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Book Review

ENERGY SIMULATION IN BUILDING DESIGN

by J. A. Clarke; published by Adam Hilger Ltd, Techno House, Redc- liffe Way, Bristol BS1 6NX, England; price: £36/$49; pp. 388; ISBN 0-85274-786-I, distributed in North America by Adam Hilger Ltd., P.O. Box 230, Accord, MA 02018, U.S.A., June 1985.

Summary From the mathematical and technical foundations of energy simula-

tion to the basic principles of energy software development, Joe Clarke's book "Energy simulation in building design" covers a wide range of issues. Clarke integrates written and graphic information effectively and presents an excellent list of references. Obviously, Clarke has been working on the subject of energy simulation for an extensive period of time and has accumulated immense knowledge in this area. If any cri- ticism is appropriate, it might be the compression and wealth of infor- mation that startles the unprepared reader. Only the reader who has engaged himself in a similar thorough process of investigating the differ- ent aspects of energy simulation, will completely understand the book reading it for the first time. As a standard text and source of informa- tion about the state of the art in large-scale building energy simulation, the book will occupy an important place. "Energy Simulation in Build- ing Design" can be used as a reference book in energy-related courses in the architectural curriculum where a standard reference book is much needed, and as an introduction for engineering courses.

Detailed comments The book is divided into eight chapters: the introduction, advanced

modeling techniques, numerical simulation by finite differences, matrix processing of energy flow equation sets, energy-related subsystems, plant simulation, software development, and validation and implementa- tion in practice. Seven appendices and an index can be found at the end. The appendices, covering the Fourier heat equation, thermophysical properties of building materials, alternative discretisation schemes, nomenclature, description of the ESP system, datastructures of the ESP system, and ESP system output examples are particularly useful utilities. They contain frequently used data and formulas which relate the theor- etical content of the eight chapters to practical applications.

After reading the preface, and Clarke's intention to "mix matters of fact and experience as appropriate", one could expect a book on expert systems in building simulation. However, Clarke suceeds in building a comprehensive model for building simulation without the help of expert systems technology, thus giving a good -- and possibly last -- overview on what is possible with straightforward algorithmic programming, before knowledge-based approaches will be introduced.

Chapter 1 -- I n t roduc t ion - presents the three objectives of the book: to demonstrate theories, to construct a simulation model, and to address

© Elsevier Sequoia/Printed in The Netherlands

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the problems of model validation and implementation. As mentioned in the Summary, this might be a little too much for a one-volume book. Clarke's philosophy is to achieve energy conservation by ensuring inte- grity of the mathematical model vis-d-vis the reality and by rigorously validating and testing the simulation tool before its use. Clarke's empha- sis on building performance, and not just the fulfillment of prescriptive requirements is very important and should be highlighted. In the des- cription of energy flowpaths and causal effects, the inclusion of the building plant between casual gains and moisture seems surprising, a more prominent place would be expected. The t rea tment of passive solar features and the description of passive solar elements is sketchy and not complete. The modeling implementation description of these passive features is good.

Chapter 2 -- Advanced modeling techniques -- presents the time- domain response functions, the frequency-domain response functions, and three different numerical methods. The capability of the response factor method to handle both periodic and non-periodic flux and tem- perature time-series is given as a reason for the higher acceptability of the response factor method in North America. Although the response factor method can usually only be applied to a system of equations which are both linear and invariable, I agree with Mitalas that such a requirement need not impose severe restrictions in a building simulation process. Experience with programs that use the response factor method, such as DOE-2, confirm this assumption. The at tention given to details such as the difference between triangular and rectangular pulse repre- sentation is convincing. I strongly agree with Gupta that switch inputs such as lighting loads are better treated by the rectangular method. The description of the time-domain response functions, frequency-domain response functions, and their application is very good, as is the descrip- tion of the numerical methods, especially their comparison. The rela- tion between the "building energy flowpaths" graphs in the Introduc- tion and in this chapter is not obvious immediately.

