Natural Ventilation of Buildings E-Book

David Etheridge

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 830

Veröffentlichungsjahr: 2011

Beschreibung

Natural ventilation is considered a prerequisite for sustainable buildings and is therefore in line with current trends in the construction industry. The design of naturally ventilated buildings is more difficult and carries greater risk than those that are mechanically ventilated. A successful result relies increasingly on a good understanding of the abilities and limitations of the theoretical and experimental procedures that are used for design. There are two ways to naturally ventilate a building: wind driven ventilation and stack ventilation. The majority of buildings employing natural ventilation rely primarily on wind driven ventilation, but the most efficient design should implement both types. Natural Ventilation of Buildings: Theory, Measurement and Design comprehensively explains the fundamentals of the theory and measurement of natural ventilation, as well as the current state of knowledge and how this can be applied to design. The book also describes the theoretical and experimental techniques to the practical problems faced by designers. Particular attention is given to the limitations of the various techniques and the associated uncertainties. Key features: * Comprehensive coverage of the theory and measurement of natural ventilation * Detailed coverage of the relevance and application of theoretical and experimental techniques to design * Highlighting of the strengths and weaknesses of techniques and their errors and uncertainties * Comprehensive coverage of mathematical models, including CFD * Two chapters dedicated to design procedures and another devoted to the basic principles of fluid mechanics that are relevant to ventilation This comprehensive account of the fundamentals for natural ventilation design will be invaluable to undergraduates and postgraduates who wish to gain an understanding of the topic for the purpose of research or design. The book should also provide a useful source of reference for more experienced industry practitioners.

