evaporation process is the combined result of many factors, such as liquid diffusion, capillary flow, evaporation and condensation, the pressure gradient, gravity and so on. In the evaporative cooling process, the original material surface layer of a continuous water film exists, which is basically like the evaporation of water film layer mentioned above, the evaporation of free surface, free from material internal factors, as this layer of water film evaporation of surface moisture content decreased, the moisture inside the material will be added to the surface to evaporate, add water if the surface speed lower than the surface evaporation rate, then the material will decrease the evaporation surface will affect the evaporation effect. Wet porous roof materials laying loose passive evaporative cooling method is suitable for a number of abundant rainfall, wind the smaller northern subtropical region, the flat roof of the building to use. The laying of solid porous material wealth for rainfall, wind speed and large tropical regions of South Asia, and the outer surface of the building to use city roads. Drought in the area of climate can also Spray Water way to the porous layer of material replenishment. <BR> Roof laying wet porous material is used first to solve the water problem roof can not be the Master, in addition to moisture content of porous materials for passive cooling effect is remarkable, building roof temperature about 25 , the temperature around the inner surface of the roof down 5 ; excellent in the existing traditional water storage roof. <BR> New developments in passive cooling technologies <BR> So far, there are many researchers on the traditional passive cooling technology for a large number of experimental studies on the basis of the original made its inadequate number of refinements. In the traditional application of passive cooling technology based on the way there after the application of a variety of ways to improve, following the application of the way some of the main brief. <BR> 1. Passive Cooling Roof <BR> 1.1 with a removable heat shield on the roof of the pool in the pool to set a layer of insulation board, in the summer, the pool during the day covered by the insulation board, insulation board at night and through the night to remove water cooling. Heat the building through the roof from the interior spread to the surrounding environment and be cool. Through the use of rooftop pool with the insulation board can make roofs reduce heat. In winter, remove the heat shield during the day in order to pool the water absorbs the sun's radiant heat and heat the building. Pool at night covered with insulation board in order to pool water to heat to buildings. Roof water on the roof of the structure require a higher, and must require a higher moisture level, or roof leaks, and maintenance inconvenient due to roof repairs can not be directly Exalted. 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