applied psychrometrics for air conditioning systems€¦ · 02/05/2020 · kg per kg of dry air...
TRANSCRIPT
By
Eng. Chandana Dalugoda, CEng MIE(SL), FASHRAE, MCIBSE, GCGI (UK), MConsE (SL) Managing Partner, Chandana Dalugoda ConsultantsColombo, Sri Lanka
Applied Psychrometrics for Air Conditioning Systems
1 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
03/03/2012
2
CourseDescription
Firstlyunderstandingthebasiccontentsofthepsychrometricchartandthendiscussthebasicpsychrometricprocesses.AdetailedPsychrometricapproachiscarriedoututilisingthedataavailablefromcoolingloadcalculationstodeterminethecoilconditionsandselectionoftheairconditioner.Allfreshair,highlatentloadandhumiditycontrolapplicationsarediscussed.ImportanceofSensibleheatratioisdiscussedanddistinguishesthedeferencebetweenhigh&lowsensibleheatapplications.ThispresentationissuitableforyoungaswellasexperiencedengineersthatprovidebasicknowledgeofPsychometryanditsapplicationsinpractice.
2 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
03/03/2012
3
LearningObjectives1. ExplainPsychrometricDefinitions2. DescribePsychrometricProperties3. UnderstandthebasicPsychrometricprocesses&theChart4. Discussairmixingprincipleandcalculations5. ExplainhowPsychrometriccalculationsuseddefinecoilconditions6. UnderstandtheimportanceofapparatusdewpointtomaintainroomRH%7. RecognisetheimportanceofBy-passFactor8. Highlatentheatapplication9. HighSensibleheatapplication10.Alloutdoorairapplication
3 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 4
PsychrometricDefinitions
Dry-bulbTemperature–Temperatureasregisteredbyanordinarythermometer
Wet-bulbTemperature–Temperatureasregisteredbyathermometerwiththebulbcoveredbyawettedwickandexposedtomovingair.(ThermodynamicWetBulb-AdiabaticSaturationtemperature)
DewpointTemperature–Temperatureatwhichcondensationofmoisturebeginswhentheairiscooled
4 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 5
RelativeHumidity–Ratioofactualwatervapourpressureofairtothesaturatedwatervapourpressureofairatthesametemperature
SpecificHumidity-WeightofwatervapouringramsorKgperKgofdryair(MoistureContent)
Enthalpy -Quantityofheatintheairaboveanarbitrarydatum,in KJ/Kg.ofdryair.
(thedatumfordryairis0oCandmoisturecontent,waterat0oC)
PsychrometricDefinitions
5 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 6
SensibleHeatFactor-RatioofSensibleHeattoTotalHeat
AlignmentCircle-Locatedat24oCDBand50%RHusedwithsensibleheatfactortoplotvariousairconditioningprocesses
PsychrometricDefinitions
6 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 7
Usefulconversionfactors
Enthalpy Btu/lbofdryairx2.33gives
KJ/Kgofdryair
Mass 1lb=7000grains=0.454Kg
Flowrate Cubicfeet/minx0.472givesl/sec
7 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 8
History-PsychrometricPioneers1.Observation&PhilosophicalPeriod
1. AanaximenesofMiletus,(6thCenturyB.C.)GreekPhilosopherin570B.C.toGaius,PlinusSecundus,(23-79A.D.)–RomanNaturalist.
2.TheExperimentalSciencePeriod1. Alberti,LeoneBattista(1414-1472)ItalianPhilosophertoBockmann,CarlWilhelm,Jr(1773-1821),
German.3.TheBeginningofUnifyingTheoryRegardingTheBehaviourofAirAndWaterVapour
1. Dalton,John(1766-1844),EnglishScientisttoSwann,W.F.G.,EnglishScientist4.TransitionFromEmpiricalToRationalPeriod
1. Carrier,WillisH.(1876-1950)toKeenanJosephH.andKeyes,FredG.(1936),professorsofMIT,USA.5.TheMatureSciencePeriod
1. Goodman,William(1903-1993)ConsultingengineerChicago,IllinoistoNelson,H.F.andSauer,H.J.(2001),USACurtesyofDonaldP.Gatley-UnderstandingPsychrometrics
8 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 9
• Dry-bulbtemperature• Wet-bulbtemperature• Dew-pointtemperature• Relativehumidity• Humidityratio• SpecificVolume• SpecificEnthalpy
PsychrometricPropertiesofAir
9 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
Dry-BulbTemperature
Dry-bulbtemperaturesarereadfromanordinarythermometerthathasadrybulb.
