Active Passive Beams Engineering Guide - Price Industries

Please refer to the Price Engineer’s HVAC Handbook for more information on Active & Passive Beams.

S E C T I O N L

Engineering GuideActive & Passive Beams

All Metric dimensions ( ) are soft conversion. © Copyright Price Industries Limited 2011. Imperial dimensions are converted to metric and rounded to the nearest millimeter. L-2L-2 All Metric dimensions ( ) are soft conversion. © Copyright Price Industries Limited 2011. Imperial dimensions are converted to metric and rounded to the nearest millimeter.

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Introduction

Active&PassiveBeamsEngineering Guide

Likeradiantheatingandcoolingsystems,activeandpassivebeamsystemsusewateraswellasairtotransportenergythroughoutthe building. Like radiant and coolingsystems,theyoffersavingsinenergy,spaceand maintenance costs. Unlike radiantheating and cooling systems, however,these technologies deliver the majorityof their cooling and heating throughconvection,oftenleadingtoafullymixedenvironment.Thissectionintroducesactiveandpassivebeamsystemsandtheirdesignconsiderations,andaddressestheuniquerequirementsofsomeofthemostcommonapplications.

Managementofheat loadscangenerallybeclassifiedintotwodifferent types:all-

air systems or hybrid systems. All-airsystems have been themost prominentinNorthAmericaduringthe20thcenturyandhavebeeninusesincetheadventofairconditioning.Thesesystemsuseairtoservice both the ventilation requirementaswell as thebuilding cooling loads. Ingeneral,thesesystemshaveacentralairhandling unit that delivers enough coolorwarmair to satisfy thebuilding load.Diffusersmountedinthezonedeliverthisair insuchawayas topromotecomfortandevenlydistributetheair.Inmanycases,theamountofairrequiredtocoolorwarmthespaceorthefluctuationsofloadsmakedesigninginaccordancetotheseprinciplesdifficult.

Hybrid systems combine an air-sideventilationsystemandahydronic(orwater-side)system.Theair-sidesystemisdesignedtomeetalloftheventilationrequirementsforthebuildingaswellassatisfythelatentloads. It is typically a 100% outside airsystemandbecausetheprimaryfunctionofthesupplyairsystemisventilationanddehumidificationasopposed tosensiblecoolingitcanbesuppliedathighersupplyairtemperaturesthanistypicaloftraditionalmixingairdistributionsystems.Thewater-sidesystemisdesignedtomeetthebalanceofthesensiblecoolingandheatingloads.These loadsarehandledbywater-basedproducts,suchasactiveandpassivebeams,which transfer heat to the zone by induction.

© Copyright Price Industries Limited 2011. All Metric dimensions ( ) are soft conversion. Imperial dimensions are converted to metric and rounded to the nearest millimeter. L-3

Active & Passive BeamsEngineering Guide


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Concepts and Benefits

Activeandpassivebeamsystemsprovideaneffectivemethodforprovidingheatingorcooling toaspacewhilepromotingahighlevelofoccupantcomfortandenergyefficiency.There are two distinct systemdesign philosophies that are consideredwhen applying hydronic heating and/orcooling:

Hydronic heating or cooling where thehydronicsystemsareintegratedwiththeprimaryventilationsystem.Theseareactivebeam systems (Figure 1).Hybridheatingorcoolingsystemswherewater-baseddevicesareusedinconjunctionwithascaled-downventilationsystem,andmanage thebulkof the sensible coolingload.Thesesystemsgenerallyusepassivebeams (Figure 2). Hydronicsystemshavebeensuccessfullyused in several applications havingdramatically different characteristics. Some examplesofareaswhereactiveandpassivebeamsystemshavebeenappliedinclude:

• GreenBuildings• PostSecondaryEducationalFacilities• LoadDrivenLaboratories• K-12Schools• OfficeBuildings• Cafeterias• TelevisionStudios

Benefits of Air-Water SystemsThere aremany benefits to heating andcooling using active or passive beams.Advantages of water-based heating andcooling systems over other mechanicalsystemsinclude:

• Energyandsystemefficiency• Reducedsystemhorsepower• Improvedindoorenvironmentalquality• Improvedindoorairquality• Increasedthermalcomfort• Reducedmechanicalfootprint• Lowermaintenancecosts• ImprovedsystemhygieneActiveorpassivebeamsystemsareagoodchoicewhere:

• Thermal comfort is a major designconsideration

• Areaswithhighsensibleloadsexist/arepresent

• Areas requiring a high indoor air quality(100%outdoorairsystem)exist/arepresent

• Energyconservationisdesired

Energy EfficiencyTheheattransfercapacityofwaterallowsforareductionintheenergyusedtotransportanequivalentamountofheatasanall-airsystem(Stetiu,1998).Thesereductionscanbefoundprimarilythroughreducedfanenergy.

Figure 1: Airflowdiagramofatypicallinearactivebeamincooling

Figure 2:Air flow diagramof a passivechilledincooling

Figure 3: Activebeamsinstalled inanoffice

Figure 4: Passivebeamsbehind aperforatedceiling

Nozzles

Plenum

Primary Air

Room Air

Coil

Room Air

Primary Air

Thehigher chilledwater supply (CHWS)temperaturesusedwithactiveandpassivebeam systems, typically around 58 °F[14.5°C],providemanyopportunitiesforareductioninenergyuse,includingincreasedwater-sideeconomizeruse.ThisincreasedCHWStemperaturealsoallows formorewet-sideeconomizerhoursthanwouldbepossiblewithothersystemswhereCHWStemperaturesaretypically~45°F[7°C].

Indoor Air QualityDepending on the application, undermaximum load, only ~15 to 40% of thecoolingairflowinatypicalspaceisoutdoorairrequiredbycodetosatisfytheventilationrequirements.Thebalanceof the supplyairflowisrecirculatedairwhich,whennottreated,cantransportpollutantsthroughthebuilding.Activeandpassivebeamsystemstransferheatdirectlyto/fromthezoneandare often usedwith a 100% outdoor airsystemthatexhaustspollutedairdirectlyto the outside, reducing the opportunityforVOCsandillnesstotravelbetweenairdistribution zones.

NoiseActiveandpassivebeamsystemsdonotusuallyhavefanpowereddevicesnearthezone.Thistypicallyresultsinlowerzone

noiselevelsthanwhatisachievedwithall-airsystems. Insituationswherepassivebeams are used in conjunction with a quiet air system, such as displacementventilation, the opportunities for noisereduction increase further.

Reduced Mechanical FootprintThe increased cooling capacity ofwaterallowsthetransportsystemtobereducedinsize.Generally,itisnotunusualtobeabletoreplace~60ft²[6m²]ofairshaftwitha6in.[150mm]waterriser,increasingtheamountoffloorspaceavailableforuseorlease.Duetothesimplicityofthesystems(i.e.reductioninthenumberofmovingpartsand theeliminationof zonefilters,drainpans,condensatepumpsandmechanicalcomponents),theretendstobelessspacerequiredintheinterstitialspacetosupporttheHVACsystem.

Lower Maintenance CostsWithnoterminalunitorfancoilfiltersformotors to replace,asimpleperiodiccoilcleaningisallthatisrequiredinordertomaintaintheproduct.

All Metric dimensions ( ) are soft conversion. © Copyright Price Industries Limited 2011. Imperial dimensions are converted to metric and rounded to the nearest millimeter. L-4


L-4 All Metric dimensions ( ) are soft conversion. © Copyright Price Industries Limited 2011. Imperial dimensions are converted to metric and rounded to the nearest millimeter.

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When to use Beam Systems

ApplicationTotal Air

Volume (Typ.)Ventilation Requirement

(Typ.)Air-Side

Load Fraction

Office 1cfm/ft2 [5L/sm2] 0.15cfm/ft2 [0.75L/sm2] 0.15

School 1.5cfm/ft2 [7.5L/sm2] 0.5cfm/ft2 [2.5L/sm2] 0.33

Lobby 2cfm/ft2 [10L/sm2] 1cfm/ft2 [5L/sm2] 0.5

PatientRoom 6 ach 2 ach 0.33

Load-drivenLab 20 ach 6 ach 0.3

Hygienic SystemWith the elimination of the majority of filtersanddrainpans, there isareducedriskofmoldorbacteriagrowthintheentiremechanical system.

Activeandpassivebeamsystemsarewell-suitedtosomeapplicationsandlesssotoothers.Asaresult,eachapplicationmustbereviewedforpotentialbenefitsaswellasthesuitabilityofthesetypesofsystems.Oneconsiderationwhichcanassistinthedecision to employhydronic systemsasopposedtoanall-airsystemistheair-sideloadfraction,orthepercentageofthetotalairsupplywhichmustbedeliveredtothezonetosatisfycodeanddehumidificationrequirements. Table 1 shows the load fractionforseveralspaces.Inthetablethebestapplicationsforhydronicsystemsarethosewiththelowestair-sideloadfractionastheyaretheonesthatwillbenefitthemostfromtheefficienciesofhydronicsystems.Anotherfactorwhichshouldbeexaminedisthesensibleheatratioorthepercentageof the cooling loadwhich is sensible asopposedtolatent.Thelatentloadsmustbesatisfiedwithanairsystemandoffersomesensiblecoolingatthesametimeduetothetemperatureofdehumidifiedair.Ifthetotalsensiblecoolingloadissignificantlyhigherthanthecapacityoftheairsuppliedto satisfy the latent loads, a beam system mightbeagoodchoice.

Commercial Office BuildingsIn an office building, active and passivebeamsystemsprovideseveralbenefits.Thelowersupplyairvolumeoftheairhandlingsystemprovidessignificantenergysavings.In addition, the smaller infrastructurerequiredtomovethislowerairflowallowsforsmallplenumspaces,translatingintoshorterfloor-to-floorconstructionorhigherceilings.Thelowersupplyairvolumeandelimination of fans at or near the spaceoffersasignificantreductioningeneratednoise.Thelowerairflowoftentranslatestoreheatrequirementsbeingreduced.Inthecaseof100%outsideairsystems,thelightingloadcapturedinthereturnplenumisexhaustedfromthebuilding,loweringtheoverallcoolingload.

SchoolsSchoolsareanotherapplication that canbenefitgreatlyfromactiveandpassivebeamsystems. Similar toofficebuildings, thebenefitsofalowersupplyairvolumetothespacearelowerfanpower,shorterplenumheight,reducedreheatrequirementsandlowernoiselevels(oftenacriticaldesignparameterofschools).

Hospital Patient Rooms

Hospitalsareuniqueapplications in thatthe supply air volume required by localcodesforeachspaceisoftengreaterthantherequirementofthecoolingandheatingload. In some jurisdictions, local coderequiresthesehigherair-changeratesforall-air systemsonly. In these cases, thetotalair-changeraterequiredisreducedifsupplementalheatingorcoolingisused.This allows for a significant reductionin system air volume and yields energysavingsandotherbenefits.

