Building Physics Heat, Air and Moisture

Contents

Preface

Acknowledgements

0: Introduction

0.1 Subject of the Book

0.2 Building Physics

0.2.1 Definition

0.2.2 Constraints

0.2.2.1 Comfort

0.2.2.2 Health and Wellbeing

0.2.2.3 Architecture and Materials

0.2.2.4 Economy

0.2.2.5 Sustainability

0.3 Importance

0.4 History

0.4.1 Applied Physics

0.4.1.1 Heat, Air and Moisture

0.4.1.2 Acoustics

0.4.1.3 Lighting

0.4.2 Thermal Comfort and Indoor Air Quality

0.4.3 Building Services

0.4.4 Building Design and Construction

0.4.5 The Situation at the University of Leuven (KULeuven) and Elsewhere

0.5 Units

0.6 Symbols

Further Reading

1: Heat Transfer

1.1 Overview

1.1.1 Heat

1.1.2 Temperature

1.1.3 Sensible and Latent Heat

1.1.4 Why are Heat and Temperature So Compelling?

1.1.5 Some Definitions

1.2 Conduction

1.2.1 Conservation of Energy

1.2.2 The Conduction Laws

1.2.2.1 First Law

1.2.2.2 Second Law

1.2.3 Steady State

1.2.3.1 One-Dimensional Flat Assemblies

1.2.3.2 Two Dimensions, Cylinder Symmetric

1.2.3.3 Two and Three Dimensions: Thermal Bridges

1.2.4 Transient

1.2.4.1 Periodic Boundary Conditions: Flat Assemblies

1.2.4.2 Any Boundary Conditions: Flat Assemblies

1.2.4.3 Two and Three Dimensions: Thermal Bridges

1.3 Heat Exchange at Surfaces

1.4 Convection

1.4.1 In General

1.4.2 Typology

1.4.2.1 Driving Forces

1.4.2.2 Flow Types

1.4.3 Quantifying the Convective Surface Film Coefficient

1.4.3.1 Analytically

1.4.3.2 Numerically

1.4.3.3 Dimensionally

1.4.4 Values for the Convective Surface Film Coefficient

1.4.4.1 Flat Surfaces

1.4.4.2 Cavities

1.4.4.3 Pipes

1.5 Radiation

1.5.1 In General

1.5.2 Definitions

1.5.3 Reflection, Absorption and Transmission

1.5.4 Radiant Bodies

1.5.4.1 Black

1.5.4.2 Grey

1.5.4.3 Coloured

1.5.5 Simple Formulae

1.6 Building-Related Applications

1.6.1 Surface Film Coefficients and Reference Temperatures

1.6.1.1 Indoors

1.6.1.2 Outdoors

1.6.2 Steady State: Flat Assemblies

1.6.2.1 Thermal Transmittance of Envelope Parts and Partitions

1.6.2.2 Average Thermal Transmittance of Parts in Parallel

1.6.2.3 Electrical Analogy

1.6.2.4 Thermal Resistance of an Unvented Cavity

1.6.2.5 Interface Temperatures

1.6.2.6 Solar Transmittance

1.6.3 Local Inside Surface Film Coefficients

1.6.4 Steady State: Two and Three Dimensions

1.6.4.1 Pipes

1.6.4.2 Floors on Grade

1.6.4.3 Thermal Bridges

1.6.4.4 Windows

1.6.4.5 Building Envelopes

1.6.5 Heat Balances

1.6.6 Transient

1.6.6.1 Periodic: Flat Assemblies

1.6.6.2 Periodic: Spaces

1.6.6.3 Thermal Bridges

1.7 Problems and Solutions

Further reading

2: Mass Transfer

2.1 Generalities

2.1.1 Quantities and Definitions

2.1.2 Saturation Degrees

2.1.3 Air and Moisture Transfer

2.1.4 Moisture Sources

2.1.5 Air and Moisture in Relation to Durability

2.1.6 Links to Energy Transfer

2.1.7 Conservation of Mass

2.2 Air

2.2.1 Overview

2.2.2 Air Pressure Differentials

2.2.2.1 Wind

2.2.2.2 Stack

2.2.2.3 Fans

2.2.3 Air Permeances

2.2.4 Airflow in Open-Porous Materials

2.2.4.1 The Conservation Law Adapted

2.2.4.2 One Dimension: Flat Assemblies

2.2.4.3 Two and Three Dimensions

2.2.5 Airflow Across Assemblies with Air-Open Layers, Leaky Joints, Leaks and Cavities

2.2.6 Air Transfer at the Building Level

2.2.6.1 Definitions

2.2.6.2 Thermal Stack

2.2.6.3 Large Openings

2.2.6.4 The Conservation Law Applied

2.2.6.5 Applications

