Building Physics - Heat, Air and Moisture

Dr. Ir. Hugo S.L.C. Hens is an emeritus professor of the University of Leuven (KULeuven), Belgium. Till 1972, he worked as a structural engineer and site supervisor at a mid-sized architectural office. In 1975, after his predecessor and promotor professor A. de Grave suddenly passed away and after defending his PhD-thesis, he stepwise developed the unit Building Physics at the Civil Engineering Department. He taught Building Physics from 1975 till 2003, Performance Based Building Design from 1975 till 2005 and Building Services from 1975 till 1977 and from 1990 till 2008. Hugo Hens authored and co-authored 68 peer reviewed journal and 174 conference papers about the research done, helped curing hundreds of building damage cases and acted as coordinator of the CIB W40 working group on Heat and Mass Transfer in Buildings from 1983 till 1993. Between 1986 and 2008, he was operating agent of the Annexes 14, 24, 32 and 41 of the IEA EXCO on Energy in Buildings and Communities. He is a fellow of the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE).

• Preface xvAbout the Author xixList of Units and Symbols xxi0 Introduction 10.1 Subject of the Book 10.2 Building Physics? 10.2.1 Definition 10.2.2 Constraints 20.2.2.1 Comfort 20.2.2.2 Health andWell-being 30.2.2.3 Architecture and Materials 30.2.2.4 Economy 30.2.2.5 Sustainability 30.3 Importance? 40.4 History 50.4.1 In General 50.4.2 Applied Physics 50.4.2.1 Heat, Air, Moisture 50.4.2.2 Acoustics 80.4.2.3 Lighting 90.4.3 Indoor Air Quality and Thermal Comfort 90.4.4 Building Services 110.4.5 Building Design and Construction 110.4.6 Hall of Fame 120.4.7 Building Physics at the KULeuven and Other Universities in the Low Countries 13Further Reading 151 Heat Transfer 171.1 In General 171.1.1 Heat 171.1.1.1 What? 171.1.1.2 Sensible Heat 171.1.1.3 Latent Heat 181.1.2 Temperature 181.1.3 Why are Heat and Temperature so Compelling? 181.1.4 Some Definitions 191.2 Conduction 191.2.1 Conservation of Energy 191.2.2 Conduction Laws 201.2.2.1 First Law 201.2.2.2 Second Law 221.2.3 Thermal Conductivity 221.2.3.1 In General 221.2.3.2 Heat Transfer Modes Fixing the Property 221.2.4 Steady-State 261.2.4.1 What? 261.2.4.2 One Dimension, Flat Assemblies 271.2.4.3 Two Dimensions, Cylinder Symmetric 331.2.4.4 Two and Three Dimensions: Thermal Bridges 351.2.5 Non-steady-state 381.2.5.1 In General 381.2.5.2 Periodic Boundary Conditions, Flat Assemblies 391.2.5.3 Any Boundary Conditions, Flat Assemblies 481.2.5.4 Two and Three Dimensions: Thermal Bridges 521.3 Heat Exchange at Surfaces by Convection and Radiation 521.3.1 What? 521.3.2 Convection 531.3.2.1 In General 531.3.2.2 Typology 551.3.2.3 Quantifying the Convective Surface Film Coefficient 551.3.2.4 Values for the Convective Surface Film Coefficient 581.3.3 Radiation 631.3.3.1 In General 631.3.3.2 Definitions 631.3.3.3 Reflection, Absorption and Transmission 641.3.3.4 Radiant Surfaces 661.3.3.5 Simple Formulae 741.4 Building-related Applications 761.4.1 Surface Film Coefficients and Reference Temperatures 761.4.1.1 Methodology 761.4.1.2 Indoors 761.4.1.3 Outdoors 781.4.2 Steady-state, Flat Assemblies 