Refrigeration and Air conditioning Lecture 6.pdf

RAC notes

1. Department of Mechanical Engineering UMT Lahore
Dr Tipu Sultan
Dr. Tipu Sultan
Assistant Professor
School of Engineering, Department of Mechanical Engineering
University of Management & Technology (UMT)
Lahore 54770, Pakistan
[email protected]
https://sen.umt.edu.pk/MechanicalEngineering1/Academics/Faculty/Dr-Tipu-Sultan.aspx
333: Refrigeration & Air Conditioning (RAC)

2. Department of Mechanical Engineering UMT Lahore
Air-conditioning processes
Various air-conditioning processes.

3. Department of Mechanical Engineering UMT Lahore
Evaporative Cooling
Coolinginhot,relativelydryclimatescanbe
accomplishedbyevaporativecooling.
Thisinvolveseithersprayingliquidwaterintoairor
forcingairthroughasoakedpadthatiskept
replenishedwithwater,asshowninFigure.
Aircoolerusedinsummerisagoodexampleof
evaporativecooling.

4. Department of Mechanical Engineering UMT Lahore
Evaporative Cooling

5. Department of Mechanical Engineering UMT Lahore
Evaporative Cooling

6. Department of Mechanical Engineering UMT Lahore
Evaporative Cooling

7. Department of Mechanical Engineering UMT Lahore
Evaporative Cooling
Owingtothelowhumidityofthemoistairenteringat
state1,partoftheinjectedwaterevaporates.
Theenergyforevaporationisprovidedbytheair
stream,whichisreducedintemperatureandexitsat
state2withalowertemperaturethantheentering
stream.
Becausetheincomingairisrelativelydry,the
additionalmoisturecarriedbytheexitingmoistair
streamisnormallybeneficial.

8. Department of Mechanical Engineering UMT Lahore
E X A M P L E
Airat38°Cand10%relativehumidityentersan
evaporativecoolerwithavolumetricflowrateof140
m
3
/min.Moistairexitsthecoolerat21°C.Wateris
addedtothesoakedpadofthecoolerasaliquidat
21°Candevaporatesfullyintothemoistair.Thereisno
heattransferwiththesurroundingsandthepressureis
constantthroughoutat1atm.Determine
a)Themassflowrateofthewatertothesoakedpad,in
lb/h,and
b)Therelativehumidityofthemoistairattheexitto
theevaporativecooler.

9. Department of Mechanical Engineering UMT Lahore
Chemical Dehumidification
Silica gel

10. Department of Mechanical Engineering UMT Lahore
Chemical Dehumidification
Dehumidificationisprocessofremovalofmoisture
fromairinaconditionedroom.Indehumidification
thecoolingcoiltemperatureiskeptbelowdewpoint
temperature,thisallowsmoistureinairtocondense
andthiscondensateisremovedcausing
dehumidificationbuttheairtemperatureisalso
reduced.
Inchemicaldehumidification,chemicallikesaltis
spreadinstreamofairwhichabsorbswatervaporbut
thetemperaturedifferencecausedcannotbe
controlled.

11. Department of Mechanical Engineering UMT Lahore
Chemical Dehumidification
Example –silica gel

12. Department of Mechanical Engineering UMT Lahore
Chemical Dehumidification
Sorbent:arematerialsthathaveanabilitytoattract
andholdgasesandliquids,otherthanwatervapor---a
characteristicwhichmakesthemusefulforchemical
separationprocesses.
Desiccants:areasubsetofsorbents,theyhavea
particularaffinityforwater.
Manymaterialscanattractandholdmoisturebut
theircapacityofdoingsoislimited(5-25%oftheir
mass).
Incontrast,acommercialdesiccantcanholdupwater
vapor10-1100%ofitsdryweight.

13. Department of Mechanical Engineering UMT Lahore
Chemical Dehumidification
Incertainapplication,thehumidityrequirementis
verylowwhichcannotbeachievedbyacoolingcoil
duetolimitationoftemperature.
Insuchcases,airpassedthroughsorbents.
Thesolidsorbentincludes:silicagel,zeolites,
syntheticzeolites,activatedalumina,carbonand
syntheticpolymers.

14. Department of Mechanical Engineering UMT Lahore
Load Ratio Line
Forairconditioningdesign,supplyairtemperatureis
3°Cto11°Clowerthantheroomcondition.
2
1
Supply air condition
Room air condition

15. Department of Mechanical Engineering UMT Lahore
Psychrometry –Climate Classification
ClimateClassification
showsthevarious
approximatezonesof
temperature and
humidity on the
psychrometricchart.