Furthermore,because thesesystemsaregenerally constant air volume with thepotentialtoreducetheprimaryair-changerates, reheat and the cooling energydiscardedaspartofthereheatprocessisasignificantenergysavingsopportunity.Depending on the application, a 100%outside air system may be used. These systems utilize no return air and therefore nomixing of return air between patientroomsoccurs,potentiallyloweringtheriskofhospitalassociatedinfections.

LaboratoriesInloaddrivenlaboratorieswherethesupplyairrateisdrivenbytheinternalgains(suchas refrigerators, testing equipment, etc.)asopposedtotheexhaustrequirements,active and passive beam systems canoffersignificantenergysavings.Intheseenvironmentsit isnotunusualtorequirea largeair-changerate inordertosatisfythe load,althoughsignificantly lessmayberequiredbycode(ASHRAE,2008;CSA,2010).

Table 1: TypicalloadfractionsforseveralspacesintheUnitedStates

Intheseapplications,thedifferencebetweenthesupplyairvolumerequiredtomanagethe sensible loads and that required tomeetthefumehoodairflowrequirementsprovides opportunity for energy savingsthroughtheapplicationofactiveandpassivebeams.Thesesavingsaretypicallyduetothereductioninfanpoweraswellastheenergyassociatedwithtreatingtheoutsideair,which,inthecaseofaloaddrivenlab,maybesignificant.

Hotels / Dorms Hotels,motels,dormitoriesandsimilartypebuildingscanalsobenefitfromactiveandpassivebeamsystems.Fanpowersavingsoften come from the elimination of fan coil units located in theoccupied space.Theenergysavingsassociatedwiththese“local”fansissimilarinmagnitudetothatoflargerairhandlingsystems.Italsoallowsfortheeliminationoftheelectricalservicerequiredfortheinstallationoffancoilunits,as well as a reduction in the maintenance ofthedrainandfiltersystems.Theremovalofthesefansfromtheoccupiedspacealsoprovideslowernoiselevels,whichcanbeasignificantbenefitinsleepareas.

LimitationsThereareseveralareasinabuildingwherehumiditycanbedifficult tocontrol,suchas lobby areas and locations of egress.These areasmay see a significant shortterm humidity load if the entrances are not isolatedinsomeway(revolvingdoorsorvestibules). Intheseareas,achoiceofacomplimentarytechnologysuchasfancoilunitsordisplacementventilationisideal.

Other applications may have high airflow/ventilationrequirements,suchasanexhaust driven lab. Themajority of thebenefitprovidedbythehydronicsystemislinkedtothereductioninsupplyairflow.Assuch, theseapplicationsmaynot seesufficientbenefittojustifytheadditionofthehydroniccirculationsystems,makingthemnotlikelytobeagoodcandidateforthistechnology.




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Passive Beams

Passive Beams Passive beams use a heat exchanger–usuallyacoil–tochangethetemperatureoftheadjacenttransferringheatandcreateadifference in density with the ambient air. Thedensitydifferencecreatesairmovementacrosstheheatexchanger,transferringheatfromtheheatexchangertotheair.

Passive beams condition a space usingnaturalconvectionandareprimarilyusedforhandlingthesensiblecoolingloadofaspace.Theyarewater-onlyproducts,andrequireaseparateairsystemforventilationair and to remove the latent load. Aswarm air in the room rises, it comes into contactwiththeheatexchangerandflowsdownwardthroughthecoolcoilsbackintothespace,asseeninFigure 5.Inheatingmode, passive beams are generally notused, though in some special instancestheywouldconditionthespaceprimarilyby thermal radiation.

Product DescriptionPassivebeamsareavailableinmodelsthateither integrate intostandardsuspendedceiling systems or are suspended freelyfromtheceiling.Theyarealsocommonlyinstalledbehindperforatedmetalceilingsforauniformarchitecturalappearance.Aperforatedmetalceilinghelpsreducedraftunderthebeam,however,aminimumfreeareaof50%isoftenrequiredtoensurethecapacityofthebeamisnotreduced.PassivebeamsinstalledbehindametalperforatedceilingcanbeseeninFigure 7.

ComponentsThebasiccomponentsofpassivebeamsinclude a heat exchanger, comprisingofextrudedaluminumfinsandcoppertubing,commonlytermedthe‘coil’,andaframeorshroud.Thesecomponentsareillustratedin Figure 8.

LocationPassivebeamsare ideallysuited toaislewaysorperimetersof largespacessuchas offices, lobbies, conference centers, libraries,oranyotherspacethatrequiresperimeteroradditionalcooling.Airflowfromapassivebeamisstraightdownsotheyarenottypicallyplacedabovewhereanoccupantwillbestationedforanextendedperiodoftime.Whilethevelocityfromapassivebeamislow,thereistheopportunityfor some people in this condition to beuncomfortable.

Figure 6:Airflowdiagramofapassivebeamincooling

Figure 5: Roomairflowpatternofapassivebeamincooling

Coil

Room Air

Primary Air

Figure 7:Passivebeamsinstalledbehindametalperforatedceiling

Face

Figure 8: Componentsofatypicalpassivechilledbeam

Frame/Shroud

Coil




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NozzlesPrimary Air

Room Air

Nozzles

Plenum

Primary Air

Room Air


Figure 11:Air flowdiagramof a typicallinearactivebeaminheating

Active Beams

Plenum

MountingBracket

Primary Air Inlet

Operable Face to allow access to the coil

Coil

Figure 12: Componentsofatypicallinearactivebeam

Figure 9:Roomairflowpatternofatypicallinearactivebeamincooling

Active BeamsActivebeamsuse theventilationsystemto increasetheoutputof thecoil,andtohandle both latent and sensible loads of a space. Unlike radiantpanelsandchilledsails, which rely primarily on thermalradiationtoconditionaspace,activebeamsheat or cool a space through inductionand forced convection. An active beamacceptsdryairfromthesystemthroughapressurizedplenum.Thisprimarysupplyairisthenforcedthroughnozzlesinordertocreateahighvelocityairpatternintheareaadjacenttothecoil.Thishighvelocitycauses a reduction in the local static pressure, inducing roomair through theheating/coolingcoil.Theinducedairthenmixeswiththeprimarysupplyairand isdischarged back into the space via slotsalongthebeam (Figure 9).AtypicalairflowdiagramofalinearactivebeamincoolingandheatingmodescanbeseeninFigure 10, and Figure 11respectively.ComponentsThe basic components of active beamsincludeaheatexchangerwithaluminumfinsandcoppertubing,commonlytermedthe‘coil,’aplenumboxwithat leastonesupplyinlet,internalnozzles,avisibleface,andaframe.Althoughtheconfigurationsofactivebeamsdiffer,allgeneralcomponentsremainthesame.Thesecomponentsareillustrated in Figures 12.

ApplicationsActive beams can be used in offices,meeting rooms, schools, laboratories,hospitals,datacenters,airports,any‘green’buildingapplication,andlargeareassuchaslobbies, conference facilities, lecture halls or cafeterias.

Twobasictypesofactivebeamsare:

• LinearActiveBeams• ModularActiveBeams

Linear Active Beams2 Way DischargeLinear active beams with two-sideddischargearedesignedtoeitherintegrateintostandardsuspendedceilingsystemsor be suspended freely in an ‘exposed’application.Thesebeamshavetwolinearairslotsthatrunthelengthofthebeam,one on either side.




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Primary Air

Room Air

Room Air

Nozzles

Primary Air

Primary Air

Room Air

Room Air

NozzlesPlenum

Primary Air

Active Beams

Figure 13: Airflowdiagramof a linearactivebeamincoolingwith1waydischarge

Figure 14:Air flowdiagramof a linearactivebeaminheatingwith1waydischarge

Figure 15:Roomairflowpatternofatypicallinearactivebeamincooling

Figure 16: Airflowdiagramofa modularbeamincooling

Figure 17: Airflowdiagramofa modularbeaminheating

1 Way DischargeLinearactivebeamswithsingle-sidedairdischargearedesignedtoeitherintegrateintostandardsuspendedceilingsystemsor be suspended freely in an ‘exposed’application. Thesebeamshaveonlyonedischargeairslotthatrunsalongonesideof the beam.

Thegeneralairflowoflinearactivebeamswith1wayairdistributionincoolingandheatingareseeninFigures 13 and Figure 14. Figure 15illustratestheroomairflowofatypical1wayactivebeam.

PRODUCT TIPLinear active beams with 1 wayair distribution are best suited for placementalongafaçadeorwall.Inapplicationswhere1waybeamsare used with 2 way beams, a symmetric face may be selected for the1wayunittoensureaconsistentappearancefromtheroom.

PRODUCT TIPActivebeamsaretypicallyavailableina2pipeor4pipeconfiguration.Beamswith2pipeconfigurationshave one supply and one returnpipe for each unit, which servesforeither/bothheatingandcoolingpurposes. Beams with 4 pipeconfigurations have two supplyandtworeturnpipesforeachunit,comprising separate loops forcoolingandheating.

Modular Active BeamsModularactivebeamscombine freshairventilation,hydronicheatingandcooling,andfour-sidedairflow.Theyaretypicallyavailableinmodularsizes,2ftx2ft[600mmx600mm],and2ftx4ft[600mmx1200mm], andare available inmodels eitherdesignedtointegrateintostandardceilingtilesorsuspendfreelyfromtheceiling.

Thetypicalairflowpatternofamodularbeamincoolingandheatingisillustratedin Figure 16 and Figure 17.Often,thesemodular beams can be customized to individuallymodulatetheairflowfromeachsideoftheunit.Forexample,onesideoftheunitcanbeblankedofftocreateamodularbeamwiththree-sidedairflow.

Beam Return




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Passive beam systems will vary inperformance, configuration and layoutdependingontheapplication.Thereare,however, some characteristics that arecommonformostsystems.Furthermore,theperformanceofpassivebeamsislargelydependent on a common set of factors.This section will discuss how factors such as chilledwater temperature affectthe performance and layout of passivebeams. Table 2showscommondesigncharacteristicsforpassivebeamsystems.

Product Selection and Location – Passive BeamsPerformanceThe performance of a passive beam isdependentonseveralfactors:

• Waterflowrate• Meanwatertemperatureand

surroundingairtemperature• Shroudheight• Freeareaoftheairpaths(internaland

externaltothebeam)• LocationandapplicationThewaterflowrateinthecoilaffectstwoperformance factors: the heat transferbetween the water and the coil, which is dependent on whether the flow islaminar(poor)orturbulent(good);andthemeanwater temperature,or theaveragetemperature,inthecoil.Thehighertheflowrate,thecloserthedischargetemperaturewillbetothe inlet, therebychangingtheaverage water temperature in the coil.Figure 18 shows the effect of the flowrate, indicated by Reynolds number, onthecapacityofatypicalpassivebeam.Asindicatedonthechart,increasingtheflowrate into the transitional and turbulent ranges (Re>2300, shaded in thegraph)causes an increase in the output of thebeam.

