Balancing Valves Handbook - PARTcommunity

BalancingValvesHandbook

3 Cimberio HandbookCimberio made in Italy

1 INTRODUCTION 4 2 THEIMPORTANCEOFFLOWREGULATION 4 2.1 Principlesforbalancinghydronicsystems 4 2.1.1 Heattransferatreducedflowrate 4 2.1.2 Heattransferatexcessiveflow 6 2.1.3 Chilledwaterterminal 6 3 REGULATINGVALVESANDFLOWMEASUREMENTDEVICES 7 3.1 Manualbalancingvalves 8 3.1.1 Examples:Comparisonbetweenabalanced andanunbalancedsystem 9 3.1.2 Doubleregulatingvalves 13 3.1.3 Regulating2-waycontrolvalve 13 3.1.4 Fixedorificeflowmeasurementdevices 14 3.1.5 Fixedorificedoubleregulatingvalves 15 3.1.6 Variableorificedoubleregulatingvalves 16 3.2 Fixedorificeversusvariableorifice 17 3.2.1 Flowmeasurementaccuracy 17 3.2.2 Whyflowmeasurementaccuracyisimportant 17 3.2.3 Conclusion 18 3.3 Automaticbalancingvalves 18 3.3.1 Constantflowregulator 18 3.3.2 Differentialpressurecontrolvalves 20 3.3.3 Pressureindependentcontrolvalves 23 4 DESIGNCONSIDERATIONS 25 4.1 Self-balancingarrangements 25 4.2 Velocities 26 4.3 Pumpselection 26 4.4 Variablespeedpumps 26 4.5 Systemcleanliness 26 4.6 Ventinganddraining 26 4.7 Access 27 5 GUIDELINESFORVALVESELECTION 27 5.1 Terminology 27 5.2 Selectioncriteria 28 5.3 Selectionprocedure 28 5.4 Softwareforselection 29 6 MEASURINGFLOWRATE 30 6.1 Fluorocarbon/mercurymanometer 30 6.2 Digitalmanometer 31 7 FLOWREGULATIONPROCEDURE 32 7.1 Proportionalbalancing 32 7.2 Indexcircuit 32 7.3 Proportionalbalancingprocedure 33 7.4 Reporting 33 8 INDEXOFFIGURES 34 9 INDEXOFTABLES 3510 BIBLIOGRAPHY 35

Index

BalancingValvesHandbook

4Cimberio made in Italy Cimberio Handbook

1.Introduction

Thisguideexplainshowtoselect,installandoperateCim-berio’srangeofregulatingvalvesandflowmeasurementdevices.Theproductsdiscussedareprimarilyintendedforuseinheatingandairconditioningsystems.

Theguideisintendedforengineersinvolvedinthedesignofsystems,andtheselectionofregulatingvalvesandflowmeasurementdevices.Itisalsoaimedatinstallingcontrac-torswhomayneedtointerprettheengineer’sinstructionsandinstalloroperatetheseproducts.

TheguidealsoestablishesthecaseforCimberio’shighaccuracyfixedorificeregulatingvalves.

This typeofvalvehasgeneralacceptance inmanypartsof the world due to the benefits of flow measurementaccuracyandperformance.ThereasonsforitsincreasingpopularityovervariableorificevalvesaresummarisedinSection3.2.

The advantages of automatic balancing valves are ana-lysedinSection3.3.

2.Theimportanceofflowregulation

Thepossibleconsequencesofinaccurateflowregulationareasfollows:

Failure to achieve design temperatures: Terminals re-ceiving too little flow may not deliver their intendedamountsofheatingorcooling.Thiswillmeanthattheareastheyservemayfailtoreachdesigntemperaturesunderpeakloadconditions.

Wastedenergy:Asystemwithpoorflowbalancingwillheatuporcooldownunevenlyi.e.theareasstarvedofflowwilltakemuchlongertoreachtheirdesigntem-perature thanareaswhichhaveexcessflowrate.Thismeansthatthesystemasawholewillhavetooperateforlongerperiodsinordertoensurethatdesigntem-peraturesareachievedduringoccupancyperiods.

Noise, erosion or air and dirt blockages: Unbalancedsystemswillhaveregionsofexcessflowandregionsofreducedflow.Excessiveflowvelocitiesmaygiverisetonoise generation and erosion of system components.Reducedflowvelocitiesmayencouragethesettlementofdirtparticlesorairbubbles.

Poorcontrolvalveresponse:Modulatingcontrolvalvesmaybeunable to controlproperly if the circuits theycontrolstartoffwithtoomuchortoolittleflow. Inacircuitreceivingtoomuchflow,thefirstpartofthecon-trolvalve’straveliswastedreturningtheflowratebacktoitsdesignvalue.Inacircuitreceivingtoolittleflow,the action of the control valve may cause a dramaticdropinheattransfereffectivelymakingthecontrolleractason/off.

Figure1Effectsofflowvariation

Difficultyadjustingsystemperformance:Ifthereisnoclearrecordofflowratesandvalvesettings,itbecomesverydifficult,duringsubsequentoperationofthesys-tem,tocorrectperformanceproblemsorfinetunethesystemtoachieveoptimumperformance.

2.1Principlesforbalancinghydronicsystems

2.1.1HeattransferatreducedflowrateThe room heat emitters undergo a reduction in outputcapacityiftheirinputflowrateisreduced.

BalancingValvesHandbookIntroduction

DESIGNFLOWRATE(Design∆T=20KandSupplytemperature=60°C)

0% 20% 40% 60% 80% 100%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

DESIGN HEAT TRANSFER %

AVARAGE TEMPERATURE °C

INLET TEMPERATURE °C

OUTLET TEMPERATURE °C


Let’s consider a classical emitter, fed at a constant tem-peratureof60°Candanalysetheinfluencethatflowvari-ationshaveontheheatoutputcapacity.

Atthedesignoperatingconditionsyouhavethenomi-nalflowratewiththetemperatureriseadaptedduringthesizingphase;

Reducingtheflowratealsoreducestheoutputcapacity(the reductionalsodependson thedelivery tempera-ture);inthiscase,iftheflowrateisreducedto40%,thecapacitywillbereducedto70%ofthenominalcapac-ity;

Thetemperatureriseincreaseswiththereductionintheflowrate;

Ifacontrolvalvereducestheoutputcapacityto50%ofthenominalcapacity,theflowrateshouldbereducedtoabout22%.

Intransferringtheheatfromtheheat-transferfluidtotheair,theparameterthateffectsefficacythemostisthere-forethedifferencebetweenthemeantemperatureofthewaterandthatoftheair.

Toremedyanundersizedemitteroneveryoftenraisesthesystem’ssupplytemperature.Thegraphbelowshowshowthenecessary capacity canbeobtainedat reducedflowrates by simply increasing the supply temperature. Forexample,consideringanemitterdesignedwithagenericflowrateQthatdevelopsacapacityofXWattsatasupplytemperatureof60°C.Ifforwhateverreasontheactualflowrateisreducedto60%,asupplytemperatureofonly65°Cneedstobemain-tainedtohave95%oftherequiredcapacity.Theproblemseemstoberesolved,butonlypartly.

Therewillsurelybeotheremittersthatwillinsteadhaveaflowratethatishigherorequaltothatneeded.Inthiscasetheoutputcapacitywillbehigherthanwhatisnec-essary.Consideringanemitterthatreceivesthedesignedflowrate,anincreaseofthesupplytemperatureto65°Ccorresponds toan increase in capacityofapproximately16%.

Thisoperationhasthefollowingnegativeeffects:Thesystemmustsupplytheemittersforlongperiodstobeabletokeepthetemperatureconstantintherooms;Anincreaseintheheatloadmakestheemitterunabletomaintainthedesigntemperature;

Flowcontrolvalves(2-waycontrolvalves,Thermostaticvalves)withastandardrange(forexample30:1)couldhave an unstable system control (on/off) due to a re-duction in the flow rate and a resulting reduction inauthority;

Thelastaspecttoconsideristhetemperaturerise,de-signingfunctionalsystemswithhighflowratesandlowtemperature rises (5-10 K), any imbalance (reductionintheflowrate) isfairlywelltoleratedevenif largerpiping, more powerful pumps and thus more energyisneeded.Whilethesystemsthatworkwithlowflowratesandhightemperaturerisesaremoreconditionedbyasystemimbalance.Theyalsohavetheadvantageofreducingcostssincetheyrequiresmallerpiping,lesspowerfulpumpsandthuslessenergy.

BalancingValvesHandbookTheimportanceofflowregulation

Figure2Effectsofsupplytemperature

140%

120%

100%

80%

60%

40%

20%

0%

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

DESIGNFLOWRATE%

60,0

65,0

70,0

75,0


2.1.2Heattransferatexcessiveflow

Byoversupplyingtheemitterwegetafairly limitedin-creaseintheoutputcapacity:a200%increaseintheflowrateisequaltoan18%increaseinoutputcapacitywith8timesthepowerabsorptionforthepump(cubicrelation-shipbetweenflowrateandcapacity).

2.1.3Chilledwaterterminal

The figure below shows a typical application in coolingsystems:fan-coilwithinlettemperatureof7.2°C,∆Tof5.6Kandincomingairat26.7°Candoutgoingairat19.4°C.