16. Department of Mechanical Engineering UMT Lahore
Comfort Air-conditioning

17. Department of Mechanical Engineering UMT Lahore
Wecannotchange
theweather,but
wecanchange
theclimateina
confinedspaceby
air-conditioning.Abodyfeelscomfortablewhen
itcanfreelydissipateitswaste
heat,andnomore.
Today,modernair-conditioningsystemscanheat,
cool,humidify,dehumidify,clean,andeven
deodorizetheair–inotherwords,conditiontheair
topeoples’desires.
Therateofheatgenerationbyhumanbody
dependsontheleveloftheactivity.Foranaverage
adultmale,itisabout87Wwhensleeping,115W
whenrestingordoingofficework,and440Wwhen
doingheavyphysicalwork.
Whendoinglightworkorwalkingslowly,abouthalf
oftherejectedbodyheatisdissipatedthrough
perspirationaslatentheatwhiletheotherhalfis
dissipatedthroughconvectionandradiationas
sensibleheat.
HUMAN COMFORT
AND AIR-
CONDITIONING

18. Department of Mechanical Engineering UMT Lahore
A comfortable environment.
Thecomfortofthehumanbody
dependsprimarilyonthreefactors:the
(dry-bulb)temperature,relative
humidity,andairmotion.
Therelativehumidityaffectsthe
amountofheatabodycandissipate
throughevaporation.Mostpeople
preferarelativehumidityof40to60%.
Airmotionremovesthewarm,moistair
thatbuildsuparoundthebodyand
replacesitwithfreshair.Airmotion
shouldbestrongenoughtoremove
heatandmoisturefromthevicinityof
thebody,butgentleenoughtobe
unnoticed.
Animportantfactorthataffectshuman
comfortisheattransferbyradiation
betweenthebodyandthesurrounding
surfacessuchaswallsandwindows.
Otherfactorsthataffectcomfortareair
cleanliness,odor,andnoise.
Inanenvironmentat10°Cwith48
km/hwindsfeelsascoldasan
environmentat-7°Cwith3km/h
windsasaresultofthebody-
chillingeffectoftheairmotion(the
wind-chillfactor).

19. Department of Mechanical Engineering UMT Lahore
Comfort Zone
Comfort Zone –
statisticalstudieshave
beenperformedonlarge
numbersofsubjectsofall
ages, sexes and
nationalitiestoarriveata
quantitativedescriptionof
humancomfort.

20. Department of Mechanical Engineering UMT Lahore
Comfort Zone
Comfortzone…comfort
isaverysubjectiveterm!
Statistically,majorityof
human beingsare
comfortablewhentempis
between18-22
0
CandRH
is40-65%

21. Department of Mechanical Engineering UMT Lahore
Indoor Air Quality
Airqualityreferstothedegreeofpurityoftheair.The
levelofairqualityaffectsbothcomfortandhealth.
Airqualityisworsenedbythepresenceof
contaminantssuchas:tobaccosmoke,dustparticles,
biologicalmicroorganisms,andtoxicgases.
Cleaningfiltersmaybeusedtoremoveparticles.
Adsorbentchemicalsmaybeusedtoremove
unwantedgases.
Indoorcontaminantscanbedilutedinconcentration
byintroducingsubstantialamountofoutdoorairinto
thebuilding.

22. Department of Mechanical Engineering UMT Lahore
Indoor Air Quality
Thesubjectofairqualityhasbeenofmajorconcern
andimportanceinrecentyears.Evidenceshowsthat
therearemanypossibleindooraircontaminantwhich
canhavecausedserioushealtheffectsonoccupants.
Thephrases“sickbuildingsyndrome”and“building
relatedillness”havebeencoinedtoreferredtothese
effects.
Therecommendedinsidedesignconditionsboth
winterandsummeraregiveninTable.