Thewaterflowrate is largelydependenton the pressure drop and return watertemperatures that are acceptable to thedesigner. Inmost cases, thewaterflowrate should be selected to be fully turbulent underdesignconditions.

The difference between the mean water temperature, t̅w,definedas:

and the surrounding (coil inlet) airtemperatureisoneoftheprimarydriversofthebeamperformance.Thelargerthisdifferenceis,thehighertheconvectiveheattransfer potential. Conversely, a lowertemperature difference will reduce theamountofpotentialenergyexchange,andtherebycapacity.Asaresult,itisdesirablefromacapacitystandpointtoselectentrywater temperatures as low as possible,

Passive Beam Selection and Design Procedure

Table 2: DesignValuesforpassivebeamsystems

IP

RoomTemperature 74°Fto78°Finsummer,68°Fto72°Finwinter

WaterTemperatures,Cooling 55°Fto58°FEWT,5°Fto8°F T

DesignSoundLevels <40NC

CoolingCapacity Upto500Btu/hft

VentilationRequirement 0.1to0.5cfm/ft2floorarea

SI

RoomTemperature 23°Cto25°Cinsummer,20°Cto22°Cinwinter

WaterTemperatures,Cooling 13°Cto15°CEWT,3Kto5K T

DesignSoundLevels <40NC

CoolingCapacity Upto500W/m

VentilationRequirement 0.5to2.5L/sm2floorarea

Figure 18: Passivebeamcapacityvs.waterflow

400 2000 4000 6000 8000 10000 12000

50

60

70

80

90

100

Cap

acity

, %

Re

Figure 19:Passivebeamcapacityvs.differencebetweenmeanwaterandroomairtemperature

00 5 10 15 20

0 2 4 6 8 10

20

40

60

80

100

120

Cap

acity

, %

tw - troom ,˚F

tw - troom ,K




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whilemaintainingitabovethedewpointintheroomtoensuresensiblecoolingonly.

Insomeinstances,itmightbeadvantageousto the designer to use higher watertemperatures,whereitmakessensefromanequipmentstandpoint. Thismayalsooffersomecontrolsimplificationwheretheoutputofthebeamisdeterminedbytheloadintheroom:

• Astheloadincreases,theairtemperaturerises and increases the difference between it and tw, thereby increasingbeamperformance.

• Astheloaddecreases,theairtemperaturefallsandreducesthecoolingcapacityofthe beam.

Apassivebeamusesbuoyancyforcesandthe“stack”effecttodriveairthroughthecoil. The stack effect is a phenomenonthat can be used to increase the rate of circulationthroughthecoilbyincreasingthemomentumof the fallingair. As theairsurroundingthecoilfinsdecreasesintemperature,itbecomesmoredensethanthesurroundingair,causingittofalldowninto the zone below. Figure 20 shows a crosssectionofapassivebeamandhowtheshroud,orskirt,ofthebeamseparatesthecoolairfromthesurroundingair,allowingittogainmomentumanddrawanincreasingvolumeofairintothecoilfromabove.

Thetallerthisstackis,themoreairisdrawnthrough the coil, increasing the coolingpotentialof thebeam. Asthevolumeofairisincreased,thevelocityoftheairfallingbelowthebeamisalsoincreased.Itisnotuncommontoadjusttheheightofthestackinordertoadjustthecapacityandvelocitiesinordertosuitapplicationrequirements.

Figure 21showstheincreaseincapacitywhenthestackheightischangedfrom6in.[150mm]to12in.[300mm]vs.thedifferencebetween troom and t̅w. Thegraphindicatesthattheincreaseincapacityfromthelargershroudreducesastheoverallcapacityofthe beam increases. A practical lowerlimitwherethemeanwatertemperatureis18°F[10K]belowtheroomtemperaturetranslatestoacapacityincreaseof25%withthetallerstack.

Becausetheairflowthroughthebeamisdrivenbybuoyancyforces,anyrestrictiontotheairpathswillimpacttheperformanceof the beam. Figure 22showsthevariousfactorsthataffectperformance,including:

• Facedesignofthebeamwhenexposed• Perforatedceilingbelowthebeamwhen

notexposed• Gapbetweenthebeamandtheslab• Restrictionsofthereturnairpathwhen

theceilingisclosed(eitherreturngrillesorperforatedceilingtiles)

Figure 20: Passivebeamairflowpattern

Figure 21: Passivebeamcapacityvs.temperaturedifference


10 5 10 15 20

0.0 2.0 4.0 6.0 8.0 10.0

1.1

1.2

1.3

1.4

1.5

1.6

Cap

acity

12

in. [

300

mm

] Shr

oud

Capa

city

6 in

. [15

0 m

m] S

hrou

d

tw - troom,˚F

tw - troom, K

Figure 22:Factorsthataffectperformanceofpassivebeams

Figure 23: Apassivebeaminstalledaboveaperforatedceiling

Slab Clearance

Face TypeReturn Air Path

Slab Clearance

Coil

Shroud/Stack

Room Air




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Thedesignofthefacematerialmayrestrictairfallingthroughtheface.Ifthebeamisinstalled behind a perforated ceiling, asshown in Figure 23,theairfallingbelowthebeamwillhit theceiling,spreadout,andfallintothezonebelowoveralargerarea.Aslongasthereisenoughfreeareaintheceilingtoallowtheairtofallthrough(aswell as rise through inorder to feedthebeamwithwarmair),thereshouldnotbeareductioninthecapacityoftheunit.Useofaperforatedceilingisalsoagoodwaytoreducevelocitiesbelowthebeam,ifrequired.

Thedistancebetweenthetopofthebeamandthestructurecanreducetheairflowandcapacityofthepassivebeamifitistoonarrow. Figure 24showstheimpactofthegapbetweenthebeamandtheslabintermsofthebeamwidth(gap/width).

Inmostcases,aclearanceof20to25%ofthe beam width is recommended. These productsaregenerally selected tobe18in.[450mm]orlessinwidth,whichwouldrequireagapupto4.5in.[115mm].

There are other factors that affect performance, including the application,choiceofventilationsystem,andlocation.Itispossibletoincreasethecapacityofthepassivebeamthroughinduction.Ifahighvelocityislocatednearapassivebeam,itmaypullairthroughthecoilatahigherratethanthenaturalconvectionwouldalone,asindicated in Figure 25.Itisalsopossibleto trap thermal plumes at the buildingenvelopeandforcethisairthoughapassivebeam, as shown in Figure 26.

The performance of the beam undernon-standard conditions, such as thosedescribedabove,canbedifficulttoestimate.Forexample, theplumecomingupfromthefaçademaybesostrong,andtheinlettotheplenumsonarrow,thattheplumecomes across the face of the beam. This woulddisturbtheairmovementthroughthecoil,dramaticallyreducingthecapacityofthebeam.Intheseinstances,itisbestto conduct a building mockup or usesimulation software to understand how the variousparametersaffecteachother.

400.07 0.09 0.11 0.13 0.15 0.17 0.19 0.21 0.23 0.25

50

60

70

80

90

100

Cap

acity

, %

Gap / Beam Width

Figure 24:Theimpactonthecapacityofthegapbetweenapassivebeamandbuildingstructure

Figure 26: Capturingtheplumeattheperimetermayincreasepassivebeamperformance

Window

Room Air

Primary AirCeiling

Figure 25:Inducingairthroughthepassivebeamwithincreasedvelocityacrosstheface

Passive Beam

Slot Diffuser

Induced Air

Primary Air





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Figure 27:Expectedvelocitiesbelowan18in.widepassivebeam

0.0100 150 200 250 300 350

96 146 196 246 296

10.0

20.0

30.0

40.0

50.0

0.3

0.25

0.2

0.15

0.1

0.05

0

60.0

Velo

city

, fpm

Velo

city

, m/s

Passive Beam Capacity, W/m

Passive Beam Capacity, Btu/hft

Avg. + 2σ

Average

Avg. – 2σ

Selection and LocationDuetotheaircascadebelowthepassivebeam, it is common to locate the beam aboveaislesor alongwalls. Dependingonthecapacityandtheexpectedvelocitybelowthebeam, theairmayposeariskof draft to occupants who are regularlylocated beneath them. Figure 27 shows thevelocitybelowan18in.[450mm]widepassivebeamvs.beamcapacity.

Inmostcases,itisdesirabletomaintainthevelocityintheoccupiedzonebelow50fpm[0.25m/s],thoughthisvaluewilldependonthetemperatureoftheair.FromFigure 27, theaveragevelocity(thesolidline)rangesfrom35fpm[0.175m/s]to50fpm[0.25m/s],operatingbetween150Btu/hft [145W/m]and300Btu/hft[290W/m].

Theinstallationheightisnotacriticalfactorbecause theplumeswillmake theirwaydownintotheoccupiedzone. Evenwithadisplacementventilationsystemwheretheremaybethermalplumesrisingfromthe occupants and heat sources, thesetendtoslidepasteachotherasopposedtomixing.

Selection of passive beams is fairlystraightforward.Manufacturersgenerallyprovidedataforstandardproductthathascapacityvs.flowrateforstandardvaluest̅w - troom.Inmostcases,itispreferabletousesoftwarebecauseitallowsgreatercontrolofthedesignparametersandmoreselectionoptions.Itisimportanttoconsiderboththecapacityaswellasthevelocitybeneaththebeam.Thisusuallymeansselectinglonger,narrower beams which typically causelowervelocitiesbelowthemforapplicationswhere theyare locatedabove stationaryoccupants.





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Design Procedure – Passive Beams

1. Determine the ventilation requirementTheventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminetheminimumfreshairflowrate:

H1

2. Determine the required supply dew-point temperature to remove the latent load

H2

Iftherequiredhumidityratioisnotpractical,recalculatethesupplyairvolumerequiredwiththedesiredhumidityratio.

3. Determine the supply air volumeThesupplyairvolumeisthemaximumvolumerequiredbycodeforventilationandthevolumerequiredforcontrollingthelatentload:

H3

4. Determine the sensible cooling capacity of the supply air

IP H4

SI H4

5. Determine the sensible cooling required from the water side

H5

6. Select a beam or series of beams Selectabeamorseriesofbeamsthatwillprovidetheappropriateamountofcoolingusinganappropriateentrywatertemperature.

7. Locate the beams to minimize draft as well as piping length




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Example 1 - Small Office Passive Beams Selection (IP)

Considerasmallofficewithasouthernexposure.Thespaceisdesignedfortwooccupants,acomputerwithLCDmonitor,T8florescentlighting,andhasatemperatureset-pointof75°F.Theroomis10ftwide,12ftlong,and9ftfromfloortoceiling.