Asforheating,theemittercurveisnotlinearandthecon-siderationsmadepreviouslygenerallyapply.

BalancingValvesHandbookTheimportanceofflowregulation

Figure3Effectsofextraflows

Figure4Effectsofflowvariationincoolingsystems

DESIGNFLOWRATE(Design∆T=20KandSupplytemperature=60°C)

TEM

PER

ATU

RE

RIS

E(°

C)

-20%

-20%

0%

0%

20%

20%

40%

40%

60%

60%

80%

80%

100%

100%

0%

0

10%

20%

2

30%

4

40%

10

8

6

50%

12

60%

70%

80%

90%

100%

120%

100%

80%

60%

40%

20%

0

0% 20% 40% 60% 80% 100% 120% 140% 160% 180% 200%

0% 0%

20%

40%

60%

80%

100%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

DESIGNFLOWRATE(Design∆T=5,6KandSupplytemperature=7,2°C)


3. Regulatingvalvesandflow measurementdevices

Thevalvesandflowmeasurementdevicesmostcommonlyusedinbuildingservicespipeworksystems,togetherwithsometypicalapplications,aredescribedinthissection.AsummaryofthedifferentvalveandflowmeasurementdevicetypesisprovidedinTable1.

1Featuredependsonthevalvemodel

DEVICE DEVICEFUNCTION FUNCTION

STANDARDTERMINOLOGY

STANDARDTERMINOLOGYDESCRIPTION DESCRIPTION

FLOWMEASUREMENT

FLOWMEASUREMENTREGULATION REGULATIONISOLATION ISOLATION

Isolatingvalve

Variableorificedoubleregulatingvalve

Regulatingvalve

Constantflowregulator(CFR)

Doubleregulatingvalve

Differentialpressurecontrolvalve(DPCV)

Fixedorificedevice

Electronicdifferentialpressurecontrolvalve(EDPCV)

Fixedorificedoubleregulatingvalve

Pressureindependentcontrolvalve(PICV)

Typicallyagateorfullboreballvalvewithlowresistanceandlittleauthorityoverflow.Regulatingvalve.

Adoubleregulatingvalvethatusesthepressuredropacrossitsplugasthemeansofdeterminingflowrate.

Typicallyaglobevalvewithsomeresistanceandgoodauthorityoverflowbutwhichcannotbelockedinanysetposition.Doubleregulatingvalve.

Self-actingcartridgevalve

Avalvethathasregulatingabilitybutwhichcanbelockedinitssetposition,andwithavalvesettingindicatortoenablethesettingtoberecorded.Fixedorificedevice.

Self-actingvalvewithaflexiblediaphragmwhosemovementisgovernedbyanadjustablespring.

Anorificedevicethatcanbeusedforflowmeasurementbymeasuringitspressuredropandrelatingthistoflowrate.Fixedorificedoubleregulatingvalve.

Self-actingvalvewhosemovementisgovernedbyanelectroniccontrollerwithadifferentialpressuresensor.

Afixedorificefittingeitherintegraltoorclosecoupledtoadoubleregulatingvalve.

2-waycontrolvalvethatincorporatesaregulatingfunctionandDPCV.

No YES

No YES

No No

YES No

YES YES

No YES

No No

YES YES

No YES

YES YES

YES YES

YES YES

YES No

No YES

YES YES

Table1Commonvalvetypesandtheirfunctions

BalancingValvesHandbookRegulatingvalvesandflowmeasurementdevices

8 Cimberio made in Italy Cimberio Handbook

3.1Manualbalancingvalves

Manualbalancingvalvesareinsertedtocreateapressuredropsothateverybranchofthesystemiscirculatingatthedesignflowrates.

Theyaretypicallyinstalledwherethereareareabranches,forexample,asseeninFigure5inaconstantflowsystemwithoutputcapacitycontrolsystembymeansofa3-waydivertingvalve.Thefunctioningcanbeschematicallyrep-resentedasfollows:ifthecontrollerrequestsenergy,thedivertingvalveopenstofeedthesupplyterminalbrancheswithheat-transferfluid;butifthesupplydoesn’tneedtobeinterruptedbecausethedesiredconditionshavebeenreachedintheclimatecontrolledarea,thevalvedeviatestheflowtowardsaby-pass.

Thisconditionwillclearlycreateahydraulicshort-circuit,sincetheopposingresistancefromtheby-passisdefinite-lylessthanthatoftheconnectedterminalbranches,andconsequently theotherbranches thatare stillopenwillreceiveareducedflow.

Thesolutionistocreateahydraulicresistanceintheby-passsothatitequalsthatoftheemitters.Thisisdonebyinstallingaregulatingvalveandproperlycalibratingthesystem.

For medium-large systems, a regulating valve shouldalso be inserted to prevent hydraulic imbalance prob-lemscausedbythenetwork’slinearlength:theterminalbranches “near” the circulator tend to have excessiveflows,whilethe“far”terminalbranchestendtohavein-sufficientflows.

TheinstallationdiagramcanbeseeninFigure6:

Thesameconsiderationscanbemadeifamixingvalveisinstalledinplaceofthedivertingvalve.

ThediagramseeninFigure7isthetypicalcheckmadeinvariablevolumesystems:theheatflowisregulatedbya2-wayvalvethatcanbeeitheroN/oFFormodulating-orratherwithaproportionaltypethermoelectricactuator.

onceagain,aregulatingvalveneedstobeinstalledduetotheproblemsofthesystem’slinearlength:asexplainedpreviously,thebranchesnearthecirculatorarealwaysfa-vouredmore(Figure8).

Figure5Constantvolumesystem:3-waydivertingvalve

Figure6Regulatingofa3-waydivertingvalvesystem

Figure7Variablevolumesystem:2-waycontrolvalve


9 Cimberio Handbook Cimberio made in Italy

ThesteelpipesareproducedaccordingtoEN10240stand-ardandhaveadiameterof2”(DN50)fortherisertubesand1”(DN25)forthebranches.Thelinearlengthofthenetwork is shown in Figure 10, the distance betweenfloorsis3mandthebranchesare5m:

Let’snowconsiderasystemwithoutbalancing(Figure11)where thereareonly2-wayvalves to control thefan-coils,resolvingthenetworkandobtainingthefol-lowingresults:

The first floor receives a flow excess of 9.2% (+2.8%heatcapacity)andthepumpheadis71.1kPa.

Cimberiohas2-wayvalveswithbuilt-inregulatingdevice(Figure9).

Anotherimportantaspecttoconsiderisifonebranchclosesbecauseithasreachedthedesiredtemperature,thenthebranchesthatarestillopenbecomeimbalancedbecauseithasaninfluenceonthehydraulicresistanceoftheentirenetwork.Thisproblemcanberesolvedusingvariablespeedpumps:anappropriatecontrollerwithinverteractionvar-ies the rotation speedand thus thepump’sheadallow-ingthedifferentialpressuretobecontrolledatitsends.It should nevertheless be considered that, in large andmedium-large systems, variable speed pumps are notenoughtokeepthedifferentialpressureswithinaccept-ablelimits,whichcanincreaseintheareabranchesandincorrespondencewiththevalvesoftheheatingunits.Thisaspectwillbecoveredinmoredetailwiththedifferentialpressurecontrolvalves.

3.1.1Examples:comparisonbetweenabalancedandanunbalancedsystem

Considerasimplesystemextendinginheightover5floorsaboveground,whichfeedsfan-coilswith25kWofheat-ingcapacityeachandadesign∆Tof15K.

Thecirculatingflowrateineachbranchcanbecalculatedusingthefollowingrelationship:

Q==1435l/h=0.3986l/sP

c·∆T

Figure92-waycontrolvalvewithregulatingdevice

Figure8Regulationofa2-waycontrolvalvesystem

Figure10Example1:smallbuilding

Figure11Example1:unbalancedsystem

1”

1”

1”

1”

1”

2”

2”

2”

2”

2”

1435l/h

1441l/h

1459l/h

1499l/h

1568l/h

44,6kPa

44,7kPa

45,1kPa

46,1kPa

47,8kPa

H=71,1kPaQ=7402l/h


Theflowrateisincreasedby39.1%andthecirculatorcon-sumesabout2.5timesmoreenergythanisactuallyrequired.

If a variable speedpump inusedanda constanthead ismaintained,whichinthiscaseis66.4kPa,wehavethefol-lowingsituation(Figure14):

Theincreaseintheflowrateisonly16.9%andthepowerconsumptionofthepumpis60%higherthannecessary.

Nowlet’slookatthesamenetwork,butbyadjustingthebalancingvalves(Figure12):

Allthebranchesreceivethedesignflowbuttheheadisreducedby6.6%andtheflowrateby3.7%.Itfollowsthatthepowerofthepumpisreducedby10.7%.

Byregulatingthesystem,energywasteforheating/cool-ingcanbeslightlyreduced:withbalancingeachterminalgetstherightamountofenergy,avoidingoversupplyingthehydraulicallyfavoureddevicesinordertosupplythedisadvantageddevices.