10
32°C DB
Dry Bulb Temperature
10 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
Wet-BulbTemperature
Wet-bulbtemperaturesarereadfromathermometerwhosebulbiscoveredbyawetwick.Thedifferencebetweenthewet-bulbtemperatureandthedry-bulbtemperatureiscausedbythecoolingeffectproducedbytheevaporationofmoisturefromthewick.Thisevaporationeffectreducesthetemperatureofthebulband,therefore,thethermometerreading.
11
27°C WB
Wet Bulb Temperature
11 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
Thethirdproperty,dew-pointtemperature,isthetemperatureatwhichmoistureleavestheairandcondensesonobjects,justasdewformsongrassandplantleaves.
12
Dew-pointTemperature
19°C DPDew Point
Temperature
12 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 13
Humidity
Watervapourcondensationonwindowduetohighhumidity
Humidityistheamountofwaterintheair.Airisamixtureofgasses&watervapour.
HighHumidityaffectsdiscomforttooccupantsinbuildings.Alsoitaffectsthefurniture,equipment&material.Oftenwallsgetdampandcausefungus&mouldstoform,causinghealthriskstohumans.Highhumiditycanshortcircuitminiatureelectroniccircuits,hencesomeITapplicationswantsclosecontrolofRelativeHumidityandTemperatureinAir-conditionedrooms.
13 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
RelativeHumidity
RelativeHumidity
Amountofmoisturethatagivenamountofairisholding
=Amountofmoisturethatagivenamountofaircanhold
Thefourthproperty,relativehumidity,isacomparisonoftheamountofmoisturethatagivenamountofairisholding,totheamountofmoisturethatthesameamountofaircanhold,atthesamedry-bulbtemperature.
DefinitionTheratiooftheactualwatervapourpressuretothesaturatedwatervapourpressureatthesamedrybulbtemperature
14
14 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 15
RelativeHumidity
40%RH
Relative Humidity
15 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
HumidityRatio(MoistureContent)Finally,humidityratiodescribestheactualweightofwaterinanair–watervapourmixture.HumidityratiocanbeexpressedasKgofmoistureperKgofdryair,orasgramsofmoistureperKgofdryair.
16
13g/KgDA
Humidity ratio
16 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
WhatisFog?
17
Fogintheforeground
Fogbeginstoformwhenwatervapourcondensesintohnyliquidwaterdropletsthataresuspendedintheair.Fogcanbeconsideredatypeoflow-lyingcloudusuallyresemblingstratus,andisheavilyinfluencedbynearbybodiesofwater,topography,andwindcondihons
17 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
FogOccursWhenAirisSaturatedWhenthedry-bulb,wet-bulb,anddew-pointtemperaturesarethesame,theairissaturated.Itcanholdnomoremoisture.Whenairisatasaturatedcondition,moistureenteringtheairdisplacesmoisturewithintheair.Thedisplacedmoistureleavestheairintheformoffinedroplets.Whenthisconditionoccursinnature,itiscalledfog
18
FogareaofthePsychrometricchart
18 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
SlingPsychrometer
19
19 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
PsychrometricChart
20
20 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 21
21 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 22
PropertiesofPsychrometricChart
22 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 23
Temperature&RH
» Comparisonofoutdoorconditionsofdeferentlocations
Unit Colombo Chennai Delhi London
drybulb °C 33 38.5 43.8 28.3
wetbulb °C 28 28.3 29.6 19.8
RH % 68 46 36 52
23 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
EXAMPLESummerDesignConditions
» 32°CDB(drybulb)» 27°CWB(wetbulb)
Forexample,let'sassumethatthesummerdesignconditionsare32°Cdrybulband27°Cwetbulb.Whatistherelativehumidity,humidityratio,anddewpoint?
