Method of Quantifying Wind-driven Natural Ventilation Flowrate and the Development of Systematic Analysis on the Relationship Between the Flowrate and Building Configuration PDF Download
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Author: Sheng Wang
Publisher:
ISBN:
Category : Building
Languages : en
Pages : 258
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Book Description
It is very challenging to design a building when one is trying to determine the wind-driven ventilation due to the instability of the wind. While a significant amount of research has been carried out to measure and estimate the wind-driven ventilation of buildings in the recent decade, few could systematically quantify the ventilation flowrates in different building types in different wind environments. In order to thoroughly investigate the research gap above, the thesis has been divided into four stages and covered by four related studies. the first stage of the four studies analyzed the relationship between facÌʹade opening size and wind-driven airflow rates through small openings by using CFD. Then, for the second stage, a Weibull model fitted wind characteristic study was carried out to try to represent variable wind by a mathematical model. A series of CFD simulation and wind tunnel experiments were conducted for the third stage to establish a methodology to use CFD simulation software carrying out virtual wind tunnel experiments. Finally, for the last stage, by applying the methodology created in the third stage, a series of building facÌʹade pressure coefficient simulations were conducted, and wind-driven ventilation of these buildings under historical wind conditions was estimated. To summarize the results of these four related studies, the opening size analysis showed the relationship between the airflow at the building opening, which is driven by the wind, opening size, and wind direction. The investigation revealed the airflow through the opening was mostly driven by the pressure difference, in which wind momentum energy dissipated at the building surface, even while the wind was not perpendicular to the facÌʹade. By changing the opening size, it also revealed that the primary driving force of the airflow through opening shifted from pressure to momentum while the opening size was increased. This study provided the threshold of opening size while pressure-driven airflow applied. The next step provided the mathematical model exploration of wind data, which delivered a method to represent wind characteristic data. The study illustrated the inaccuracy of using TMY3 wind data to estimate wind-driven ventilation when comparing to ASOS data. Weibull model fitted into ASOS data showed the potential of using the mathematical model to generate wind data. The thirst step demonstrates the use of a virtual wind tunnel developed to systematically obtain building facade pressure coefficient and the accompanying framework to duplicate this process to fit any building. This virtual wind tunnel analysis was validated against a real wind tunnel experiment (by FIU WoW facility) and the method and framework of acquiring pressure data under different wind conditions via the virtual wind tunnel are expected to generate high-value results for other researchers. Finally, by applying the virtual wind tunnel based data (pressure coefficients), the estimation of wind-driven ventilation rates was calculated for different building and different locations. The calculated flowrates was used in investigating the efficacy and viability of using wind-driven natural ventilation to fulfill current ventilation requirements.
Author: Sheng Wang
Publisher:
ISBN:
Category : Building
Languages : en
Pages : 258
Get Book Here
Book Description
It is very challenging to design a building when one is trying to determine the wind-driven ventilation due to the instability of the wind. While a significant amount of research has been carried out to measure and estimate the wind-driven ventilation of buildings in the recent decade, few could systematically quantify the ventilation flowrates in different building types in different wind environments. In order to thoroughly investigate the research gap above, the thesis has been divided into four stages and covered by four related studies. the first stage of the four studies analyzed the relationship between facÌʹade opening size and wind-driven airflow rates through small openings by using CFD. Then, for the second stage, a Weibull model fitted wind characteristic study was carried out to try to represent variable wind by a mathematical model. A series of CFD simulation and wind tunnel experiments were conducted for the third stage to establish a methodology to use CFD simulation software carrying out virtual wind tunnel experiments. Finally, for the last stage, by applying the methodology created in the third stage, a series of building facÌʹade pressure coefficient simulations were conducted, and wind-driven ventilation of these buildings under historical wind conditions was estimated. To summarize the results of these four related studies, the opening size analysis showed the relationship between the airflow at the building opening, which is driven by the wind, opening size, and wind direction. The investigation revealed the airflow through the opening was mostly driven by the pressure difference, in which wind momentum energy dissipated at the building surface, even while the wind was not perpendicular to the facÌʹade. By changing the opening size, it also revealed that the primary driving force of the airflow through opening shifted from pressure to momentum while the opening size was increased. This study provided the threshold of opening size while pressure-driven airflow applied. The next step provided the mathematical model exploration of wind data, which delivered a method to represent wind characteristic data. The study illustrated the inaccuracy of using TMY3 wind data to estimate wind-driven ventilation when comparing to ASOS data. Weibull model fitted into ASOS data showed the potential of using the mathematical model to generate wind data. The thirst step demonstrates the use of a virtual wind tunnel developed to systematically obtain building facade pressure coefficient and the accompanying framework to duplicate this process to fit any building. This virtual wind tunnel analysis was validated against a real wind tunnel experiment (by FIU WoW facility) and the method and framework of acquiring pressure data under different wind conditions via the virtual wind tunnel are expected to generate high-value results for other researchers. Finally, by applying the virtual wind tunnel based data (pressure coefficients), the estimation of wind-driven ventilation rates was calculated for different building and different locations. The calculated flowrates was used in investigating the efficacy and viability of using wind-driven natural ventilation to fulfill current ventilation requirements.
