Research Of Rain's Effect On Heat Transfer Of Walls In Hot-humid Climate

The climate in hot-humid area has features of strong solar radiation, abundant precipitations, high-speed monsoon and intense evaporation in the whole year. The buildings in that area consume more energy while providing poorer indoor thermal environment than the ones in other climate zones in China. It has become an urgent task to research on the features of building climatology in this area so as to save building energy through climate-adaptive architectural design. This thesis focuses on the effects of precipitations on heat transfer through exterior walls by taking Guangzhou as an example. It also presents the possibilities by employing passive cooling technologies on exterior walls to reduce indoor air temperature and conserve building energy.Through statistics analysis on precipitation strength and frequency in Guangzhou area, this thesis concludes the annual, monthly and daily patterns of precipitations in Guangzhou. The features of hourly precipitation in different days are concluded based on the analysis of monthly precipitation. Fifty-one typical precipitation days are chosen to represent the annual precipitation features through the analysis of three-year weather data.The heat and mass transfer procedures of exterior walls in raining days and normal days are measured respectively at the same time in experimental rooms. The microwave moisture meter was utilized in the experiments. And its calibration procedures in pure material of exterior walls were proposed in the thesis. The moisture content in wall materials was measured. The results in normal days referred to the original states of the walls and appealed their comparative properties. The experiments in raining days measured the heat transfer through walls in quantity. The relationships among temperature, moisture and heat flex in exterior walls and outdoor meteorological parameters were analyzed.The water spray experiments were carried out in order to verify the possibilities of passive cooling through porous materials on exterior walls. The comparisons of measurements of temperature and moisture in wet and normal walls with various spray duration and time present that spray walls can effectively reduce the surface temperature on both sides of the wall and its heat flux. The heat flux of the inner side of the wall can be reduced as much as 49.9%.A simulation software of heat and mass transfer was utilized to simulate the differences in heat transfer under raining and normal conditions. Firstly, the software was calibrated with experiments. The simulation results of temperature and moisture agreed in 91% while the ones of heat flux in 68%. The heat flux through exterior walls in typical precipitation days of Guangzhou was simulated under conditions of raining or not. The simulation results revealed little differences with a reduction of 25.6%. Finally, heat transfer procedures of exterior walls of air-conditioned rooms in rainy days were simulated. The possibilities of saving energy through raining and spraying on exterior walls were analyzed. The results revealed that large heat can be prevented to transfer into indoor by combining with raining and spraying exterior walls, the higheste reduction was 69%. The usage of passive cooling can save remarkable building energy.