Leseprobe

Contents

Cover

Title Page

Copyright

Dedication

Preface

Acknowledgements

Principal Notation

Subscripts

Superscripts

Abbreviations

Chapter 1: Introduction and Overview of Natural Ventilation Design

1.1 Aims and Scope of the Book

1.2 Natural Ventilation in Context

1.3 Overview of Design

1.4 Notes on Sources

References

Chapter 2: Physical Processes in Natural Ventilation

2.1 Introduction

2.2 The Effect of Gravity on Ventilation Flows

2.3 Types of Flow Encountered in Ventilation

2.4 Fluid Mechanics – Other Important Concepts and Equations

2.5 Steady and Unsteady Ventilation

2.6 Flow Through a Sudden Expansion

2.7 Dimensional Analysis

2.8 Heat Transfer between Air and Envelope

2.9 Definitions Relating to Ventilation Rate

2.10 Errors and Uncertainties

2.11 Mathematical Models

2.12 Boundary Conditions

Bibliography

Chapter 3: Steady Flow Characteristics of Openings

3.1 Introduction

3.2 Classification of Openings

3.3 Still-air Discharge Coefficient

3.4 Installation Effects on Cd

3.5 Openings in Combination

3.6 Determination of Cd

3.7 Uncertainties in Design Calculations

3.8 Other Definitions of Discharge Coefficient

3.9 Large (and Very Large) Openings

3.10 Relevance to Design

References

Chapter 4: Steady Envelope Flow Models

4.1 Introduction

4.2 Basic Theory

4.3 Single- and Multi-cell Models

4.4 Simple Analytic Solutions

4.5 Non-uniform Density

4.6 Turbulent Diffusion

4.7 Large Openings

4.8 Adventitious Openings

4.9 Explicit Method of Solution

4.10 Uncertainties in Envelope Flow Models

4.11 Combined Envelope Models and Thermal Models

4.12 Models for Very Large Openings

4.13 Relevance to Design

References

Chapter 5: Unsteady Envelope Flow Models

5.1 Introduction

5.2 Flow Equation

5.3 Pressure Difference across Openings

5.4 Mass Conservation Equation

5.5 Envelope Flow Models

5.6 Comparisons with Measurement

5.7 Mean Flow Rates

5.8 Instantaneous Flow Rates

5.9 Unsteady Flow Models in Design

5.10 Relevance to Design

References

Chapter 6: Internal Air Motion, Zonal Models and Stratification

6.1 Introduction

6.2 Governing Equations

6.3 Primary and Secondary Flows

6.4 Zonal Models

6.5 Coarse-grid CFD

6.6 Integrated Zonal and Envelope Flow Models

6.7 Stratification

6.8 Relevance to Design

References

Chapter 7: Contaminant Transport and Indoor Air Quality

7.1 Introduction

7.2 Concentration at a Point

7.3 Conservation Equations for Bounded Spaces, Envelope Models

7.4 Conservation Equations for Large Unbounded Volumes as Used in Zonal Models

7.5 Analytic Relations for Concentration at a Point

7.6 Analytic Relations for Uniform Concentration

7.7 Analytic Relations for Non-uniform Concentration

7.8 Calculations with CFD, Coarse-grid CFD and Zonal Models

7.9 Definitions Relating to Contaminant Removal

7.10 Relevance to Design

References

Chapter 8: Age of Air and Ventilation Efficiency

8.1 Introduction

8.2 Theoretical Modelling of Age Properties at a Point

8.3 Multi-zone (Multi-chamber) Models

8.4 Ventilation Efficiency

8.5 Analytic Relationships

8.6 Experimental Determination of Age (Using a Tracer)

8.7 Unsteady Age Distributions

8.8 Relevance to Design

References

Chapter 9: Computational Fluid Dynamics and its Applications

9.1 Introduction

9.2 Basics of CFD

9.3 Important Modelling Issues

9.4 Calculation of External Wind Flow

9.5 Calculation of Internal Flows

9.6 Whole-field Calculations

9.7 Other Applications

9.8 Relevance to Design

References

Chapter 10: Scale Modelling

10.1 Introduction

10.2 Requirements for Similarity

10.3 Wind Alone

10.4 Buoyancy Alone

10.5 Wind and Buoyancy Combined

10.6 Use of Water as the Modelling Fluid

10.7 Relevance to Design

References

Chapter 11: Full–scale Measurements

11.1 Introduction

11.2 Laboratory Measurements of Cd and Effective Area

11.3 Measurement of Adventitious Leakage Using Steady Pressurisation

11.4 Unsteady Techniques for Measurement of Low-pressure Leakage

11.5 Field Measurement of Ventilation Rates

11.6 Other Measurements

11.7 Relevance to Design

References

Chapter 12: Design Procedures

12.1 Introduction

12.2 Feasibility of Natural Ventilation (Stage 1)

12.3 Ventilation Strategies (Stage 2)

12.4 Envelope Design (Stage 3)

12.5 Internal Environment (Stage 4)

12.6 Data Specification

12.7 Low-energy Cooling Systems

12.8 Control Systems

12.9 Commissioning (Stage 5)

12.10 Some General Observations and Questions Relating to Design

References

Index

This edition first published 2012

© 2012 John Wiley & Sons, Ltd.

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Library of Congress Cataloguing-in-Publication Data

Etheridge, David (David W.)

Natural ventilation of buildings: theory, measurement and design / David Etheridge.

p. cm.

Includes bibliographical references and index.

ISBN 978-0-470-66035-5 (cloth)

1. Natural ventilation. I. Title.

TH7674.E84 2012

697.9'2–dc23

2011020607

Print ISBN: 9780470660355

ePDF ISBN: 9781119951780

oBook ISBN: 9781119951773

ePub ISBN: 9781119954378

Mobi ISBN: 9781119954385

To Rosamund, Catharine, Paul and Thomas

Preface

The publication in 1996 of the book that I co-authored with Mats Sandberg coincided with my leaving industrial R&D and taking up a post at the University of Nottingham. The publication of this book coincides with another change in my career. By the time it is published, I will have retired from the University (although I will continue to be active in ventilation in a private capacity).

My time at Nottingham gave me the opportunity to concentrate my research, and teaching, on natural ventilation. One outcome of this is the present book, which differs from the earlier one in two important respects. It is concerned specifically with natural ventilation and it includes coverage of design. Some parts of the book are based on lectures that I gave to final-year undergraduates, so I have included them in the intended readership.