24
24 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda32°C DB
27°C WB
68%
25.4°C DP
25
Given32◦CDBand27◦CWB.Whatisthedew-pointtemperature,RH%&MoistureContent
20.5g/KgDA
25 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
30°C DB
20.4°C WB
40%
Given30oCDBand40%RHWhatisthewetbulbtemperature
26
26 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
32°C DB
27°C WB0.0208 Kg/Kg
34 KJ/Kg
Given15oCDBand12oCWB,whatisthemoisturecontentandenthalpy
27
27 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
PsychrometricsProcesses
28
28 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 29
PsychrometricProcesses
1. OA-SensibleCooling2. OB-Cooling&De-Humidification3. OC-De-Humidification4. OD-Heating&De-humidification5. OE-SensibleHeating6. OF-Heating&Humidification7. OG-Humidification8. OH-Cooling&humidification
29 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
SensibleCooling
21
30
Nochangeinmoisturecontent
h2
h1
Ø1
Ø2
w1=w2
SensiblecoolingtDB2>tDB1tWB2>tWB1
RH2<RH1
w2=w1
h2>h1Vs2>Vs1
t2t1
Sensible Cooling
ActiveChilledBeam
30 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
SensibleHeating
21
31
Nochangeinmoisturecontent
h2
h1
Ø1
Ø2
w1=w2
SensibleHeatingtDB1<tDB2tWB1<tWB2
RH1>RH2
w1=w2
h1<h2Vs1<Vs2
t2t1
Sensible Heating
HotWaterCoil
31 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
Humidification/De-humidification
Humidification
0
Enth
alpy
decr
ease
1
2
De-humidification
Enth
alpy
Incr
ease
32
w0
w2
w1
Ø1
Ø2
Ø0
HumidificationtDB0=tDB1twb1>twb0RH0<RH1
w1>w0
h1>h0Vs1>Vs0
t2t1=
De-HumidificationtDB0=tDB2Twb0>twb2RH2<RH0
w0>w2
h0>h2Vs0>Vs2
32 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
2
1
Cooling & de-humidification
33
Actualcooling&de-humidificationprocess
h2
h1
Ø1
Ø2
w1
Cooling&De-humidification
w2
t2 t1
Cooling&De-HumidificationtDB1>tDB2tWB1>twb2RH1<RH2
w1>w2
h1>h2Vs1>Vs2
Cooling&De-humidifyingCoil
33 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
2
1Heating & humidification
34
SpaceconditioningPsychrometricprocess
h2
h1
Ø1
Ø2
w1
Heating&Humidification
w2
Heating&HumidificationtDB1<tDB2tWB1<twb2RH1>RH2
w1<w2
h1<h2Vs1<Vs2
t2t1
34 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
2c
1Cooling & humidification
35
PsychrometricprocessforDesertCoolerstw&hconstant
Cooling&humidification Cooling&HumidificationtDB1>tDB2atWB1<tWB2a
RH1<RH2a
w1<w2a
Evaporativecooling
tWB1=twb2h1=h2b
Cooling & humidification
Evaporative cooling2b
2a
t1
35 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 36
EvaporativeCooling
36 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
1
37
Chemicalde-humidificationDesiccantdrying
Heating&de-humidification C&HtDB1<tDB2tWB1>twb2RH1>RH2
w1>w2
h1>h2Vs1<Vs2
Heating & de-humidification
t1
1
2
Ø1
Ø2
w1
w2
t2
Chemical de-humidifiers
37 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
AirMixingCalculation
2
1
38
Mixingconditionh2
h1
w1
t2 t1
w2
w33
t3
t3 = (t1 x m1) + (t2 x m2) (m1 + m2)
38 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
AppliedPsychrometricsforAirConditioningSystems
39
39 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 40
PsychrometricAnalysisofAirConditioningSystem
Outdoorconditions :Chennai38.5CDB,28.3CWBIndoorconditions :24CDB,50%(17CWB) Fromcoolingloadcalculations,totalcoolingcapacity:26.5kW,Sensiblecapacity :16.5kWOccupancy :50peopleDeterminetheenteringandleavingconditionsofthecoil&supplyairvolume
Airconditioner
38.5°CDB28.3°CWB
Roomconditions24°CDB17°CWB
24°CDB17°CWB
24°CDB17°CWB
1
534
22
Lectureroom50people115m2
40 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 41
Step-1Locatepoints1&2onthechart
1
250 RH%
Indoor&outdoorConditions
38.5CDB/23.2CWB
24CDB/50%RH
41 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 42
