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Title: Experimental and numerical investigation of air cross-contamination around typical high-rise residential building in Hong Kong
Authors: Liu, Xiaoping
Degree: Ph.D.
Issue Date: 2011
Abstract: The dispersion of air pollutant in complex building environment has become of great concern for the modern society as more and more people live in large and crowded cities in many parts of the world. For high-rise residential buildings, understanding the air flow and pollutant dispersion characteristics around buildings is essential to minimize the risk of outdoor pollution into buildings. The contaminant distribution and transmission route near a building can be extremely complicated due to the interaction between plumes of pollutants and building structure. Reliable prediction of the pollutant concentration field near a building is therefore of vital importance in providing comfortable and healthy indoor conditions free of outdoor air pollution. Air cross-contamination in high-density residential building environment can have a wide range of negative consequences for the residents' health and productivity, particularly during the period of a highly infectious disease outbreak. The primary aim of this work is to evaluate the risk of air cross-contamination around two typical forms of high-rise residential building in Hong Kong under two different naturally-ventilated conditions, i.e. buoyancy-dominated and wind-dominated conditions, respectively. First a series of numerical studies were carried out to investigate the mechanism of contaminant transmission under the condition of single-sided natural ventilation, using Computational Fluid Dynamics (CFD) method. The focus is on one of the typical designs in HRR buildings with a rectangular plan layout and having a common-corridor separating the two sides, each of which has a flat-facade with openable windows. When the wind speed is low, with doors closed and windows opened, the flats become single-sided natural ventilation driven by buoyancy effects. It was found that under specific weather conditions, the presence of the pollutants originating from the lower floor is generally two orders of magnitude lower in the immediate upper floor. The results identified that the air pollutants can travel from a lower flat to an adjacent upper flat in the vertical direction through open windows caused by the indoor/outdoor temperature-difference induced buoyancy, revealing windows flush with the facade can be a major route of the air cross-contamination in high-rise residential buildings. Also, the study attempted to evaluate the effects of an architectural feature in minimizing such cross contamination. Moreover, with regards to ventilation design, the possible optimal strategies were preliminarily evaluated by CFD methods.
Subsequently, an experiment study was carried out to further investigate the dispersion characteristics around another typical building with more complex building shape under wind effect. The experiments were performed in a boundary layer wind tunnel using tracer gas technique. Two different model scales, 1:150 and 1:30, were designed for different purposes, representing a 33-story, and a 10-story residential building in prototype, respectively. The tracer gas concentrations on the envelop surfaces were measured using fast flame ionization detectors, while the pressure distributions along building facade were also examined. Through the pressure and concentration distribution, the possible transport process of air pollutant induced by cross-contamination was thoroughly examined. The first stage of the experiment was designed to be undertaken in the high speed section for model A, which was constructed as a block without any openings on the building envelope. The experimental results indicate that the flow pattern around the High-Rise Residential (HRR) building has the potential to transport gaseous pollutant within the re-entrance space under the wind effect. It was revealed that the pollutant can spread in both vertical directions, not only in the upward direction that was found under buoyancy effect, but also in the downward direction. Furthermore, dispersion can also occur in the horizontal direction, indicating a potential risk of cross-contamination in the horizontal adjacent flats. The experiment data were also used to evaluate the CFD methods, illustrating that CFD method with three kinds of k - ε turbulence models is not recommended in predicting the near building pollutant dispersion. The second stage of the experiment was performed in the low speed section for model B, with openable windows, which was designed in a larger model scale that allowed greater spatial resolution of concentration data. It was noticed that the dispersion route is quite sensitive to both the source location and the wind direction, and dispersion trends were found similar to the first stage experiment results. In particular, the region of influence in both vertical and horizontal directions, together with contamination degrees induced by cross-contamination was determined. Moreover, comparisons were made between open-window and no-window situations. The mean concentration distributions under both configurations were found to be similar, implying that the presented window-wall-ratio was not large enough to influence the basic flow pattern. The concentration fluctuations were also examined to illustrate the unsteady dispersion characteristics. The study on this physical process is not only helpful to reduce the hazardous effect of routine release of harmful indoor air pollutants, but also useful for the purpose of prevention and control of accidental infectious diseases outbreak. The features revealed by the investigation indicate that early intervention for high-rise residential blocks may be implemented in terms of diagnosis and isolation if an emerging, highly infectious disease is suspected. The identification of this transmission path also shed light on both architectural and ventilation design in high-rise residential blocks to avoid cross indoor air contamination, which deserves further investigations.
Subjects: Indoor air pollution -- Mathematical models
Air flow -- Mathematical models
High-rise apartment buildings -- Aerodynamics -- Mathematical models
High-rise apartment buildings -- China -- Hong Kong
Hong Kong Polytechnic University -- Dissertations
Pages: i, xvi, 201 leaves : ill. ; 30 cm.
Appears in Collections:Thesis

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