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Building Physics - Heat, Air and Moisture: Fundamentals and Engineering Methods with Examplesand Exercises, 2nd Edition

ISBN: 978-3-433-03027-1
330 pages
September 2012
Building Physics - Heat, Air and Moisture: Fundamentals and Engineering Methods with Examplesand Exercises, 2nd Edition (3433030278) cover image
Bad experiences with construction quality, the energy crises of 1973 and 1979, complaints about 'sick buildings', thermal, acoustical, visual and olfactory discomfort, the need for good air quality, the move towards more sustainability, all have accelerated the development of a field, which until some 40 years ago was hardly more than an academic exercise: building physics.
Building physics combines several knowledge domains such as heat and mass transfer, building acoustics, lighting, indoor environmental quality and energy efficiency. In some countries, also fire safety is included. Through the application of existing physical knowledge and the combination with information coming from other disciplines, the field helps to understand the physical phenomena governing assembly, building envelope, whole building and built environment performance, although for the last the wording `urban physics? is used. Building physics has a true impact on performance based building design.
This volume focuses on heat, air, moisture transfer and its usage in building engineering applications.
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Preface VII

0 Introduction 1

0.1 Subject of the book 1

0.2 Building Physics 1

0.2.1 Definition 1

0.2.2 Criteria 2

0.2.2.1 Comfort 2

0.2.2.2 Health 3

0.2.2.3 Architecture and materials 3

0.2.2.4 Economy 3

0.2.2.5 Sustainability 3

0.3 Importance of Building Physics 3

0.4 History of Building Physics 5

0.4.1 Heat, air and moisture 5

0.4.2 Building acoustics 5

0.4.3 Lighting 6

0.4.4 Thermal comfort and indoor air quality 6

0.4.5 Building physics and building services 7

0.4.6 Building physics and construction 7

0.4.7 What about the Low Countries? 8

0.5 Units and symbols 9

0.6 Literature 12

1 Heat Transfer 13

1.1 Overview 13

1.2 Conduction 15

1.2.1 Conservation of energy 15

1.2.2 Fourier’s laws 16

1.2.2.1 First law 16

1.2.2.2 Second law 17

1.2.3 Steady state 18

1.2.3.1 What is it? 18

1.2.3.2 One dimension: flat assemblies 18

1.2.3.3 Two dimensions: cylinder symmetric 26

1.2.3.4 Two and three dimensions: thermal bridges 27

1.2.4 Transient regime 32

1.2.4.1 What? 32

1.2.4.2 Flat assemblies, periodic boundary conditions 33

1.2.4.3 Flat assemblies, random boundary conditions 45

1.2.4.4 Two and three dimensions 48

1.3 Convection 49

1.3.1 Heat exchange at a surface 49

1.3.2 Convective heat transfer 50

1.3.3 Convection typology 52

1.3.3.1 Driving forces 52

1.3.3.2 Flow type 52

1.3.4 Calculating the convective surface film coefficient 53

1.3.4.1 Analytically 53

1.3.4.2 Numerically 53

1.3.4.3 Dimensional analysis 54

1.3.5 Values for the convective surface film coefficient 56

1.3.5.1 Flat assemblies 56

1.3.5.2 Cavities 59

1.3.5.3 Pipes 61

1.4 Radiation 61

1.4.1 What is thermal radiation? 61

1.4.2 Quantities 62

1.4.3 Reflection, absorption and transmission 62

1.4.4 Radiant surfaces or bodies 64

1.4.5 Black bodies 65

1.4.5.1 Characteristics 65

1.4.5.2 Radiant exchange between two black bodies: the view factor 67

1.4.5.3 Properties of view factors 69

1.4.5.4 Calculating view factors 69

1.4.6 Grey bodies 72

1.4.6.1 Characteristics 72

1.4.6.2 Radiant exchange between grey bodies 73

1.4.7 Coloured bodies 75

1.4.8 Practical formulae 75

1.5 Applications 77

1.5.1 Surface film coefficients and reference temperatures 77

1.5.1.1 Overview 77

1.5.1.2 Indoor environment 77

1.5.1.3 Outdoor environment 81

1.5.2 Steady state, one dimension: flat assemblies 84

1.5.2.1 Thermal transmittance and interface temperatures 84

1.5.2.2 Thermal resistance of a non ventilated, infinite cavity 88

1.5.2.3 Solar transmittance 90

1.5.3 Steady state, cylindrical coordinates: pipes 93

1.5.4 Steady state, two and three dimensions: thermal bridges 94

1.5.4.1 Calculation by the control volume method (CVM) 94

1.5.4.2 Practice 95

1.5.5 Steady state: windows 98

1.5.6 Steady state: building envelopes 99

1.5.6.1 Overview 99

1.5.6.2 Average thermal transmittance 99

1.5.7 Transient, periodic: flat assemblies 100

1.5.8 Heat balances 101

1.5.9 Transient, periodic: spaces 102

1.5.9.1 Assumptions 102

1.5.9.2 Steady state heat balance 102

1.5.9.3 Harmonic heat balances 103

1.6 Problems 107

1.7 Literature 120

2 Mass Transfer 123

2.1 Generalities 123

2.1.1 Quantities and definitions 123

2.1.2 Saturation degrees 125

2.1.3 Air and moisture transfer 126

2.1.4 Moisture sources 128

2.1.5 Air, moisture and durability 129