12 ft

9 ft 10 ft

SMALL OFFICE

Window

Space ConsiderationsOneoftheprimaryconsiderationswhenusinganactiveorpassivebeamsystemishumiditycontrol.Aspreviouslydiscussed,itisimportanttoconsiderboththeventilationrequirementsandthelatentloadwhendesigningtheair-sideofthesystem.ASHRAEStandard62.1-2010stipulatestheventilationrequirements,buttheseareoftennotsufficienttocontrolhumiditywithoutspecializedequipment.

Theassumptionsmadeforthisexampleareasfollows:

• Load/personis250Btu/hsensibleand155Btu/hlatent• Lightingloadinthespaceis6.875Btu/hft²• Computerloadis300Btu/h(CPUandLCDMonitor)• Totalskinloadis1450Btu/h• Specificheatanddensityoftheairare0.24Btu/lb°Fand0.075lb/ft³respectively• Designconditionsare75°F,with50%relativehumidity• Designdewpoint=55°F

Determine:

a)Theventilationrequirement.b)Thesuitableairandwatersupplytemperatures.c)Asuitablepassivebeamtomeetthecoolingrequirement.d)Apracticallayoutforthespace.

Design Considerations

Occupants 2

Set-Point 75°F

FloorArea 120ft²

ExteriorWall 108ft²

Volume 1080ft³

qoz 800Btu/h

ql 825Btu/h

qex 1450Btu/h

qT 3075Btu/h




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Solution:

a)DeterminetheventilationrequirementTheventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminetheminimumfreshairflowrateforatypicalofficespace:

b) Determine the required supply dew-point temperature to remove the latent loadFromequationH2:

Usingtheventilationrate:

Atthedesignconditions(75°F,50%RH),thehumidityratiois65gr/lb,requiringadifferenceinhumidityratiobetweenthesupplyandroomairof:

Fromthefigurebelow,thedewpointcorrespondingtothehumidityratiois40°F,whichistoocoolforstandardequipment.

Evaluatingthehumidityratioatseveraltemperatures:

Humidity Ratio

DewPoint lb/lb gr/lb

40 0.00543 38

45 0.0065 46

50 0.0075 53

55 0.0095 67

0.0095

0.00650.0075

0.0054

0.000

0.002

0.004

0.010

0.012

0.014

0.016

0.018

0.020

0.022

0.024

0.026

0.028

0.030

35 40

12.5

13.0

13.5 10%

20%

30%40%

50%60%70%80%90

%

14.0

14.5

15.0

45 50 55 7560 65 70 80 85 90 95 100 105 110 115 120

65

Dry Bulb Temperature, ºF

Enthalpy - Btu/lb

of Dry

Air

Hum

idity Ratio, lbw /lb

DA

70

75

80

85

15

20

25

30

35

40

45

50

60 65

Volume - ft3/lb of Dry Air

Saturation Temperature, ºF

Relative Humidity

40

45

50

55

60

35




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Evaluatingthehumidityratioatseveraltemperaturesshowninthetableledtotheselectionofadewpointof50°Finordertouselessexpensiveequipmentwhilealsominimizingthesupplyairvolumerequiredtocontrolhumidity.Therequiredairvolumetosatisfythelatentloadis:

Thesupplyairvolumetotheofficeisthemaximumvolumerequiredbycodeforventilationandthevolumerequiredforcontrollingthelatentload:

Determine the sensible cooling capacity of the supply air UsingequationH4:

Determine the sensible cooling required from the water side

Assumingachilledwatersupplytemperature2°FabovethedesigndewpointinordertoavoidcondensationprovidesamaximumtemperaturedifferencebetweentheMWTandTroomof75°F-57°F=18°F.Usingselectionsoftwaretogenerateasuitableselectionprovidesthefollowingperformance:

Performance

Capacity 2049Btu/h

Length 72in.

Width 24in.

Waterflowrate 1.01gpm

Waterpressuredrop 4.9fthd

Itispracticaltolocatepassivebeamsalongawallwhereoccupantsarenotregularlylocated.Inthiscase,theareabesidethedeskisagoodchoice.

Person

SMALL OFFICE

Passive Beam




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Example 1 - Small Office Passive Beams Selection (SI)

Considerasmallofficewithasouthernexposure.Thespaceisdesignedfortwooccupants,acomputerwithLCDmonitor,T8florescentlighting,andhasadesigntemperatureset-pointof24°C.Theroomis3mwide,4mlong,and3mfromfloortoceiling.

3 m

4 m

3 m

SMALL OFFICE

Window

Space ConsiderationsOneoftheprimaryconsiderationswhenusinganactiveorpassivebeamsystemishumiditycontrol.Aspreviouslydiscussed,itisimportanttoconsiderboththeventilationrequirementsandthelatentloadwhendesigningtheairsideofthesystem.ASHRAEStandard62.1-2010stipulatestheventilationrequirements,buttheseareoftennotsufficienttocontrolhumiditywithoutspecializedequipment.

Theassumptionsmadefortheexampleareasfollows:

• Load/personis75Wsensibleand55Wlatent• Lightingloadinthespaceis25W/m²• Computerloadis90W(CPUandLCDMonitor)• Totalskinloadis405W• Specificheatanddensityoftheairare1.007kJ/kgkand1.3kg/m3respectively• Designconditionsare24°C,with50%relativehumidity• Designdewpoint=13°C

Determine:a)Theventilationrequirement.b)Thesuitableairandwatersupplytemperatures.c)Asuitablepassivebeamtomeetthecoolingrequirement.d)Apracticallayoutforthespace.


Occupants 2

Set-Point 24°C

FloorArea 12m²

ExteriorWall 12m²

Volume 36m³

qoz 240W

ql 300W

qex 405W

qT 945W




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Solution:a) Determine the ventilation requirementTheventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminetheminimumfreshairflowrateforatypicalofficespace:

b) Determine the required supply dew-point temperature to remove the latent loadFromequationH2:


Atthedesignconditions(24°C,50%RH),thehumidityratiois9.5g/kg,requiringadifferenceinhumidityratiobetweenthesupplyandroomairof:

Fromthefigurebelow,thedewpointcorrespondingtothehumidityratiois5°C,whichistoocoolforstandardequipment.Evaluatingthehumidityratioatseveraltemperatures:

Humidity Ratio

Dew Point g/kg

5 5.5

7.5 6.75

10 8

12.5 9.25


Dry-Bulb Temperature, ºC

Entha

lpy - k

J/kg o

f Dry

Air

30

25

20

15

10

050454035302520150

0

45

40

35

30

25

20

15

50

55

60

65

70

75

85

90

95

100

105

105110 115 120 125

Volume - m3/kg of Dry Air

Saturation Temperature, ºC

Relative Humidity

Hum

idity Ratio, gw /kg

DA

30

10

5

15

20

0.78

0.80

0.82

0.84

0.86

0.90

0.92

0.94

0.96

10%

20%

30%40%

50%60

%70%80

%90%

25

9.2586.755.5

10 12.5 245 7.5




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Evaluatingthehumidityratioatseveraltemperaturesshowninthetableledtotheselectionofadewpointof10°Cinordertouselessexpensiveequipmentwhilealsominimizingthesupplyairvolumerequiredtocontrolhumidity.Therequiredairvolumetosatisfythelatentloadis:


Determine the sensible cooling capacity of the supply airUsingequationH4:

Determine the sensible cooling required from the water side

Assumingachilledwatersupplytemperature1Kabovethedesigndewpointinordertoavoidcondensationprovidesamaximumtemperaturedifferencebetweenthe t̅w and troomof24°C–14°C=10K.Usingselectionsoftwaretogenerateasuitableselectionprovidesthefollowingperformance:

Performance

Capacity 567W

Length 1800mm

Width 600 mm

Waterflowrate 230L/h

Waterpressuredrop 14.6kPa

Itispracticaltolocatepassivebeamsalongawallwhereoccupantsarenotregularlylocated.Inthiscase,theareabesidethedeskisagoodchoice.


Person

SMALL OFFICE

Passive Beam




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Active beam systems will vary inperformance, configuration and layoutdependingontheapplication.Thereare,however, some characteristics that arecommonformostsystems.Furthermore,theperformanceofactivebeamsislargelydependent on a common set of factors.This section will discuss how factors such as supply air volume and chilled watertemperature affect the performance andlayoutof activebeams. Table 3 shows commondesigncharacteristicsforactivebeam systems.

Product Selection and Location – Active BeamsPerformanceThe performance of an active beam isdependentonseveralfactors:

• Activebeamconfiguration• Coilcircuitry• Primaryairflow(plenumpressure)• WaterflowAsdiscussedpreviously,thereareseveralconfigurationsofactivebeams.Themostcommonisthelineartype,whichisavailableinboth1wayand2wayairpatterns.Athirdtypeismodularandtypicallyhasa4waydischarge.

Activebeamsareappropriateforheatingandcooling.Thecoilcircuitryhasalargeeffectonthebeamperformance.Ifthebeamistobeusedforcoolingandheating,itwouldusuallyhavea4pipecoil.A4pipecoilsharesfinsbetweentwoseparatecircuits.Ifthebeamisusedforeithercoolingorheatingonly,thebeammaymakeuseoftheentirecoilwithasinglecircuit,therebyallowingadditional heat transfer from the water to theair.Theprimarydriverofactivebeamcapacityistheplenumpressure.Figure 30 and Figure 31showtheairpathoflinearandmodularbeamsincooling.

Asdiscussed,itistheprimaryairthatinducestheroomairthroughthecoil, therateofwhich is determined by the nozzle size and theplenumpressure.Agoodmeasurefortheoverallperformanceofanactivebeamisknownasthetransferefficiency.Thisisthe ratio of total heat transferred by the coil perunitvolumeofprimaryair:

Typicalvaluesfortransferefficiencyvarybyapplicationtypebutingeneral,thehighertheefficiency,themoreenergysavingsareavailableforagivensystem.Thetransferefficiencyislargelydependentontheair-side load fraction and the sensible heat ratio.

Active Beam Selection and Design Procedure

IPRoomTemperature 74°Fto78°Finsummer,68°Fto72°FinwinterWaterTemperature,Cooling 55°Fto58°FEWT,5°Fto8°F TDesignSoundLevels <40NCCoolingCapacity Upto1000Btu/h/ftWaterTemperature,Heating 110°Fto130°FEWT,10°Fto20°F THeatingCapacity Upto1500Btu/h/ftVentilationRequirement 0.1to0.5cfm/ft2floorareaVentilationCapability 5to30cfm/ftPrimaryAirSupplyTemperature 50°Fto65°FInletStaticPressure 0.2in.w.g.to1.0in.w.g.externalSIRoomTemperature 23°Cto25°Cinsummer,20°Cto22°CinwinterWaterTemperature,Cooling 13°Cto15°CEWT,3Kto5K TDesignSoundLevels <40NCCoolingCapacity Upto1000W/mWaterTemperature,Heating 60°Cto70°CEWT,5Kto12K HeatingCapacity Upto1500W/mVentilationRequirement 0.5to2.5L/sm2floorareaVentilationCapability 7to40L/sm2

PrimaryAirSupplyTemperature 10°Cto18°CInletStaticPressure 50Pato250Paexternal

Table 3: Designvaluesforactivebeamsystems

Figure 28: Lineartypeactivebeam Figure 29:Modulartypeactivebeam


Nozzles

Plenum

Primary Air

Room Air

Figure 31: Airflowdiagramofamodularbeamincooling

Room Air

NozzlesPlenum

Primary Air




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Thehigherthesensibleloadfractionis,thesmallerthebeamnozzlecanbe,resultinginahigherinductionratio,definedastheratiooftheinducedmassairflowtothatoftheprimaryair:

The selection of smaller nozzles also results in higher plenum pressures for a fixedprimaryairflowrate.Largernozzleswillhavealowerinductionratiobutallowmoreprimaryairtobesupplied,thoughatalowertransferefficiency,asshowninFigure 32.