801.4.2.1 Thermal Transmittance of Envelope Assemblies, Partitions and PartyWalls 801.4.2.2 Average Thermal Transmittance of Envelope Parts in Parallel 831.4.2.3 Electrical Analogy 841.4.2.4 Thermal Resistance of Non-ventilated Cavities 841.4.2.5 Interface Temperatures 861.4.2.6 Effect of Ever Thicker Insulation Layers on the Thermal Transmittance 871.4.2.7 Solar Transmittance 881.4.3 Local Inside Surface Film Coefficients 911.4.4 Steady-state: Two and Three Dimensions 921.4.4.1 Pipes 921.4.4.2 Floors on Grade 931.4.4.3 Thermal Bridges 941.4.4.4 Windows 981.4.4.5 Building Envelopes 991.4.5 Heat Balances 1001.4.6 Non-steady-state 1011.4.6.1 Periodic Boundary Conditions: Flat Assemblies 1011.4.6.2 Periodic Boundary Conditions: Spaces 1011.4.6.3 Any Boundary Conditions: Thermal Bridges 105Problems and Solutions 106Further Reading 1182 Mass Transfer 1212.1 In General 1212.1.1 Facts 1212.1.2 Definitions 1222.1.3 Saturation Degree Scale 1232.1.4 Air and Moisture Transfer 1232.1.5 Moisture Sources 1252.1.6 Air and Moisture in Relation to Durability 1272.1.7 Links with Energy Transfer 1272.1.8 Conservation of Mass 1282.2 Air 1292.2.1 In General 1292.2.2 Air Pressure Differentials 1302.2.2.1 Wind 1302.2.2.2 Stack Effect 1302.2.2.3 Fans 1332.2.3 Air Permeability and Air Permeances 1332.2.4 Airflow in Open-porous Materials 1352.2.4.1 The Conservation Law Adapted 1352.2.4.2 One Dimension: Flat Assemblies 1382.2.4.3 Two and Three Dimensions 1392.2.5 Airflow Through Assemblies with Air-open Layers, Leaky Joints, Leaks, Cavities, etc. 1402.2.6 Airflow at the Building Level 1412.2.6.1 Definitions 1412.2.6.2 Thermal Stack 1422.2.6.3 Large Openings 1422.2.6.4 The Conservation Law Applied 1432.2.6.5 Applications 1452.2.7 Combined Heat and Airflow Through Assemblies Composed of Open-porous Layers 1482.2.7.1 Heat Balance 1482.2.7.2 Steady-state: Flat Assemblies 1482.2.7.3 Steady-state, Two and Three Dimensions 1522.2.7.4 Non-steady-state, Flat Assemblies 1522.2.7.5 Non-steady-state, Two and Three Dimensions 1532.2.7.6 Air-permeable Layers, Joints and Leaks 1532.2.7.7 Vented Cavities 1532.3 Water Vapour 1562.3.1 Water Vapour in the Air 1562.3.1.1 In General 1562.3.1.2 Quantities 1562.3.1.3 Vapour Saturation Pressure 1572.3.1.4 Relative Humidity 1572.3.1.5 Changes of State in Humid Air 1612.3.1.6 Enthalpy of Humid Air 1622.3.1.7 Measuring Air Humidity 1622.3.2 Vapour Balance in Spaces 1632.3.3 Relative Humidity On Inside Surfaces 1652.3.4 Vapour in Open-porous Materials 1682.3.4.1 Different from Air? 1682.3.4.2 Sorption/Desorption Isotherm 1682.3.5 Vapour Transfer in the Air 1722.3.6 Vapour Flow by Diffusion in Open-porous Materials and Building Assemblies 1742.3.6.1 Flow Equation 1742.3.6.2 Vapour Resistance Factor μ 1752.3.6.3 Mass Conservation 1762.3.6.4 Applicability of the Diffusion Concept 1772.3.6.5 Steady State: Flat Assemblies 1772.3.6.6 Steady State: Two and Three Dimensions 1862.3.6.7 Non-steady State 1872.3.7 Vapour Flow by Diffusion and Moist Air Moving Through Open-porous Assemblies 1892.3.7.1 In General 1892.3.7.2 Isothermal, Single- and Multi-layered Assemblies 1902.3.7.3 Non-isothermal, Single- and Multi-layered Assemblies 