The inclusion of design has been particularly important to me. As well as devoting the first and final chapters to design, I have tried to make it a common thread throughout the book. A related theme that occurs in most of the chapters is the topic of errors and uncertainty. During my career I have worked in the aircraft industry on the design of wings, and in the gas industry on the development of flow meters for custody transfer of natural gas. In both cases the design process is relatively precise: errors and uncertainties of a few percentage points can be significant; the design aims can be precisely specified; the end product can be accurately checked to see that it meets the specification. With a few notable exceptions (e.g. the measurement of adventitious leakage and the discharge coefficients of openings), none of these features applies to natural ventilation design. It is perhaps not surprising, therefore, that natural ventilation design is perceived as a risky business, with consequential demands on the judgement and experience of design teams. One manifestation of the problem lies in the assumptions and approximations that are needed in mathematical and physical modelling. This raises the important issue of the sensitivity of models to these assumptions. I have therefore included some discussion of sensitivity, but it has not been possible to give it the attention it deserves. The same comment applies to the topic of control systems. Control systems are particularly important, because they offer a direct means of reducing risks.

The final stage of writing has been the search for errors. In my experience, errors of fact and of interpretation have a characteristic in common with adventitious leakage; they can never be entirely eliminated, no matter how hard one tries. I suspect therefore that some remain, and I apologise for them here.

Finally, I hope that in spite of its failings, this book will make a contribution to advancing the cause of naturally ventilated buildings.

Acknowledgements

My time in the Department of Architecture and Built Environment has been a very enjoyable one and I cannot let pass the opportunity to express my thanks to all my colleagues for making it so. The mix of architecture and technology is rewarding on several planes, and long may it remain so. My special thanks go to Brian Ford for commenting on drafts of Chapters 1 and 12, and to Guohui Gan and Andrew Howarth for their comments on Chapters 9 and 6 respectively.

I am also grateful for the opportunity to come into contact with many students from home and abroad, both undergraduate and postgraduate. In their different ways, they kept me on my toes and I have learnt much from them. It would be wrong to single out names, but some will be found in the reference lists.

Writing a book can be a selfish process and it is only too easy to forget the demands that it places on others. I therefore want to record my thanks to my wife Ros. Having had previous experience of me writing a book, she took the opportunity to fulfil an ambition and work with VSO in Malawi for 18 months. Part of the plan was that I could finish the writing, which had already been going on for too long. It did not quite work out like that, partly because I had four very enjoyable visits to Africa. However, I can at least claim that some good has come from the book.

Finally, my thanks go to the editorial and production staff at John Wiley & Sons for their help and guidance in turning my efforts into the finished article.

Principal Notation

Only the principal notation is given here. However, partly for ease of reading, all symbols are defined in the text of the chapters in which they occur. Another reason for this is that some symbols are used to denote several different quantities. For example, is used to denote the power law exponent in equation (3.29), the number of cells in an envelope (Section 7.3.1) and the concentration of molecules at a point (Sections 7.1.3 and 8.1.3). The first two uses are not classed as principal and are therefore not listed here.