Author: Liang Chung James Lo
Publisher:
ISBN:
Category :
Languages : en
Pages : 366
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Book Description
Designing wind driven cross ventilation for a building is challenging due to the dynamic characteristics of wind. While numerous studies have studied various aspects of cross ventilation, few have had an opportunity to examine the topic with a holistic approach utilizing multiple research techniques. Thus, this dissertation combined three different investigation methods: wind tunnel analysis, full scale experiments and computational fluid dynamics (CFD) to examine the physics of wind driven cross ventilation. Following the systematic approaches of the three methods, this study first conducted full scale measurements of wind properties, fac̦ade pressures, air flow rates through small window openings, and tracer gas concentrations in a multi-zone test house. Secondly, a scaled model of the test house was studied in a boundary layer wind tunnel (BLWT) for its fac̦ade pressures and ventilation rate under various wind incident angles. Finally, a CFD model of the test house was simulated under various constraints to determine the factors which affect indoor air distribution during wind driven cross ventilation events. The full scale experimental results showed a strong correlation between the cross ventilation rate and the wind velocity component normal to the inlet openings. This correlation suggested that the cross ventilation flow rate could be estimated from wind conditions alone. A closer examination of the wind characteristics also revealed that the cyclical pattern of changing wind direction could be impacted by obstructions which are kilometers upwind, suggesting that distant landscapes could have an impact on cross ventilation flows. The combination of CFD and full scale measurements also showed that local heat sources can generate significant buoyancy driven flow and affect indoor mixing during wind-driven cross ventilation scenarios. Experimentally validated parametric CFD analyses demonstrated the effect of interior heat loads in driving internal airflow, and suggest that a small source (35W/m2) can increase the indoor mixing from less than 1 ACH to 8 ACH between indoor spaces. Finally, the wind tunnel and CFD coupled analysis was found to predict the cross ventilation flow which was also validated against the full scaled measurements. The prediction, which may only be applicable to similar building types with small openings, showed significant agreement that such method has potential as an innovative design tool for natural ventilation in buildings.
Author: Y. Chartier
Publisher: World Health Organization
ISBN: 9241547855
Category : Medical
Languages : en
Pages : 132
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Book Description
This guideline defines ventilation and then natural ventilation. It explores the design requirements for natural ventilation in the context of infection control, describing the basic principles of design, construction, operation and maintenance for an effective natural ventilation system to control infection in health-care settings.
Author: Hugh Leung
Publisher:
ISBN: 9781374799318
Category :
Languages : en
Pages :
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Book Description
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 models Ventilation - Testing
Author: Panagiota Karava
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Natural/hybrid ventilation systems with motorized operable windows, designed and controlled to utilize the potential for cross-ventilation, represent an area of significant interest in sustainable building design as they can substantially reduce energy consumption for cooling and ventilation. Presently, there is a need for accurate prediction models that can contribute to the improvement of indoor environmental quality and energy performance of buildings, and the increased use of low energy, naturally driven cooling systems. In this regard, the present research aims to enhance airflow prediction accuracy for natural ventilation design of buildings considering advanced experimental and simulation methods. The study considers a Boundary Layer Wind Tunnel (BLWT) approach to investigate the wind-induced driving forces and ventilation flow rates in various building models subject to cross-ventilation. The Particle Image Velocimetry (PIV) technique was used for the first time to evaluate accurately the air velocity field for various cross-ventilation configurations. Detailed measurements were performed to determine mean and fluctuating internal pressures since they affect airflow prediction, occupants' thermal comfort, as well as cladding and structural wind load design of buildings with operable windows. PIV data for the inflow velocity were compared with those by using conventional techniques (e.g., hot-film anemometry) and results show differences, between the two methods, up to a factor of 2.7. This clearly indicates that accuracy can be enhanced with carefully conducted PIV experiments. The study provides guidelines for implementation of cross-ventilation in design practice. These guidelines were developed on the basis of parametric experimental investigations, which quantify the impact of relative inlet-to-outlet size and location on ventilation airflow rates and thermal comfort of building occupants. The study develops a novel simulation methodology combined with a sensitivity analysis focused on modelling issues, such as the impact of zoning assumptions, to predict the envelope pressures and related air-exchange rates in buildings due to wind, stack, and mechanical system effects. An integrated simulation tool (ESP-r) was used to model the airflow/energy interactions in an existing high-rise residential building, and simulation results agree well with monitoring data.
