Air Conditioning System Design

418 Pages·2017·13.924 MB·English

by  Roger Legg (Eds.)

AIR
CONDITIONING
SYSTEM DESIGN
AIR
CONDITIONING
SYSTEM DESIGN
ROGER LEGG
Retired, previously senior lecturer at London
South BankUniversity
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DEDICATION
To staff and students,
past and present,
of the
‘National College’.
v
Thegeneralantiphlogisticremediesare…freeadmissionofpurecoolair.
JohnAlikin,‘ElementsofSurgery’,1779
… the dreadful consequences which have been experienced from breathing air
insituationseitheraltogetherconfinedorillventilated…ifothersareinthesame
apartment,thebreathfromeachpersonpassesfromonetoanother,anditisfre-
quentlyinthiswaythatdiseasesarecommunicated.
TheMarquisdeChabannes,1818
Theveryfirstruleofnursing…isthis:tokeeptheairhebreathesaspureasthe
externalair,withoutchillinghim.
FlorenceNightingale,1863
vii
FOREWORD
Air conditioning is no longer regarded as the luxury that it once was, and
thereisnowanincreasingdemandforapplicationsrangingthroughdomes-
tic, commercial, industrial, and transport and for specialized installations
suchashospitals,researchfacilities,datacentres,andcleanrooms.Theengi-
neeringsystemsinmodernbuildingsandinstallationsmakeasignificantcon-
tributiontotheoverallbuildingperformanceintermsofenergyuse.Systems
needtobeincreasinglysophisticatedintheirdesign,installation,operation,
control, and maintenance at a time when there is increasing pressure for
greater energy efficiency.
Thishasledtoademandformorequalifiedengineersandotherprofes-
sionals involved in building design. All those involved need to understand
the underlying principles of the topics covered in this volume.
The book, which is a complete revision of Roger’s previous work
published by Batsford in 1991, contains new chapters on unitary systems
and chilled beams. It provides a good technical foundation of building
service engineering and covers significant proportions of the syllabus
requirementsofacademiccoursesinthisdiscipline.Thetheoreticalcoverage
isbackedwithrelevantworkedexamplesandtheuseofdatafromthelatest
editionsofCIBSEandASHRAEpublications,whichshouldmakethistext
appeal to students and practising professionals in both Europe and North
America.
Theauthoriswellqualifiedinthisdisciplinehavingtaughtthesubjectfor
morethan30yearsattheInstituteofEnvironmentalEngineering(formerly
the National College for Heating, Ventilation, Refrigeration and Fan
Engineering, South Bank University, London). In addition, he has used
contributions from key specialists to support specific areas; these included
AssociateProf.RistoKosonen,Prof.TimDwyer,Mr.TerryWelch,Prof.
Ron James, Prof. John Missenden, and Mr. Stan Marchant.
Prof. Michael J. Farrell
London 2017
(Retired,previouslyprinciplelectureratLondonSouthBankUniversity
and head of the Institute of Environmental Engineering)
xv
ACKNOWLEDGMENTS
Iamindebtedtomyex-colleaguesatSouthBankUniversityformuchprac-
ticalhelp,encouragement,andadviceinthewritingofthisbook.Inparticular,
I am mostgratefulto Mr.Terry Welch forVRV systemsand the discussion
inChapter7;toProf.RonJamesandTerryWelchforChapter9,onrefrig-
eration and heat-pump systems; to Stan Marchant for the text on cooling
towers in Chapter 10; to Prof. Tim Dwyer who contributed the overview
of control systems in Chapter 17; and to Prof. John Missenden who pro-
vided the text for control valves in Chapter 17. My thanks are also due to
Prof. Risto Kosonen of Aalto University, Sweden, for writing Chapter 8.
My son Mark gave me a great deal of help with word processing. Lastly,
my thanks are due to Brian Guerin, Edward Payne, and other members of
Elsevierfortheirdedicationinbringingthisbooktoitscompletion.
BROMLEY 2017 RCL
Theauthorandpublishersthankthefollowingforpermissiontousecertain
materialfrombooksandarticlesandtouseillustrationsasabasisforfiguresin
this volume:
Tables 1.4 and 14.1 and Figs 1.16, 4.5, 7.2, 10.11, and 13.1 from the
CIBSEGuidebypermissionoftheCharteredInstituteofBuildingServices
Engineers.
Fig. 1.4 courtesy of the FISCHER company.
Fig. 3.2 (redrawn) by permission of McGraw Hill Book Co.
Table4.4warmtemperaturesintheUnitedKingdom,CIBSEGuideA.
Fig. 6.16 VAV Redrawn from Fig. 3.27 of the C1BSE Guide B, by
permission of the Chartered Institute of Building Services Engineers.
Fig. 7.7 based on illustrations, courtesy of Trox Brothers Ltd.
