1807–2007 Knowledge for Generations

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Peter Booth Wiley
Chairman of the Board

Professor Dr. Ir. Hugo S.L.C. Hens
K.U. Leuven
Faculty of Engineering
Department of Civil Engineering
Laboratory of Building Physics
Kasteelpark Arenberg, 40
3001 Leuven
Belgium

Cover illustration: Thermal bridge, calculated with TRYSCO (Physibel CV, Maldegem, Belgium)

Bibliographic information publishd by the Deutsche Nationalbibliothek
The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie;
detailed bibliographic data are available in the Internet at http://dnb.d-nb.de>

ISBN 978-3-433-01841-5

©2007 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH und Co. KG, Berlin

All rights reserved (including those of translation into other languages). No part of this book may be reproduced in any form – by photoprinting, microfilm, or any other means – nor transmitted or translated into a machine language without written permission from the publisher. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law.

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Printing: Strauss GmbH, Mör|enbach

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Wiley Bicentennia| Logo: Richard J. Pacifico

To my wife, children and grandchildren

In remembrance of Professor A. de Grave,
who introduced Building Physics as a new discipline
at the University of Louvain, K. U. Leuven, Belgium, in 1952

Preface

Overview

Until the first energy crisis of 1973, building physics survived as a somewhat dormant field in building engineering, with seemingly limited applicability in practice. While soil mechanics, structural mechanics, building materials, building construction and HVAC were seen as essential, designers only demanded advice on room acoustics, moisture tolerance, summer comfort or lighting when really needed or when, after construction of their designs, when problems arose. Energy was even not a concern, while indoor environmental quality was presumably guaranteed thanks to the ever present infiltration, to opening windows and to the heating system. The energy crises of the seventies, persisting moisture problems, complaints about sick buildings, thermal, visual and olfactory discomfort, the move towards more sustainability, changed it all. The societal pressure to diminish energy consumptions in buildings without degrading usability acted as a trigger that activated the whole notion of performance based design and construction. As a result, building physics and its potentiality to quantify performances was suddenly pushed to the frontline of building innovation.

As all engineering sciences, building physics is oriented towards application. Hence, creativity in application demands a sound knowledge of the basics in each of the branches building physics encompasses: heat and mass, acoustics, lighting, energy and indoor environmental quality. Integrating these basics into an up to date text on heat and mass has been the main goal of this book, with mass limited to air, water vapour and moisture. The book is the result of thirty years of teaching architectural, building and civil engineers, coupled to thirty five years of experience, research and consultancy in the field. Apart of that, where and when needed, inputs and literature from over the world is used, reason why each part is followed by an extended literature list.

In an introductory chapter, building physics is presented as a discipline. Then, the first part concentrates on heat transport, with conduction, convection and radiation as main topics, followed by concepts and applications, typical for building physics. The second part treats mass transport, with air, water vapour and moisture as most important components. Again, much attention is devoted to the concepts and applications which relate to building physics. The last part finally discusses combined transport of heat and mass, who in fact act as if they were Siamese twins. The first and second part is followed by exemplary exercises, with some of them solved and the others offered to the reader as an element of training.

The book is written in SI-units. It should be especially usable for undergraduate and graduate studies in architectural and building engineering, although also mechanical engineers, studying HVAC, and practising building engineers, who want to refresh their knowledge, may benefit from it. The level of presentation anyhow assumes that the reader has a sound knowledge of calculus and differential equations along with some background in physics, thermodynamics, hydraulics, building materials and building construction.

Acknowledgments

A book of this magnitude reflects the work of many, not only the author. Therefore, first of all, we like to thank the thousands of students we had during our thirty years of teaching building physics. They gave us the opportunity to test the content of the book and helped in upgrading it by the corrections they proposed and the experience they offered in learning what parts should be better explained.

The book should not have been written the way it is, if not standing on the shoulders of those, who preceded us. Although we started our carrier as a structural engineer, our predecessor, Professor Antoine de Grave, planted the seeds that slowly fed our interest in building physics. The late Bob Vos of TNO, the Netherlands, and Helmut Künzel of the Fraunhofer Institut für Bauphysik, Germany, showed the importance of experimental work and field testing for understanding building performance, while Lars Erik Nevander of Lund University, Sweden, taught that solving problems in building physics does not always ask complex modelling, mainly because reality in building construction is ever again much more complex than any model may be.