2.1.6 Link between mass and energy transfer 130

2.1.7 Conservation of mass 131

2.2 Air transfer 132

2.2.1 Overview 132

2.2.2 Air pressure differences 133

2.2.2.1 Wind 133

2.2.2.2 Stack effects 134

2.2.2.3 Fans 135

2.2.3 Air permeances 135

2.2.4 Air transfer in open-porous materials 139

2.2.4.1 Conservation of mass 139

2.2.4.2 Flow equation 139

2.2.4.3 Air pressures 139

2.2.4.4 One dimension: flat assemblies 140

2.2.4.5 Two and three dimensions 142

2.2.5 Air flow across permeable layers, apertures, joints, leaks and cavities 143

2.2.5.1 Flow equations . 143

2.2.5.2 Conservation of mass: equivalent hydraulic circuit 143

2.2.6 Air transfer at building level 144

2.2.6.1 Definitions 144

2.2.6.2 Thermal stack 145

2.2.6.3 Large openings 145

2.2.6.4 Conservation of mass 146

2.2.6.5 Applications 148

2.2.7 Combined heat and air transfer 151

2.2.7.1 Open-porous materials 151

2.2.7.2 Air permeable layers, joints, leaks and cavities 157

2.3 Vapour transfer 160

2.3.1 Water vapour in the air 160

2.3.1.1 Overview 160

2.3.1.2 Quantities 161

2.3.1.3 Maximum vapour pressure and relative humidity 161

2.3.1.4 Changes of state in humid air 166

2.3.1.5 Enthalpy of humid air 166

2.3.1.6 Measuring air humidity 167

2.3.1.7 Applications 167

2.3.2 Water vapour in open-porous materials 172

2.3.2.1 Overview 172

2.3.2.2 Sorption isotherm and specific moisture ratio 173

2.3.2.3 Physics involved 174

2.3.2.4 Impact of salts 177

2.3.2.5 Consequences 177

2.3.3 Vapour transfer in the air 177

2.3.4 Vapour transfer in materials and assemblies 179

2.3.4.1 Flow equation 179

2.3.4.2 Conservation of mass 182

2.3.4.3 Vapour transfer by ‘equivalent’ diffusion 182

2.3.4.4 Vapour transfer by ‘equivalent’ diffusion and convection 197

2.3.5 Surface film coefficients for diffusion 204

2.3.6 Applications 207

2.3.6.1 Diffusion resistance of a cavity 207

2.3.6.2 Cavity ventilation 207

2.3.6.3 Water vapour balance in a space: surface condensation and drying 210

2.4 Moisture transfer 211

2.4.1 Overview 211

2.4.2 Moisture transfer in a pore 211

2.4.2.1 Capillarity 211

2.4.2.2 Water transfer 213

2.4.2.3 Vapour transfer 222

2.4.2.4 Moisture transfer 224

2.4.3 Moisture transfer in materials and assemblies 224

2.4.3.1 Transport equations 224

2.4.3.2 Conservation of mass 227

2.4.3.3 Starting, boundary and contact conditions 227

2.4.3.4 Remark 228

2.4.4 Simplifying moisture transfer 228

2.4.4.1 The model 228

2.4.4.2 Applications 230

2.5 Problems 245

2.6 Literature 263

3 Combined heat-air-moisture transfer 267

3.1 Overview 267

3.2 Material and assembly level 267

3.2.1 Assumptions 267

3.2.2 Solution 267

3.2.3 Conservation laws 268

3.2.3.1 Mass 268

3.2.3.2 Energy 269

3.2.4 Flow equations 272

3.2.4.1 Heat 272

3.2.4.2 Mass, air 272

3.2.4.3 Mass, moisture 273

3.2.5 Equations of state 273

3.2.5.1 Enthalpy/temperature, vapour saturation pressure/temperature 273

3.2.5.2 Relative humidity/moisture content 273

3.2.5.3 Suction/moisture content 273

3.2.6 Starting, boundary and contact conditions 274

3.2.6.1 Starting conditions 274

3.2.6.2 Boundary conditions 274

3.2.6.3 Contact conditions 274

3.2.7 Two examples of simplified models 275

3.2.7.1 Non hygroscopic, non capillary materials 275

3.2.7.2 Hygroscopic materials at low moisture content 276

3.3 Building level 277

3.3.1 Overview 277

3.3.2 Balance equations 277

3.3.2.1 Vapour 277

3.3.2.2 Air 279

3.3.2.3 Heat 279

3.3.2.4 Closing the loop 282

3.3.3 Hygric inertia 283

3.3.3.1 Generalities 283

3.3.3.2 Sorption-active thickness 283

3.3.3.3 Zone with one sorption-active surface 286

3.3.3.4 Zone with several sorption-active surfaces 287

3.3.3.5 Harmonic analysis 288

3.3.4 Consequences 289

3.3.4.1 Steady state 289

3.3.4.2 Transient 289

3.4 Problems 292

3.5 Literature 303

Postscript 305

Problems and Solutions 307

 

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Prof. em. Dr.-Ing. Hugo S. L. C. Hens, Katholische Universität Löwen/Belgien, lehrte Bauphysik von 1975 bis 2003, Gebäudeplanung von 1970 bis 2005 und Technische Gebäudeausrüstung von 1975 bis 1977 sowie von 1990 bis 2008. Bis 1972 war er als Tragwerksplaner für Wohnhäuser, Büro- und Geschossbauten in einem Architekturbüro tätig. Er hat als Autor bzw. Koautor über 150 Veröffentlichungen verfasst und hunderte Schadensgutachten erstellt. Während zehn Jahren koordinierte er die internationale Arbeitsgruppe CIB W40 "Heat and Mass Transfer in Buildings". Von 1986 bis 2008 war er im Rahmen des Forschungsprogramms "Energy Conservation in Buildings and Community Systems" der Internationalen Energieagentur IEA für die Erarbeitung von Annex 14, Annex 24, Annex 32 und Annex 41 verantwortlich. Er ist Mitglied der American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE).
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