Fig. 9.4 courtesy of ICI Chemicals and Polymers Ltd.
Fig.10.6drawingofjacketedsteamhumidifierbasedonArmstrongvia
website.
Plates 11.3 and 10.8 supplied by Thermal Technology Ltd.
Fig. 11.4 by permission of Fl€akt Woods Limited.
Figs 12.2Bb and 11.4 supplied by Vokes Ltd.
Fig. 12.4 courtesy of Flaxt Woods—the United Kingdom.
xvii
xviii Acknowledgments
Fig. 13.7 Moody chart from D S Miller Internal FlowSystems, Second
edition, 1990, BHRA, Cranfield, the United Kingdom, with permission
(notethatthecharthassomeadditionalinformationthathasbeenremoved).
Figs13.7,14.5,14.7,14.11,and14.13(basedonfiguresinInternalFlow
Systems (Second Edition) 1990, BHRA, Cranfield, the United Kingdom)
by permission of DS Miller.
Fig. 16.8 hooded vane anemometer, courtesy of Inlec the United
Kingdom Ltd.
Fig. 16.9A courtesy of Holmes Valves Ltd.
Figs 16.11 and 16.13 courtesy Crane Fluid Systems.
Figs 16.9B, 16.11, and 16.15 courtesy of Crane Ltd.
Fig.19.1bypermissionoftheBuildingServicesResearchandInforma-
tion Association.
CHAPTER 1
Properties of Humid Air
Airistheworkingfluidforairconditioningsystems.Itisthereforeimportant
for the engineer to have a thorough understanding of the properties of air,
beforegoingontoconsidertheprocessesthatoccurwhenairpassesthrough
the various plant items that make up systems. The word psychrometry is
often used for the science that investigates the properties of humid air,
and the chart that shows these properties graphically is known as the
psychrometric chart.
Inthischapter,thevariousairpropertiesaredefined,andtheappropriate
equationsaregiven.Inderivingtheequations,itisusualtoconsidertheairas
consistingoftwogases,dryairandwatervapour.Eventhoughoneofthese
isstrictlyavapour,bothareconsideredtoobeytheidealgaslaws.Lastly,the
tables and chart, from which numerical values of the air properties are
obtained for practical calculations, are described and illustrated.
ATMOSPHERIC PRESSURE
Atanypointintheearth’satmosphere,thereexistsapressureduetothemass
of air above that point—the atmospheric pressure. Standard atmospheric
pressure at sea level is 1013.25mbar (usually approximated to 1013mbar),
butduetochangesinweatherconditions,therearevariationsfromthisstan-
dard pressure. For example, among the minimum and maximum values
recorded in London are 948.7mbar (in 1821) and 1048.1mbar (in 1825),
respectively; those recorded for North America are 892mbar (Long Key,
Florida, in 1935) and 1074mbar (Yukon Territory, Canada, in 1989) [1].
Atmospheric pressure varies with height above sea level, and for altit-
udes at which mankind lives, the rate of decrease (lapse rate) for a stan-
dard atmosphere may be taken as a reduction of 0.13mbar per meter of
height above sea level and an increase of 0.13mbar per meter of depth below
sea level.
AirConditioningSystemDesign ©2017ElsevierLtd.
http://dx.doi.org/10.1016/B978-0-08-101123-2.00001-7 Allrightsreserved. 1
2 AirConditioningSystemDesign
Example 1.1
Determine the standard atmospheric pressure for Nairobi, which is at an
altitude of 1820m above sealevel.
Solution
Standardsea-level atmospheric pressure 1013
Lapse rate¼(cid:2)1820(cid:3)0.13 (cid:2)237
Standardatmospheric pressure for Nairobi 776mbar
Atmospheric pressure may be measured by using a number of instru-
ments.Inthelaboratory,itisusualtouseaFortinbarometer,whileforsite
work an aneroid barometer is the most usual instrument. For continuous
recording, a barograph is used.
DRY AIR AND WATER VAPOUR
Dryairconsistsofanumberofgasesbutmainlyofoxygenandnitrogen.Itis
necessary to know the molecular mass of the dry air, and this is calculated
from the proportion each individual gas makes in the mixture. Table 1.1
gives this data, together with the calculation.
The sum of the molecular mass fractions is 28.97 and this is the value
taken as the mean molecular mass of dry air.
Watervapourissaidtobeassociatedwiththedryair.Itsmolecularmassis
obtained from the masses of its chemical composition H O, i.e.,
2
M ¼ð2(cid:3)1:01Þ+ð1(cid:3)16Þ¼18:02
H2O
Table1.1 Determinationofmolecularmassofdryair
Proportionby Molecular Molecularmass
volume(%) mass(%) fraction(%)
Gas (1) (2) (1)×(2)
Nitrogen, N 78.03 28.02 21.86
2
Oxygen, O 20.99 32.00 6.72
2
Carbondioxide, CO 0.03 44.00 0.01
2
Hydrogen, N 0.01 2.02 0.00
2
Argon, Ar 0.92 39.91 0.38
Molecular mass fraction 28.97