Figure 33showsthewater-sideperformanceofatypicalbeamvs.airflow.Thecurvescorrespond with various nozzle sizesincreasingindiameterfromlefttoright.Thelengthofthecurvesisdefinedbystandardoperating pressures. It is noted fromthegraphsthatthecapacityofthebeamincreasesasmoreairissupplied,thoughnot in a linear fashion.

Figure 34 shows how the increase in capacity isdependentontheairvolume.Asshowninthefigure,asthenozzlesizeincreases to provide a five-fold increaseinairvolume,onlya175%increaseinthewater-side capacity is realized,while thetransferefficiencyhasreducedby65%.

Thewaterflowrateinthecoilaffectstwoperformancefactors:

The heat transfer between the water and thecoilwhichisdependentonwhethertheflowislaminar(poor)orturbulent(good).

Themeanwatertemperature,ortheaveragetemperatureinthecoil.Thehighertheflowrate,thecloserthedischargetemperaturewill be to that of the inlet, assumingnochangeinheattransfer,therebychangingtheaveragewatertemperatureinthecoil.

Figure 32: Transferefficiencyisreducedbyincreasingnozzlesize

Tran

sfer

Effi

cien

cy

Smaller Nozzle Larger Nozzle

Figure 33:Capacityofatypicalactivebeamvs.primaryairflow

Figure 34: Capacityvs.airvolume

00

0 10 20 30 40 50 60 70

10 20 30 40 50

400

200

600

800

1000

1200

1400

0

200

400

600

800

1000

1200

Cap

acity

, Btu

/hft

Cap

acity

, W/m

Air Flow, cfm/ft

Air Flow, L /sm

0100 200 300 400 500 600

100

120

140

160

180

20

40

60

80

200 Capacity Increase

Transfer Efficiency

Incr

ease

in W

ater

-Sid

e Ca

paci

ty, %

Increase in Air Volume, %




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Figure 35 shows the effect of the water flowrate,indicatedbyReynoldsnumber,on thecapacityofa typicalactivebeam.As indicatedon thechart, increasing theflowrateintothetransitionalandturbulentranges(Re>2300,showninblueonthegraph)causesanincreaseintheoutputofthe beam.

Thewaterflowrate is largelydependenton the pressure drop and returnwatertemperature that are acceptable to thedesigner. Inmost cases, thewaterflowrate should be selected to be fully turbulent underdesignconditions.

The difference between the mean water temperatureandtheroomairtemperatureisoneoftheprimarydriversofthebeamperformance. The larger this differenceis,thehighertheconvectiveheattransferpotential,asshowninFigure 36.Conversely,alowertemperaturedifferencewillreducethe amount of exchange, and therebycapacity. Asaresult, it isdesirablefroma capacity standpoint to select an entrywatertemperatureaslowaspossible,whilemaintainingitabovethedewpointintheroomtoensuresensible-onlycooling.

Insomeinstances,itmightbeadvantageousto have higher supply and returnwatertemperatures,whereitmakessensefromanequipmentstandpoint. Thismayalsooffersomecontrolsimplificationwheretheoutputofthebeamisdeterminedbytheloadintheroom:

Astheloadincreases,theairtemperaturerises and increases the difference between it and t̅w, thereby increasing beamperformance.

Astheloaddecreases,theairtemperaturefallsandreducesthecoolingcapacityofthebeam.


Figure 35: Activebeamcapacityvs.waterflow

400 2000 4000 6000 8000 10000 12000

50

60

70

80

90

100

Cap

acity

, %

Re

Figure 36: Activebeamcapacityvs.differencebetweenthemeanwaterandroomairtemperatures

00 5 10 15 20

0 2 4 6 8 10

20

40

60

80

100

120

Cap

acity

, %

tw - troom ,˚F

tw - troom , K




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Design Procedure – Active Beams

1. Determine the ventilation requirementTheventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminetheminimumfreshairflowrate:

H1

2. Determine the required supply dew-point temperature to remove the latent load

H2

Iftherequiredhumidityratioisnotpractical,recalculatethesupplyairvolumerequiredwiththedesiredhumidityratio.

3. Determine the supply air volumeThesupplyairvolumeisthemaximumvolumerequiredbycodeforventilationandthevolumerequiredforcontrollingthelatentload:

H3

4. Determine the sensible cooling capacity of the supply air

IP H4

SI H4

5. Determine the sensible cooling required from the water side

H5

6. Select a beam or series of beams Selectabeamorseriesofbeamsthatwillprovidetheappropriateamountofcoolingandheatingusingappropriateentrywatertemperaturesandthrowdistances.

7. Review that the primary air calculation in (3) is still appropriate

H6

8. Lay out the beams in such a way that the comfort in the space is maximized




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©CopyrightPriceIndustriesLimited2011. AllMetricdimensions()aresoftconversion. Imperialdimensionsareconvertedtometricandroundedtothenearestmillimeter.

Example 2 - Small Office Active Beam Selection (IP)

12 ft

9 ft 10 ft

SMALL OFFICE

Window

ConsiderthesmallofficepresentedinExample1-SmallOfficePassiveBeamSelection.


Occupants 2

Set-Point 75°F

FloorArea 120ft²


Volume 1080ft³

qoz 800Btu/h

ql 825Btu/h

qex 1450Btu/h

qT 3075Btu/h

Qs 38cfm

ts 50°F

tCHWS 57°F

Determine

a)Asuitableactivebeamtomeetthecoolingrequirement.b)Apracticallayoutforthespace.

SolutionFromexample1-SmallOfficePassiveBeamSelection.

Performance

TotalCapacity 3075Btu/h

AirflowRequiredforDehumidification 38cfm

SupplyAirTemperature 50°F

CHWSTemperature 57°F




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Usingselectionsoftwaretoselectbeamswiththeseparametersprovidesseveralpossiblesolutions:

Example 2 - Small Office Active Beam Selection (IP)

Parameter Option 1 (ACBL) Option 2 (ACBL) Option 3 (ACBM)

TotalCapacity 3074Btu/h 3076Btu/h 3077Btu/h

Length 72in. 48in. 48in.

Width 24in. 24in. 24in.

Airflow 35cfm 40cfm 40cfm

Throw@50fpm 10ft 13ft 10ft

AirPressureDrop 0.75in. 0.42in. 0.56 in.

TransferEfficiency 88Btu/hcfm 77Btu/hcfm 77Btu/hcfm

WaterFlowRate 0.41gpm 1.2gpm 0.61gpm

WaterPressureDrop 0.63fthd 3.1fthd 1.26fthd

NC 15 18 17

Thefirstoptionmeetsthecapacityrequirementsthoughhasslightlylowerairflowthanthatrequiredtohandlethelatentloads;itisalsothemostefficientoption.Thesecondandthirdoptionsbothmeetthecapacityandairflowrequirements.

Revisitingtheairvolumerequired:

Fortheprivateoffice,eitherselection(2)or(3)isappropriate.Themodularunithastheadvantageoflowerthrowandwouldresultinloweroccupiedzonevelocities.Thelinearunitcanbeselectedwithanintegratedreturngrille,increasingtheoveralllengthofthebeamwhileallowingthereturntoappeartobeapartofthebeam.Bothoftheselayoutsareshownbelow:

Section ViewPlan View

PersonPerson

2 wayBeam

IntegratedReturn

Return

SMALL OFFICE

Person

SMALL OFFICE

Person

CE

ModularBeam

Window

Window




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Example 2 - Small Office Active Beam Selection (SI)

12 ft

9 ft 10 ft

SMALL OFFICE

Window

ConsiderthesmallofficepresentedinExample1-SmallOfficePassiveBeamSelection.


Occupants 2

Set-Point 24°C

FloorArea 12m²

ExteriorWall 12m²

Volume 36m³

qoz 240W

ql 300W

qex 405W

qT 945W

Qs 22.5L/s

ts 10 °C

tCHWS 14 °C

Determine

a)Asuitableactivebeamtomeetthecoolingrequirement.b)Apracticallayoutforthespace.

SolutionFromexample1-SmallOfficePassiveBeamSelection.

Performance

TotalCapacity 945W

AirflowRequiredforDehumidification 22.5L/s

SupplyAirTemperature 10°C

CHWSTemperature 14°C




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Usingselectionsoftwaretoselectbeamswiththeseparametersprovidesseveralpossiblesolutions:

Example 2 - Small Office Active Beam Selection (SI)


TotalCapacity 945W 946W 952 W

Length 1.8m 1.2m 1.2m

Width 0.6 m 0.6 m 0.6 m

Airflow 16.5L/s 22.5L/s 22.5L/s

Throw@50fpm 3.9m 3.7m 3m

AirPressureDrop 187Pa 107Pa 100Pa

TransferEfficiency 48Ws/L 25Ws/L 25Ws/L

WaterFlowRate 93L/h 216L/h 148L/h

WaterPressureDrop 1.88kPa 8.07kPa 4.18kPa

NC 15 21 17

Thefirstoptionmeetsthecapacityrequirementsthoughhasslightlylowerairflowthanthatrequiredtohandlethelatentloads;itisalsothemostefficientoption.Thesecondandthirdoptionsbothmeetthecapacityandairflowrequirements.

Revisitingtheairvolumerequired:

Fortheprivateoffice,eitherselection(2)or(3)isappropriate.Themodularunithastheadvantageoflowerthrowandwouldresultinloweroccupiedzonevelocities.Thelinearunitcanbeselectedwithanintegratedreturngrille,increasingtheoveralllengthofthebeamwhileallowingthereturntoappeartobeapartofthebeam.Bothoftheselayoutsareshownbelow:

Section ViewPlan View

PersonPerson

2 wayBeam

IntegratedReturn

Return

SMALL OFFICE

Person

SMALL OFFICE

Person

CE

ModularBeam

Window

Window




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In active beamselection, there is often atrade-offrequiredbetweentheprimaryairvolume and the beam length. When thetotal capacity of the beam is consideredthereisanincreaseinthecapacitywithanincreaseintheprimaryairvolume;though,as indicated in Figure 37, thisislargelyduetotheincreasedcapacityoftheprimaryairandonlyslightlyduetoanincreaseintheperformanceofthecoolingcoil.Theoveralleffectofanincreaseinprimaryairvolumeis invariably a reduction in the transferefficiencyofthebeam;therefore,caremustbetakenwhenincreasingtheairvolumepastwhat is required to satisfy theventilationrequirementsandlatentloads.