SymbolMeaningUnitarea of opening or a building surface[m2]Archimedes number, defined by equation (4.43)[–]buoyancy parameter defined by equation (5.51)[–]reference value of at high in equation (5.36)[–]amplitude of wind pressure gust in equation (5.63)[–]mass concentration of a gas in air[kg m−3]speed of sound in air, used in Chapter 5[m s−1]mass concentration relative to exterior, equation (7.19)[kg m−3]specific heat of air[J kg−1 K−1]volumetric concentration of a contaminant[−]discharge coefficient, defined by equation (3.1)[−]modified discharge coefficient, defined by equation (3.27)[−]loss coefficient, defined by equation (2.29)[−]pressure coefficient, defined by equation (2.42)[−]hydraulic diameter of an opening, defined by equation (3.4)[m]diameter of a circular opening[m]compressibility parameter, defined by equation (5.45)[−]molecular diffusion coefficient of a gas in air (Section 2.4.2)[m2 s−1], , turbulent diffusion coefficients, defined by equation (7.26)[m2 s−1]opening parameter, defined by equation (5.44)[−]flow rates of heat in equations (2.43), (4.63) and (12.1)[W]f ()denotes a function[−]frequency distribution for in a small volume , defined by equation (8.2)[s−1]frequency distribution for in a small volume [s−1]frequency distribution for in a small volume [s−1]inertia parameter defined by equation (5.46)[−]Froude number, defined by equation (10.44)[−]force in direction[N]force per unit mass due to gravity[m s−2]Galileo number, defined by equation (10.75)[−]Grashof number, defined by equation (10.78)[−]height between openings[m]height of interface between zones[m]reference height[m]frequency distribution of ages of the molecules in a room[s−1]frequency distribution of residence times for a room[s−1]thermal conductivity[W m−1 K−1]kinetic energy per unit mass of turbulent velocity component (Section 9.2.4.2)[J kg−1]scale factor (for length), Section 10.2[−]inertia length of an opening, defined by equation (5.9)[m]length of opening along flow path e.g. equation (5.12)[m]reference length[m]mass of a defined volume of air or gas[kg]mass flow rate[kg s−1]-wise momentum of a control volume, equation (2.21)[kg m s−1]flow rate of x-wise momentum through a defined area[kg m s−2]x-wise momentum flux (flow per unit area), equation (6.15)[kg m−1 s−2]number of molecules of contaminant per unit volume at a point[m−3]concentration of molecules with entry time in a small volume [m−3]total number of molecules per unit volume[m−3]concentration of molecules with age in a small volume defined by equation (8.5)[m−3]number of air molecules in a room with age [−]number of air molecules in a room[−]rate at which air molecules are leaving/entering a room[s−1]piezometric pressure (pressure due to motion)[Pa]pressure due to motion in Section 4.2.4[Pa]piezometric total pressure defined by equation (2.26)[Pa]pressure due to wind (piezometric)[Pa]absolute (thermodynamic) pressure[Pa]hydrostatic pressure[Pa]total pressure defined by equation (2.25)[Pa]Peclet number, defined by equation (10.45)[−]Prandtl number, defined by equation (10.47)[−]volume flow rate through an opening[m3 s−1]time-averaged value of [m3 s−1]fresh-air flow rate[m3 s−1]volume flow rate[m3 s−1], adventitious leakage at 50 Pa and 4 Pa[m3 s−1]percentage of time that a stack flow is positive (inward)[%]circulation ratio, defined by equation (7.71)[−]air change rate, defined in Sections 2.9 and 8.1.6[h−1]Reynolds number, defined by equation (2.18)[−]Reynolds number based on length of opening, equation (3.18)[−]opening Reynolds number based on , equation (3.2)[−]Reynolds number based on , defined by equation (2.19)[−]surface area[m2]sign of a quantity e.g. in equation (4.22)[−]Sign[]sign of quantity in [][−]rate of emission of contaminant from source[kg s−1]Schmidt number, defined by equation (8.28)[−]turbulent Schmidt number, defined by equation (7.28)[−]Strouhal number, defined by equation (10.23)[−]time[s]time at which a molecule entered a room, equation (8.1)[s]mean entry time of molecules at a point[s]temperature[K] or [°C]velocities in directions[m s−1]steady part of see equation (2.20)[m s−1]random turbulent part of see equation (2.20)[m s−1]spatial mean velocity through an opening, equation (3.3)[m s−1]coherent part of in unsteady turbulent flow, equation (9.12)[m s−1]wind speed, reference velocity[m s−1]speed based on buoyancy, defined by equation (4.45)[m s−1]entrainment velocity at the boundary of a shear layer[m s−1]volume[m3]cross-flow velocity in external region of an opening[m s−1]volume passed during a period of flow reversal[m3]non-dimensional , defined by equation (5.62)[−]weather parameter defined by equation (5.52)[−]orthogonal axes[m]cross-flow direction[rad] or [degree]entrainment coefficient, see equation (6.2)[−]the ratio of specific heats (exponent for an isentropic process)[−]coefficient of surface wind pressure difference[−]net inflow of -wise momentum, equation (5.1)[kg m s−2]piezometric pressure difference[Pa]difference in total pressure[Pa]density difference[kg m−3]volume element[m3]ventilation efficiency, defined by equation (8.53)[%]dissipation rate of turbulent kinetic energy per unit mass (Section 9.2.4.2)[W kg−1]viscosity[N s m−2]equivalent turbulent viscosity, defined by equation (9.10)[N s m−2]resistance coefficient, defined by equation (2.27)[−]component of due to wall shear stress[−]density[kg m−3]standard deviation of [−]age of a molecule, defined by equation (8.1)[s]age at a point, defined by equation (8.4)[s]age at a point with steady turbulent flow[s]average age of the air in a room[s]residence time at a point[s]average residence time for a room[s]representative timescale for ventilation, defined by equation (8.11)[s]minimum time for the air in a room to be completely changed[s]wind direction[rad] or [degree]velocity potential, defined by equation (2.32)[m2 s−1]angular frequency[Hz]

