Chartered Institute of Building Services Engineers: Environmental Design

This sixth edition of Guide A contains significant changes from the previous edition. The

review of the whole range of topics covered by the volume, during a period when traditional

design criteria and calculation methods were being reconsidered, resulted in an iterative

process of revision, the consequence of which was a series of sectional drafts which were not

always compatible. The task of bringing these together into a coherent single volume has

contributed to the delayed publication of this Guide. The Institution has recently reviewed

and amended its publications strategy to ensure that this and other major Guides are

updated on a rolling programme, so that similar delays will not occur in future.

I would like to take this opportunity of thanking Institution members for their forbearance

with the delay and commend this new edition to them. It provides the basis for selecting

comfort criteria, along with the data and calculation methods required for good practice

design. As a learned society, the Institution is recognised as the authoritative body in the

theory and practice of building services engineering and the CIBSE Guide is often used in

litigation as the foundation for resolving disputes concerning professional practice.

The changes made in the sixth edition, compared to the fifth, can be briefly summarised, as

follows:
— Section 1: Environmental criteria for design covers the same basic topics of

temperature, humidity, lighting and acoustics, as did the previous edition, but each

has been extensively revised to provide more comprehensive data and

recommendations for particular situations. The most significant change has been to

replace the notion of a single ‘comfort’ temperature by summertime and wintertime
temperature ranges, based on percentage mean vote (PMV). Also, new sections have

been added dealing with indoor air quality, air filtration strategy and the

electromagnetic and electrostatic environment.
— Section 2: External design data replaces the former section A2: Weather and solar

data. The cold and warm weather data for the UK have been fully revised using

meteorological provided by the Meteorological Office for the period 1976-1995,

with detailed data for eight locations being included. The information is provided

in a form that allows the external design limit conditions to be selected by the

designer to meet the client’s requirements regarding design risk. A selection of

international heating and cooling design temperatures is included, drawn from data

published by ASHRAE. These data are reproduced by kind permission of

ASHRAE. Detailed solar data have been included for three UK locations, London

area (Bracknell), Manchester (Aughton) and Edinburgh (Mylnefield). Tables of

predicted irradiances for latitudes 0–60°N/S, based on computer algorithms, are

also included. For reasons of space, some of these data are located on the computer

disk that accompanies this Guide.
— Section 3: Thermal properties of building structures. This section is cited in Part L of

the Building Regulations as one of the accepted means of complying with the

regulatory requirements concerning the conservation of fuel and power. It has been

fully revised and expanded and now includes more detailed calculation procedures

to deal with the various types of window frame and glazing. Many of the relevant

national, European and international standards have been, or are currently being

revised and great efforts have been made to ensure that the calculation procedures

given in the Guide are consistent with these standards. The tables of thermal

properties of materials have been substantially increased, drawing from research

undertaken by the Building Environmental Performance Analysis Club.
— Section 4: Air infiltration and natural ventilation explores the mechanisms of

infiltration and natural ventilation, the forces creating these phenomena and

methods for calculating infiltration and ventilation rates. A computer program

listing is provided for calculating air change rates in single zone enclosures. This is

reproduced by the kind permission of the Air Infiltration and Ventilation Centre.

This section takes account of guidance contained in CIBSE Applications Manual

AM10: Natural ventilation in non-domestic buildings.
— Section 5: Thermal response and plant sizing brings together the subject areas formerly

covered in three separate Guide sections, i.e. A5: Thermal response of buildings, A8:
Summertime temperatures in buildings and A9: Estimation of plant capacity, and

provides a more coherent exploration of these topics. The new section considers a

range of calculation procedures, from simple steady-state heat losses and the

estimation of summertime temperatures through to computer-based dynamic

modelling. The admittance procedure is retained as a simple dynamic model,

suitable for application at an early stage in the design process. Guidance is provided

on which methods are suitable for particular applications and examples of their use

are given. This section also includes the data and equations necessary to apply the

various models.

Cooling load tables are provided for three UK locations, London, Manchester and

Edinburgh. These are based on the measured solar irradiances given in Section 2.

Similar tables provide estimated cooling loads for latitudes 0–60°N/S, based on the

predicted solar irradiances given in Section 2. These are included on the computer

disk that accompanies this Guide. Various appendices provide detailed derivations

of the equations and calculation techniques presented in the section.
— Section 6: Internal heat gains replaces section A7 of the fifth edition, which had the

same title. The section has been comprehensively revised and includes data for a

much wider range of equipment and systems, including computers and office

machines. Guidance is given on diversity factors and on the division of heat gains

into their radiant and convective components.
— Section 7: Moisture transfer and condensation. This replaces section A10 of the

previous edition of Guide A. While the calculation procedures have been retained

largely unchanged, the explanatory text has been revised and expanded and new

example calculations have been added. Tables of resistivities for common building

materials are now contained in Section 3.

The Institution appreciates the importance of its publications to its members’ day-to-day

activities. Guide A is accepted as the foundation for professional practice and applications

in building services engineering and it is therefore in all our interests that it is kept up-todate.

In order to do this, the Institution needs the help of CIBSE members and other users

of the Guide to identify areas where the present guidance is inadequate or needs to be

improved. The Institution will shortly start work on the seventh edition of Guide A and

members’ input is essential to its success. A time scale of three to five years is envisaged for

its preparation and the CIBSE Publications Department would be pleased to hear from

users of the Guide, both members and non-members, who feel that they can contribute to

this work.

Finally, having mentioned the importance of members’ views for future editions, I must

express my sincere thanks to the authors and contributors to this sixth edition of Guide A.

They include CIBSE members, some non-members and the staff at CIBSE, to all of whom

the Institution and I are extremely grateful.