The Investigation Of Airborne Pollutant Dispersion Around High-Rise Residential Buildings Based On Natural Ventilation

With the rapid development of urbanization, the atmospheric environment is becoming more and more serious for the modern society as most people live in large and crowed cities and spend their about 80~90% time in indoor environment. Especially for the outbreak of a respiratory disease and the dispersion of airborne pollutant around high-rise residential buildings, for instance the outbreak of Severe Acute Respiratory Syndrome in spring 2003, bird flu in summer 2006 and A(H1N1) in summer 2009, lead to a great infectious risk for people's health, even a public panic for the airborne virus. The contaminant distribution and transmission route near a building could be very complicated due to the interaction between approaching wind and building structures. Therefore, reliable prediction of the pollutant concentration field near the building is essential important in improving the ventilation design and taking the preventive action.The wind tunnel simulation and CFD technology will be carried out in this paper to investigate the dispersion and transmission around the high-rise residential building in Hong Kong. A series of testing is accomplished for different tracer gas resource to study the dispersion characteristics near the typical building with more complex building structure under wind effect. The experiments were taken in a boundary layer wind tunnel using tracer gas technique. Two different models were designed for different purpose, a 1:150 scale model represents a 33-story high-rise residential building in prototype and a 1:30 scale model stands for a 10-story one. The wind pressure coefficient distribution along the building facades was examined and analyzed, comparing the CFD simulation, while the tracer gas concentration on the windows location every floor was measured using a fast ionization detectors. The dispersion process of the airborne pollutant under the natural ventilation was thoroughly investigated by analyzing the wind pressure coefficient and tracer gas concentration distribution along the envelop surfaces.The model 1, which was a block building model without any opening on the surface of the model, was designed to be carried out in the high speed section of the wind tunnel. The objective of this experiment was investigated the flow pattern around the high-rise residential building and further to in search of the potential dispersion transport and route of the airborne pollutant within the re-entrance space under the natural ventilation situation. It was not only revealed the distribution of the positive wind pressure zone and negative wind pressure zone along the building surface, but also showed the airborne pollutant can diffuse in both vertical direction and horizontal direction. It must be mentioned that the airborne could coinstantaneously flow and diffuse upward and downward along the building surfaces within the re-entrances space. This indicated that there was a potential risk of infection in the whole building, both the vertical and horizontal neighbors. The experiment data were also used to evaluate the CFD models, the k ?εturbulent models was used to search for the wind pressure coefficient distribution and tracer gas concentration distribution along the building facades. It showed that three turbulent model can simulate the wind pressure on the envelop surfaces very well. However, the concentration distribution based on the CFD models was not very well. The modified models could still used to forecast the concentration the concentration distribution.The model 2, which was a larger model scale with the opening windows on the building surfaces, was designed to be carried out in the low speed section of the wind tunnel. The purpose of this experiment was to analyze the possible flow route of the airborne pollutant around the high-rise residential building. It is found that the concentration distribution is very sensitive to both the source location and the wind direction. Comparisons were carried between the closed-window and open-window situations. The normalized concentration under the open-window situation is about one order lower than the close-window situation, through the dispersion trend was similar under both situations.The concentration fluctuations were also examined to illustrate the unsteady dispersion characteristics. Besides, an infectious risk model was built to forecast the infection probability. This paper on the dispersion and transmission of the airborne pollutant is not only to reduce the hazardous effect of routine release of harmful indoor or outdoor airborne pollutant, but also useful for the prevention and control of accidental infectious diseases outbreak.