Inorder todetermine if it isnecessary toincreasetheairvolumebeyondthatwhichisrequired,severalfactorsshouldbeweighed:

1. Beam SizeWithhighercapacityperunitlengthofbeamitispossibletoreducethesizeofthebeam,whichmayreducethevisualimpactoftheHVACsystem.Itmayalsohelptofitbeamsintospaceswithhighspecificloads,suchasacornerofficeinahotclimatelikePhoenixorDubai.

2. First CostThe reduction inoverall sizeof thebeamdoesoffersomefirstcostsavings,thoughtheseshouldbecomparedtothefirstcostadditionsrequiredoftheairhandlingsystem,includingequipmentandductwork.Inmostapplications,thesecostsaresimilarandmaynotofferthebenefitsought.

3. EnergyBy decreasing the transfer efficiency (orincreasing the percentage of the loadmanagedbyairratherthanwater),thereisusuallyareductionintheoverallefficiencyofthesystem.Inmostcases,itismoreefficienttopumpenergythroughthebuildingwithwater than air, and so an increase in the load managedbyairmaycauseanincreaseinthesystemhorsepower.

4. NoiseActivebeamnoiseislargelydependentonprimaryairflow,thereforeanincreaseintheprimaryairvolumetothebeamwillincreasethenoiselevelsinthespace.

5. ControlWithadditional air supplied to thebeam,there is an increased risk of overcoolingthezoneunderpart-loadconditions.Thesesystemsaretypicallyconstantvolume,whichreducesthesystem’sabilitytocontrolthezonetemperatureiftheminimumcapacityof the beam is increased due to an increase inprimaryairvolume.

Managing Primary Air Volume and Capacity

6. Life-Cycle CostThistypeofdesigndecisionisoftenbestmadewithalife-cyclecostanalysistodeterminethecostimpactoverthelifeofthebuilding.

Thereareapplicationswhereanincreaseinairvolumeisareasonabledesigndecision,eitherduetoverylargespecificloadsorhighventilationrates,suchasinahealthcareapplication.Insituationswherethespecificloadishigh,therearesomeoptionsthatwillallowthesystemtomeettherequiredcapacitybutwillalsomaximizetheenergyefficiency:

1. Select an active beam and a passive beam together.

Thisallowsthedesigner tominimizetheairandaddsensiblecoolingcapacitywhererequired.Thisalsosignificantlyincreasesthe transfer efficiency of the room by keepingtheairvolumeaslowaspossiblewhileincreasingthesensiblecapacity.

2. Employ a variable air volume (VAV) strategy.

Whether for an individual office or fora larger zone,VAV allows the system tosupplythecapacityrequiredunderdesignconditionswhileallowingtheairvolumetobeturneddowntominimumduringoff-peakhours.Themostefficientconfigurationwouldhavetheairturnup/downonlyasthesecondstageofcooling,asshowninthediagrambelow.

Max. Water Flow

Min. Water Flow

Dead Band

Tset-point

CHW

S Flo

wHWS Flow

Max. Air Flow

Air fl

ow

Air flow

Min. Air Flow

Cool WarmRoom Condition

Figure 37:VAVcontrolsequence




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Example 3 - Small Office with High Internal Gains (IP)

ConsiderthesmallofficepresentedinExample1,thoughnowinahotclimatewithanincreasedsolargain:

12 ft

9 ft 10 ft

SMALL OFFICE

Window


Occupants 2

Set-Point 75°F

FloorArea 120ft²


Volume 1080ft³

qoz 800Btu/h

ql 825Btu/h

qex 6575Btu/h

qT 8200Btu/h

Qs 38cfm

ts 50°F

tCHWS 57°F

Compare

a)AsuitableactivebeamwithconstantairsupplytoonewithVAV,assuming2175Btu/hofenvelopeloadinoff-peakhours.b)Asuitableactivebeamtoacombinationofactiveandpassivebeams.

Solution

a)Usingsoftware,selectabeamwiththefollowingrequirements.

Performance


AirFlowrequiredforDehumidification 35cfm


CHWSTemperature 57°F




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Whenthesamebeamisturneddowninairflow,thefollowingperformanceisachieved:

Inthiscase,increasingthesupplyairvolumewasrequiredinordertomeetthecapacityrequired:

Parameter Peak Load Off-Peak Load

TotalCapacity 8202Btu/h 3817Btu/h

Length 96 in. 96 in.

Width 24in. 24in.

AirFlow 140cfm 55 cfm

Throw 18ft 10ft

AirPressureDrop 0.88in.w.g. 0.15in.w.g.

TransferEfficiency 59Btu/hcfm 69Btu/hcfm

WaterFlowRate 1.23gpm 1.23gpm

WaterPressureDrop 5.8fthd 5.8fthd

NC 32 <15

Withnowaterflowthebeamoutputduetoprimaryaircoolingwouldbe3780Btu/h,whichmeetsthecoolingrequirementbutwilldosobymaintaininghighairflow(lessefficient).




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Thebeamismoreeffectivelymodulatedincapacitybyvaryingtheairvolumeinsteadofthewatervolume.Ifthebeamweredesignedwithconstantairvolumeandon-offcontrolofthecoil,therewouldbesignificantswingsinthetemperatureoftheairintheroomduringoff-peakhoursduetothehighcapacityofthebeamunderdesignconditions.

ThemainadvantagetotheVAVsystemisenergysavingsandtightercontrol.Asseeninthefigure,thecapacityfortheselectedbeamiseffectivelycontrolledthroughmodulationoftheairvolume,offeringenergysavingsbyresettingthesupplyvolumeofthelessefficientairsystemandhandlingahigherpercentageoftheroomloadwiththehydronicsystem.

3000

2000

1000

050 70 90 110 130 150

4000

5000

6000

7000

8000

9000

Cap

acity

, Btu

/h

Air Volume, cfm

PersonPerson

Beam

SMALL OFFICE

Window Max Load

Thelayoutisthesameasinexample1.Reviewingthethrowpatternatpeakload:

b) Using software again, an active beam and passive beam are selected together

Parameter Passive Beam Active Beam Total


Length 96 in. 96 in. -

Width 24in. 24in. -

AirFlow 0 55 cfm 55 cfm

Throw - 15ft -

AirPressureDrop n/a 1in. 1in.

TransferEfficiency n/a 100Btu/hcfm 149Btu/hcfm


WaterPressureDrop 9.8fthd 9.9 ft hd 9.9 ft hd

NC - 20 20




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Inthisexample,anactivebeamandapassivebeamwereselectedtobethesamesizetosimplifythelayout.Furthermore,thewater-sidepressuredrophasbeenselectedtobeequivalenttomakethepipingmorestraightforward.Thesebeamscouldbelaidoutandpipedasshown:


Person

SMALL OFFICECHW

SCH

WR

Window

Passive Beam

Active Beam

Inthiscasetheairpatternfromtheactivebeampassesoverthefaceofthepassivebeam,thereforetheconcernofvelocitybelowthepassivebeamislargelyeliminated.Furthermore,thistypeofarrangementtendstoincreasetheairvolumethroughthepassivebeam,whichwouldtypicallyresultinanincreaseinperformance.

Comparingthetwooptions:

Parameter Active Beam Active &Passive Beam


AirFlow 140cfm 55 cfm

Throw 18ft 15ft

AirPressureDrop 0.88in. 1in.



WaterPressureDrop 5.8fthd 9.9 ft hd

NC 32 20

Thedifferencebetweenthetwoislargelyinthesupplyairvolumeandnoise.Selection(1)requiresanadditional85cfm,or250%theamountofairrequiredinthesecondselectionandalsohasasignificantlyhigherNClevel.Thiswilltranslateintolargerairhandlingequipmentandductwork(evenfortheVAVcase),addingcostaswellasadditionalenergytomovetheairthroughthebuilding.Insomeareas,theselectionofthesystemwithlowersupplyairvolumetranslatesintosignificantenergysavings:

Thisenergysavingsisforthesensiblecoolingoftheoutdooraironly;additionalsavingswouldexistinthelatentcoolingandtransportenergyoftheadditionalairvolume.Thereisadditionalcostinthepassivebeam,thoughitmaybeoffsetbytheincreaseinequipmentanddistributioncostaswellastheenergyrequiredforthehigherairvolumecase.Thiswillhowever,dependlargelyontheapplicationandbuildingdesign.

Annual degree -hours

Annual ton - hours saved per office

Total annual kWh saved per office

Phoenix 76121 582.33 3654

Atlanta 46253.4 353.84 2220

Minneapolis 25494.8 195.04 1224

Seattle 19345.8 148.00 929

WashingtonDC 36635.9 280.26 1759




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HydronicHeating&CoolingSystemsEngineering Guide

Example 3 - Small Office with High Internal Gains (SI)

ConsiderthesmallofficepresentedinExample1,thoughnowinahotclimatewithanincreasedsolargain:


Occupants 2

Set-Point 24°C

FloorArea 12m²

ExteriorWall 12m²

Volume 36m³

qoz 240W

ql 300W

qex 1860W

qT 2400W

Qs 22.5L/s

ts 10 °C

tCHWS 14 °C

Compare

a)AsuitableactivebeamwithconstantairsupplytoonewithVAV,assuming580Wofenvelopeloadinoff-peakhours.b)Asuitableactivebeamtoacombinationofactiveandpassivebeams.

Solution

a)Usingsoftware,selectabeamwiththefollowingrequirements.

Performance

TotalCapacity 2400W

AirFlowrequiredforDehumidification 22.5L/s


CHWSTemperature 14°C

3 m

4 m

3 m

SMALL OFFICE

Window




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Inthiscase,increasingthesupplyairvolumewasrequiredinordertomeetthecapacityrequired:

Parameter Peak Load Off-Peak Load

TotalCapacity 2400W 1140W

Length 2.4m 2.4m

Width 600 mm 600 mm

AirFlow 66L/s 26L/s

Throw 4.9m 2.4m

AirPressureDrop 221Pa 35Pa

TransferEfficiency 19Ws/L 27Ws/L

WaterFlowRate 218L/h 218L/h

WaterPressureDrop 14.6kPa 14.6kPa

NC 33 <15

Withnowaterflowthebeamoutputduetoprimaryaircoolingwouldbe1130W,whichmeetsthecoolingrequirementbutwilldosobymaintaininghighairflow(lessefficient).

Thebeamismoreeffectivelymodulatedincapacitybyvaryingtheairvolumeinsteadofthewatervolume.Ifthebeamweredesignedwithconstantairvolumeandon-offcontrolofthecoil,therewouldbesignificantswingsinthetemperatureoftheairintheroomduringoff-peakhoursduetothehighcapacityofthebeamunderdesignconditions.

