Numerical Simulation Of Coupled Heat Transfer For Natural Ventilating Rooms

In the area with a hot weather in summer and a cold one in winter, there is usually no central heating in winter when the air humidity is high and temperature is low indoors, which implies the bad thermal environment; However, summer of these areas is hot. So the air condition has been used in most of the buildings, which causes high energy consumption. While in nowadays building industry the natural ventilation is a widely used technology that can improve the thermal environment of the building and reduce the energy consumption of air conditions. The natural ventilation can replace or partly replace the air condition.In the natural ventilation condition, heat transfer inside of the building is affected by the outdoor temperature and solar radiation, which is an unsteady three-dimensional coupled heat transfer with complex boundary. The traditional harmonic response method cannot calculate exactly the heat transfer of a natural ventilation building. With the method of numerical simulation, this thesis calculates the natural ventilation rooms of different wind speed, insulation position, insulation thickness and storey height in an unsteady simulation way, and get a result that is compared with the one calculated by the harmonic response method, which provides the revision of civil building pyrology standard with new ideas.The research results are included as follows:(1)When calculating the delay time of wall and the heat flux, the differences between the result calculated by the numerical simulation and that calculated by the harmonic response method are obvious. The delay time calculated by the numerical simulation is longer than the result of the harmonic response.(2)The faster the wind speed and the stronger the heat transfer indoors and outdoors are, the closer the temperature indoors and outdoors is. With the development of the wind speed, both the mean value and the peak value of the wall temperature indoors will increase, while the valley will decrease so does the delay time. Although more ventilation quantity will cause the mean value and peak value of the temperature and wall temperature indoors to increase, they can reach the peak value and begin to decrease earlier. Thus rooms with more ventilation quantity will be cooler in the evening.(3)It is not necessary to adopt very thick insulation layer for a natural ventilation room with a slow wind speed outdoors in the area where summer is hot and winter is cold. According to the convenience of the construction, 0.02m can be adopted.(4)The inner insulation will reduce the delay time of the wall a lot, and the external insulation will make the amplitude of the surface temperature inside the wall decrease. So the inner insulation is suitable to the part-time air-conditioned room, while the external insulation is fit for the natural ventilation and all-day air-conditioned room. When considering the decrease of the wall temperature indoors, the external insulation is superior to the inner insulation.(5)Increasing the storey height of the room will cause the temperature indoors to rise when the wind is at a very slow speed.