Calculation Of Indoor Air Temperature And Analysis Of Relative Factors In Natural Ventilated Buildings Coupled With Thermal Mass

With the direction of sustainable development, nowadays people in increasing numbers begin to notice the importance of natural ventilation. Applying the technology of natural ventilation can improve indoor thermal comfort, and reduce air-conditioning consumption. The role of natural ventilation is related close with thermal mass. The main focus of this paper is to study theoretically and numerically the coupling between ventilation and thermal mass in naturally ventilated building. The content is help to choosing building's material and designing or controlling natural ventilation.Thermal mass can be classified as external thermal mass and internal thermal mass. The external envelopes such as external walls and roofs belong to this category. They connect the outdoor environment and the indoor environment. Most of previous researchers focused on the impact of building envelopes on the heating/cooling loads of buildings assuming the indoor air temperature is constant, but few focused on the impact of it on natural ventilated building. Furniture, and internal wall are internal thermal mass. Usually, the temperature distribution of the internal thermal mass is assumed to be uniform and equal to the indoor air temperature, but the problem would be complicated if the elements are not meet the condition of lumped method. Moreover, natural ventilation can be induced by wind or stack force. When the buildings are ventilated by wind, the ventilation flow rate can be treated as given value. But when the buildings are ventilated by stack force, the ventilation flow rate has nonlinear relation with indoor air temperature. In view of these problems, following work are carried out in the paper.(1) Stack equivalent flow rate and its calculating method are presented. Temperature variation of indoor air in natural ventilated building is periodic whatever the power induced is constant wind pressure or stack effect pressure, so the problem of natural ventilation with stack effect pressure may be treated as ventilation with constant wind pressure. Indoor air temperature of natural ventilated building with stack effect can be calculated out easily by using stack equivalent flow rate.(2) By using numerical simulation method, the effects of external and internal thermal mass on decrement factor and time lag of indoor air temperature are analyzed, including thermal conductivity, volume heat capacity, area and depth etc. In the model, the heat transfer of all thermal mass are treated as one dimension unsteady heat transfer problem. The conclusions are help for natural ventilation's design.(3) On the base of harmonic response method and the temperature shift of interior side of external thermal mass, the indoor air temperature of natural ventilated building coupling with thermal mass is calculated. Heat transfer number and time constant represent the effect of external and internal thermal mass individually. By using the model, the effects of external and internal thermal mass on indoor air temperature are analyzed. Moreover, the response time of building with intermittent cooling/heating, and natural ventilation potential of different city can be calculated and analyzed by the model.(4) On the basis of previous model, virtual sphere is introduced in analyzing and calculating the effect of internal thermal mass in natural ventilated building. The method can receive more accurate results in considering the effect of internal thermal mass with various shapes, various materials, and uneven temperature.(5) Night ventilation is analyzed by the model as phase ventilation and the calculation method about indoor air temperature is presented. This method is validated by night ventilation experiment. The effect of ventilation time, internal heat gains, flow rate of night ventilation, thermal mass, and diurnal temperature range on efficiency of night ventilation are analyzed. The limit for heat gains in building with night ventilation and the optimal flow rate are pointed out. The conclusions are help for night ventilation's design and application.