Moisture Transport Mechanism For Building Humidity Environment By Natural Ventilation In Hot And Humid Area

With the rapid development of urban construction, economy and population in the hot and humid regions in south China, air-conditioning cooling and dehumidification load in summer greatly increases. Deep understanding of indoor heat and moisture transport mechanism is a key to adjust properly indoor thermal and humidity environment.The methodology of computational fluid dynamics has advantages of rich information and short research cycle.The paper is mainly using numerical method to explore indoor humidity environment and its flow characteristics caused by the natural ventilation.This dissertation firstly adopts theoretical analysis and numerical simulation to investigate natural ventilation driven by the thermal pressure.Regarding of unilateral double opening natural convection,mathematical models of coupled heat and moisture transfer between indoor and outdoor were set up.Following that,the effects of temperature gradient and water vapor mass fraction gradient on indoor air distribution,ventilation rate,the distribution of temperature and relative humidity were investigated.Numerical results show that indoor flow field structure does not change obviously with changing temperature differences between indoor and surrounding environment.The mass flow rate decreases with decreasing temperature differences between indoor and outdoor,which coincides with that of theoretical analysis.Comparisons between the numerical simulation and experimental results demonstrate that present numerical simulation program is sound.Laminar natural convection in the closed building enclosure was late simulated and analyzed,with the effects of indoor heat and moisture source strengths on the air distribution,temperature field and relative humidity field being discussed.The numerical simulation results showed that the change of water vapor mass fraction on the surface of heat and moisture source has basically no effect on the flow field structure and temperature distribution,but strongly influenced the distribution of relative humidity.Surface temperatures of heat source have put direct effect on the indoor distribution of the temperature,flow field and relative humidity.In addition,building natural ventilation with unilateral middle opening was also discussed.With the increase of unilateral middle opening area,the region affected directly by the moist air outdoor expanded continuously.The balance position of temperature and relative humidity at vertical direction of central cavity descends continuously.Horizontal maximum velocity on the opening increases and the intensities of heat and moisture transfer rates indoor promote correspondingly. As the temperature of moist air indoor rises,the position of maximum relative humidity moves from heat and moisture source to the opening. As the opening moves up,the intensity of heat and moisture transfer decayed gradually.Moisture gradient near the heat and moisture source at the bottom increases.At the same time,levels of indoor moisture concentration tend to be uniform.At last,this paper discusses the building model of natural ventilation with bilateral middle opening.With the enlargement of bilateral opening,the region affected directly by ambient moist air expands.The balance position of temperature and relative humidity at vertical direction of central cavity descends continuously,and the horizontal maximum velocity on opening increases.Displacement ventilation flow rate of opening becomes larger and the intensity of indoor heat and moisture transfer rates increases.As the indoor temperature rises,the position of maximum relative humidity moves from the surface of heat and moisture source to the open gradually.Understanding the mechanism of coupled heat and moisture transfer by natural convection inside the partial enclosures gives the primary foundations for fluid flow mechanism of building humidity environment driven by the natural ventilation in the hot and humid area. This research could provide the guidance and optimization of the building natural ventilation environment.In particular,present thesis could benefit the designers to keep suitable thermal and humidity environment by natural ventilation,through passively adjusting ventilation ports and indoor thermal sources.