ThemainadvantagetotheVAVsystemisenergysavingsandtightercontrol.Asseeninthefigure,thecapacityfortheselectedbeamiseffectivelycontrolledthroughmodulationoftheairvolume,offeringenergysavingsbyresettingthesupplyvolumeofthelessefficientairsystemandhandlingahigherpercentageoftheroomleadwiththehydronicsystem.

020 30 40 50 60 70

500

1000

1500

2000

2500

3000

Air Volume, L/s

Capa

city

, W


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Inthisexample,anactivebeamandapassivebeamwereselectedtobethesamesizetosimplifythelayout.Furthermore,thewater-sidepressuredrophasbeenselectedtobeequivalenttomakethepipingmorestraightforward.Thesebeamscouldbelaidoutandpipedasshown:

Person

SMALL OFFICECHW

SCH

WR

Window

Passive Beam

Active Beam

Thelayoutisthesameasinexample1.Reviewingthethrowpatternatpeakload:

b) Using software again, an active beam and passive beam are selected together

Parameter PassiveBeam ActiveBeam Total

TotalCapacity 811W 1606W 2417W

Length 2.4m 2.4m -

Width 600 mm 600 mm -

AirFlow 0 26L/s 26L/s

Throw - 3.7m 3.7m

AirPressureDrop n/a 296 Pa 296 Pa

TransferEfficiency n/a 45Ws/L 76Ws/L

WaterFlowRate 193L/h 220L/h 413L/h


NC - 21 21

PersonPerson

Beam

SMALL OFFICE

Window Max Load


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ND

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Inthiscasetheairpatternfromtheactivebeampassesoverthefaceofthepassivebeam,thereforetheconcernofvelocitybelowthepassivebeamislargelyeliminated.Furthermore,thistypeofarrangementtendstoincreasetheairvolumethroughthepassivebeam,whichwouldtypicallyresultinanincreaseinperformance.Comparingthetwooptions:

Thedifferencebetweenthetwoislargelyinthesupplyairvolumeandnoise.Selection(1)requiresanadditional40L/s,or250%theamountofairrequiredinthesecondselection,andalsohasasignificantlyhigherNClevel.Thiswilltranslateintolargerairhandlingequipmentandductwork(evenfortheVAVcase),addingcostaswellasadditionalenergytomovetheairthroughthebuilding.Insomeareas,theselectionofthesystemwithlowersupplyairvolumetranslatesintosignificantenergysavings:

Parameter Active Beam Active &Passive Beam


AirFlow 66L/s 26L/s

Throw 4.9m 3.7m

AirPressureDrop 221Pa 296 Pa




NC 33 21

Annual degree - hours

Total annual kWh saved per office

Phoenix 76121 3654

Atlanta 46253 2220

Minneapolis 25495 1224

Seattle 19346 929

WashingtonDC 36636 1759

Thisenergysavingsisforthesensiblecoolingoftheoutdooraironly;additionalsavingswouldexistinthelatentcoolingandtransportenergyoftheadditionalairvolume.Thereisadditionalcostinthepassivebeam,thoughitmaybeoffsetbytheincreaseinequipmentanddistributioncostaswellastheenergyrequiredforthehigherairvolumecase.Thiswillhowever,dependlargelyontheapplicationandbuildingdesign.


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Example 4 - Active Beams in a Computer Lab (IP)

This space is a school computer lab designed for 26 occupants, 26 computers with one LCD monitor each, a projector,threeprinters,T8florescent lighting,andhasa temperatureset-pointof75°Fat50%RHin thesummer.Theroomis50 ft long, 50ftwide,andhasafloor-to-ceilingheightof9ft.Theceilingisexposed,withpossibleductconnectionsintheinteriorofthespace.

Space Considerations

• Someoftheassumptionsmadeforthisspaceareasfollows:• Infiltrationisminimal,andisneglectedforthepurposesofthisexample.• Thespecificheatanddensityoftheairforthisexamplewillbe0.24Btu/lb°Fand0.075lb/ft2respectively.• Theairhandlingsystemutilizesenergyrecoverytoprovide65°Fat50°Fdewpoint.Determinetheventilationrequirement

Design Considerations Total

OccupantLoad 250Btu/hperson 6500Btu/h

LightingLoad 3Btu/hft2floor 7500Btu/h

ComputerLoads 450Btu/hperson 11700Btu/h

ProjectorLoad 188Btu/h 188Btu/h

PrinterLoads 444Btu/h 444Btu/h

EnvelopeLoad 14.6Btu/hft2façade 6570Btu/h

Total Load 32902 Btu/h

LatentLoad-OccupantLoad 200Btu/hperson 5200Btu/h

Theventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminetheminimumfreshairflowrateforatypicalofficespace:

Determinetherequiredsupplydew-pointtemperaturetoremovethelatentload

Usingahumidityratioofthesupplyairat50°Fdewpointandthedesignconditions(75°F,50%RH):

Printers Projector

COMPUTER LAB

50 ft

50 ft


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Thesupplyairvolumetotheofficeisthemaximumofthevolumerequiredbycodeforventilationandthevolumerequiredforcontrollingthelatentload:

Using software to select a beam with the following requirements:

Example 4 - Active Beams in a Computer Lab (IP)

Performance


AirFlowRequiredforDehumidification 632cfm


Arrivesatthefollowingoptions:



Quantity 4 6 6

Length 120in. 96 in. 48in.

Width 24in. 24in. 24in.

AirFlow 640cfm 780cfm 870cfm

Throw 11ft 17ft -

AirPressureDrop 0.99 in. 0.76in. 0.83in.

TransferEfficiency 50.3Btu/hcfm 42.4Btu/hcfm 37.9Btu/hcfm


WaterPressureDrop 9.9 ft hd 4.6fthd 0.71fthd

NC 27 30 -

Oftheseoptions,thesecondcombinationofsix8ftlongbeamsisthebestcombinationofcapacity,efficiencyandthrow.Withsixbeams,thesecouldbelaidoutasshownbelow:

COMPUTER LAB

Printers Projector

CHW

SCH

WR

BeamBeam Beam

BeamBeam Beam




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Example 4 - Active Beams in a Computer Lab (SI)

Thisspaceisaschoolcomputerlabdesignedfor26occupants,26computerswithoneLCDmonitoreach,aprojector,3printers,T8florescentlighting,andhasatemperatureset-pointof24°Cat50%RHinthesummer.Theroomis15mlong,15mwide,andhasafloor-to-ceilingheightof3m.Theceilingisexposed,withductconnectionspossibleintheinteriorofthespace.

15 m

15 m

Printers Projector

COMPUTER LAB

Space ConsiderationsSomeoftheassumptionsmadeforthisspaceareasfollows:

• Infiltrationisminimal,andisneglectedforthepurposesofthisexample.• Thespecificheatanddensityoftheairwillbe1.007kgKand1.3kg/m3respectively.• Theairhandlingsystemutilizesenergyrecoverytoprovide18°Cat10°Cdewpoint.

Design Considerations Total

OccupantLoad 75W/person 1950W

LightingLoad 25W/m2floor 5625 W

ComputerLoads 130W/person 3380W

ProjectorLoad 55 W 55 W

PrinterLoads 130W 130W

EnvelopeLoad 46W/m2façade 2070W

Total Load 13210 W

LatentLoads-OccupantLoad 60W/person 1560W

Determine the ventilation requirementTheventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard62-2004todeterminetheminimumfreshairflowrateforatypicalofficespace:

Determinetherequiredsupplydew-pointtemperaturetoremovethelatentload.

Usingahumidityratioofthesupplyairat10°Cdewpointandthedesignconditions(24°C,50%RH):




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Using software, select a beam with the following requirements:

Example 4 - Active Beams in a Computer Lab (SI)

Performance

TotalCapacity 13210W

AirFlowRequiredforDehumidification 320L/s


Arrivesatthefollowingoptions:


TotalCapacity 13221W 13216W 13220W

Quantity 6 7 8

Length 3000mm 2400mm 1200mm

Width 600 mm 600 mm 600 mm

AirFlow 426L/s 497L/s 696L/s

Throw 3.3m 6 m -

AirPressureDrop 220 Pa 250 Pa 193Pa

TransferEfficiency 31Ws/L 17Ws/L 19Ws/L

WaterFlowRate 302L/s 345L/s 368L/s


NC 27 33 -

Oftheseoptions,thesecondcombinationofsix2.4mbeamsisthebestcombinationofcapacity,efficiencyandthrow.Withsixbeams,thesecouldbelaidoutasshownbelow:

COMPUTER LAB

Printers Projector

CHW

SCH

WR

BeamBeam Beam

BeamBeam Beam




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Example 5 - Active Beams in Laboratories (IP)

Thishospital laboratory isused for the testingofspecimensassociatedwithpatientcare.The layout featuresone islandbenchand twowall benches to accommodate amaximumof ten clinical lab technicians. Florescent lighting, refrigerationequipmentandotherbenchdevices all generateheatwithin the lab.Thereare also two low-flow fumehoods in the cornersof the room,operatingataconstantvolumeexhaustflowrateof480cfmeach.Theroomis36 ft longby20 ftwide,withaceilingheightof 12ft.Thespaceisaninteriorzoneofthebuildingwithnoenvelopeload.

Aisle

Aisle Fume Hood

Fume Hood

20 ft

36 ft.

Cabinets/Work Surface


• Load/personis250Btu/hsensibleand200Btu/hlatent• Lightingloadinthespaceis8.3Btu/hft2

• Thespecificheatanddensityoftheairforthisexampleare0.24Btu/lb°Fand0.075Btu/hft2respectively• Minimumexhaustflowrateof6achinaccordancewithASHRAEStandard170-2008• Maintaina20%offsetbetweensupplyandexhaustvolumeinordertomaintainnegativepressure


Area 720ft2

CeilingHeight 12ft

DesignConditions Summer–75°F,50%RH

Occupants 10

OccupantLoad 2500Btu/hsensible 2000Btu/hlatent

LightingLoad 6000Btu/hsensible

EquipmentLoad 31800Btu/hsensible

Total load, qt40300Btu/hsensible 2000Btu/hlatent

Number of lab hoods 2

FumeHoodExhaustAirVolume 960 cfm




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1. Determine the exhaust requirementTheexhaustrequirementisdictatedbytheexhaustrequiredbythefumehoods,aswellasbylocalcodes.Forexample,usingASHRAEStandard170-2008todeterminetheminimumfreshairflowrate:

2. Determine the ventilation requirementInordertomaintainnegativepressure,theventilationrequirementistakenas80%oftheexhaustairflowrate:

3.Determinetherequiredsupplydew-pointtemperaturetoremovethelatentloadFromequationH2:

Atthedesignconditions(75°F,50%RH),thehumidityratiois65gr/lbofdryair,requiring:

Fromthefigurebelow,thedewpointcorrespondingtothehumidityratiois54°F.Thisisreadilyachievedbystandardequipment,andthereforedoesnotneedtobeadjusted.Withtheairchangerequirementdeterminedbycodenearlyequivalenttotheairvolumerequirementdictatedbythefumehoodexhaust,wewill,inthisapplication,opttouseaconstantvolumesupplyairsystem.