Chapter 3 -- Numerical simulation by finite differences -- deals with system discretisation, finite difference energy flow equations, and struc- turing the equations for mult i -component simulation. The example given for the simulation of an active/passive system is helpful and neces- sary because it relates the previously treated theory to reality. However, the extensive matrix processing activities, necessary for the simulation, could be described in more detail to refresh the reader's memory if he does not have the references at hand. In general, architects and practi- tioners will probably not be able to understand chapters 2, 3, and 4 because of the mathematical content . This is not meant as a criticism, but as recognition of a reality.

Chapter 4 -- Matrix processing of energy flow equation sets -- addres- ses the establishment of the equation set for solution, the fast simulta- neous solution by matrix processing, and mixed frequency inversion. It is a mathematically oriented chapter which could benefit from more graphical explanations and from implementation hints. The informa- tion is presented in an extremely condensed form. Small application examples that allow the user to test the theory on a personal computer would be highly appreciated.

Chapter 5 -- Energy-related subsystems -- deals with geometrical considerations, insolation of exposed building surfaces, shortwave radia- t ion processes, longwave radiation processes, surface convection, air

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flow, casual heat sources, and climate. The chapter is more concrete than the previous ones, and therefore, very helpful for architects and designers. The geometrical considerations, the insolation transformation equations and the solar position algorithms are described very clearly and comprehensively. They can be used very well for teaching purposes in architecture courses. The treatment of building geometry clearly demonstrates the necessity of a general purpose building representation that can be used for energy simulations but also for other kinds of per- formance simulations such as cost, acoustics, lighting, and structures.

Chapter 6 - Plant simulation - addresses sequential versus simulta- neous approaches, air-conditioning systems, active solar systems, wet central heating systems, simultaneous building/plant modeling, control system simulation, and future developments in systems simulation. The chapter contains in its last paragraph a very appropriate hint to the future use of expert systems. Expert systems and knowledge-based approaches to building performance problems will have a tremendous impact on building energy simulations. They allow not only intelligent interfaces to any simulation programs, but also the integration of the wealth of experiences gathered by simulation experts, engineers, and building owners, into the simulation program. The rest of the chapter follows the approach of the previous chapters, except, as it seems, in a slightly more sketchy way. Very important is the description of the sequential versus simultaneous techniques in plant simulation and their impact on the accuracy of prediction.

Chapter 7 - Software development - covers structuring the overall system, software requirements, indicative performance data, and devel- opment environment. It will be extremely helpful for anybody who is attempting to put together a large or small simulation program, but it also helps to understand existing programs better. The described overall system structuring is complete and very ambitious. Similarities to exist- ing large programs - such as DOE-2 - are obvious. The description of software requirements is again quite helpful in the context of teaching because of the clarity in presentation.

Chapter 8 - Validation and implementation in practice - is the briefest of the chapters which should not be an indication for its impor- tance. As every user of simulation programs experiences, the model vali- dation is the crucial test for the usefulness of the program. This chapter deserves more attention, especially the description of the basic assump- tions for analytical and empirical validation.

The appendices fall into two categories: general utilities such as the Fourier heat equation, alternative discretisation schemes, nomenclature and thermophysical properties of building materials, and ESP (Environ- mental Systems Performance) program-specific material dealing with a general description, the data structures, and output examples of the ESP system. The ESP program and all the participant programs in the IEA Annex 4 evaluation can be better understood and compared after the reading of this book.

Conclusion “Energy analysis in building design” is probably one of the last books

that tries to simulate a building’s thermal behavior with a purely algo- rithmic approach. The complexity of the resulting program demands mainframe computing power for acceptable execution speed. The growing market share of microcomputer-based energy analysis and

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simulation and the associated problem of simplified simulation and analysis programs as well as the potential impact of knowledge-based simulation approaches are beyond the scope of this book, as well as the possible integration of a large energy simulation program into an inte- grated design environment. With his demonstrated knowledge in the area, Clarke should be encouraged to address these issues in a follow-up book. This would substantially increase the audience of the book. The extensive use of graphics for explanation, the well thought-out integra- tion of tables in the text, as well as the extensive list of references after each chapter are exemplary.

Gerhard Schmitt Department of Architecture

Carnegie-Mellon University Pittsburgh, PA 15213, U.S.A.