Manual adjustment is a simple and effective procedureevenifthereare limits: invariablevolumesystemsare-ductionintheflowrateinjustonebranchinfluencestheflowratesintheremainingbranches.Ifweconsidertheextremecase inwhichall thedevicesareclosedexcepttheoneclosesttothecirculatorandthatthisdoesn’thaveaspeedadjustment(traditionalpump),the resulting situation is shown in the drawing below(Figure13).

Figure13Example1:traditionalpump

Figure14Example1:variablespeedpump-constanthead

Figure12Example1:balancedsystem

1435l/h

1435l/h

1435l/h

1435l/h

1435l/h 1997l/h

44,6kPa

44,6kPa

44,6kPa

44,6kPa

44,6kPa 92kPa

H=66,4kPaQ=7175l/h

H=94kPaQ=1997l/h

oFF

oFF

oFF

oFF

oN

1667l/h65,1kPa

H=66,4kPaQ=1667l/h

oFF

oFF

oFF

oFF

oN


Andfinally,introducingaproportionalheadcontroller,weobtainthefollowing(Figure15).

Theflowrateisat92.1%andthepumpconsumes78.1%ofthepower.From the simple distribution network that we analyzedwecanconcludethat:

Balancingcan slightly reduce theenergyused for thecirculationoftheheat-transferfluid;

The manual valves balance the system in an effec-tive manner when there are no closures or shutter-ing of the flows of the individual terminal branches;Variablespeedpumpshelpreduceconsumptionbutdonotallowtheentiresystemtobemonitored.Theymustbeusedwithdevicesinstalledatsensitivepointsinthenetwork in order to correct any imbalances that thepumpscan’tdetectontheirown.

Thesedevicesareautomaticvalvesthat,aswewillseeinthefollowingchapters,canresolvethisproblem.

Butifweconsideramediumsizesystem,likethatseeninFigure16,thesituationdrasticallyworsens:

Ifthesystemisunbalanced(Figure17)thereisanextremeovercompensation,theterminalbranchesonthebottomfloorsaregreatlyover-supplied:theycanevenreachthreetimesthedesignflow.

Asyougoupthefloorsthetrendreverses,untilyougettothetopfloorswherethereisaflowratedeficitthatcanbeasmuchas42.7%.

Figure15Example1:variablespeedpump-proportionalhead

-1° level

1° floor

0 level

2° floor

3° floor

4° floor

5° floor

6° floor

0 level

-1° level

1° floor

2° floor

3° floor

4° floor

5° floor

6° floor

Figure16Example2:layout

Figure17Example2:unbalancedsystem

<-30%

-20÷-30%

-10÷-20%

-5÷-10%

5÷-5%

5÷10%

10÷20%

20÷30%

<30%

Table2Pumpstechnologiescomparison

Technology Flowrate

+16.9%Constanthead

Proportionalhead

Power

+60%

Traditional +39.1% +169%

-7.9% -22%

1321l/h40,6kPa

H=41,4kPaQ=1321l/h

oFF

oFF

oFF

oFF

oN


+18%

+17%

+16%

+15%

+13%

+10%

+08%

<5%0 level

-1° level

1° floor

2° floor

3° floor

4° floor

5° floor

6° floor

Thesituationimproveswithavariablespeedpump,andthe error is 18% with constant head pumps (Figure 20)and13%withproportionalheadpumps(Figure21).

+23%

+21,5%

+21%

+20%

+18%

+16%

+13%

+06%0 level

-1° level

1° floor

2° floor

3° floor

4° floor

5° floor

6° floor

Byregulatingthesystemusingbalancingvalves,wegetthe situation seen in Figure 18, where all the terminalbranchesreceivethedesiredflowrate.

In the case where the top floor of the building is com-pletelyshutoff(Figure19),withatraditionalpumptherewouldbeageneralincreaseintheflowrateswithapeakof23%.

+13%

+12%

+11%

+10%

+08%

+06%

+04%

-03%0 level

-1° level

1° floor

2° floor

3° floor

4° floor

5° floor

6° floor

Figure18Example2:balancedsystem

-1° level

1° floor

0 level

2° floor

3° floor

4° floor

5° floor

6° floor

Figure19Example2:traditionalpump

Figure20Example2:variablespeedpump-constanthead

Figure21Example2:variablespeedpump-proportionalhead


3.1.2-Doubleregulatingvalves

Theinstallationofdoubleregulatingvalvesatappropri-atepointsinthesystemisabasicrequirementforeffec-tive system regulation. Purpose manufactured doubleregulating valves should always be specified; gate typeisolatingvalvesorfullboreballvalvesarenotsuitableforregulation.

Doubleregulatingvalvesdifferfromordinaryregulatingvalvesinthattheflowsettingisnotlostwhenthevalveisclosed.


Figure22Doubleregulatingvalves

3.1.3-Regulating2-waycontrolvalve

Theyare2-wayvalveswiththermoelectricactuatorwhichcanberegulatedbyaswitchinstalledbelowtheheadandareusedinsystembrancheswheretheflowrateneedstoberegulatedorcut.

They can be regulated from fully open to the requiredflowsettingposition,andthenlockedatthatposition.

Thevalvemaythenbeclosedandreopenedtothesamesetting.Thebodyofthevalvealsofeaturesadialindicat-ingthesettingofthevalve.

Thisenablestheusertorecordthesettingforfuturerefer-enceFigure22.ShowsexamplesofCimberiodoubleregu-latingvalves.

727

Theactuatorscanoperateatdifferentelectricalvoltagesandcanbenormallyopen(N.o.),normallyclosed(N.C.)andpro-portional(inputsignalfrom0to10V).

Figure23Regulating2-waycontrolvalvewithactuator

788

Doubleregulatingvalves:section

Regulating2-waycontrolvalvewithactuator:section

Figure22

727

Figure23Regulating2-waycontrolvalvewithactuator

788788



3.1.4-Fixedorificeflowmeasurementdevices

Asimpleorificedeviceisacircularmetalplatewithacen-trallypositionedorificethatproducesarestrictioninthefluidflowcausingapressuredifferentialacrosstheplate.This pressure differential can be used to calculate flowrate.

Toachieveaccuracyrequirescarefuldimensioningoftheorifice and associated pressure tappings. Therefore theuse of manufactured fixed orifice fittings incorporatingthenecessarypressuretappingsisrecommended.

Fixedorificedevicesare sensitive toupstreamflowcon-ditions. Fittings that distort the pattern of flow such asbendsorrestrictionswillcausetheflowmeasurementac-curacytodeteriorate.

In order to achieve reliable flow measurement accuracyit is recommendedthata straight sectionofpipebe in-stalledupstreamofeachdevicemeasuringatleast5pipediametersinlength(Figure24).

Downstreamconditionsareless importantandforheat-ing/coolingapplicationscangenerallybeignored.

Figure 25 shows examples of Cimberio fixed orifice de-vices.

Theaccuracyoffixedorificeflowmeasurementdevicesistipically±5%.

Figure25Fixedorificeflowmeasurementdevices

721

Figure24Installation

Fixedorificeflowmeasurementdevices:section



3.1.5-Fixedorificedoubleregulatingvalves

Thefixedorificedoubleregulatingvalveisadoubleregu-latingvalveeitherclose-coupledtoafixedorificefitting,orwithanintegralfixedorificeasillustratedinFigure26.

Theflowmeasurementfunctionisseparatedfromthebal-ancing function, they can be regulated to nearly closedpositions,achievingexcellentaccuracy.

Itpermitsflowmeasurement,regulationandisolationtobecarriedoutatonelocation.Thedeterminationoftheflowrateisobtainedbyreferencetoasinglelinepressuredifferential/flowratechart.

Theregulatingvalve isusuallyanobliquepatternglobe

valveforsmallersizesorabutterflytypeforlargerpipediameters.

Computional fluid dynamics software has been used todemonstratethestablepressureandflowpatternsacrossbalancingvalvesatdifferentsettings(Figure27and28).Theanalysisshowsthat,duetothecompactbodyofthevalve,turbulentzonesandeddycurrentsareminimised,therebyensuringstableperformance.

Figure26Fixedorificedoubleregulatingvalves

747

Figure27Fixedorificedoubleregulatingvalves:pressures

Figure28Fixedorificedoubleregulatingvalves:velocities

Fixedorificedoubleregulatingvalves:section

Figure26Figure26Figure26

747


Figure29Variableorificedoubleregulatingvalves

787

3.1.6Variableorificedoubleregulatingvalves

Variableorificedoubleregulatingvalvesdifferfromfixedorificedoubleregulatingvalvesinthattheyusethepres-suredropacrossthevalveopeningforflowmeasurement.

Hencethetermvariableorifice;forthesevalvesthereisavariableopeningacrosswhichthepressuredifferentialismeasured.

Thesizeoftheopeningvariesdependingonthevalveset-ting.

Figure30showsvariableorificedoubleregulatingvalves.


Variableorificevalvesseldomachievetheaccuracyandre-liabilityoffixedorificevalves.

Theprecisioncandeterioratecreatingflowmeasurementdistorsionsbeyondacertainclosurepoint.

Inordertoavoidcommissioningproblems,theuseofthisvalvesshouldbelimitedtosituationswherethevalveswillnotneedtobethrottledbelow25%open.