0.000

0.002

0.004

0.006

0.012

0.014

0.016

0.018

0.020

0.022

0.024

0.026

0.028

0.030

35 40

12.5

13.0

13.5 10%

20%

30%40%

50%60%70%80%90

%

14.0

14.5

15.0

45 50 60 65 70 80 85 90 95 100 105 110 115 120

65

Dry Bulb Temperature, ºF

Enthalpy - Btu/lb

of Dry

Air

Hum

idity Ratio, lbw /lb

DA

70

75

80

85

15

20

25

30

35

40

45

50

60 65

Volume - ft3/lb of Dry Air

Saturation Temperature, ºF

Relative Humidity

40

45

50

55

60

35

0.00930.0087

54 75




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4. Select the active beams using software with the following requirements:

Parameter Option 1 Option 2

Configuration Linear–CoolingOnly Linear–CoolingOnly

Size 120inx24in. 120inx24in.

Quantity 4 4


CHWSTemperature 57°F 58°F


WaterPressureDrop 4.8fthd 6.7fthd

AirFlow 864cfm 864cfm

Throw 14ft 14ft

AirPressureDrop 0.67in.w.g. 0.78in.w.g.


NC 31 31

Requirements


AirVolume 768cfm


SupplyWaterTemperature 57°F

RoomSet-PointTemperature 75°F

Thesetwoselectionsarelargelysimilarwithbothmeetingthecapacityrequiredattheventilationrate.Thewaterflowrateishigherinthesecondcase,asisthechilledwatersupplytemperature.Thisallowsformorerangetomodulatethewaterflowtocontrolroomtemperatureastheloadsinthelabchangeovertime.Furthermore,theincreaseinCHWStemperaturewillincreasethereturnwatertemperaturetothesystem,potentiallyincreasingtheefficiencyofthechillerplant.

Optingforoption(2)andamodulatingcontrolsequence,whichwillallowtheairsystemtotheoptimizedfortheventilationrate,andsimplecontrolofthebeamstoaccommodateanyloadfluctuations:

Max. Flow

Min. FlowHW Flow

Dead Band

Tset-point

CW Flo

w





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Alternatively,theCHWStemperaturecanbemodulatedtocontroltheload,thoughitwillincreasethecomplexityofthewatersystem.

Withtheselectionof10ftlongbeamswithCoandawingstoensurepatterninanexposedapplication,thesecanbearrangedintworowsparalleltotheshortdimensionintheroom:


Withthisspacing,the14ftthrowto50fpmwillcovertheroomwellwith9ftofthrowtothewallandopposingairpatternand5ftfromtheceilingtothetopoftheoccupiedzone.Itislogicaltorunthesupplyandreturnpipingdownthemiddleoftheroomandhavethewaterconnectionsforthebeamsfaceeachother,asindicatedonthediagram.

Aisle

Aisle Fume Hood

Fume Hood


CHW

SCH

WR

BeamBeam

BeamBeam

Occupied Zone

8 ft

5 ft

8 ft




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Example 5 - Active Beams in Laboratories (SI)

Thishospitallaboratoryisusedforthetestingofspecimensassociatedwithpatientcare.Thelayoutfeaturesoneislandbenchandtwowallbenchestoaccommodateamaximumoftenclinicallabtechnicians.Florescentlighting,refrigerationequipmentandotherbenchdevicesallgenerateheatwithinthelab.Therearealsotwolow-flowfumehoodsinthecornersoftheroomoperatingataconstantvolumeexhaustflowrateof225L/seach.Theroomis11mlongby6mwide,withaceilingheightof3.75m.Thespaceisaninteriorzoneofthebuildingwithnoenvelopeload.

Aisle

Aisle Fume Hood

Fume Hood

6 m

11 m



• Load/personis75Wsensibleand60Wlatent• Lightingloadinthespaceis25W/m²• Thespecificheatanddensityoftheairforthisexampleare1.007kgKand1.21kg/m³respectively• Minimumexhaustflowrateof6achinaccordancewithASHRAEStandard170-2008• Maintaina20%offsetbetweensupplyandexhaustvolumeinordertomaintainnegativepressure


Area 66 m2

CeilingHeight 3.75m

DesignConditions Summer–24°C,50%RH

Occupants 10

OccupantLoad 750Wsensible 600 W latent

LightingLoad 1650Wsensible

EquipmentLoad 9500 W sensible

Total load, qt11900Wsensible

600 W latent

Number of lab hoods 2

FumeHoodExhaustAirVolume 450L/s




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1. Determine the exhaust requirementTheventilationrequirementshouldbecalculatedtomeetventilationcodes.Forexample,usingASHRAEStandard170-2008todeterminetheminimumfreshairflowrate:

2. Determine the ventilation requirementInordertomaintainnegativepressure,theventilationrequirementistakenas80%oftheexhaustairflowrate:

3. Determine the required supply dew-point temperature to remove the latent loadFromequationH2


Atthedesignconditions(24°C,50%RH),thehumidityratiois9.5g/kg,requiring:

Fromthefigurebelow,thedewpointcorrespondingtothehumidityratiois12.5°C.Thisisreadilyachievedbystandardequipment,andthereforedoesnotneedtobeadjusted.Withtheairchangerequirementdeterminedbycodenearlyequivalenttotheairvolumerequirementdictatedbythefumehoodexhaust,wewill,inthisapplication,opttouseaconstantvolumesupplyairsystem.


Dry-Bulb Temperature, ºC

Entha

lpy - k

J/kg o

f Dry

Air

30

25

20

15

10

5

0504540353025201550

0

45

40

35

30

25

20

15

50

55

60

65

70

75

85

90

95

100

105

105110 115 120 125

Volume - m3/kg of Dry Air

Saturation Temperature, ºC

Relative Humidity

Hum

idity Ratio, gw /kg

DA

30

10

5

15

20

0.78

0.80

0.82

0.84

0.86

0.90

0.92

0.94

0.96

10%

20%

30%40%

50%60

%70%80

%90%

25

9.238.45

12.5 24




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4. Select the active beams using software with the following requirements:

Requirements

TotalCapacity 11900W

AirVolume 360L/s

SupplyAirTemperature 12.5°C

SupplyWaterTemperature 14°C

RoomSet-PointTemperature 24°C

Parameter Option 1 Option 2

Size 300mmx600mm 300mmx600mm

Configuration Linear–CoolingOnly Linear–CoolingOnly

Quantity 4 4


CHWSTemperature 14°C 15°C



AirFlow 453L/s 453L/s

Throw 4.6m 4.6m

AirPressureDrop 202 Pa 202 Pa


NC - -

Thesetwoselectionsarelargelysimilarwithbothmeetingthecapacityrequiredattheventilationrate.Thewaterflowrateishigherinthesecondcase,asisthechilledwatersupplytemperature.Thisallowsformorerangetomodulatethewaterflowtocontrolroomtemperatureastheloadsinthelabchangeovertime.Furthermore,theincreaseinCHWStemperaturewillincreasethereturnwatertemperaturetothesystem,potentiallyincreasingtheefficiencyofthechillerplant.

Optingforoption(2)andamodulatingcontrolsequencewhichwillallowtheairsystemtotheoptimizedfortheventilationrateandsimplecontrolofthebeamstoaccommodateanyloadfluctuations:

Max. Flow

Min. FlowHW Flow

Dead Band

Tset-point

CW Flo

w





EN

GIN

EE

RIN

G G

UID

E -

AC

TIV

E &

PA

SS

IVE

BE

AM

S


Alternatively,theCHWStemperaturecanbemodulatedtocontroltheload,thoughitwillincreasethecomplexityofthewatersystem.

Withtheselectionof3mlongbeamswithCoandawingstoensurepatterninanexposedapplication,thesecanbearrangedintworowsparalleltotheshortdimensionintheroom:

Aisle

Aisle Fume Hood

Fume Hood


CHW

SCH

WR

BeamBeam

BeamBeam

Withthisspacing,the4.5mthrowto0.25m/swillcovertheroomwellwith3mofthrowtothewallandopposingairpatternand1.5mfromtheceilingtothetopoftheoccupiedzone.Itislogicaltorunthesupplyandreturnpipingdownthemiddleoftheroomandhavethewaterconnectionsforthebeamsfaceeachother,asindicatedonthediagram.

Occupied Zone

3 m

1.5 m

3 m




EN

GIN

EE

RIN

G G

UID

E -

AC

TIV

E &

PA

SS

IVE

BE

AM

S

Active&PassiveBeamsEngineering Guide

References

ASHRAE(2004).Standard 62-2004—Ventilation for acceptable indoor air quality.Atlanta,GA:AmericanSocietyfor Heating,RefrigeratingandAir-ConditioningEngineers.

ASHRAE(2007).Humidity control design guide.Atlanta,GA:AmericanSocietyforHeating,RefrigeratingandAir- ConditioningEngineers.

ASHRAE(2008).Standard 170-2008—Ventilation of health care facilities. Atlanta,GA:AmericanSocietyofHeating, Refrigerating,andAir-ConditioningEngineers.

ASHRAE(2009).ASHRAE handbook—Fundamentals.Atlanta,GA:AmericanSocietyofHeating,Refrigerating,and Air-ConditioningEngineers.

ASHRAE(2010).Standard 62.1-2010—Ventilation for acceptable indoor air quality.Atlanta,GA:AmericanSocietyof Heating,Refrigerating,andAir-ConditioningEngineers.

CSA(2010).CSA Z317.0-10—Special requirements for heating, ventilation, and air-conditioning (HVAC) systems in health care facilities.Mississauga,ON:CanadianStandardsAssociation.

Mumma,S.A.(2002).Chilledceilingsinparallelwithdedicatedoutdoorairsystems:Addressingtheconcernsof condensation,capacityandcost.ASHRAE Transactions 2002(2),220–231.

Price Industries (2011). Price engineer’s HVAC handbook—A comprehensive guide to HVAC fundamentals. Winnipeg,MB:PriceIndustriesLimited.

Stetiu,C.(1998).RadiantcoolinginU.S.officebuildings:Towardseliminatingtheperceptionclimateimposedbarriers. DoctorialDissertation,EnergyandResourcesGroup,UniversityofCaliforniaatBerkeley,CA.

Virta,M.,Butler,D.,Gräslund,J.,Hogeling,J.,Kristiansen,E.L.,Reinikainen,M.,&Svensson,G. (2004).REHVA guidebook no. 5: Chilled beam application guidebook.Brussels,Belgium:FederationofEuropeanHeatingand Air-conditioningAssociations(REHVA).

Active Passive Beams Engineering Guide - Price Industries

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