Table Of ContentRefrigeration and
Air-Conditioning
Refrigeration: The process of removing heat.
Air-conditioning: A form of air treatment whereby temperature,
humidity, ventilation, and air cleanliness are all controlled within
limits determined by the requirements of the air conditioned
enclosure.
BS 5643: 1984
Refrigeration and
Air-Conditioning
Third edition
A. R. Trott and T. Welch
OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI
Butterworth-Heinemann
Linacre House, Jordan Hill, Oxford OX2 8DP
225 Wildwood Avenue, Woburn, MA 01801-2041
A division of Reed Educational and Professional Publishing Ltd
A member of the Reed Elsevier plc group
First published by McGraw-Hill Book Company (UK) Ltd 1981
Second edition by Butterworths 1989
Third edition by Butterworth-Heinemann 2000
© Reed Educational and Professional Publishing Ltd 2000
All rights reserved. No part of this publication
may be reproduced in any material form (including
photocopying or storing in any medium by electronic
means and whether or not transiently or incidentally
to some other use of this publication) without the
written permission of the copyright holder except
in accordance with the provisions of the Copyright,
Designs and Patents Act 1988 or under the terms of a
licence issued by the Copyright Licensing Agency Ltd,
90 Tottenham Court Road, London, England W1P 9HE.
Applications for the copyright holder’s written permission
to reproduce any part of this publication should be
addressed to the publisher
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Cataloguing in Publication Data
A catalogue record for this book is available from the Library of Congress
ISBN 0 7506 4219 X
Typeset in India at Replika Press Pvt Ltd, Delhi 110 040, India
Printed and bound in Great Britain
Contents
1 Fundamentals 1
2 The refrigeration cycle 14
3 Refrigerants 28
4 Compressors 36
5 Oil in refrigerant circuits 57
6 Condensers and water towers 63
7 Evaporators 83
8 Expansion valves 93
9 Controls and other circuit components 104
10 Selection and balancing of components 121
11 Materials. Construction. Site erection 131
12 Liquid chillers. Ice. Brines. Thermal storage 144
13 Packaged units 154
14 Refrigeration of foods. Cold storage practice 162
15 Cold store construction 170
16 Refrigeration in the food trades – meats and fish 188
17 Refrigeration for the dairy, brewing and soft drinks
industries 193
18 Refrigeration for fruit, vegetables and other foods 201
19 Food freezing. Freeze-drying 205
20 Refrigerated transport, handling and distribution 208
21 Refrigeration load estimation 214
22 Industrial uses of refrigeration 223
23 Air and water vapour mixtures 227
24 Air treatment cycles 240
25 Practical air treatment cycles 255
vi Contents
26 Air-conditioning load estimation 263
27 Air movement 273
28 Air-conditioning methods 297
29 Dehumidifiers and air drying 316
30 Heat pumps. Heat recovery 320
31 Control systems 324
32 Commissioning 333
33 Operation. Maintenance. Service. Fault-finding. Training 338
34 Efficiency and economy in operation 351
35 Catalogue selection 357
Appendix Units of measurement 367
References 369
Index 373
Preface
Refrigeration and its application is met in almost every branch of
industry, so that practitioners in other fields find that they have to
become aware of its principles, uses and limitations. This book aims
to introduce students and professionals in other disciplines to the
fundamentals of the subject, without involving the reader too deeply
in theory. The subject matter is laid out in logical order and covers
the main uses and types of equipment. In the ten years since the last
edition there have been major changes in the choice of refrigerants
due to environmental factors and an additional chapter is introduced
to reflect this. This issue is on-going and new developments will
appear over the next ten years. This issue has also affected servicing
and maintenance of refrigeration equipment and there is an increased
pressure to improve efficiency in the reduction of energy use. This
edition reflects these issues, whilst maintaining links with the past
for users of existing plant and systems. There have also been changes
in packaged air-conditioning equipment and this has been introduced
to the relevant sections. The book gives worked examples of many
practical applications and shows options that are available for the
solution of problems in mechanical cooling systems. It is not possible
for these pages to contain enough information to design a complete
refrigeration system. The design principles are outlined. Finally,
the author wishes to acknowledge help and guidance from colleagues
in the industry, in particular to Bitzer for the information on new
refrigerants.
