Table Of ContentBuilding energy and
environmental modelling
CIBSE Applications Manual AM11: 1998
The Chartered Institution of Building Services Engineers
222 Balham High Road, London SW12 9BS
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without the prior permission of the Institution.
© April 1998 The Chartered Institution of Building Services
Engineers London (reprinted 2010)
Registered charity number 278104
ISBN 0 900953 85 3
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Acknowledgements
The Task Group, authors and editors acknowledge financial
support from the Department of Environment, Transport and
the Regions under the Partners in Technology Scheme, and
the in-kind contribution received from a large number of
CIBSE and Building Environmental Performance Analysis Club
members.
Foreword
This Applications Manual has been produced by collaboration between the Chartered
Institution of Building Services Engineers (CIBSE), the Building Research Establishment
(BRE) and the Building Environmental Performance Analysis Club (BEPAC) with fin -
ancial support from the UK Department of the Environment, Transport and the Regions
under its Partners in Technology scheme. The project was managed by BRE and steered by
a CIBSE Task Group appointed by the Institution’s Technical Publications Policy Com-
mittee. The Manual provides guidance on the selection and use of building energy and
environmental modelling (BEEM) software, which is gaining increasing importance as
an aid to engineers for designing energy-efficient buildings. The collaboration aimed to
accelerate dissemination of much-needed information and guidance in this area.
CIBSE members have a major role in providing a healthy, comfortable and reliable
environment for people to live and work in, while minimising any harmful impact of
buildings on the wider environment and maximising the sustainability of global resources.
BEEM software should assist engineers in their innovative approach to building design,
and in optimising life-cycle energy and financial costs.
The task group aimed to furnish guidance on the appropriate application of BEEM
software, to promote good practice and to offer reference material to support practising
engineers. The Manual is intended to be complementary to the CIBSE Guide, which sets
the basis for the design of a building’s energy and environmental systems. The Manual also
emphasises the need for close collaboration among the design team, in particular between
archit ects and building services engineers. BEEM software can facilitate this comm uni-
cation, and so the Manual is commended to the architect colleagues of services engineers.
The Manual was drafted by authors selected from academic, research and consulting
engineering organisations. The time and effort expended by the authors far outweighed
their financial reward. Similarly, a great deal of time and resources were contributed ‘in
kind’ by a large number of CIBSE and BEPAC members who reviewed and commented on
successive drafts of the Manual. The voluntary contribution of the task group in steering
the origination of the Manual and developing its contents deserve especial thanks.
Foroutan Parand (Project Task Group Chairman)
Building Energy and Environmental Modelling Task Group
F Parand Chairman(Building Research Establishment)
E Allan (Brian Warwicker Partnership)
D Arnold (Troup Bywaters & Anders)
J A Clarke (University of Strathclyde)
P G Foster (Building Design Partnership)
C Ho (Building Simulation)
P Ruyssevelt (HGA Ltd)
P Warburton (Arup Associates)
G Whittle (Simulation Technology Ltd)
B W Copping Secretary(CIBSE)
Authors
J W Hand (University of Strathclyde)
S J Irving (Oscar Faber)
K J Lomas (De Montfort University)
L B McElroy (Scottish Energy Design Advisory Service)
F Parand (Building Research Establishment)
D Robinson (Anglia Polytechnic University/Building Research Establishment)
P Strachan (University of Strathclyde)
Technical Editors
D Bartholomew (David Bartholomew Associates)
D Robinson (Anglia Polytechnic University/Building Research Establishment)
Contract Editor
J Wilson
CIBSE Co-ordinating Editor
B W Copping
Note from the publisher
This publication is primarily intended to provide guidance to those responsible for the
design, installation, commissioning, operation and maintenance of building services. It is
not intended to be exhaustive or definitive and it will be necessary for users of the guidance
given to exercise their own professional judgement when deciding whether to abide by or
depart from it.