During the four decennia at the Laboratory of Building Physics, several researchers and PhD-students got involved. I am very grateful to Gerrit Vermeir, Jan Carmeliet and Staf Roels, who became colleagues at the university, to Piet Standaert, Filip Descamps, now part-time professor at the Free University Brussels (VUB); Arnold Janssens, now associate professor at the University of Ghent (UG); Dirk Saelens, Hans Janssen, now associate professor at the Technical University Denmark (TUD); Rongjin Zheng and Bert Blocken, now associate professor at the Technical University Eindhoven (TU/e), who all contributed to this book by their work. The experiences gained by leading four Annexes of the IEA, Executive Committee on Energy Conservation in Buildings and Community Systems, further-on forced me to rethink parts of the text over time. The many ideas I exchanged and got in Canada and the USA from Kumar Kumaran, Paul Fazio, Bill Brown, William B. Rose, Joe Lstiburek and Anton Ten Wolde were also of great help in drafting the text

A number of reviewers took time to evaluate the book. Although we do not know their names, we like to thank them. Many merits also go to Miss Gerrie Doche from Montreal, Quebec, Canada, who made the first translation of the text from Dutch into English.

Finally, I like to thank my family. My loving mother who died too early. My father, who at a respectable age, still shows interest in our work. My wife, Lieve, who managed living together with a professor who was so busy, my three children who had to live with that busy father, and my many grandchildren who do not know their grandfather is still busy.

Leuven, February 2007

Hugo S. L. C. Hens

0 Introduction

0.1 Subject of the Book

This is the first of a series of books on a Building Physics and Applied Building Physics:

Building Physics: Heat, Air and Moisture Transport

Applied Building Physics: Boundary Conditions, Building Performance and Material Properties

Applied Building Physics and Performance Based Design 1

Applied Building Physics and Performance Based Design 2

For the Anglo-Saxon notion, the phrase ‘Building Physics’ is somewhat unusual. ‘Building Science’ is the more usual expression. However the two do not cover the same field of knowledge. Building science in fact is broader in its approach. It encompasses all subjects related to buildings that claim to be ‘scientific’. This is especially clear when looking at journals that publish on ‘Building Science’. The range of subjects treated is remarkably wide, ranging from control issues in HVAC, to city planning and organizational issues.

In this book on ‘Building Physics: Heat, Air and Moisture Transport’, the subject is the physics behind heat, air and moisture transfer in materials and building parts. Applied Building Physics deals with climate and the usability conditions confronting building physics. Furthermore, the performance concept and some performance requirements are discussed, and tables with material properties are given. Applied Building Physics and Performance Based Design 1 and 2 then use the performance concept as a tool in the design and construction of buildings. As such, both integrate the fields of building construction, building materials, building physics and structural mechanics.

0.2 Building Physics

0.2.1 Definition

Building Physics is an applied science that studies the hygrothermal, acoustical and light-related properties of building components (roofs, façades, windows, partition walls, etc.), rooms, buildings and building assemblies. The basic considerations are the user requirements for thermal, acoustic and visual comfort, the user’s health requisites and the more-or-less compelling demands and limitations imposed by architectural, material-related, economical and ecological considerations.

The term ‘applied’ indicates that Building Physics is directed towards problem solving: the theory as a tool, not as a purpose. From the definition, the field covered contains three sub-sectors. The first, hygrothermal, stands for heat, air and moisture, and deals with heat, air and moisture transport in materials, building components and buildings, and between buildings and the outside environment. Specific topics are: thermal insulation and thermal inertia, moisture and temperature induced movements, strains and stresses; the moisture balance (rain, initial moisture, rising damp, sorption, surface condensation, interstitial condensation); salt transport; air-tightness and wind resistance; energy demand and energy consumption; ventilation of buildings, indoor air quality, wind comfort, etc. The second sub-sector, building acoustics, studies noise problems in and between buildings and their environment. The main topics are: air and impact noise transmission by walls, floors, façades and roofs; room acoustics and the abatement of installation and environmental noises. Finally, the third sub-sector, lighting, addresses issues with respect to day-lighting, as well as artificial lighting and the impact of both on energy consumption.

0.2.2 Criteria

Building Physics has to deal with a variety of criteria: on the one hand requirements related to human comfort and health, on the other hand, architectural, material-related, economical and ecological facts and restrictions.

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Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!

Lesen Sie weiter in der vollständigen Ausgabe!