1912.3.8 Surface Film Coefficients for Diffusion 1952.3.8.1 Derivation 1952.3.8.2 Applications 1982.3.9 Evaluating Interstitial Condensation in Practice 2012.3.9.1 Boundary Conditions Used 2012.3.9.2 Calculation Sequence 2032.3.9.3 Example 2042.4 Moisture 2092.4.1 In General 2092.4.2 Water Flow in a Pore 2092.4.2.1 Capillarity 2092.4.2.2 Poiseuille’s Law 2112.4.2.3 IsothermalWater Flow in a Pore ContactingWater 2122.4.2.4 IsothermalWater Flow in a Pore AfterWater Contact 2182.4.2.5 Non-isothermalWater Transfer in a Pore AfterWater Contact 2182.4.2.6 Remark 2192.4.3 Vapour Flow in a Pore ContainingWater Isles with Air Inclusions in Between 2192.4.3.1 A Short Description 2192.4.3.2 Isothermal 2192.4.3.3 Non-isothermal 2202.4.4 Moisture Flow in and Through Materials and Assemblies 2212.4.4.1 Transport Equations 2212.4.4.2 Moisture Permeability 2232.4.4.3 Mass Conservation 2232.4.4.4 Starting, Boundary and Contact Conditions 2242.4.4.5 Remarks 2242.4.5 Simple Moisture Flow Model 2252.4.5.1 How to Do? 2252.4.5.2 Applying the Simple Model 227Problems and Solutions 240Further Reading 2613 Heat, Air and Moisture Combined 2653.1 Why? 2653.2 Material and Assembly Level 2653.2.1 Assumptions 2653.2.2 Solution 2663.2.3 Conservation of Mass 2663.2.4 Conservation of Energy 2673.2.5 Flux Equations 2703.2.5.1 Heat 2703.2.5.2 Mass, Air 2703.2.5.3 Mass, Moisture 2703.2.5.4 Remark 2713.2.6 Equations of State 2713.2.6.1 Enthalpy and Vapour Saturation Pressure in Relation to Temperature 2713.2.6.2 Relative Humidity in Relation to Moisture Content 2713.2.6.3 Suction in Relation to Moisture Content 2713.2.7 Start, Boundary and Contact Conditions 2713.2.8 Two Examples of Simplified Models 2723.2.8.1 Assemblies Composed of Non-Hygroscopic, Non-Capillary Materials 2723.2.8.2 Assemblies Composed of Fine Porous, Hygroscopic Materials 2743.3 Whole Building Level 2743.3.1 In General 2743.3.2 Balance Equations 2753.3.2.1 Vapour 2753.3.2.2 Air 2763.3.2.3 Heat 2763.3.2.4 Closing the Loop 2783.3.3 Sorption Active Surfaces and Hygric Inertia 2793.3.3.1 In General 2793.3.3.2 Sorption-Active Thickness 2803.3.3.3 Zone with One Sorption-Active Surface 2823.3.3.4 Zone with Several Sorption-Active Surfaces 2833.3.3.5 Harmonic Analysis 2843.3.4 Consequences 284Problems and Solutions 287Further Reading 3004 Heat, Air and Moisture Material Property Values 3034.1 In General 3034.2 Dry Air andWater 3044.3 Thermal Properties 3054.3.1 Definitions 3054.3.2 Standard Values 3054.3.2.1 Regardless of Being on the In- or on the Outside of the Thermal Insulation 3054.3.2.2 Depending on Being on the In- or on the Outside of the Thermal Insulation 3094.3.3 Surfaces, Radiant Properties 3164.3.4 Measured Values 3174.3.4.1 Thermal Conductivity, Test Methods 3174.3.4.2 Test Results 3184.4 Air Properties 3254.4.1 Standard Values 3254.4.2 Measured Values 3254.4.2.1 Air Permeance, Test Method 3254.4.2.2 Test Results 3274.5 Moisture Properties 3364.5.1 Standard Values 3364.5.1.1 Building and Finishing Materials 3364.5.1.2 Insulation Materials 3404.5.2 Measured Values 3404.5.2.1 Diffusion Resistance Factor (μ), Test Method 3404.5.2.2 Test Results 342Further Reading 357Postscript 359Index 361