Influence Of Clear Sky Index On Heat Transfer Energy Consumption Of Civil Building Exterior Wall In Hot Summer And Cold Winter Zone

China's civil building energy consumption accounts for an increasing trend of total energy consumption in China.HVAC energy consumption accounts for more than 50% of the total energy consumption of civil buildings.The energy consumption of non transparent envelope is an important part of HVAC energy consumption.The solar radiation intensity is the main factor affecting the heat transfer energy consumption of the external structure of the building,and the solar radiation intensity is directly related to the clear sky index.It is particularly important to improve the accuracy of the dynamic change of building envelope under different weather conditions.Based on the example of Nanchang in the hot summer and cold winter zone,the influence of different clear index(0.2~0.7)on the external thermal energy consumption of buildings in winter(January 2nd)and summer(July 21st)is analyzed.The main conclusions are as follows:(1)Based on the data of the correlation between the clear sky index and solar radiation and outdoor air temperature in Nanchang area,the relationship between the clear sky index and the internal and external surface temperature of the external wall is calculated by numerical simulation.The trend of temperature rise inside and outside the exterior wall slows down.The maximum and minimum values of the internal surface temperature in winter vary with the clear sky index.The maximum and minimum values of the inside and outside surface temperature in summer are similar to those of the clear sky index.The average temperature of the outer surface of the external wall increases with the increase of the clear sky index in winter.However,with the further increase of clear sky index,the lowest temperature of the external surface of the external wall decreases in winter.(2)The heat transfer of external walls under different weather conditions is studied.The results show that during the summer,when the clear air index is greater than 0.2,both the day and night heat is transmitted to each other through the external surface of the external wall to form the external wall heat transfer cooling load.The maximum heat gain of the west wall is that the insulation of the west wall is conducive to reducing the energy consumption of cooling.When the clear sky index is 0.2~0.7,the heat of the north wall,the east wall and the west wall will be transmitted from indoor to outside day and night.When the clear sky index is small,the heat of the south wall will come out from the inside to the outside,no matter during the day or at night,but when the clearness index is greater than 0.6,there will be two-way heat transfer in the south wall.In some periods,the solar radiation absorbed by the south wall will be larger.The heat is transmitted to the interior through the outer wall of the south wall.It can be found that when the weather is clear,it can make full use of the solar radiation to the south wall to reduce the heating energy consumption.(3)The change rule of the total daily heat gain of the building exterior wall along with the clear sky index is studied.It is found that,regardless of winter or summer,the wall orientation has a significant effect on the daily heat transfer energy consumption of the wall.In winter,the total solar heat of the south wall gradually increases with the increase of the clear index.When the clear air index is greater than 0.3,the total net heat gain from the outer surface of the south wall changes from negative to positive.The total solar heat of the north wall,east wall and outer wall of the west wall decreases with the increase of the clear index.This is because the greater the clear sky index,the lower the diurnal temperature range and the lower the evening sky cloudiness,and the longer the wall surface temperature is lower than the outdoor air temperature.The total solar heat inside the surface increases with the increase of the clear sky index.According to the relationship between the clear sky index and the total heat gain of the inner wall,the heat transfer energy consumption of the wall decreases with the increase of the clear sky index in winter.The energy consumption of the south wall is the smallest and the heat transfer energy consumption of the west wall is the largest.In summer,the total solar heat of each facing the external wall increases with the increase of clear air index.The total daily heat gain on the outer surface of the north wall is not obvious with the increase of the clear index.The south wall is the second largest and the west wall is the largest.This shows that the heat transfer of the west wall is the most unfavorable to reduce the air conditioning refrigeration load.Therefore,reducing the solar radiation absorption ratio is beneficial to reducing the heat gain during the western wall,and we should also pay attention to the heat insulation measures of the west wall in summer.In this paper,a semi empirical formula of the clear sky index and wall heat transfer energy consumption under different weather conditions is given.The coefficients of determination are all 0.999.,which can provide the foundation and more accurate data support for building energy efficiency research.