Step-2DeterminetheSHRanddrawtheRSHFlineThroughthepoint-2
RSHF=SH/TH=16.5/23.5=0.7
1
24
ConstructingSHRline
38.5CDB/23.2CWB
24CDB/50%RH
0.7SHRline
0.7SHR
42 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 43
Step-3Findtheleavingconditionofthecoil.Allwaysairleavesthecoolingcoilalmostsaturated,thusleavingaircanbeassumedAs90%RH.RSHFlineintersectswith90%saturationline,givesthecoilleavingcondition.ThisisOFFCoiltemperature,10CDB,9.4CWB
24
90RH%
CoilLeavingConditions
38.5CDB/23.2CWB
10.7CDB/9.8CWB
0.7SHRlineCoilleavingat10C
5
SpecificVolume0.814m3/kg
24CDB/50%RH
1
SpecificVolume0.899m3/kg
43 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 44
Step-4Tofindtheenteringconditionsofthecoil,airmixingequationisused. t3=[(t1xm1)+(t2xm2)]/(m1+m2)However,atthisstagewedonothavem2,thatissupplyairflowrate.
Henceweshallfirstdeterminethem2supplyairflowrate.
Tofindthesupplyairvolumeinwecanusethefollowingformula q=mCpΔT
q=ρvCpΔT(massflowrateisreplacedwithdensity&volumeflowrate
Then; v=q/ρvCpΔT
Volumeflowratev=16.5/(1.2x1.02x(24-10)) =0.9628m3/sSpecificvolumeatsupplyairconditionreadfromthechartas0.814m3/kg
Thenmassflowrateofsupplyair;m=v/vs=0.9628/0.855=1.182kg/s
44 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 45
Step-4continued….
TofindthemassflowrateoffreshairVolumeflowrateV=50x8.0L/s.p(approximation.NeedstofindVbz) =0.4m3/sSpecificvolumeatoutdoorconditionreadfromthechartas0.90m3/kgThenmassflowrateoffreshair=v/vs=0.4/0.90=0.44kg/s
Step-5
Tofindtheenteringconditionsofthecoil,airmixingequationisused. t3=[(t1xm1)+(t2xm2)]/(m1+m2)m2=1.182,m1=0.44 t3=[(38.5x0.44)+(24x1.187)]/(0.44+1.187) t3=27.9=28.0C
45 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 46
1
2
5
Step-6
Drawaverticallinefrom28Cuntilitintersectstheline1-2andthisisairmixingatcoilenteringpoint.ThisisONCoiltemperature.ThisisONCoiltemperature28CDB,19CWB
3
4
ADP-apparatusdewpoint
Coilleaving
Coilentering
CoilEnteringCondition
28CDB/19CWB
46 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 47
1
2
5
PsychromtericProcessesofTheAir-ConditioningSystem
Ifweneglectthefanheatandductheatgains,theairconditioningsystemLookslikebelow.3Psychrometricprocessesthatareinvolved;1. Airmixing2. Cooling&de-humidification3. Heating&humidification 3
4
Heating&
humidification
AirmixingCooling&de
-
humidification
AirConditioningCycle
47 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 48
1
2
5
PsychromtericProcessesofTheAirConditioningSystem
Withfanheatandductheatgains,theairconditioningsystemisgivenbelow.4Psychrometricprocessesthatareinvolved;
1. Airmixing2. Cooling&de-humidification3. Heating&humidification4. Sensibleheating
3
4Heatin
g&
humidification
AirmixingCooling&de
-
humidification
Fan&ductheat
ActualAirConditioningCycle
48 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 49
ΔhRoom
RoomloadcanbedeterminebyQ=Δh room x m
RoomTotalLoad
1
2
5
3
4
49 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 50
ΔhCoil
CoilcapacityCoilcapacitycanbedeterminebyQ=Δhcoil x m
CoolingCoilCapacity
1
2
5
3
4
50 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 51
PsychrometricAnalysisofActualAirConditioningSystem
1.Coilprocess:mtocc2.Coilleaving:cc3.Heatgainsupplyplenum:cctosf4.Supplyfan:sf5.Heatgainfromsupplyfan&duct:sftos6.Roomprocess:stoR7.Heatgainreturnplenum:Rtorp8.Heatgainreturnduct&fan:rptor
51 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 52
Tomaintainindoordesignconditionsof24CDB&do%RH,CoilDPshouldbebelow13C,RequiresCHWreturnnear13C.IfCHWreturnincreaseabove13Cwouldincreasetheroomconditions.CHWoutlettemperaturerestrictedminimum4.5C,toavoidfreezing.Hence,chilleroperatingconditionsusedasCHWout6.6C(44F)&CHWreturn12.7C(54F).
