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Building Physics -- Heat, Air and Moisture: Fundamentals and Engineering Methods with Examples and Exercises

Building Physics -- Heat, Air and Moisture: Fundamentals and Engineering Methods with Examples and Exercises

Hugo S. L. Hens

ISBN: 978-3-433-60130-3

Jan 2012

284 pages


Bad experiences with construction quality, the energy crises of 1973 and 1979, complaints about 'sick buildings', thermal, acoustical, visual and olfactory discomfort, the move towards more sustainability, have all accelerated the development of a field, which until 35 years ago was hardly more than an academic exercise: building physics.
Through the application of existing physical knowledge and the combination with information coming from other disciplines, the field helps to understand the physical performance of building parts, buildings and the built environment, and translates it into correct design and construction.
This book is the result of thirty years teaching, research and consultancy activity of the author.
The book discusses the theory behind the heat and mass transport in and through building components. Steady and non steady state heat conduction, heat convection and thermal radiation are discussed in depth, followed by typical building-related thermal concepts such as reference temperatures, surface film coefficients, the thermal transmissivity, the solar transmissivity, thermal bridging and the periodic thermal properties. Water vapour and water vapour flow and moisture flow in and through building materials and building components is analyzed in depth, mixed up with several engineering concepts which allow a first order analysis of phenomena such as the vapour balance, the mold, mildew and dust mites risk, surface condensation, sorption, capillary suction, rain absorption and drying. In a last section, heat and mass transfer are combined into one overall model staying closest to the real hygrothermal response of building components, as observed in field experiments.
The book combines the theory of heat and mass transfer with typical building engineering applications. The line from theory to application is dressed in a correct and clear way. In the theory, oversimplification is avoided.
This book is the result of thirty years teaching, research and consultancy activity of the author.

0 Introduction.

0.1 Subject of the Book.

0.2 Building Physics.

0.2.1 Definition.

0.2.2 Criteria. Comfort. Health. Architectural and Material Facts. Economy. Environment.

0.3 Importance of Building Physics.

0.4 History of Building Physics.

0.5 References.

0.6 Units and Symbols.

1 Heat Transfer.

1.1 Overview.

1.2 Conduction.

1.2.1 Conservation of Energy.

1.2.2 Fourier’s Laws. First Law. Second Law.

1.2.3 Steady State. What Is It? One Dimension: Flat Walls. Two Dimensions: Cylinder Symmetry. Two and Three Dimensions: Thermal Bridges.

1.2.4 Transient Regime. What is Transient? Flat Walls, Periodic Boundary Conditions. Flat Walls, Transient Boundary Conditions. Two and Three Dimensions.

1.3 Convection.

1.3.1 Overview. Heat Transfer at a Surface. Convection.

1.3.2 Convection Typology. Driving Forces. Type of flow.

1.3.3 Calculating the Convective Surface Film Coefficient. Analytically. Numerically. Dimensional Analysis.

1.3.4 Values for the Convective Surface Film Coefficient. Walls. Cavities. Pipes.

1.4 Radiation.

1.4.1 Overview. Thermal Radiation. Quantities. Reflection, Absorption and Transmission. Radiant Surfaces.

1.4.2 Black Bodies. Characteristics. Radiation Exchange Between Two Black Bodies: The Angle Factor. Properties of Angle Factors. Calculating Angle Factors.

1.4.3 Grey Bodies. Characteristics. Radiation Exchange Between Grey Bodies.

1.4.4 Colored Bodies.

1.4.5 Practical Formulae.

1.5 Applications.

1.5.1 Surface Film Coefficients and Reference Temperatures. Overview. Inside Environment. Outside Environment.

1.5.2 Steady-state, One-dimension: Flat Walls. Thermal Transmittance and Interface Temperatures. Thermal Resistance of a Non-ventilated Infinite Cavity. Solar Transmittance.

1.5.3 Steady State, Cylindrical Coordinates: Pipes.

1.5.4 Steady-state, Two and Three Dimensions: Thermal Bridges. Calculation by the Control Volume Method (CVM). Thermal Bridges in Practice.

