WhattoExpect• Mechanicalregulationmethods
• VFDbasics• HowVFDssaveenergy• BACnetbasics• UsingVFDsandBACnettogethertosaveadditionalenergy
BeforeWeStart…Howmanyare:• Maintenance?• Buildingengineers?• Buildingmanagers?• Consultingengineers?• Distributors?• OEMs?• Others?
BuildingAutomationSystem(BAS)Objective
Buildingperformanceandcomfort– Whatiscontrolled?
• Flow– Air– Water
RegulatingFlowMechanicalMethods
– Dampers– Valves– Variablepulley
Possibleissues– Motorisconstantlyrunningatfullspeed– Motorcycledon/offtoregulateflow
• Largevariancefromsetpoint
MotoratFullSpeedWhyisamotorrunningatfullspeedanissue?
– Alwaysdrawingcurrent• Systemlosses(I2R)• Lowpowerfactor
MotorCyclingWhyiscyclingamotoronandoffanissue?
– Startingamotoracrossthelineresultsin6–8timesmotornameplatecurrent.
• Mechanicalstress• Electricalstress• Canresultindemandchargesduringpeaktimes!
Startingcurrent
Motorfullloadcurrent
6xto8xMotorFLA
Time
Curren
t
AlternateOptionIsthereanalternateoption?
– RegulatemotorspeedwithaVFD.
Time
Motorsp
eed
MotorratedspeedSystemfeedback
WhatisaVFD?VFD=VariableFrequencyDrive
– Alsoknownas• Drive• Adjustablefrequencydrive(AFD)• Adjustablespeeddrive(ASD)• Inverter
HowDoesaVFDWork?• IncomingpowerisatafixedACvoltageandfixedfrequency,e.g.460Vac,60Hz.
• InordertocontrolanACmotor,thevoltageandfrequencyneedtobeadjusted.
VFDBasicOperation• VFDtakestheincomingvoltageandconvertstoDC.
• ItinvertstheDCbacktoACbypulsingitinaregulatedfashion(pulse-widthmodulationorPWM).
PowerFactorPowerfactorcanbeviewedashowefficientlytheloaddrawspower.
– Lowerpowerfactor=higherdisplacement=higherreactivepower
PowerFactor
AngulardisplacementbetweenVoltageandCurrent
VoltageCurrent
Θ
ReactivePowerReactivepoweriswastedenergy.
– HigherreactivepowerincreaseskVA.
– HigherkVArequiresalargertransformer.
– HigherkVAcanincreaseutilitycompanydemandcharges.
VFDInputCurrentVFDdrawscurrentonlywhenneeded.
– Reactivepower≈0– Apparentpower≈realpower
PowerFactorwithStandardVFD
Voltageandcurrentnearlyin
sync
VoltageCurrent
VFDFrontEnd• VFDfrontendconsistsofdiodebridge• CurrentflowsthroughthediodebridgetochargetheDCcapacitors(DCbus)– ThisonlyhappenswhenDCbusvoltageislowerthanincomingACvoltage
3-phaseinput
DCcapacitor
Diode Bridge
DC Bus
AffinityLaws
05
101520253035404550556065707580859095
100
% of
…...
Speed (RPM)
Flow - Torque - Output Power
Flow Rate Torque (Pressure) Output Power
𝐹𝑙𝑜𝑤↓1 /𝐹𝑙𝑜𝑤↓2 = 𝑅𝑃𝑀↓1 /𝑅𝑃𝑀↓2
𝑇𝑜𝑟𝑞𝑢𝑒↓1 /𝑇𝑜𝑟𝑞𝑢𝑒↓2 = (𝑅𝑃𝑀↓1 /𝑅𝑃𝑀↓2 )↑2
𝑃𝑜𝑤𝑒𝑟↓1 /𝑃𝑜𝑤𝑒𝑟↓2 = (𝑅𝑃𝑀↓1 /𝑅𝑃𝑀↓2 )↑3
Two Motors Run by Drives
SavingsExampleAcross the Line
1 fan @ full speed
100% Speed à 100% Flow 100% Speed à 100% Torque 100% Speed à 100% Power
2 fans x 12.5% Power each fan = 25%
75% Power Reduction!
2 fans each @ half speed
50% speed à 50% Flow 50% speed à 25% Torque
50% speed à 12.5% Power
Pulse-widthModulationVFDsusesInsulated-GateBipolarTransistors(IGBT)foroutput
– InvertsDCbacktoAC• Accomplishesthisthroughpulse-widthmodulation
IGBT
AdditionalBenefitsLessmechanicalwear
– Beltslastlongerwithcontrolledrampofmotor
Lowersystemcomplexity– Reducesneedtodeterminetheoptimalgearboxorpulleyratio.
Betterregulation– Acrossthelineoperationresultinasinglespeed.Thisspeedmightnotbeoptimal.
BACnetOverviewBACnetisBuildingAutomationControlnetwork
– CreatedandMaintainedbyASHRAE• 1995–BecameASHRAE/ANSIStandard135• 2003–BecameISO16484-5
– ProvidesinteroperabilitythroughthoroughtestingoutlinedbyBACnetTestingLaboratories(BTL)
PICSProtocolImplementationConformanceStatement(PICS)
– RequiredforALLdevices– Definesthedevice
• Devicetype• Objectssupported• Connectiontype• …andmore!
BACnetObjectsWhatisanObject?
– Canbethoughtasa“Datapoint”– Definedbyproperties
Property Value
Object_Identifier AV10
Object_Name OutputFrequency
Object_Type AnalogValue
Present_Value 21.21
Units Hz
Client/ServerModel• Client–Sends
informationrequestorcommandtoserver.
• Server–Respondstoclient’sinformationrequestorperformsrequestedcommand.
Whatisyouroutputfrequency(AV10)?
I’moutputting21.21Hz.
BACnetAdvantage#1Simplification
– ReducefrommanywirestoTWO.• Start,stop,frequencyreference,andmiscellaneousmonitorsneedatleastonewireforeachsignals.
WhatWeAccomplished• Drawbacksofmechanicalregulation
• VFDbasics• HowVFDsprovideenergysavings• BACnetbasics• Howthecombinationcanincreasesavings