Contents
1 Introduction 1
1.1 Background 1
1.2 Objectives 2
1.3 Readership 2
1.4 Scope and structure 3
1.5 Using the manual 4
References 5
2 Role of modelling in the design process 6
2.1 Principal benefits of environmental modelling 6
2.2 Whom modelling can help 8
2.3 Integration of modelling into design and operation 10
2.4 Modelling uncertainty and risk 11
References 11
3 Categories of BEEMsoftware and their uses 12
3.1 Level of sophistication 12
3.2 Thermal performance 13
3.3 Lighting and visualisation 15
3.4 Ventilation and air movement 17
3.5 Specialist software 19
3.6 Typical design issues 19
3.7 Program integration 19
References 19
4 Establishing a simulation capability 20
4.1 Software selection 20
4.2 Infrastructure for effective use of simulation 28
References 33
5 How to use BEEMsoftware 34
5.1 Identification of design questions 34
5.2 Translating design questions into modelling tasks 35
5.3 Planning the modelling study 35
5.4 Input data requirements 41
5.5 Interpretation and presentation of results 49
5.6 Quality assurance 50
5.7 User skills and training 50
References 51
6 Case studies 52
6.1 Selection of case studies 52
6.2 Victoria Quay — large prestige office 53
6.3 Vellore Medical Centre — simple low budget study 58
6.4 Birmingham Museum — HVACplant for environmental control 61
6.5 Buffer house — new build house design 66
6.6 Short case studies 67
References 70
Appendix A: Glossary 71
Appendix B: Checklist for choosing BEEMsoftware 74
Appendix C: Supplementary data 88
Appendix D: Further sources of information 94
Index 96
INTRODUCTION 1
1 Introduction
Contents Summary
1.1 Background
Energy costs and carbon dioxide emissions for office buildings can vary by about a
1.2 Objectives factor of eight, indicating the significant opportunity that exists for energy savings.
1.3 Readership
The room thermal response in modern, well insulated buildings is highly dynamic.
1.4 Scope and structure
Building energy and environmental modelling (BEEM) soft ware allows comparison of
1.5 Using the manual
different design and refurb ishm ent options in order to optimise building performance
and to improve the quality of buildings. It encourages the adoption of innovative
design features, and assists communication within the design team.
Many BEEM software tools exist; this manual provides guidance on the selection and
appropriate use of these tools, and on initiating modelling studies from brief develop -
ment to results interpretation.
The scope of the manual is limited to the modelling of thermal, airflow and lighting
performance in buildi ngs, with a focus on thermal modelling.
Building services engineering practices are the principal target readership, but the
manual shouldalso be of interest to architects, developers, facility managers and users
of buildings.
1.1 Background With increasing levels of insulation, airtightness and inter -
nal gains of buildings, the room heat balance has become
delicate and dynamic. New materials and tech niques
Concern for the environment, and in particular the recog-
emerge continuously which affect building environ mental
nition that buildings are responsible for up to a half of the
response. Advances in control technology allow finer con -
total carbon dioxide (CO ) emissions in the UK(1), has
2 trol of equipment and can achieve higher efficiency than
generated a new interest in saving energy in buildings.
hitherto. However, arriving at reliable solutions requires,
among other measures, appropriate design, analysis and
As at 1991, annual fuel bills for offices in the UK ranged simulation tools.
from £4 to £30 per square metre of gross internal area(2).
This spread of fuel costs shows that there is significant Building energy and environmental modelling (BEEM)
potential for reducing energy costs and, given that CO software can be used to predict the dynamic response and
2
emissions are directly related to fuel use, the level of emis - performance of buildings and to assess and compare the
sions. Strategic decisions, such as air conditioning vers us effects of different design options. The information thus
natural ventilation, quality of design and construction, and obtained can help the design team make properly informed
the occupant’s use of the building, each contribute to the value judgements about the costs and benefits of different
spread of fuel costs. design and/or refurbishment strategies and options.
Better use of daylight, the use of natural ventilation instead Steady-state and steady-cyclic calculations can be sufficient
of, or assisted by, mechanical ventilation and cooling, and for calculating the size of air-conditioning systems for design
the adoption of passive solar heating/cooling concepts have purposes under specified conditions. However, when tem-
won wide acceptance among designers, clients, developers poral variation of ventilation, internal gains and climate
and users. Well designed naturally ventilated and daylit need to be considered — e.g. in designing naturally
buildings can create internal conditions that occupants find ventilated, passive and mixed-mode buildings — their use
more pleasant than those found in some air-conditioned can be limited. Similarly, they may not provide sufficient
buildings(3). When air conditioning is considered to be the infor mation for designers to ‘fine tune’ the design of the
optimum solution due to user and site requirements, building, its systems and controls.
careful consideration of design options can reduce the air
cond it ioning loads and hence energy consumption and BEEMsoftware has emerged in response to these limitations.
costs. The range is very wide and covers:
2 BUILDINGENERGYANDENVIRONMENTALMODELLING
— Simplified programs, for overall energy cons ump- ability. Its use, therefore, requires consideration of the
tion assessment, peak temperature prediction, associated benefits, costs and fitness for purpose.
heating/cooling loads calculations etc.
— Sophisticated programs, for hourly simulation of
heat, light and air movement. 1.2 Objectives
— Complex specialist packages, for lighting, comp u-
tational fluid dynamics (CFD), two- and three- This manual has been written to help in the selection and
dimensional conduction calculations etc. application of BEEMsoftware in practice.