23. Department of Mechanical Engineering UMT Lahore
Indoor Air Quality

24. Department of Mechanical Engineering UMT Lahore
Indoor Air Quality
SickBuildingSyndrome(SBS)
SickBuildingSyndromeincludesthefollowing
symptomology:
complaintsofacutediscomfort(e.g.headache;eye,
noseorthroatirritation;drycough;dryoritchyskin;
dizzinessandnausea;difficultyconcentrating;fatigue;
andsensitivitytoodors;rash)
unknowncauseofsymptoms
mostsymptomsvanishshortlyafteroccupantsleave
thebuilding

25. Department of Mechanical Engineering UMT Lahore
Indoor Air Quality
BuildingRelatedIllness:bydefinition,differentthan
SickBuildingSyndrome.BuildingRelatedIllnessis
generallyallergicreactionsorinfections,andsymptoms
andpatternsareasfollows:
complaintsofspecificsymptomssuchascough,chest
tightness,fever,chills,andmuscleaches
symptomscanbeclinicallydefined
causeofsymptomsisknown
complaintscancontinueafterhavingleftthebuilding

26. Department of Mechanical Engineering UMT Lahore
Indoor Air Quality

27. Department of Mechanical Engineering UMT Lahore
Indoor Air Quality
Generally,specificdesignconditionsarerequiredin
industrialapplicationsforoneormoreofthefollowing
reasons:
1)Aconstanttemperaturelevelmayberequiredfora
closetolerancemeasuringmachiningorgrinding
operationstopreventexpansionorcontractionofthe
machinesparts,machineproductsandmeasuring
devices.
2)ControlledRHisrequiredtomaintainthestrength,
pliabilityandregainofhygroscopicmaterialssuchas
textileandpaper.

28. Department of Mechanical Engineering UMT Lahore
Indoor Air Quality
(3)TheDBTandRHcontrolarerequiredtoregulatethe
rateofchemicalorbiologicalreactions,suchasdryingof
varnishesorsugarcoatings,preparationofsynthetic
fibersorchemicalcompounds,fermentationofyeastetc.

29. Department of Mechanical Engineering UMT Lahore
Introduction
Principles of air-conditioning
Type of air-conditioning
Air Conditioning System

30. Department of Mechanical Engineering UMT Lahore
Introduction
Definition-Airconditioningistheprocessofaltering
the properties
ofair(primarilytemperatureandhumidity)tomore
favorableconditions.
Thecontroloftheseconditionsmaybedesirableto
maintainthehealthandcomfortoftheoccupants,or
tomeettherequirementsofindustrialprocesses
irrespectiveoftheexternalclimaticconditions

31. Department of Mechanical Engineering UMT Lahore
Principles of Air-conditioning
Thegoalistokeepitmorecomfortableinsidethe
housethanitisoutside.

32. Department of Mechanical Engineering UMT Lahore
Type of Air-conditioning
Window air-conditioning system
Split air-conditioning system
Centralized air-conditioning system
Package air-conditioning system

33. Department of Mechanical Engineering UMT Lahore
Windows Air-conditioning System
Windowairconditionersareoneofthemost
commonlyusedandcheapesttypeofairconditioners.
Toinstalloneoftheseunits,youneedthespaceto
makeaslotinthewall,andthereshouldalsobesome
openspacebehindthewall.
Windowair-conditionerunitsarereliableandsimple-
to-installsolutiontokeeparoomcoolwhileavoiding
thecostlyconstructionofacentralairsystem.
Betteryet,whenthesummerheatdiesdown,these
unitscanbeeasilyremovedforstorage,andyoucan
usethewindowsillforotherpurpose

34. Department of Mechanical Engineering UMT Lahore
Windows Air-conditioning System

35. Department of Mechanical Engineering UMT Lahore
Split Air-Conditioning System
Thesplitairconditionercomprisesoftwoparts:the
outdoorunitandtheindoorunit.
Theoutdoorunit:fittedoutsidetheroom,houses
componentslikethecompressor,condenserand
expansionvalve.
Theindoorunit:comprisestheevaporatororcooling
coilandthecoolingfan.Forthisunityoudon’thaveto
makeanyslotinthewalloftheroom.
Further,thepresentdaysplitunitshaveaestheticlooks
andaddtothebeautyoftheroom.Thesplitair
conditionercanbeusedtocooloneortworooms.

36. Department of Mechanical Engineering UMT Lahore
Split Air-Conditioning System

37. Department of Mechanical Engineering UMT Lahore
Split Air-Conditioning System

38. Department of Mechanical Engineering UMT Lahore
Centralized Air-Conditioning System
Thecentralairconditioningplantsorthesystemsare
usedwhenlargebuildings,hotels,theaters,airports,
shoppingmallsetc.aretobeairconditioned
completely.
Thewindowandsplitairconditionersareusedfor
singleroomsorsmallofficespaces.
Ifthewholebuildingistobecooleditisnot
economicallyviabletoputwindoworsplitair
conditionerineachandeveryroom.
Further,thesesmallunitscannotsatisfactorilycoolthe
largehalls,auditoriums,receptionsareasetc.