1.5.5 Transient, Periodic: Flat Walls.

1.5.6 Heat Balances.

1.6 Problems.

1.7 References.

2 Mass Transfer.

2.1 In General.

2.1.1 Quantities and Definitions.

2.1.2 Saturation Degree Scale.

2.1.3 Air and Moisture Transfer.

2.1.4 Moisture Sources.

2.1.5 Air, Moisture and Durability.

2.1.6 Linkages between Mass-and Energy Transfer.

2.1.7 Conservation of Mass.

2.2 Air Transfer.

2.2.1 In General.

2.2.2 Air Pressure Differences. Wind. Stack Effects. Fans.

2.2.3 Air Permeances.

2.2.4 Air Transfer in Open-porous Materials. Conservation of Mass. Flow Equation. Air Pressures. One Dimension: Flat Walls. Two- and Three-dimensions.

2.2.5 Air Flow Through Permeable Layers, Apertures, Joints, Leaks and Cavities. Flow Equations. Conservation of Mass, Equivalent Hydraulic Circuit.

2.2.6 Combined Heat- and Air Transfer. Open-porous Materials. Air Permeable Layers, Joints, Leaks and Cavities.

2.3 Vapour Transfer.

2.3.1 Water Vapour in the Air. Overview. Quantities. Maximum Vapour Pressure and Relative Humidity. Changes of State in Humid Air. Enthalpy of Moist Air. Characterizing Moist Air. Applications.

2.3.2 Water Vapour in Open-porous Materials. Overview. Sorption Isotherm and Specific Moisture Ratio. The Physics Behind. Impact of Salts. Consequences.

2.3.3 Vapour Transfer in the Air.

2.3.4 Vapour Transfer in Materials and Construction Parts. Flow Equation. Conservation of Mass. Vapour Transfer by ‘Equivalent’ Diffusion. Vapour Transfer by (Equivalent) Diffusion and Convection.

2.3.5 Surface Film Coeffi cients for Diffusion.

2.3.6 Some Applications. Diffusion Resistance of a Cavity. Cavity Ventilation. Water Vapour Balance in a Room in Case of Surface Condensation and Drying.

2.4 Moisture Transfer.

2.4.1 Overview.

2.4.2 Moisture Transfer in a Pore. Capillarity. Water Transfer. Vapour Transfer. Moisture Transfer.

2.4.3 Moisture Transfer in Materials and Construction Parts. Transfer Equations. Conservation of Mass. Starting, Boundary and Contact Conditions. Remark.

2.4.4 Simplified Moisture Transfer Model. Assumptions. Applications.

2.5 Problems.

2.6 References.

3 Combined Heat, Air and Moisture Transfer.

3.1 Overview.

3.2 Assumptions.

3.3 Solution.

3.4 Conservation Laws.

3.4.1 Conservation of Mass.

3.4.2 Conservation of Energy.

3.5 Flow Equations.

3.5.1 Heat.

3.5.2 Mass, Air. Open Porous Materials. Air Permeable Layers, Apertures, Joints, Cracks, Leaks and Cavities.

3.5.3 Mass, Moisture. Water Vapour. Water.

3.6 Equations of State.

3.6.1 Enthalpy/Temperature and Water Vapour Saturation Pressure/Temperature.

3.6.2 Relative Humidity/Moisture Content.

3.6.3 Suction/Moisture Content.

3.7 Starting, Boundary and Contact Conditions.

3.7.1 Starting Conditions.

3.7.2 Boundary Conditions.

3.7.3 Contact Conditions.

3.8 Two Examples of Simplified Models.

3.8.1 Heat, Air and Moisture Transfer in Non-Hygroscopic, Non-Capillary Materials.

3.8.2 Heat, Air and Moisture Transfer in Hygroscopic Materials at Low Moisture Content.

3.9 References.

4 Postscript.

Das Buch Building Physics von Hugo Hens ist ein englischsprachiges Fachbuch, das sich mit den Themen Wärme, Luft und Feuchtigkeit befasst. Die Tatsache, dass der Autor Professor an einer europäischen Universität ist (K.U. Leuven), kommt dem Lesen des englischsprachen Textes sehr entgegen. Die Kapitel sind -wenn auch sehr wissenschaftlich -dennoch gut verständlich. Damit bieten sie eine gute Grundlage, insbesondere für Studenten, die englischen Fachbegriffe zu den genannten Themen aufzunehmen. Der Spagat zwischen wissenschaftlichen Grundlagen und der Erläuterung bauphysikalischer Praxisprobleme gelingt dem Autor gut. Für eine Neuauflage wäre zur Vervollständigung des Gebietes der Bauphysik eine Ergänzung der bau- und raumakustischen Themen wünschenswert.
Dr. Normen Langner, Bauhaus Universität Weimar