Theoretical Analysis And Experimental Study On The Influence Of Heat Reflective Coatings On Building Energy Consumption

Due to the rapid growth of social economy and urbanization,the energy consumption of building sector accounts for about 1/3 of the total social final energy consumption and contributes 40% of carbon emissions in China.Among them,the building energy consumption by heating,ventilation and air conditioning systems accounts for about 50%-70% of the total building energy consumption.Under China's "double carbon" goal,it is an urgent need for the construction industry to seek environmental and cost-effective technical measures to reduce the energy consumption of air conditioning and heating.Passive energy-saving technology is the first choice to achieve the goal of "double carbon" in the field of construction.The thermal performance of the building envelope is an important factor affecting the energy consumption of the heating and air-conditioning system.Therefore,increasing the thermal insulation performance of the building envelope is the key to implementing passive energy conservation in buildings.At present,the mainstream practice of building thermal insulation is mainly to use thermal insulation materials with low thermal conductivity on the surface of the envelope structure to reduce the heat transfer loss of the envelope structure.However,traditional building insulation materials have some problems in safety and construction.Based on the problems existing in traditional thermal insulation,solar-reflective thermal insulation and cooling coating have attracted the attention of the scholars from home and abroad.In order to explore the effect of solar-reflective coating,this study investigates the thermal insulation performance of the coatings under different reflectance and its comprehensive influence on heating/cooling loads and energy consumption of the buildings.The influences of some design parameters such as orientations of building walls,building shape coefficients and thermal performance of envelope structure,on the energy consumption of building are also conducted.Firstly,the calculation method of solar radiation at different facing walls of the building is introduced in detail.Combined with the solar radiation model,a composite heat transfer numerical model of the envelope structure is established to analyze the influence of solar-reflective coatings on the temperature and heat transfer rate distributions of the envelope structure under different building parameters.Secondly,A temperature measuring box was made for the experimental study to test,the thermal insulation performance of the existing solar-reflective coating in the laboratory.The inner and outer surface temperatures of the solar-reflective coating test panel and the reference panel,as well as the temperature in the box were tested and analyzed.The thermal insulation effect of the reflective coating was discussed,and the influence of different solar radiation intensity on the coating was investigated.Finally,the experimental data was used to verify the theoretical model.The test results show that the inner surface temperature of the reflective coating box was reduced by 3.78?,5.63?,and 7.12? respectively,compared with the non-reflective coating when the power of the solar simulator was 600 W,800W,and 900 W respectively,the outer surface temperature decreased by 4.74°C,5.97°C and 7.36°C respectively,the air temperature differences in the two boxes were 2.16°C,2.83°C,and 3.50°C respectively.This shows that the solar-reflective coating has a significant thermal insulation and cooling effect,and the stronger the solar radiation intensity,the better the heat insulation and cooling effect of the solar-reflective coating.Then,using the concept of outdoor comprehensive temperature,the effect of solarreflective coating is simulated by changing the solar radiation absorption coefficient in the calculation formula of outdoor comprehensive temperature.The coating has a better cooling effect with a lower outdoor comprehensive temperature.Based on the established composite heat transfer model,the influence of solar-reflective coating on the heat transfer characteristics of building walls is analyzed.Taking Jinan area as an example,by changing the absorption coefficient of solar-reflective coating,the heat transfer model is used to simulate the temperature and heat transfer rate distribution of the wall under different working conditions.The temperature field and heat flow rate distribution on the inner and outer surfaces of the wall are analyzed and compared with different conditions.Finally,the energy-saving effects of the walls with different orientations under the combined effect of enhancing heat insulation in summer and reducing radiant heat gain in winter are discussed.The research results show that the cooling rate of the wall will increase with the increase of the reflectivity.When the reflectivity increases to a certain extent,the effect of the reflectivity on the heat transfer of the wall will no longer be significant.When the reflectance of the coating is increased from 0.2 to 0.8 in summer,the thermal insulation and cooling effect of the wall with different orientations is ranked as west > east > south > north.In winter,the effect of increasing heat loss on the wall is given as,south > east > west > north.Comprehensive consideration throughout the year,the total energy saving effect of different facing walls is ranked as,east > west > north > south.Finally,the dissertation takes an office building as a case study,and uses the De ST simulation software to calculate and analyze the energy saving effects of the solarreflective coating on buildings under different climatic zones.The most economical and energy-saving wall combination in different climate zones is given,and the influences of the shape coefficient and the heat transfer coefficient of the envelope structure on the building energy saving are analyzed.In cold areas,the most economical wall combination is east,west and north using solar-reflective coating simultaneously,and the annual energy saving rate is 1.48%.In hot-summer and cold-winter areas,the most economical wall combination is east,west,south and north using solar-reflective coating simultaneously,and the annual energy saving rate is 2.86%.In hot-summer and warm-winter areas,the most economical wall combination method is to use solarreflective coating in east,west,south and north directions simultaneously,and the annual energy saving rate is 6.25%.In addition,the application of solar-reflective coating in buildings with a small shape coefficient and a large envelope heat transfer coefficient is more conducive to energy saving.