Figure30and31showthedistributionofpressuresinthevalveandthefluxofvelocities.

Figure30Variableorificedoubleregulatingvalves:pressures

Figure31Variableorificedoubleregulatingvalves:velocities

Variableorificedoubleregulatingvalves:section

Figure29

787


Ifavalveispartiallyblockedthenahigherthannormalpressuredropsignalwillbeindicatedacrossitstappingssuggestingtotheuserthattheflowratethroughthevalveismuchhigherthanitactuallyis.Ifthevalvehasaminus12%errorunder cleanwater conditions, thiscould increase to minus 20% or more in real systemswith circulating dirt. The problem persists even whenthevalveiscompletelyblocked.Apressuredifferentialmaystillexistacrossthevalvesuggestingthatthereisflowwheninfact,thereisnoneatall.

3.2.2Whyflowmeasurementaccuracyisimportant

The importanceofflowmeasurementaccuracy is some-timesignoredonthegroundsthatmanytypesofheatingorcoolingemittersarerelativelyinsensitivetoflowratevariations.However, inaccurateflowmeasurementhasasignificant impact on plant sizing and energy consump-tions,ascaneasilybedemonstrated.Supposethattheminimumacceptablecoolingheattrans-ferforaparticularsituationwas10kWandthatanythinglessthanthiswouldleadtounder-coolingoftheroomorzone.ThiskWloadata6degree∆Tgivesaflowrateof0.40l/s.Hence,anyflowratelessthan0.40l/scouldresultinun-der-cooling.However,ifwhenitcomestomeasuringthisflow, the accuracy of measurement is potentially minus20%(ascouldbethecaseusingapartiallyblockedvari-ableorificevalve),thenasafetymarginmustbeaddedtotheoriginalloadandflowratetoallowforthis.Applying the same logic to a range of estimated flowmeasurement accuracies, one can establish the graphshowninFigure32.

Figure32Impactofflowmeasurementaccuracyonheatingandcool-

ingsafetymargins

3.2Fixedorificeversusvariableorifice

3.2.1Flowmeasurementaccuracy

Thefixedorificepatternofvalve isabletomaintainfarhigherlevelsofflowmeasurementaccuracyandrepeat-ability than the variable orifice valve for the followingreasons:

Theorificeisfixed:for a fixed orifice valve, as implied by the name, theorifice does not change. There is therefore a sin-gle kvs value for the flow measurement device andhenceasingle linegraphofflowrateversuspressuredrop. Because the orifice is fixed and has no movingparts, its accuracy can be guaranteed at any degreeof valve closure. The accuracy of a fixed orifice de-vice can be maintained within ±5% no matter whatthe setting of the attached double regulating valve.Foravariableorificevalvethevalvesettingandhenceorificedimensionwillvarysothatadifferentkvsvalueisrequiredforeachvalvesetting.Asthevalveclosestheareaopentoflowbecomesverysmall.Whenthevalveisnearlycloseditbecomesverydifficulttoensurefixedandrepeatablekvsvaluesacrossallproducts.Asare-sult,somevariableorificevalvesexhibitagraduallyde-terioratingflowmeasurementaccuracy(ofupto±12%orworse),asthevalveisclosed.

Accuracyisunaffectedbysystemdirt:mostheatingandcoolingsystemswillcontaincirculat-ingparticlesofmaterialwhichenteredthesystemdur-inginstallation.Suchmaterialcouldincludedirt,sand,jointingmaterials,orwheresteelpipesareused,corro-siondebris.

For a fixed orifice valve, such material is unlikely toblockthecircularopeningoftheorifice.

orifice sizes for the smallest valves are at least 4 mmin diameter, which is enough to allow most debristhrough.Hence,flowmeasurementaccuracyisusuallyunaffectedbycirculatingdirtparticles.

Foravariableorificevalvethat ispartiallyclosed,dirtcanbecometrappedaroundtheplugofthevalvecaus-ing the valve resistance to increase. Small diametervalvesthatarepartiallyclosed(50%orless)mayhaveopenings of less than 0.5mm around the valve plugwhichmakethemverysusceptibletoblockage.



Figure33Cartridgeandcrosssection

Itcanbeseenthatifflowmeasurementaccuracycanbeimprovedtobetterthanminus5%,whichisthecaseforfixed orifice valves, then the required safety margin onflowrateandkWoutputneedonlybejustover5%.Thisrepresentsafarmoreacceptablelevelofriskfortheper-formanceofthesystem.

3.2.3Conclusion

Itcanbeconcludedthatinthepast,manysystemshavebeendesignedwithsignificantsafetymarginsthathaveallowedsuccessfulsystemperformanceeventhoughflowrates were not accurately measured and set. However,this has been at the expense of over-sized heating andcoolingplantandconsequentwasteofenergy.Inviewofthetighteningrequirementsoninstalledcostandenergyconsumption, it canno longerbeassumed thatheatingandcoolingloadswillincorporatehealthysafetymarginswhichcanbeusedtooffsettheconsequencesofinaccu-rateflowmeasurement.

There isnowaclearneedforflowbalancingandmeas-urementdevicesthatgiveashighanaccuracyaspossible,andforaprocedurethatensuresthatanaccuratebalanceisachieved.Inthisrespect,fixedorificeregulatingvalveshave major advantages over variable orifice regulatingvalves.

3.3Automaticbalancingvalves

An automatic balancing valve has an automatic devicethatmaintainsaconstantflowinhydronicsystemswhentherearepressurefluctuations.Theyareusedinbothcon-stantvolumesystemsandinvariablevolumesystems.

3.3.1ConstantFlowRegulator

These are the simplest automatic valves and they main-tainaconstantflowwhichissetthroughthechoiceofanappropriatelysizedcartridge.Everycartridgehasacorre-spondingflowrateandrecognitioncodeandthesevaluesarereportedonthevalve’slabel.

Theoperatingprinciple isfairlysimple:observingFigure33weseethattheflowentersthelowerpartofthecar-tridge,wherethereisacalibratedhole.

Whenpassing,thefluidopposesathrustwhichbalancesthespringinsertedinsidethecartridge.Thebalancingofthehydraulicthrust-forceandtheresponseofthespringissuchthatitconditionstheopeningoftheoutlet.

Thereishoweverasystemoperatinglimit.Ifthepressureisnothighenough,thespringcontractingforcewouldbetoohighandthevalvewouldremainfullyopen.

The minimum opening differential pressure is approxi-mately15-20kPaanddependsonthetypeofcartridge.Thisispartofthevalve’scharacteristicdataandiscalledthestart-uppressure.

For large water networks, numerous cartridges can becombinedinsideonewaferbody,thuscreatinganauto-maticbalancingvalvehaving the same flow rateas thesumoftheflowsoftheindividualcartridges.


790790790790


Asseeninthefigurebelow,automaticvalveswithther-moelectricactuatorsforcontrollingtheopeningandclos-ingoftheflowarealsoavailable:

Thevalvecanalsobeusedasananti-condensationsystem,whereaminimumreturntemperaturetotheboileristypi-cally required in biomass systems. This condition can beguaranteedbyinsertinganappropriatelysizedautomaticvalve.

ACFRcanbeinsertedinsatellitesystemsinordertoin-creasethesystem’senergyefficiencyrating.Thevalvecanbeinstalledattheprimaryoutletoftheheatexchanger.

CFR’scanbeinstalledinconstantvolumesystems.Atypi-caldiagramisgiveninFigure34.Ascanbeseen,thesystemiscontrolledusingadiverting/mixingvalve thatdeviates the flow inahydraulic shortcircuit,by-passingtheemitters.

ByinstallingaCFRinthereturnbranch-generallysubjecttolessheatstress-theflowrateinthebranchwillremainconstantinanysituation.

The same diagram can be used for systems with amixingvalve.

CFRscanalsobeusedwithvariablespeedpumpsincon-stantvolumesystems,usinganactuator,generallya2-waycontrolvalve(regulatingvalvewiththermoelectricactua-tor).Theflowinthebranchcanbestoppedwhenthede-siredtemperatureisreached.

Inthiswaythebranchesthatarestillopenwillnotbeaf-fectedbyflowratevariations.

Figure34CFRinconstantvolumesystems

Figure35CFRinvariablevolumesystems

Figure38CFRwithheatexchanger

Figure35

Figure36CFRwithactuator

Figure36

Figure37Anti-condensation



Thevalvecanalsobeusedasaflowrestrictorinsanitaryhotwatersystems.Asillustratedbelow:

3.3.2DifferentialPressureControlValves

Thesevalvescontroladifferentphysicalpropertythantheprevious others: the differential pressure between twopointsinthesystem.

UsingaDPCVensuresaconstantheadinallthebranchesthatthevalveisconnectedto.

Asmentionedpreviously,aDPCVneedstobeinstalledinmedium-largesizesystems:variablespeedpumpsarenotabletocontrolanextensivesystemsincetheyaregener-allyinstalledinremotelocationswithrespecttotheusers.

Theyaretypicallyinstalledatthebaseoftherisertubes,asshowninFigure43,inbuildingswithonlyafewfloorsabove ground, or directly in the floor branches for tallbuildings(Figure44).