ImportanceofApparatusDewPoint
1
2
3
4
DP13C
MinimumCoilConditions4.5C
RoomConditions24CDB/50%RH
52 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
53
BypassFactor(BF)
AB
Tadp
TeDB
TlDB
Isafunctionofthephysicalandoperatingcharacteristicsoftheconditioningapparatusand,assuch,representsthatportionofairwhichisconsideredtopassthroughtheconditioningapparatuscompletelyunaltered.
BypassFactorisaffectedby 1.Availableapparatusheattransfersurface
Finspacing,numberofrowsetc. 2.VelocityofairthroughthecoilBypassFactor=A/B
BF=(tldb–tadp)/(tedb–tadp)
53 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 54
TypicalBypassFactors
Depthofcoils(rows)
Withoutsprays Withsprays8fins/in 14fins/in 8fins/in 14fins/in
Velocity(fpm)300-700 300-700 300-700 300-700
2 0.42–0.55 0.22–0.383 0.27–0.40 0.10–0.234 0.19–0.30 0.05–0.14 0.12–0.22 0.03–0.105 0.12-0.23 0.02-0.09 0.08–0.14 0.01–0.086 0.08–0.18 0.01–0.06 0.06–0.11 0.01–0.058 0.03–0.08 0.02–0.05
(ForFinnedCoils)
54 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 55
ApplicationsCoil
bypassfactorTypeofapplication Example
0.30to0.50Asmalltotalloadoraloadthatissomewhatlargerwithalowsensibleheatfactor(highlatentload)
Residence
0.20to0.30Typicalcomfortapplicationwitharelativelysmalltotalloadoralowsensibleheatfactorwithasomewhatlargerload
Residence,smallretailshop,Factory
0.10to0.20Typicalcomfortapplication Departmentstore,Bank,
Factory
0.05to0.10 Applicationswithhighinternalsensibleloadsorrequiringalargeamountofoutdoorairforventilation
Departmentstore,restaurant,Factory
0to0.10 Alloutdoorairapplication Hospitaloperatingtheatre,Factory
55 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 56
SpecificationsoftheAirconditioneris;1.TotalcoolingcapacitykW2.SensiblecoolingcapacitykW3.SensibleHeatRatioSHR4.CoilconditionsONcoil/OFFcoiltemperature5.SupplyairvolumeL/s6.OutdoorfreshairvolumeL/s
SpecificationsofAirConditioner
56 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 57
1
2
5
WhenhighoccupancyprevailssuchasAuditoriumorBanquetHall,psychrometricProcessbecomeHighLatentloadapplication.Whenthelatentloadincreases,RoomSHRlinedonotintersectwithcoilratioline,whichisthecoilleavingconditions.Fromtheleavingconditions,ahorizontallinehastoDraw,untilRoomSHRlineintersects.Thishorizontallinerepresentthereheatrequiredafterthecoiloutlet.Thisre-heatingwoodbeanenergywaste,henceheatexchangerssuchasHeatpipeorface-bypassisusedWithoutelectricalenergybeingused.