— Integrated design and analysis systems which com -
bine a number of the above categories. The CIBSE Guide A(4) sets the basis for the design of a
building’s energy and environmental systems. Most
calculation methods proposed in the Guide have been
The main common characteristic of BEEM software is the
designed to be simple, applicable to most common
ability to simulate one or more of the heat, light, mass (air
situations and manual where possible. This Applications
and moisture) and sound transfer mechanisms within a
Manual provides complementary and supplementary
building and its components as they are exposed to driving
information for the evaluation, analysis and optimisation of
forces which, normally, vary with time. These driving
forces include climate, occupants, environmental con di tion - building performance through BEEMsoftware.
ing systems (e.g. heating, cooling, lighting and ventilation
systems) and noise generated within or outside the build- With the trend towards energy efficiency and more
ing. BEEM software emulates the dynamic intera ction of stringent control over microclimate, building designers are
these forces with the building fabric to predict its energy expected to carry out performance assessm ents far beyond
and environmental performance. the capacity of manual calculation procedures. However,
despite the increasing amount of BEEM software and
Occasionally, physical models can be a viable alternative to multitude of studies of these(5, 6, 7, 8), there has been little
BEEMsoftware, e.g. for daylighting and ventilation. In many coherent guidance on its selection and application. This
cases, the cost and time will rule out physical models as manual aims to fill this gap by:
practical alternatives to computational modelling.
— raising the awareness of building services engineers,
Frequently, the use of BEEMsoftware may be the only feas-
architects and clients to the capability of BEEM
ible method of assessing the uncertainty and risks involved
software
with a particular design and its performance under
different scenarios of internal and external conditions. — giving a concise account of the issues of importance
when selecting such software, for those who wish to
BEEM software allows designers to consider ‘what if’ establish an in-house modelling capability
questions in order to optimise the design. Innovative ideas
can be examined before firm decisions are made. By con - — giving practical guidance to users of BEEMsoft ware
to carry out modelling in an appropriate way with
sideri ng various design options, BEEM software can assist
due regard for quality assurance.
architects, engineers, cost consultants and clients with their
communication and inform their decision-making process.
Using BEEM software, the cost of owning and operating 1.3 Readership
buildings can be predicted, the risk of changing building
usage assessed and life cycle costs calculated. Increasingly,
in competitive fuel markets, BEEM software is used to aid This manual will be of interest to anyone who plays a role in
energy purchase strategies relying on the prediction of load creating energy-efficient buildings that produce a healthy,
shapes. comfortable and productive indoor environment. Among
this group will be architects, building services engineers,
In brief, BEEMsoftware: clients, facility managers and local authority building
controllers.
(a) enables designers to consider different design
options which leads to:
The principal target readership of this manual is building
— improved energy and environmental services consultants and contractors in addition to firms
performance of buildings which intend to establish an in-house BEEM capability or
are considering the use of specialist firms that offer such
— adoption of innovative design concepts
services.
(b) improves communication between the design team
Two groups of readers are particularly targeted:
(c) reduces life cycle costs
— partners, managers, or engineers responsible for
(d) reduces investment risk.
deciding the firm’s quality and capability strategies
and developing staff resources and training
The use of BEEM software, however, involves costs and
requires trained personnel. There are also pitfalls, such as — engineers and modelling specialists whose day-to-
the application of software beyond its limits of applic- day job it is to carry out design and modelling.
INTRODUCTION 3
For companies that already have an established modelling — What are the risks in its use?
capability, this manual aims to be a useful reference for
their experienced modellers and a guide for novice users. The use of environmental model ling as an aid to the design
team is also reviewed throughout various stages of the life
Practising engineers and architects will benefit from read - cycle of a building, from design to commissioning and
ing parts of the manual so that they are aware of the options operation.
and possibilities that BEEMtools offer (see section 1.5).
Section 3
The manual will also be of interest to software vendors
wish ing to provide engineers with information about
software assumptions, training and easy-to-use software. This section describes different types of BEEMsoftware and
answers such questions as:
— What are the major classes of BEEMsoftware?
1.4 Scope and structure — What are the major types of applications of BEEM
software?
The manual provides a general introduction to energy and — What are the limitations in its use?
environmental modelling, but focuses on the following
areas which have been the subject of much research and
Section 4
development:
— thermal and energy modelling This section gives guidance on establishing an in-house
modelling capability and:
— lighting and daylighting modelling
— Discusses the issues involved in selecting the
— airflow modelling.
appropriate tool for a particular job in hand and for
the main routine jobs. It includes hardware and
Thermal modelling is dealt with in some detail in order to
software costs, user training, resources required
give specific guidance by means of specific examples.
and accuracy of results.