Thislasttypeofinstallationisusedtoobtainanexcellentregulating valve authority: a branched circuit sufficient-lyclosetothepump,subjecttoafairlyhighdifferentialpressureisconsidered.


Figure41Differentialpressurecontrolvalve

767

Figure39Waterheatingsystems-Boilers

Figure40Waterheatingsystems-Heatexchangers

Figure40

Differentialpressurecontrolvalve:section

767767



Figure42Electronicdifferentialpressurecontrolvalve

771

Figure43Differentialpressurevalveontheriser

Figure44Differentialpressurevalveonthemanifold

Electronicdifferentialpressurecontrolvalve:section

Figure42Figure42Figure42Figure42

771


Figure46Authority

Forthevalvetoeffectivelyperformtheregulationactionitmusthaveauthority inthecircuittobecontrolled,orratheritmustcreateapressuredropthatiscomparabletothatoftherestofthecircuittoberegulated.

Alowauthoritycausesalinearvariationtotheflowratewithopeningof the stem,whileahighauthority (>0.5)causesanon-linearpercenttypeopening.

Nowlet’sconsideringthesamecircuitwithadifferentialpressurecontrolvalveinstalledandthe∆psetat44kPa.

In this situation the circuit to be controlled will always besubject to the same differential pressure, but what’s moreimportantisthatthe2-wayvalvewillhaveanelevatedau-thority:

Thesameholdstrueforelectronicvalves:

Asnoted,thevalveauthorityisdefinedas:

Where∆p total is intendedtobethetotalpressuredropoftheconcernedcircuittoberegulated,includingthatofthevalve(2-waycontrolvalve,thermostaticvalve).

The2-waycontrolvalvehasamodestpressuredropwithrespecttothecircuittobecontrolled,andtheauthorityvalueis:

Thevalvehasalmostlinearcharacteristics,asseeninthegraph:

Figure46

ß===0.167∆pvalve∆ptotal

20120

ß===0.455∆pvalve∆ptotal

2020+24

∆pvalve∆ptotal

ß=


Figure45BranchwithoutDPCV

Figure47BranchwithDPCV

Figure48BranchwithEPCV


Figure51PICVstructure

3.3.3PressureIndependentControlValves

Asmentionedinthepreviousparagraph,thePICVsareacombinationofthreevalves:

DPCV;Regulatingvalve;2-waycontrolvalve.

Thestructureofthevalvecanbeseeninthefigure.

The fluid passes through the adjustable opening of themodulatingcontrolcomponentandactsagainstthepushofthespringinstalledinthecartridge,balancingtheforceandchangingthesectionoftheoutletholes.

Usingtheactuatororthemanualcommand,theflowratecanbeshutteredbasedontheneeds.

Thepreviousdiagramsshowatwo-wayvalveforcontrol-lingtheflow,aregulatingvalveandtheDPCVtoregulatethemaximumflowrateandtoadjustitbasedontheca-pacitytotransmittotheclimatizedrooms.Workingoutthepositionof thecomponentsused,wecangetadia-gramlikethis:

Thepreviousdiagramsshowatwo-wayvalveforcontrol-lingtheflow,aregulatingvalveandtheDPCVtoregulatethemaximumflowrateandadjustitbasedonthecapac-itytotransmittotheclimatizedrooms.Workingoutthepositionofthecomponentsused,wecangetadiagramlikethis:

Figure49Pressureindependentcontrolsystem

Figure49 Figure50BranchwithPICV

Figure52CimberioPICV

777

Pressuretestpoint

DPCV2-portvalve

andDRV

Figure52CimberioPICV

777

and


0,0000

0,1000

0,2000

0,3000

0,4000

0,5000

0,6000

0 50 100 150 200 250 300 350

FLO

W R

ATE

(l/s

)

DIFFERENTIAL PRESSUTE (kPa)

Pre-set 0,5

Pre-set 1,0

Pre-set 1,5

Pre-set 2,0

Pre-set 2,5

Pre-set 3,0

Pre-set 3,5

Pre-set 4,0


3.3.3.1Operatingprinciples

Regulation

When theelectric actuatororplastic cap ismissing, thevalve is normally closed by a swing. on the contrary, iftheplasticcapisscrewedortheelectricactuatorinstalledtherein,theywintheforceoftheswingandopenthevalve(seepicture).Theinletwatergoesthroughamodulatingcontrolcomponentwhosegeometrycanbemodifiedbyturningthepresettingdial,accordingtotherequiredflowrateinthesystembranchwherethevalveisinstalled.

Control

TwodifferentpressuresoperateontheDPCcartridge.Thefirstone is transmitted through thepassage connectingthevalveinlettothelowersectionof“p+”cartridge(seehydraulicschemepicture46);thesecondoneisregisteredatvalveoutletbytheflowrateselectingdevice“pa”.In order to keep constant the difference between thementionedpressures, theDPC cartridgeobturatoroper-atesbyclosingthewateroutletboretoreachthepresetflowrate,regardlessoffluctuatingpressureconditionsofthesystem.

ThegraphbelowshowsthecharacteristiccurvesofaPICVforthevariouspresetpositions.

Figure53PICVlayout

Figure53

Figure54FlowratevsDifferentialpressure

Flowrate-Differentialpressure

Modulation

Theelectricalactuatorperformsthemodulatingfunctionchangingthesectionofflowpassage.Whencontinuousmodulation is carried out, the temperature is kept un-der control.Thevalvekeeps the sameobturator stroke,regardlessof thepresettingdialposition.With continu-ousmodulation,controlisexcellentevenwithsmallflowopening.Thiseliminatetheon/offeffect.


4.Designconsiderations

4.1Self-balancingarrangements

Bycarefulsizingofpipes,flowratescanbemadetoap-proximately achieve a self-balance. A self-balancing ar-rangement will reduce the time required to regulatebranchflowratesandwilloftenmakeitunnecessarytobalanceflowsthroughterminalunits.However,thereareusuallycostandperformancepenaltiesthatmustbetak-enintoconsiderationwhenattemptingthissolution.

The self-balancing characteristics of a pipe distributionsystemmaybeimprovedbyconsideringthefollowingde-signoptions:

Reversereturn

Asimple reverse return layout is shown inFigure55. Inorderforthistypeofsystemtoself-balance,eachoftheterminalcircuitpressuredropsmustbeequal.Henceeachcircuit requires identical terminal units and similar pipelengthsandfittings.

Furthermore,opposingpressurelossesintheflowandre-turn mains must also be kept as similar as possible. ForexampleifthepressurelossinABvariessignificantlyfromthepressurelossinCDthentheself-balancingpropertiesmaybelost.

Reversereturnsystemsinvariablyinvolveextrapipework

sincealongerrunofreturnpipeisrequiredtocompletethecircuit.Thiscanincreasetheoverallcostofthesystemandincreasesystemresistanceleadingtohigherpumpen-ergyconsumption.

Itisthereforeimportanttoensurethattheuseofreversereturn systemscanbeeconomically justified incompari-sonwithaconventionallayoutwithregulatingvalves.

Lowlossheaders

Incircuitsbasedon lowlossheadersthe idea is tokeepthepressure loss inthemainsas lowaspossiblesothatthepressuredifferentialavailabletoeachcircuitisrough-lythesame.

Inorderforthisarrangementtoworktheterminaldeviceshavetobeidentical i.e.thesameflowrequirementandthesameresistancetoflowrate.Lowlossheadersrequirethatpipe circuits are sizedoneor two sizes larger thanwouldnormallybethecase.

Calibratedvalves

Itispossibletocalculatethetheoreticalpressurelossre-quiredacrossaregulatingvalveinordertoregulatetheflowratesinthesystem.Fromthesevaluestheindividualsettingsofeachregulatingvalvecanbepredicted,therebyavoidingtheneedforaproperflowbalancingprocedure.

Inpractice,anybalanceachievedinthiswayislikelytobeextremelycrudewiththepotentialforlargevariationsinflowrate.Thisisbecausethetheoreticalresistancesofcom-ponentsarenotveryaccurateandthemanufacturer’spres-surelossdatamaynotalwaysbeuptodate.

ManifoldDistribution

Manifolddistributionencouragesself-balancingbycreat-ingroughlyequalpressurelossesacrosseachcircuit.Thepressure differential across each circuit is the same be-causethemanifoldportsareveryclosetogether.Inordertotakeadvantageofthisproperty,thesuppliedterminalcircuitsmustagainbeas similaraspossible i.e. identicalterminalunitsandsimilarpipelengths.

Figure55Reversereturnlayoutforterminalbranches

BalancingValvesHandbookDesignconsiderations

AB

C D


4.2Velocities

Flowvelocitieswillbedeterminedbythechosenrangeofacceptablepressuredropspermetreofpipelength(typicallybetween100and350Pa/mformaindistribu-tionbranches).However, it isdesirabletoachieveve-locitieswithin the rangeof the recommendedvaluesgiveninTable2.

Very low velocities may reduce the accuracy of flowmeasurementdevicesandcouldfailtopreventtheoc-currenceofstaticairpocketsinthesystem.