39. Department of Mechanical Engineering UMT Lahore
Centralized Air-Conditioning System

40. Department of Mechanical Engineering UMT Lahore
Packaged Air-Conditioning System
Thewindowandsplitairconditionersareusuallyused
forthesmallairconditioningcapacitiesupto5tons.
Thecentralairconditioningsystemsareusedfor
wherethecoolingloadsextendbeyond20tons.
Thepackagedairconditionersareusedforthecooling
capacitiesinbetweenthesetwoextremes.
Thepackagedairconditionersareavailableinthefixed
ratedcapacitiesof3,5,7,10and15tons.
Theseunitsareusedcommonlyinplaceslike
restaurants,telephoneexchanges,homes,smallhalls,
etc.

41. Department of Mechanical Engineering UMT Lahore
Packaged Air-Conditioning System

42. Department of Mechanical Engineering UMT Lahore
New Invented Technology for Air-Conditioning System
DISTRICT
COOLING
SYSTEM
CHILLED BEAM
SYSTEM

43. Department of Mechanical Engineering UMT Lahore
District Cooling System
DistrictCoolingSystems(DCS)isasystemwhich
distributechilledwaterorothermedia,usually
providedfromadedicatedcoolingplant,tomultiple
buildingsforairconditioningorotheruses.

44. Department of Mechanical Engineering UMT Lahore
District Cooling System
TheObjectives:
Tocentralizedproductionofchilledwaterbyusing
districtcoolingplant.Thegeneratedchilledwaterwill
thenbechanneledtovariousbuildingblocksthrough
pre-insulatedseamlessundergroundpipes.

45. Department of Mechanical Engineering UMT Lahore
District Cooling System
TheAdvantages
1.Improveenergyefficiency
2.Protectenvironment
3.Savespaces
4.Improveurbanview
5.Reducemanpowerforoperationandmaintenance

46. Department of Mechanical Engineering UMT Lahore
District Cooling System
HowTheSystemWork?
DCmeansthecentralizedproductionanddistributionof
coolingenergy.Chilledwaterisdeliveredviaan
undergroundinsulatedpipelinetooffice,industrialand
residentialbuildingstocooltheindoorairofthebuildings
withinadistrict.Speciallydesignedunitsineachbuilding
thenusethiswatertolowerthetemperatureofairpassing
throughthebuildingsACS.
Theoutputofonecoolingplantisenoughtomeetthe
cooling-energydemandofdozensofbuildings.DCcanbe
runonelectricityornaturalgas,andcanuseeitherregular
waterorseawater.Alongwithelectricityandwater,DC
constituteanewformofenergyservice.

47. Department of Mechanical Engineering UMT Lahore
DCS Network Diagram

48. Department of Mechanical Engineering UMT Lahore
DCS Network Diagram

49. Department of Mechanical Engineering UMT Lahore
DCS-Application in Malaysia
KUALA LUMPUR
INTERNATIONAL AIRPORT

50. Department of Mechanical Engineering UMT Lahore
Chilled Beam System
ItisatypeofconvectionHVACsystemdesignedtoheator
cooledhighrisebuildingsuchascommercialbuilding.
It’sprimarilygivesoffitscoolingeffectthroughconvection
byusingwatertoremoveheatfromaroom.
Pipesofwaterpassedthroughthebeamsuspendedshort
distancefromtheceilingofaroom.
Asthebeamchillstheairaroundit,theairbecomesdenser
andfallstothefloor.
Itisreplacedbywarmerairmovingupfrombelow,causing
aconstantflowofconvectionandcoolingtheroom.

51. Department of Mechanical Engineering UMT Lahore
Chilled Beam System

52. Department of Mechanical Engineering UMT Lahore
Advantages
Simple to design and control
Smaller ductwork
Less mechanical space
Less maintenance
Increase comfort

53. Department of Mechanical Engineering UMT Lahore
Disadvantages
Notwellknowninourindustry
Higherconstructioncost
Manyengineersaren’tfamiliarwiththistechnology
Dewpointconcerns,buildingmusthaveagood
controlofhumiditytopreventcondensationonchilled
beamsurface.