3
4
Reheat
Supplyairtoconditionedspace
HighLatentLoad
Re-Heating
57 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 58
Electricre-heatingcoilsareplaceddownstreamofthecoolingcoilforde-humidificationofsupplyairinhighlatentloadapplications.Usuallytheseare3-stagedelectricheatersworkingon3-phaseelectricity.WithincreasingelectriccostsusageofelectricheatingisdiscouragedbyASHRAEStandards
ElectricHeatersuseforRe-Heating
58 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 59
Wrap-around,de-humidification,noncontrolledheatpipe(DHP)useforre-heatingtheairleavingevaporatorforde-humidificationwithzeroenergyinput.
Heatfromreturnairpickedupbyupstreamheatpipecoilandtransferittothedownstreamheatpipecoilplacedafterthecoolingcoil,whichre-heatstheairtoachievefurtherde-humidificationrequired.
Theseweresuccessfullyusedinworld’ssecondPassiveHouseRatedbuildinginSriLanka,tomaintainrelativehumiditydownto52~54%withoutcontrol.
HeatPipeuseforRe-HeatingwithZeroEnergyInput
59 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 60
Face&BypassDampersforRe-HeatingwithZeroEnergyInputTherearesetofphaseandbypassdampersareinstalledupstreamofthecoolingcoil.Normaloperationairpassesthroughfacedampersandenterthecoolingcoil,wherebypassdampersareclosed.Whenyouneedextrade-humidificationforhighlatentlands,bypassdampersopensandsomeofthereturnairbypassesthecoilandenterssupplyairstreamthusaddingmoreheatingtoair.
60 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 61
2
ServerroomCoolingLoadscomprisesofSensibleheatingonlyandroomSHR=0.9maybe1.00.Nolatentloadsoroomratioandcoilratiolinesarehorizontal.Moisturecontentofairisconstant.Coilloadisfrom4to1andtheroomloadis4to3.
SuchapplicationisServerRoomairconditioning.Deferencebetweenserverroom&comfortcoolingisheatdensity;5000W/m2vs250W/m2.Highdensityheatandclosecontroloftemperature/relativehumidityaretheDesigntargetsofITcooling.
3
Supplyairtoconditionedspace
HighSensibleHeatApplications
Δh Coil
2
3
14
RoomAir
Supplyfanoutlet
HeatingCoiloutletCoolingCoiloutlet
Δh Room
61 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 62
ITCooling&ServerRoomApplications
ServerroomorITcoolingrequireclosecontrolofTemperature&Humidity.Indoorconditionsasper1999ASHRAEApplications;22℃±1℃and50±5%RH.Typicalsupplyairtemperature14℃andreturnairtemperatureis24℃&45%RH.
62 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 63
2
Coilneedstohandlelargelatentload,coildepthupto8to10rowsmayrequire.Evaporatorcapacitycontrolrequiredwithfreezingprotection.Usuallycoilloadsare2.5to3.0timeslargerthancomfortACsystems.ApplicationsareOperatingRooms,ICU,CCRetc.
OutdoorairDirectlypassthroughthecoolingcoilandCooled&De-humidifiedtocoilleavingconditionsandenterstheroom.Noairwillbecirculated,allairisexhaustedwhilekeepingspacepositivelypressurised.
3
Supplyairtoconditionedspace
ALLOutdoorAirApplications
ΔhCoil
2
3
1
OutdoorAirIntake
RoomCondition
63 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda 64
AllFreshAirApplicationsforOperatingTheatres
100%freshairfromoutdoors,filteredandcooled&de-humidifiedbeforeenteringtheOT.Allroomairexhausted,creatingpositivepressureintheOT.SupplyairUni-directionalflow(laminarflow)iscreatedandreturnair(exhaustair)pickedupbywallextractgrillsatfloorlevel.
64 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020
©ChandanaDalugoda
Q&A
10/4/2016
65
65 2-APPLIED PSYCHROMETRICS FOR AC SYSTEMS - May 2, 2020