4.3Pumpselection

The design of a multi-circuit water distribution systemshouldincludeacalculationofeachcircuit’sresistanceatthedesignwaterflowrate.Thecircuit that ispredictedtopresentthegreatestresistance isknownasthe indexcircuit.Usually,butnotalways, this is thecircuit servingtheterminalunitslocatedfurthestfromthepumpsource.Apumpshouldbeselectedtooperatewithinthestablepart of its characteristic, and be capable of producingbetween110%and115%ofthetotaldesignflowagainsttheestimatedindexcircuitresistance.

4.4Variablespeedpumps

It is sometimes argued that systems which use variablespeedpumpsand2-waycontrolvalvesdonotrequireflowregulation.Thebeliefisthatoncethe2-wayvalvesbeginto closedown,anyflowbalanceachievedwhen the sy-stemwasfullyopenwillbelost.

BalancingValvesHandbookDesignconsiderations

Excessiveflowvelocitiesmaygiverisetonoisegenerationanderosionofsystemcomponents.

Table2Recommendedrangeofwatervelocities

Furthermoreifsystemflowratesareoutofbalancethenthesystemwillgraduallyself-compensate,sincehighflowregions will heat up or cool down more quickly; then,whenthe2-wayvalvesclosedown,flowwill increase inpartsofthesystemthatwereoriginallystarvedofflow.

Inrealitythisargumentdoesnotholdup.Asystemwithunbalancedflowswilltakemuchlongertoreachdesigntemperatures.Areasthatarereceivingtoomuchflowwillnotreachtheirdesigntemperaturesverymuchfasterthaniftheflowswerecorrect.

This isbecause theheat transferacrossmostemitters isrelativelyinsensitivetolargeincreasesinflowrate.Hencethe flow could be double its design value but the heattransfermayonlybe10%more.Theconsequencewouldbeasystemthatwouldtakemuchlongertoachieveuni-formtemperaturesaroundthebuildingandwhichwouldneedtooperateformuchlongerperiods.

4.5Systemcleanliness

Dirtinthesystemcanadverselyaffecttheaccuracyofflowmeasurementdevicesandthereforesystemcleanlinessisofprimeimportance.Adequatefacilitiesmustbebuilt-inatthedesignstagesothatthesystemcanbeflushedtoremove dirt and jointing materials. Where appropriate,strainersshouldbelocatedtotrapcirculatingdirtparticlesbefore they reach small diameter regulating valves andcontrolvalves.

4.6Ventinganddraining

Airtrappedwithinapipeworksystemcanpresentseriousproblemsduringregulationbydistortingmeasuredflowrates.Thesedistortionsmaybeduetopumpsurging,cau-singrapidlyvaryingflowrates,orairbindingofterminalunits causing apparent blockages. Alternatively, systemairmaycausefalsereadingsatflowmeasurementdevicesduetoairpocketsinthepressuretappingpoints.

Featuresmustbebuiltintothepipeworksystemtoenablealltheairtobevented.Thesefeaturescantaketheformofairbottles,witheithermanualorautomaticairvents,orsimpleaircocksatthehighpointsinthesystemandatallplantitemsandterminalunits.

VELOCITY(m/s)PIPEDIAMETER

(mm) Minimum

Copper/Steel

0.6

1.25

15-50

oVER50

Copper

1.0

1.5

Steel

1.5

3.0

Maximum


4.7Access

Adequatespaceisnecessary,notjustforinstallationbutalsotopermitaccessforcommissioningandmaintenance.Attentionshouldbegivenatthedesignstagetoensurethatserviceductsandarchitecturalfeatures,suchasfalseceilings,willbe compatiblewith theanticipateddegreeofaccessibility.

Accesstoflowmeasurementdevicesandregulatingvalvesshouldbeaprimeconsideration.Inparticular:

at least 100 mm clearance from pressure test pointsmustbeallowedtoenablethemanometertubestobeconnectedwithoutbending;

access to double regulating valves must be such thatscalesandmarkingsareclearlyvisible;

thethicknessofpipeworkandductworkinsulation,andthesupportandbracketingarrangementsmustbean-ticipated;

thepositionsofaccesspanelsinfalseceilings,etc.mustbe properly co-ordinated with the flow measurementdeviceandregulatingvalvepositions.

5.Guidelinesforvalveselection

Thefollowinggeneralguidelinesareprovidedtoassistthedesignerintheselectionandapplicationofflowmeasure-mentdevicesandregulatingvalves.

5.1Terminology

Whenselectingvalvesitishelpfultounderstandthecom-monterminologythat isappliedtoregulatingvalves. Inparticularkvvaluesandkvsvalues.

Kv

Thekvvaluerepresentstheflowratethroughafullyopenvalveatatemperaturebetween5°Cand40°C,andmea-suredincubicmetresperhourthatwillinduceapressurelossof1bar(100kPa).Hencethekvvalueiseffectivelyameasureofthevalve’sresistance.

Whereavalveisclosecoupledtoaflowmeasurementde-vice,thekvvaluerepresentstheresistanceacrossthefullyopenvalveandflowmeasurementdevicecombined.

BalancingValvesHandbookGuidelinesforvalveselection

UsingSIunits,thepressuredropacrossafullyopenvalvecanbecalculatedfromtheequation:

whereQ=flowrateinl/s,and∆P=pressurelossinPa.

kvvaluesexpressresistanceasaninverse-inotherwordsthegreaterthevalve’sresistancethesmalleritskvvalue.Designengineersaremoreusedtothinkingofresistanceintermsofthepressurelosscoefficient(zeta).Thepressu-relossthroughanyfittingorcomponentcanbecalcula-tedfromtheequation:

wherep=fluiddensity inkg/m3,v=velocity inm/sand∆P=pressurelossinPa.

Thehigher thepressure loss coefficient, thegreater theresistanceof thefitting. For convenience, thisguideex-pressesfullyopenvalveresistancesintermsofbothkvandvaluesbasedonvelocitiesinmildsteelpipes.

Kvs

This term applies to the pressure differential across thetappingsonaflowmeasurementdevice.The“s”denotes“signal”,sinceitrelatestothepressurelosssignalmeas-ured by the commissioning specialist. For a given flowmeasurementdevicewithaknownkvsvaluethecommis-sioningspecialistcancalculateflowratefromthepressurelosssignalusingthefollowingequation:

whereQ=flowrateinl/s,and∆P=pressurelossinkPa

(the overall pressure drop through the device). Becausethereisanincreaseinstaticpressuredownstreamoftheorifice, theoverallpressure loss is actually less than themeasuredpressuredropacrossthetappings.Todetermi-netheoverallpressurelossthroughaflowmeasurementdevice,useitspressurelosscoefficient()inEquation2.

∆p=·p·v2

2

p=·

Q=·∆pkvs36

∆p=1.296·10·6 ( )2Q

kv

Equation1

Equation2

Equation3

device,useitspressurelosscoefficient()inEquation2.



5.3Selectionprocedure

1.Produce a system schematic diagram illustrating howthepipesinterconnecttoprovidefluidflowtoeachter-minalunit.

2.Fromheatingandcoolingloadcalculations,determinethedesignflowratesforallpartsofthesystem.

3.Identifysuitablelocationsfordoubleregulatingvalves.Valves must be provided in the system wherever it isnecessary toadjust theflowrate.Thiswillusually in-cludethefollowinglocations:

a.primary headers, main risers, branches and sub-branches;

b.terminalbranches;c. by-passesfrom3-waycontrolvalves;d.pumpsets;e.boilersandchillers(especiallywhereunitsareinpar-

allel);f. zone control circuits incorporating a secondary

pump.

4 Fromthevalveselectiontable(seetheexampleinTable4),selectthevalvewhoseminimumflowrateisclosestto,butlessthan,thedesignflowrate.

Ifpipeshavebeen sized inaccordancewithinnormalvelocityandpressurelosslimits,thentheselectedvalvewillhavethesamediameterastheadjoiningpipes.

5.2Selectioncriteria

When sizing fixed orifice double regulating valves, thefollowingissuesshouldbetakenintoconsideration.

1.Valvesshouldbesizedtomatchthesizeoftheadjoin-ingpipewheneverpossible.Cimberioregulatingvalvesaredesignedtoaccommodatestandardflowrangesforgivenpipe sizes.Dropping toa smaller than line sizevalvecouldriskhighpressure lossesandexcessiveve-locitiesthroughthevalve.

2.Priortosizingtheflowmeasurementdevice,thetypeof instrument to be used for measuring the pressuredifferentialmustbeconsideredandtheupperworkinglimitspecifiedaccordingly.Therangesoftypicalinstru-mentscommonlyusedformeasurementofpressuredif-ferentials,areasfollows:

a.mercurymanometer: 1to65kPaor0to125kPa;b.flurocarbonmanometer: 1to4.6kPaor0to8.8kPa;c. differentialdigitalmanometer/flowmeter: 1to150kPa.

3.Flowmeasurementdevicesshouldbeselectedandsizedtomeetthefollowingrequirementsatthedesignflowrate:

a.theminimumpressure:differentialsignalshouldbenotlessthan1kPa;

b.double regulating valves should be selected to en-surethattherequiredpressuredropoccursatvalvesettingsnotlessthan25%open(tominimisetheriskofdirtblockage).

