Influences Of Wind Velocity, Direction And Insulation Ways On Solar Energy Gain Of Building South Walls In Winter

At present, the energy consumption in China is huge. With the standard of living improved, Building energy consumption is confronted with enormous challenge. Decreasing the use of conventional energy, reducing energy consumption of heating/cooling load and exploiting and mutilating renewable energy have become an important stratagem for the sustainable development. Making full use of solar energy in winter has great significance to reduce the heating energy consumption of building. In addition, making full use of solar energy in the winter has been a main way to reduce heating energy consumption, and it has been provedThe heat storage of the wall, especially the heat storage of the heat preservation wall, is an important part of building envelope energy saving technology. It plays an important role in regulating the indoor temperature, improving the indoor environment comfort and reducing the energy consumption, related issues are also increasingly concerned. After heating the wall, the solar radiation is partly stored by the wall, and the heated wall will also distribute some energy to the atmosphere through heat convection. Therefore, the net absorption of solar energy absorbed by the wall is not only affected by the absorption coefficient of the wall, but also controlled by the wall surface temperature and the external surface of the convection heat transfer coefficient.The insulation technology of the wall is the key of the exterior wall heat preservation, according to the insulation layer in the wall of different position, external wall insulation is mainly divided into internal insulation and external insulation. As the insulation layer has good heat preservation and heat insulation performance, the external surface temperature of the wall outside of the solar radiation is very different, which leads to the difference of the heat transfer between the wall and the atmosphere, as well as the real absorbing rate of the south wall.Moreover, in addition to indoor and outdoor temperature, humidity and radiation and other factors, the external environment wind speed and direction is also the main factor to determine the wall heat transfer coefficient and the wall surface heat transfer process. The change of wind peed and wind direction can cause the change of the heat transfer coefficient of the exterior surface of the building, and then affect the actual heat dissipation of the wall.In this paper, heat transfer processes of the building envelopes in winter in the middle and lower reaches of the Yangtze River are studied by employing numerical simulations. The time series of the temperature of the exterior surfaces of different insulation walls(internal insulation and external insulation), convective heat transfer coefficient and the daily net heat gain of the two walls are analyzed by using the CFD simulation, with the change of wind velocities and directions.The results show that ambient wind velocities and directions have significant influences on the variations south wall’s external surface temperature and heat transfer coefficient. The temperature of the outer surface of the leeward wall is larger than the windward surface temperature, and the smaller of the wind velocity, the larger of the temperature of the outer surface.The instantaneous temperature has the maximum value from leeward side, and the windward side has the minimum value. In addition, the smaller of the wind speed, the greater of the temperature fluctuation. Moreover, comparing with the internal insulation, the temperature of external insulation wall’s inside surfaces differ a lot, and the attenuation effect of the outdoor temperature is more obvious. In addition, comparing with the internal insulation, the temperature of the form of external insulation is larger, and the attenuation of the outdoor temperature is more obvious.For the heat dissipation and net gain, wind direction and velocity both have influence on the two insulation forms, the net gain of leeward wall is larger than the windward wall, and the net gain of the wall in a day decrease with the increasing of wind velocity. However, the real solar energy absorbing rate of the wall is no longer significantly reduced when the wind velocity reaches 3m/s.The influence of wind direction and wind speed on the solar gain and heat dissipation of the wall in the form of external insulation is slight. But in the form of internal insulation, the solar gain and heat storage performance of the wall is significantly better than that of the external insulation wall. Therefore, the use of internal insulation will be more conducive to the realization of the area of winter building energy efficiency. The thermal energy storage performance of the internal insulation of the south wall is obviously superior to that of the external insulation. Therefore, the use of internal insulation is more conducive to the realization of the area of winter building energy efficiency.