Solar Radiation Heat Calculation Model Of Exterior Window-shading System For Design-day Cooling Load

China’s building energy conservation work has experienced a three-step development strategy.The basic technological path is to reduce building energy consumption and carbon emissions to the greatest extent through passive building design,active and efficient energy system and the application of renewable energy.Among them,passive design is the foundation of building energy saving design,while external window is the weak link of building envelope,which is of great significance to the building energy saving work in China.The integrated design of exterior Windows and shading facilities can effectively control the incoming solar radiation in summer and reduce the air-conditioning load.The integrated system composed of exterior Windows and sunshade facilities is called exterior window-sunshade system.It is a very complicated process to calculate the daily radiant heat that enters the room through different types of exterior window-shading system.The calculation of the daily radiant heat and cooling load of exterior window-shading system is the basis for calculating the design of daily radiant heat and cooling load.However,China’s"Code for Design of Heating,Ventilation and Air Conditioning in Civil Buildings"(GB 50736-2012)directly provides the calculation formula of daily radiant heat and cooling load,which combines the calculation of heat and cooling load.Although this method is convenient for engineering application,it is too simplified.At the same time,there is no value of correction coefficient for different types of glass and shading.In fact,there is no basis for calculating the daily heat and cooling load of design formed by different exterior window-shading systems.In view of the lack of accurate solar heat gain calculation model of external window shading system for design cooling load calculation in China’s current HVAC code,based on the study of design daily cooling load calculation method and external window solar heat gain calculation model,an hourly solar heat gain calculation model of external window shading system suitable for design daily cooling load calculation is established,and a calculation case is given,The table convenient for manual calculation and the application method of calculation model in design daily cooling load are provided.The research of this paper will provide HVAC designers,architects and relevant researchers with a more accurate solar heat gain calculation method of external window shading system,and promote the development of design daily cooling load calculation method.The main research work is as follows:(1)Analyzes the heat transfer process of solar radiation heat gain of external window shading system,defines the parameters required for solar radiation heat gain calculation of external window shading system;Design daily cooling load calculation methods and solar heat gain calculation models of windows in cooling load calculation are analyzed.Then the existing solar heat gain calculation models of external windows based on standard transparent materials and solar heat gain coefficient are compared and analyzed.It is concluded that the solar heat gain calculation model based on standard transparent materials is too simplified.The hourly solar incidence angle tables of four orientations in five thermal design zones and major cities in China are established to facilitate calculation,search and use.(2)Referring to ASHRAE’s method,according to the calculation model of solar heat gain based on solar heat gain coefficient,combined with the calculation method of direct radiation transmission ratio X_D and scattered radiation projection ratio X_d of sunshade components in current"Code for thermal design of civil building"(GB 50176-2016),scattering radiation projection calculation method,set up outside the window sunshade system day hourly calculation model of radiation heat gain,daily radiation heat gain can be used as design cooling load calculation basis,The calculation case of the calculation model is also provided.The numerical table of solar heat gain coefficient(SHGC)of main glass products in China was established and analyzed,and the fitting formula of SHGC at different incident angles was obtained.The manual calculation table of solar radiation heat gain calculation model of exterior window-shading system is established,which is convenient for searching and using in calculation.(3)The concept of solar heat gain coefficient is extended,the solar heat gain coefficient is used to characterize the solar heat gain performance of the whole external window shading system,and then the variation law of the solar heat gain coefficient of the external window shading system in the whole year is analyzed,and it is pointed out that the solar heat gain coefficient of external window shading system is a dynamic value.In the energy-saving design of building external window,the calculation of solar heat gain coefficient should be considered from the seasonal variation of orientation and solar altitude angle,At the same time,the solar heat gain coefficient of the external window shading system can′t be simply regarded as a fixed value;At the same time,the influence of solar heat gain of different external window shading systems on air conditioning load is studied,and the influence degree of solar heat gain coefficient on design daily load and annual air conditioning load is analyzed.