Table4ValveselectiontableDN15

DN(mm)

Minimumflowrate

(l/s)Model

MaximumBalancingPressure

(kPa)

kv kvs

15

0.015

0.028

0.055

–

–

0.015

0.028

0.055

0.028

721L

721M

721S

727L

727S

737L

737ML

721

7737S

–

–

–

542000Q2

2366Q2

542000Q2

542000Q2

2366Q2

2366Q2

414.6

92.1

21.9

65.8

7.1

480.4

157.9

29.4

100.4

–

–

–

1.278

3.905

0.473

0.825

1.911

1.035

0.473

0.976

1.799

–

–

0.473

0.976

1.799

0.976Figure56ResidualPressure

Circuit1residualpressure=∆Pindex-∆Pcircuit1

∆Pcircuit1 ∆Pindex


5.Havingselectedthevalves,calculatethepressurelossesacrossthosevalvesintheindexcircuit.Thesepressurelossesneedtobetaken intoaccountwhensizingthepump. To calculate the pressure drop across the fullyopen valve use the equations provided under section5.1above.

6.For thosevalves thatareat thebeginningofbranch-esorwhichareclosetothepump,checkthatthede-signpressure losses across themwill notexceed theirmaximumbalancingpressure.Thedesignpressuredropacrosseachvalveissometimesreferredtoastheresid-ualpressureandisthedifferencebetweenthepressuredroparoundthefurthestbranchandtheoneinques-tion.Figure56 explainshow residualpressure canbecalculated.

7.Havingcalculatedtherequiredresidualpressure,checkthatitsvalueislessthanthevalve’smaximumbalanc-ing pressure. The maximum balancing pressure is thepressuredropacrossthevalveatits25%openposition.A simple equation to calculate the maximum balanc-ingpressureforeachvalvecanbereadfromTable3.Iftheresidualpressureexceedsaparticularvalve’smaxi-mumbalancingpressure,itmaybenecessarytoselect2valves,andinstalltheminseriessothateachonecanremovehalfofthetotalpressureloss.


8.Havingselectedallofthevalves,theselectioninforma-tion shouldbe recorded in the formofa table cross-referenced to the relevant specification clauses anddrawings.Theinformationshouldinclude:

a.manufacturer’smodelandreferencenumbers;b.valvesizesandkvorkvsvalues;c. intendedlocations;d.designflowrates;e.anticipatedpressurelosssignalsatdesignflowrates.

5.4Softwareforselection

Manualsizingiscertainlynotverypractical.Thereiscal-culationsoftwareavailable,suchasCIMsize,thatcansizethevalvequicklyandeffectively,thusreducingthechanceoferror.

Theprogramscanalsocreateusefulreportsforcommis-sioningthesystemandthespecificationswiththenumberandtypeofvalvesrequired.

Figure57CIMsize1.0

screenshot


Figure58Fluorocarbon/mercurymanometer

6.Measuringflowrate

Inordertoestablishtheflowratethroughafixedorificedouble regulating valve it will be necessary to measurethepressuredifferentialacrosstheorifice.Havingmeas-uredthepressuredifferential,andknowingtheorificekvsvalue,theflowratecanthenbecalculatedusingthefol-lowingequation:

whereQ=flowrateinl/s,and∆P=pressurelossinkPa

Alternatively, forCimberiovalves,flowratecanbereaddirectly from pressure loss versus flow rate graphs con-tainedintheCommissioningValvebrochure.

Pressuredifferentialcanbemeasuredusingamanometer.Thetwomostcommontypesofmanometerinusearethefluorocarbon/mercurymanometerandtheelectronicdig-italmanometer.Thefunctionandoperationofthefluoro-carbon/mercurymanometerisdescribedinthefollowingsection.

6.1Fluorocarbon/mercurymanometer

The fluorocarbonormercurymanometer indicatespres-surebytheheightofacolumnof fluorocarbonormer-cury.Theinstrumentissimple,hasnomovingparts,andregularcalibrationisnotrequired.Providedcertainbasicproceduresarefollowed,theinstrumentwillgivereliableandreproduciblereadings.

Agoodqualitymanometerwillhave the following fea-tures:

alargefluidreservoirwithmeansofzeroadjustment;a safety chamber to reduce the risk of blowing themercuryoutofthemanometeriftheinstallationpres-sure is greater than the range of the manometer;interchangeable connections for use on various pipeandflowmeasurementdevicetappings;

sealable couplings to prevent loss of water from themanometerlines;

avalvechamberforpurgingairoutofthemanometerandassociatedpipework;

BalancingValvesHandbookMeasuringflowrate

colour coded high and low pressure connecting lines(red/highpressure,blue/lowpressure).

The following routine is used when setting up to takemeasurements with the fluorocarbon/mercury manom-eter:

1 Ensure that the manometer and hoses are suitableforthestaticpressureandtemperatureinthesystem.Thisisparticularlyimportantwithdifferentialpressuremeasurement.Thedifferentialmayonlybesome6kPabut the pressure with respect to atmospheric on themanometercouldbeinexcessof500kPainahighrisebuildingorpressurisedhightemperaturehotwatersys-tem;

2 Ensure that the manometer is of a suitable range tomeasure the anticipated maximum differential pres-sure;

3 Supportthemanometerfirmlyinaverticalpositionsothatitcannoteasilybedislodged;

4 Ensurethatallthemanometerchamberby-passvalvesaresecurelyclosed;

5 Connect theappropriatecouplings (binderprobes) tothemanometerlines;

6 Connect the manometer to the high pressure side oftheflowmeasurementdevice;

Q=·∆pkvs36


Figure61SoftwarePcomPRoforCIMDRoNIC726AC6

Figure59DigitalmanometerCIMDRoNIC726DM10

726

7. Holdingthelowpressuremanometerlineoverabuck-etordrain,openthemanometerby-passvalve;

8. open the low pressure and high pressure chambervalvesandallowwatertoflowthroughtheconnect-inglinesandintoabucketofwateruntilallairbub-blesareexpelled;

9. Isolatethemanometerlinesfromtheflowdevicebyclosing the by-pass high pressure and low pressurevalves.Connectthelowpressurecouplingtothelowpressuretestpoint,openitsisolatingvalveandthenreopen the by-pass valve. Zero the manometer bymovingthescaleagainstthemeniscus.

10.Re-openthehighpressureandlowpressurevalves;

11. Slowlyclosetheby-passvalve,watchingthefluorocar-bon/mercury.Whenthevalveisfullyclosedthediffer-entialpressurecanberead;

12.Todisconnectthemanometeropenthebypassvalve,close the high pressure and low pressure chambervalves, re-close the bypass valve. Close the isolatingvalves on the pressure points, then carefully discon-nectthemanometerlinesfromtheflowmeasurementdevice.

BalancingValvesHandbookMeasuringflowrate

6.2Digitalmanometer

Electronicshaveallowedmeasuringequipmenttoimprove,reducingtheirvolumesandweights.Therearedevicesavail-able that can measure both the differential pressure andcalculatetheflowratecirculatinginthevalve(byinsertingtheKvvalue).TherearealsotrueCommissioningunitsthatnotonlycanmeasurepressure/flowrates,butsystematicallyplanandperformthecommissioningofthesystem.

Theseunitshavealargedatabasewiththeavailablebalanc-ingvalvesandcaneasilyperformtheproportionalbalanc-ing,storingallthemeasuredflowratesforeachvalveinareport.Theseflowratescanberecalculatedbythesystemdesignerinordertoverifythecalculationmodelusedand,ifnecessary,interveneifthereareanyanomalies.

Ausefulsoftwareprogramisalsoavailablethatschedulesthecommissioning,generatingareportthatprovidesalloftheinformationinordertoperformthecorrectbalancingofeachvalve.

DM10

Figure60DigitalmanometerCIMDRoNIC726

726AC6


BalancingValvesHandbookFlowregulationprocedure

7.Flowregulationprocedure

Theon-siteregulationofawaterdistributionsystemin-volvestwobasicprocesses:

1.Theadjustmentofbranchregulatingvalvestoobtainflowratesthatareincorrectratiotoeachother.Thisisachievedbythetechniqueofproportionalbalancing.

2.Theadjustmentofthetotalflowrategeneratedbythepumptoobtainthedesignflowrate.Thisisachievedei-therbythrottlingdownthepumpregulatingvalve,byvaryingthepumpspeed,orbysubstitutingthepumpimpeller,asappropriate,andasagreedwiththedesignengineer.

7.1Fluorocarbon/mercurymanometer

The technique of proportional balancing is accepted asthe most appropriate method of effectively regulatingdistributionsystems.

Considerabranchpipe(Figure59)withseveralterminalunits.Theflowofwaterthrougheachterminalrepresentsacertainproportionorpercentageofthetotalflowinthebranch.

Figure62Basisforproportionalbalancing

Unlesstheterminalbranchregulatingvalvesarealteredthese proportions will remain the same, whatever theflowrateinthemainpipe.