2.2.7 Combined Heat and Air Flow in Open-Porous Materials

2.2.7.1 Heat Balance Equation

2.2.7.2 Steady State: Flat Assemblies

2.2.7.3 Steady State: Two and Three Dimensions

2.2.7.4 Transient: Flat Assemblies

2.2.7.5 Transient: Two and Three Dimensions

2.2.7.6 Air Permeable Layers, Joints, Leaks and Cavities

2.2.7.7 Vented Cavity

2.3 Water Vapour

2.3.1 Water Vapour in the Air

2.3.1.1 Overview

2.3.1.2 Quantities

2.3.1.3 Vapour Saturation Pressure

2.3.1.4 Relative Humidity

2.3.1.5 Changes of State in Humid Air

2.3.1.6 Enthalpy of Humid Air

2.3.1.7 Measuring Air Humidity

2.3.1.8 Vapour Balance Indoors

2.3.1.9 Relative Humidity at a Surface

2.3.2 Vapour in Open-Porous Materials

2.3.2.1 Different Compared with Air?

2.3.2.2 Sorption/Desorption Isotherm and Specific Moisture Ratio

2.3.3 Vapour Transfer in the Air

2.3.4 Vapour Flow by Diffusion in Open-Porous Materials and Assemblies

2.3.4.1 Flow Equation

2.3.4.2 Mass Conservation

2.3.4.3 Applicability of the Diffusion Concept

2.3.4.4 Steady State: Flat Assemblies

2.3.4.5 Steady State: Two and Three Dimensions

2.3.4.6 Transient Regime

2.3.5 Vapour Flow by Diffusion and Convection in Open-Porous Materials and Assemblies

2.3.6 Surface Film Coefficients for Diffusion

2.3.7 The Surface Film Coefficient for Diffusion Applied

2.3.7.1 Diffusion Resistance of an Unvented Cavity

2.3.7.2 Do Vented Cavities Enhance Drying?

2.3.7.3 Surface Condensation and the Vapour Balance Indoors

2.4 Moisture

2.4.1 Overview

2.4.2 Water Flow in a Pore

2.4.2.1 Capillarity

2.4.2.2 Poiseuille's Law

2.4.2.3 Isothermal Water Flow in a Pore Contacting Water

2.4.2.4 Isothermal Water Flow in a Pore After Water Contact

2.4.2.5 Non-Isothermal Water Flow in a Pore After Water Contact

2.4.2.6 Remark

2.4.3 Vapour Flow in a Pore That Contains Water Isles

2.4.3.1 Isothermal

2.4.3.2 Non-Isothermal

2.4.4 Moisture Flow in a Pore that Contains Water Isles

2.4.5 Moisture Flow in Materials and Assemblies

2.4.5.1 Transport Equations

2.4.5.2 Moisture Permeability

2.4.5.3 Mass Conservation

2.4.5.4 Starting, Boundary and Contact Conditions

2.4.5.5 Remarks

2.4.6 Simplified Moisture Flow Model

2.4.6.1 How it Looks

2.4.6.2 Applying the Simplified Model

2.5 Problems and Solutions

Further Reading

3: Combined Heat, Air and Moisture Flow

3.1 Introduction

3.2 Material and Assembly Level

3.2.1 Assumptions

3.2.2 Solution

3.2.3 Conservation of Mass

3.2.4 Conservation of Energy

3.2.5 Flux Equations

3.2.5.1 Heat

3.2.5.2 Mass, air

3.2.5.3 Mass, Moisture

3.2.6 Equations of State

3.2.6.1 Enthalpy and Vapour Saturation Pressure Versus Temperature

3.2.6.2 Relative Humidity Versus Moisture Content

3.2.6.3 Suction Versus Moisture Content

3.2.7 Starting, Boundary and Contact Conditions

3.2.8 Two Examples of Simplified Models

3.2.8.1 Non-Hygroscopic, Non-Capillary Materials

3.2.8.2 Hygroscopic Materials at Low Moisture Content

3.3 Whole Building Level

3.3.1 Balance Equations

3.3.1.1 Vapour

3.3.1.2 Air

3.3.1.3 Heat

3.3.1.4 Closing the Loop

3.3.2 Sorption-Active Surfaces and Hygric Inertia

3.3.2.1 Generalities

3.3.2.2 Sorption-Active Thickness

3.3.2.3 Zone with One Sorption-Active Surface

3.3.2.4 Zone with several sorption-active surfaces

3.3.2.5 Harmonic Analysis

3.3.3 Consequences

3.4 Problems and Solutions

Further Reading

Postscript

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