Subscripts

in, outconditions on the inlet and outlet sides of an openingint, extconditions inside and outside a buildingoopeningssteady flow conditionssupply conditionFfresh airFfan (Section 10.3.4.1)I, Econditions inside and outside a buildingrefreference quantityU, Lconditions in the upper and lower zones in a roomvair vent (Section 11.2)0, Hconditions at height equal to zero and 0reference quantity0value at height equal to zero

Superscripts

—overbar denotes time average.dot above symbol denotes rate of change with time*non-dimensional variableprime denotes turbulent component

Abbreviations

ABLatmospheric boundary layerACalternating (sinusoidal) pressure technique, defined in Section 11.4BMSbuilding management systemCFDcomputational fluid dynamics, defined in Sections 2.11.4 and 9.1COPcoefficient of performance, defined in Section 12.7CTAconstant temperature hot-wire anemometer, Section 10.3.6.1DCconventional steady pressure technique, defined in Section 11.4DNSdirect numerical simulation of turbulence, defined in Section 9.2.2DSFdouble-skin facade, defined in Section 12.3.3DTMdynamic thermal model (Section 2.11.3)LBMlattice Boltzmann method (Section 9.1)LDAlaser Doppler anemometer, Section 10.3.6.1LESlarge-eddy simulation of turbulence, defined in Section 9.2.3N–SNavier–Stokes equations, defined in Sections 2.2.1 and 9.2.1PCMphase change material, defined in Section 12.7.1PDCpositive downdraught cooling, defined in Section 12.7.2PDECpositive downdraught evaporative cooling, defined in Section 12.7.2PIVparticle imaging velocimetry, defined in Section 11.6POEpost-occupancy evaluation, defined in Section 11.1PSpseudo-steady envelope flow model, defined in Section 5.5.4PSVparticle streak velocimetry, defined in Section 11.6QCquasi-steady compressible envelope flow model, defined in Section 5.5.4QIquasi-steady incompressible envelope flow model, defined in Section 5.5.4QPquasi-steady pulse technique for leakage, defined in Section 11.4QTquasi-steady temporal inertia envelope flow model, defined in Section 5.5.1RANSReynolds-averaged Navier–Stokes equations, defined in Section 9.2.4URANSunsteady Reynolds-averaged Navier–Stokes equations, defined in Section 9.2.4

Chapter 1

Introduction and Overview of Natural Ventilation Design

1.1 Aims and Scope of the Book

1.1.1 Aims

There are two aims of this book. The first is to provide a reasonably comprehensive and up-to-date account of the theory and measurement of natural ventilation. The second is to describe how theory and measurement can be applied to the design of naturally ventilated buildings.

The application of research findings to design is not a simple process. It is necessary to make approximations and assumptions. Choosing the appropriate technique for a particular design problem requires not only an understanding of the important physical factors involved in the problem, but also an appreciation of the limitations of the various techniques that are available. In essence, it is important that the designer should know what techniques are available and have some understanding of them. It is equally important that researchers should have an understanding of the problems faced by designers. It is hoped that this book will at least provide an introduction to these issues.

An earlier work (Etheridge and Sandberg, 1996), co-authored by Mats Sandberg and the present author, covered both mechanical and natural ventilation. The present book differs in two respects. It is concerned only with natural ventilation and it specifically includes coverage of design. There have been developments since the earlier work was published and emphasis is given to these. To this extent the book can be considered a sequel to the earlier work. However, the important fundamentals, in the context of natural ventilation, are still covered. In this sense, the book is self-contained and access to the earlier work is not required. However, the coverage of some well-established techniques (and techniques that are now rarely used) makes use of specific references to the earlier work. The manner in which this has been done is described in Section 1.4.1.