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This dissertation, Analysis of Natural and Hybrid Ventilation in Simple Buildings by Hugh, Leung, 梁修賢, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled ANALYSIS OF NATURAL AND HYBRID VENTILATION IN SIMPLE BUILDINGS submitted by Leung Hugh for the degree of Master of Philosophy at The University of Hong Kong in February 2003 The main objective of this thesis is to study analytically the main physical parameters affecting natural ventilation flow rates in some simple building models. The ventilation air flows are driven by either natural forces such as thermal buoyancy and wind forces alone, or by combined natural and mechanical forces, i.e. mixed- mode ventilation. This analytical study is an extension of earlier studies on natural ventilation in a simple building with two vertically displaced openings. Our suggested new building models include a single-zone building with three openings, and a two-opening hybrid building with a mechanical fan. The effects of physical and geometrical parameters such as the size and location of openings and the driving forces upon ventilation flow rates are investigated. Our new analytical solutions can provide a simple analysis tool for parameter studies and give some physical insights on natural and mixed-mode ventilation. The analytical study on natural and mixed-mode ventilation also provides detailed and accurate information that can be used for validating numerical models of natural and hybrid ventilation and developing simple vent sizing methods. The effect of stratification is also considered in a single-zone building with three openings, and 2this has made some of our analyses useful for studying smoke movement in building fires, although they have neglected the effect of compressibility. Existing empirical formulae used for calculating the combined ventilation flow rate in a mixed-mode ventilation system, such as the quadratic superposition formula, are based on a simple physical assumption that the driving pressures due to natural and mechanical forces can be added linearly. This assumption is shown to be invalid in the current study when natural and mechanical forces are at similar magnitudes. The results from these simplified empirical formulae are compared with the derived analytical solutions. Our comparisons show that the errors due to the quadratic superposition formula can be quite large when both natural and mechanical forces have a similar magnitude. In the study of natural and mixed-mode ventilation, solution multiplicity behaviour was identified previously when thermal buoyancy force opposes the wind force under identical physical conditions. Our study on stratified flows in a building with three openings suggests that two smoke layers may also exist for the same set of parameters. We also show that mechanical fans can reduce and in some situations eliminate the existence of multiple solutions. This might explain why that solution multiplicity has not been a major concern in a modern building ventilation design, where mechanical fans are mostly used. __________________________ Leung Hugh Total words: 410 3 DOI: 10.5353/th_b2666310 Subjects: Ventilation - Mathematical modelsVentilation - Testing

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