The manual covers: — Discusses the capabilities of BEEM software for
different types of application, in order to consider
(a) Applicability: BEEM software is normally a complex
its ‘fitness for purpose’, and gives general guidance
package of various calculation procedures; it
on training requirements and quality assurance in
should only be used when it is appropriate to do so.
its use.
(b) Selection: a large number of BEEM software tools — Provides a checklist for selecting software.
exist; choosing the right tool for the job is the first
important task in modelling. — Proposes a proforma for documenting the main
features, capabilities and training requirements of
(c) Quality: there is always the possibility of errors
BEEM software, on the basis of which selection can
within software, mistakes in implementation and/
be made.
or the misa pplication of software. Consideration
should be given to validation of software and
procedures for their use. Section 5
(d) User skills: the effect of user errors and assump tions
This section provides guidance on how to use the BEEM
on the results obtained can far outweigh the
software effectively and:
accuracy of BEEM software. Appropriate training,
together with the establishment and use of quality — Discusses the influence that users and their
assurance procedures, is an important part of assump tions have on the results obtained from
developing a modelling capability. BEEMsoftware.
(d) Input data: access to guidance and sources of infor - — Gives basic procedures for quality assurance in the
mation for deriving appropriate input data is use of BEEMsoftware.
pertinent to good modelling.
— Discusses the practical issues involved in tran s -
lating a real building (design) into software input.
Section 2
— Provides information concerning the sources of
data and how to prepare data in a systematic way.
This section discusses the applicability of BEEM software
and answers such questions as:
Section 6
— Why should it be used?
— What benefits can be accrued from its use? This section describes a number of relevant case studies and:
— When should it be used? — Shows the use of BEEMsoftware in practice.
— Where does it fit in the design process? — Discusses its benefits in particular applications.
4 BUILDINGENERGYANDENVIRONMENTALMODELLING
— Gives examples of the rationale behind some design 1.5 Using the manual
decisions made on the basis of the BEEMresults.
Target readership
It also includes a number of short case studies which:
Sections 2, 3, 4 and 6 should be read as they set the scene
— Further illustrate the diversity of design problems and give an insight into modelling, its use and whether it is
which can be tackled by simulation. something the reader should become involved with.
— Show the potential of BEEM software to influence
design decisions and yield energy consumption Those wishing to establish in-house modelling capability
savings.
Section 4 is mainly of interest to those who are considering
— Illustrate a diversity of modelling techniques creating an in-house BEEM capability. To appreciate the
applied to commercial building projects. issues involved, they should read sections 2 and 3 first.
Section 4 will also be relevant to experts already using BEEM
— Serve as examples of the processes discussed in this software but who require additional modelling software or
manual and the application of some of the guidance need to confirm whether the software they possess and use
given in other sections. is appropriate for the job in hand.
Modellers
Appendices
Section 5 is mainly of use to modellers and their immediate
managers who require practical guidance in defining
Four appendices contain supp lem entary data and tables,
modelling strategy, preparing data and interp reting results.
charts, procedures and checklists including:
If the reader is concerned with quality assurance issues,
both sections 4 and 5 should be read. Sections 3, 4, 5 and
— glossary of terms
some appendices are expected to be used as a source of
reference by those whose day-to-day job it is to carry out
— checklist for selecting software
modelling studies.
— guidance on weather data and sources of infor-
mation Initiating the modelling study
— guidance on occupancy-related data and sources of This manual gives guida nce on initiating modelling studies
information from development of the brief to interpretation of results.
Figure 1.1 identifies these stages and related issues and
— where to find further information and advice. shows where to find relevant information in the manual.
Capital versus life cycle costs (2·1·4)
Development
Environmental standards (2·1·1)
of brief
Space flexibility and adaptability (2·2·1, 2.2.2)
Identification of Tool flexibility/robustness (2·1·3)
design issues
Design criteria/purpose of study (5·1, 5·2)
Tool Capabilities/robustness and accuracy (2·1·3, 4·1·11)
selection
Ease of use (4·1·4, 4·1·8)
Training and QA (4·2·2, 4·2·4, 5·6, 5·7)
Modelling
Consistent approach (3·1, 4·2·4)
methodology
Design stage and quality of data (2·3, 5·4)
Agreeing
Design criteria (5·3)
base data
Climate data, internal heat gains, material and construction (5·4)
Modelling assumptions (3·1, 5·3, 5·5)
Understanding
Parameter sensitivity (5·3)
the results
Figure 1.1 Initiating the
Key design messages, transparency for communication (5·5)
modell ing study