Author: Chartered Institution of Building Services Engineers
Publisher:
ISBN:
Category : Ventilation
Languages : en
Pages : 114
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Book Description
Author: Mat Santamouris
Publisher: Routledge
ISBN: 1136570721
Category : Architecture
Languages : en
Pages : 332
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Book Description
Ensuring optimum ventilation performance is a vital part of building design. Prepared by recognized experts from Europe and the US, and published in association with the International Energy Agency's Air Infiltration and Ventilation Centre (AIVC), this authoritative work provides organized, classified and evaluated information on advances in the key areas of building ventilation, relevant to all building types. Complexities in airflow behaviour, climatic influences, occupancy patterns and pollutant emission characteristics make selecting the most appropriate ventilation strategy especially difficult. Recognizing such complexities, the editors bring together expertise on each key issue. From components to computer tools, this book offers detailed coverage on design, analysis and performance, and is an important and comprehensive publication in this field. Building Ventilation will be an invaluable reference for professionals in the building services industry, architects, researchers (including postgraduate students) studying building service engineering and HVAC, and anyone with a role in energy-efficient building design.
Author: H.B. Awbi
Publisher: Routledge
ISBN: 1134489617
Category : Architecture
Languages : en
Pages : 535
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Book Description
Hazim Awbi's Ventilation of Buildings has become established as the definitive text on the subject. This new, thoroughly revised, edition builds on the basic principles of the original text drawing in the results of considerable new research in the field. A new chapter on natural ventilation is also added and recent developments in ventilation concepts and room air distribution are also considered. The text is intended for the practitioner in the building services industry, the architect, the postgraduate student undertaking courses or research in HVAC, building services engineering, or building environmental engineering, and the undergraduate studying building services as a major subject. Readers are assumed to be familiar with the basic principles of fluid flow and heat transfer and some of the material requires more advanced knowledge of partial differential equations which describe the turbulent flow and heat transfer processes of fluids. The book is both a presentation of the practical issues that are needed for modern ventilation system design and a survey of recent developments in the subject
Author: Francis Allard
Publisher: Earthscan
ISBN: 9781873936726
Category : Architecture
Languages : en
Pages : 378
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Book Description
AIOLOS is a computational tool for the calculation of the airflow rates in naturally ventilated buildings.
Author: Yun Zhang
Publisher:
ISBN:
Category : Building
Languages : en
Pages : 0
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Book Description
The ventilation with outside air has received tremendous attention since the outbreak of the COVID 19 pandemic. Wind-driven cross ventilation has been reported to be an efficient strategy to enhance the indoor and outdoor air exchange for this purpose. However, there is a lack of an accurate tool for the rapid estimation of airflow rate. The candidate pressure-based orifice equation involves two parameters, pressure coefficient, and free stream wind speed, which have not been fully understood due to its oversimplification. This work aims to fill the gap. First, a pressure-based instantaneous airflow rate (Qins) is proposed to mitigate the discrepancy between measured airflow of a series of wind tunnel tests estimated from averaged pressure. Second, a spatiotemporal analysis is carried out on instantaneous pressure to understand the turbulent flow and hence provide evidence for such fluctuation-induced airflow. At last, the spatial and temporal variation of urban wind is investigated by comparing local wind with airport wind. This work approaches these questions by investigating the underlying flow behavior. A series of wind tunnel tests were reviewed to establish the relationship between pressure and wind-driven cross-ventilation. Then, the discrepancy between airflow rate measurement and averaged pressure is justified by both a steady-state CFD simulation and a temporal analysis on instantaneous pressure. It's found when the wind is parallel to openings, a strong temporal correlation between pressure on two lateral walls results in zero time-averaged pressure difference. In contrast, the measured airflow rate is greater than zero and is more consistent with an accumulative instantaneous airflow rate (Qins) which is accounts for pressure difference over small time step. The proposed, novel K-mean clustering method detects a coherent and organized flow structure that is likely linked to von Karman vortex shedding. Such flow structures are periodic and result in intermittent pressure differences at a relatively small time step for both isolated buildings or more complex urban-like settings. It attributes to the fluctuation-induced airflow rate, which the Qins is promising to capture. The investigation on wind variation found an overall strong to moderate correlation between local wind speed and that of the airport in the three cities discussed. However, the correlation is a function of topographic features of the region, say a region with homogenous roughness (building heights) primarily indicates a strong correlation between the local and airport wind. The correlation becomes weaker when wind speed is low in the summer months. On the other hand, our studies have demonstrated systematic patterns of wind direction shifts. Future work is encouraged to better model the local wind data from airport wind under real urban environments. The potential solution to solving insufficient training data is discussed. As an attempt to understand the mechanism of fluctuation-induced cross-ventilation, the study presents systematic and generic knowledge of instantaneous flow structures induced by wind-building interaction as an alternative to other time-consuming and source-intensive methods like CFD, wind tunnel test, and field measurements. The results could be used as a semi-quantitative description of the transient behavior of flow around buildings and hence provides evidence for a periodic function that acts as the driving force for cross ventilation. Those results are beneficial in terms of natural ventilation design as well. For instance, we found that the density, surrounding building height, and building roof significantly impact the flow rate achieved by a sheltered building. A favorable building orientation could be [theta]=45 to the prevailing wind if the target building has the same height as surrounding buildings or [theta]=20 for a "moderately dense" case.