Tobalanceoneterminalunitagainstanother,therefore,itisonlynecessarytoadjusttheregulatingvalvessothattheterminalunitssharetheflowinthecorrectproportions.Itdoesnotmatterwhattheactualflowrateisatthetime.Whenthemainflowfromthepumpisregulatedtoitsde-signflowrate,eachterminalunitshouldalsobepassingitsdesignflow,sinceeachhasbeensettotakeitscorrectproportion.

7.2Indexcircuit

Theindexcircuitisthecircuitthat,withthesysteminanunbalancedstate,exhibitsthegreatestresistancetoflow.Itcanbeidentifiedbycalculationasthecircuitwiththehighestpressurelossarounditwhendesignflowratesareassumed. on site it can be identified by flow measure-mentasthecircuitforwhichtheratioofmeasuredflowtodesignflowrateislowest.

All systems have a single overall index circuit againstwhichthepumppressureiscalculated.

Furthermore,foranybranchservingsub-branches,therewill be an index sub-branch. Similarly each sub-branchmayserveanumberofterminalbranches,oneofwhichwillbetheindexterminalbranch.

If all branches are of equal resistance, the main systemindex circuit is likely to be from the pump to the mostremote terminal, since this circuit has the longest pipelengths.Similarly,sub-branchindexcircuitsarelikelytobefromthestartofthesub-branchtothemostremoteter-minaltheyserve.However,ifterminalbranchresistancesvary then the system indexandbranch indexeswill notnecessarilycoincidewiththemostremoteterminals.Thelocationofeachindexwillthendependonwhichcircuithasthehighestcombinationofpipeandterminalbranchpressurelosses.

Asthecircuitstartingwiththehighestresistance,thereisnoneedtoregulateflowatanindex.Attheendofthebalancingprocess,theindexcircuitshouldalwayshaveafullyopendoubleregulatingvalve.

Initialflowrate0.4l/s

Finalflowrate0.8l/s

0,08l/s20%

0,16l/s20%

0,10l/s25%

0,20l/s25%

0,10l/s25%

0,20l/s25%

0,12l/s30%

0,24l/s30%


7.3Proportionalbalancingprocedure

Thebalancingproceduremustalwaysstartfromthemostremotebranchandworkbacktowardsthenearest.HenceforthesystemshowninFigure60,Theflowratestoter-minalbranchesT3,T2andT1wouldeachbebalancedinturnagainsttheflowattheindex,T4.

Thebalancingprocedureisasfollows:

1.Usingthefixedorificedeviceatthemainbranch,meas-urethetotalflowenteringthecircuit.Ensurethatthisflowrateisbetween110%and120%ofitsdesignflowrate.Itmaybenecessarytoclosedownotherbranchestoachievethis;

2.Usingthefixedorificedeviceoneachterminal,meas-ure the flowrates througheach terminalbranch.Foreachterminalbranchcalculatethe%designflowrate:%designflowrate=(measuredflowrate/designflowrate)x100. Ifthesignalsatanyoftheflowmeasure-mentdevicesarebelowthemeasurementrangeofthedevice (i.e. less than 1kPa), further increase the totalflowrateenteringthebranchbyclosingdownadjacentbranches;

3.Identifytheindexterminalbranch.Thiswillbetheonewith the lowest % design flow rate. Usually, but notalways thiswillbe theendbranch (furthest fromthepump). If theendbranch isnot the index, thencloseits regulatingvalveuntil its%designflowrate isap-proximately 10% less than that at the true index (sothattheendbranchbecomesanartificial index).Thisneedstobedonewhilesimultaneouslymeasuringtheflowinthetrueindex,sinceitsflowwillchangeastheendbranchisadjusted;

BalancingValvesHandbookFlowregulationprocedure

4.Connectamanometertothefixedorificedeviceintheendterminalbranch.Workingbacktowardsthenear-est branch, adjust each terminal branch regulatingvalveuntilits%designflowratebecomesequaltothatattheendsub-branch.Thisneedstobedonewhilesi-multaneouslymeasuringtheflowrateattheendsub-branchsinceitsflowwillchangeasupstreamvalvesareadjusted;

5.Havingachievedequal%designflowratesforeachofthe sub-branches, the sub-branch flow rates are nowbalanced.Thebalancecannotbedisturbedbythead-justmentofupstreamvalves.Hence,upstreambranchescanbebalancedinexactlythesameway;

6.oncetheentiresystemhasbeenbalanced,adjusttheflowfromthepumpto110%ofthetotaldesignflowrate for the system. All branches and sub-branchesshouldnowhaveflowratesclosetotheir100%designvalues.

7.4Reporting

Havingachievedanaccuratebalanceofflowrates,eachofthedoubleregulatingvalvescanbelockedinposition.ForCimberioregulatingvalves,thisisachievedbyopen-ingtheendcaptorevealanAllenkeyoperatedlockingmechanism.By tightening the screw, thevalve is lockedinthesetpositionsothatthevalvecanbeclosed,butonre-openingthevalvewillnotopenbeyondthelockedpo-sition.Hencetheflowbalanceisretained.

Asarecordforfuturesystemdesignchecking,faultfind-ingandmaintenance,itisalsoessentialthattheoriginalvalvesettingsandmeasuredflowratesarerecordedintheformofatable.

Figure63Proportionalbalancingprocedure

T4 T3 T2 T1


BalancingValvesHandbookIndexoffigures

Figure1 Effectsofflowvariation 4Figure2 Effectsofsupplytemperature 5Figure3 Effectsofextraflows 6Figure4 Effectsofflowvariationincoolingsystems 6Figure5 Constantvolumesystem:3-waydivertingvalve 8Figure6 Regulatingofa3-waydivertingvalvesystem 8Figure7 Variablevolumesystem:2-waycontrolvalve 8Figure8 Regulationofa2-waycontrolvalvesystem 9Figure9 2-waycontrolvalvewithregulatingdevice 9Figure10 Example1:smallbulding 9Figure11 Example1:unbalancedsystem 9Figure12 Example1:balancedsystem 10Figure13 Example1:traditionalpump 10Figure14 Example1:variablespeedpump-constanthead 10Figure15 Example1:variablespeedpump-proportionalhead 11Figure16 Example2:layout 11Figure17 Example2:unbalancedsystem 11Figure18 Example2:balancedsystem 12Figure19 Example2:Traditionalpump 12Figure20 Example2:variablespeedpump-constanthead 12Figure21 Example2:Variablespeedpump-proportionalhead 12Figure22 Doubleregulatingvalves 13Figure23 Regulating2-waycontrolvalvewithactuator 13Figure24 Installation 14Figure25 Fixedorificeflowmeasurementdevices 14Figure26 Fixedorificedoubleregulatingvalves 15Figure27 Fixedorificedoubleregulatingvalves:pressures 15Figure28 Fixedorificedoubleregulatingvalves:velocities 15Figure29 Variableorificedoubleregulatingvalves 16Figure30 Variableorificedoubleregulatingvalves:pressures 16Figure31 Variableorificedoubleregulatingvalves:velocities 16Figure32 Impactofflowmeasurementaccuracy onheatingandcoolingsafetymargins 17Figure33 Cartridgeandsection 18Figure34 CFRinconstantvolumesystems 19Figure35 CFRinvariablevolumesystems 19Figure36 CFRwithactuator 19Figure37 Anti-condensation 19Figure38 CFRwithheatexchanger 19Figure39 Waterheatingsystems-Boilers 20Figure40 Waterheatingsystems-Heatexchangers 20Figure41 Differentialpressurecontrolvalve 20Figure42 Electronicdifferentialpressurecontrolvalve 21Figure43 Differentialpressurevalveontheriser 21Figure44 Differentialpressurevalveonthemanifold 21Figure45 BranchwithoutDPCV 22Figure46 Authority 22Figure47 BranchwithDPCV 22Figure48 BranchwithEPCV 22Figure49 Pressureindependentcontrolsystem 23Figure50 BranchwithPICV 23Figure51 PICVstructure 23Figure52 CimberioPICV 23Figure53 PICVlayout 24Figure54 FlowratevsDifferentialpressure 24Figure55 Reversereturnlayoutforterminalbranches 25Figure56 ResidualPressure 28Figure57 CIMsize1.0screenshot 29Figure58 Fluorocarbon/mercurymanometer 30Figure59 DigitalmanometerCIMDRoNIC726DM10 31Figure60 DigitalmanometerCIMDRoNIC726 31Figure61 SoftwarePcomPRoforCIMDRoNIC726AC6 31Figure62 Basisforproportionalbalancing 32Figure63 Proportionalbalancingprocedure 33

8.Index offigures


Table1 Commonvalvetypesandtheirfunctions 5Table2 Pumpstechnologiescomparison 11Table3 Recommendedrangeofwatervelocities 22Table4 ValveselectiontableDN15 25

CommissioningWaterSystems-BSRIA,BG2/2010

2012ASHRAEHandbook-HVACSystemsandEquipment

2011ASHRAEHandbook-HVACApplications

Impiantitermotecnici–prof.GiulianoCammarata

Leretididistribuzione–MarioDoninelli

Icircuitieiterminalidegliimpiantidiclimatizzazione-MarioDoninelli.

9. Index oftables

10.Bibliography

BalancingValvesHandbookIndexoftables-Bibliography

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s k y p e : c i m b e r i o s k 1 , c i m b e r i o s k [email protected]

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