T.C. Welch
October 1999
1 Fundamentals
1.1 Basic physics – temperature
The general temperature scale now in use is the Celsius scale, based
°
nominally on the melting point of ice at 0 C and the boiling point
°
of water at atmospheric pressure at 100 C. (By strict definition, the
°
triple point of ice is 0.01 C at a pressure of 6.1 mbar.) On the
°
Celsius scale, absolute zero is – 273.15 C.
In the study of refrigeration, the Kelvin or absolute temperature scale
is also used. This starts at absolute zero and has the same degree
intervals as the Celsius scale, so that ice melts at + 273.16 K and
water at atmospheric pressure boils at + 373.15 K.
1.2 Heat
Refrigeration is the process of removing heat, and the practical
application is to produce or maintain temperatures below the
ambient. The basic principles are those of thermodynamics, and
these principles as relevant to the general uses of refrigeration are
outlined in this opening chapter.
Heat is one of the many forms of energy and mainly arises from
chemical sources. The heat of a body is its thermal or internal
energy, and a change in this energy may show as a change of
temperature or a change between the solid, liquid and gaseous
states.
Matter may also have other forms of energy, potential or kinetic,
depending on pressure, position and movement. Enthalpy is the
sum of its internal energy and flow work and is given by:
H = u + Pv
In the process where there is steady flow, the factor Pv will not
2 Refrigeration and Air-Conditioning
change appreciably and the difference in enthalpy will be the quantity
of heat gained or lost.
Enthalpy may be expressed as a total above absolute zero, or any
other base which is convenient. Tabulated enthalpies found in
reference works are often shown above a base temperature of
° °
– 40 C, since this is also – 40 on the old Fahrenheit scale. In any
calculation, this base condition should always be checked to avoid
the errors which will arise if two different bases are used.
If a change of enthalpy can be sensed as a change of temperature,
it is called sensible heat. This is expressed as specific heat capacity,
i.e. the change in enthalpy per degree of temperature change, in
kJ/(kg K). If there is no change of temperature but a change of
state (solid to liquid, liquid to gas, or vice versa) it is called latent
heat. This is expressed as kJ/kg but it varies with the boiling
temperature, and so is usually qualified by this condition. The
resulting total changes can be shown on a temperature–enthalpy
diagram (Figure 1.1).
Sensible heat of gas
Latent
heat of
e melting Latent heat of boiling
ur373.15 K
at
er
mp Sensible heat of liquid
273.16 K
e
T
Sensible heat of soild
334 kJ 419 kJ 2257 kJ
Enthalpy
Figure 1.1 Change of temperature (K) and state of water with enthalpy
Example 1.1 For water, the latent heat of freezing is 334 kJ/kg and
the specific heat capacity averages 4.19 kJ/(kg K). The quantity of
°
heat to be removed from 1 kg of water at 30 C in order to turn it
°
into ice at 0 C is:
4.19(30 – 0) + 334 = 459.7 kJ
Example 1.2 If the latent heat of boiling water at 1.013 bar is 2257
kJ/kg, the quantity of heat which must be added to 1 kg of water at
°
30 C in order to boil it is:
Fundamentals 3
4.19(100 – 30) + 2257 = 2550.3 kJ
Example 1.3 The specific enthalpy of water at 80°C, taken from
°
0 C base, is 334.91 kJ/kg. What is the average specific heat capacity
°
through the range 0–80 C?
334.91/(80 – 0) = 4.186 kJ/(kg K)
1.3 Boiling point
The temperature at which a liquid boils is not constant, but varies
with the pressure. Thus, while the boiling point of water is commonly
°
taken as 100 C, this is only true at a pressure of one standard
atmosphere (1.013 bar) and, by varying the pressure, the boiling
point can be changed (Table 1.1). This pressure–temperature
property can be shown graphically (see Figure 1.2).
Table 1.1
Pressure (bar) Boiling point (°C)
0.006 0
0.04 29
0.08 41.5
0.2 60.1
0.5 81.4
1.013 100.0
Critical
temperature
Liquid
e curve
Pressur Solid Boiling point
Gas
Triple
point
Temperature
Figure 1.2 Change of state with pressure and temperature
Description:Air-conditioning: A form of air treatment whereby temperature, humidity, ventilation, and air cleanliness are all controlled within 4 Refrigeration and Air
