Impact Of Indoor And Outdoor Temperature On Capacity Of Building Envelope To Absorb Solar Energy

With the rapid development of urbanization in china, the population of urban increase rapidly also caused the expansion of the demand for housing. The huge scope of building has also led to many questions, particularly in the increase of energy consumption. China is a large country of energy consumption, and it ranks second in the world energy usage. In total energy consumption of China, the building energy consumption accounts for 30% ~ 40%. According to statistics, the data in previous studies of new and existed residential buildings which can meet the design criterion of energy efficiency building is less than 1%, and in the existed residential buildings,there are about 210 billion square meters of building which have the problems of bad heating preservation and heating insulation, little air-tight capability and lower efficiency of heating system. Therefore, building energy conservation has become an important strategic problem in China.Building envelope includes external walls, doors, windows and roofs. The wall as the main body of the structure which fully absorbs the solar energy is the main way to reduce the heat load of air conditioning in winter. The wall which heated by solar radiation emitting heat into the atmosphere through convection, thus the net solar radiation gain of the wall is not only affected by the absorption coefficient of the wall surface, but also controlled by the wall surface temperature and the heat transfer coefficient.In addition, strengthening the thermal preservation system of wall structure can effectively reduce the heat loss of buildings, which is very important for building energy conservation.In general, most of wall heat preservation types can be divided into inner and external heat preservation. The layers of inner and external heat preservation walls which exposed to outdoor is different, the former is reinforced concrete structure with large heat capacity, the latter is rock-mineral cotton insulating materials with small heat capacity, so there exists great differences between the wall exterior surfaces of inner and external heat preservation wall, which caused different heat losses through convection from the two walls that heated by the solar radiation, andthen it will affect the actual absorption of solar energy of wall.The middle and lower reaches of the Yangtze river is not a central energy using region.Different thermal demands and energy using time make different indoor temperature, outdoor air temperature is lower than indoor air temperature in winter, so the heat loss caused by the temperature difference between indoor and outdoor will be increased with the rise of the indoor temperature, the utilization of solar energy by the wall is reduced greatly. In conclusion, the outdoor temperature affects the temperature of the wall exterior surfaces, and the temperature difference between indoor and outdoor affects the heat loss of buildings, therefore, outdoor temperature and indoor temperature both are the important factors that affect the actual absorption of solar energy of wall.Outdoor air temperature is constantly changing, so the heat transfer processes of the building envelopes is unsteady, in order to seek the relationship between the net solar radiation gain of the wall with different insulation ways and indoor and outdoor temperature, this paper takes Shanghai which is the representative of the middle and lower reaches of the Yangtze river region as the research background, employing the numerical simulations method to research the influence of different insulation ways and indoor and outdoor temperature on solar energy gain of the wall,which can provide theoretical basis for optimization of building energy conservation design.The results show that the higher the outdoor temperature and the lower indoor temperature,the more solar radiation absorption of the wall. whatever the outdoor and indoor temperature is,The daily net solar energy gain of inner heat preservation wall is more about twice than that of external heat preservation wall, which indicates that the inner heat preservation wall is more advantageous to the absorption of solar energy, and the advantages of solar energy absorption by inner heat preservation wall under partial time energy using type is more obvious with the rise of the outdoor temperature. Considering the energy using characteristics of the middle and lower reaches of the Yangtze river region in our country, most of the residential buildings using energy when people in while not using energy when people out, which lead to a partial space and partial time energy using type. Compared with some central energy using regions where are cold in winter, the indoor average temperature of these regions is lower. So the inner heat preservation wall is more advantageous to the achievement of building energy conservation in winter.