Proceedingsof9thWindsorConference:MakingComfortRelevantCumberlandLodge,Windsor,UK,7-10April2016.NetworkforComfortandEnergyUseinBuildings,http://nceub.org.uk

ProcessControlofPersonalizedHeating

MichalVeselý1,YangZhao2,MarissaVos2,WimZeiler2

1DepartmentofBuiltEnvironment,EindhovenUniversityofTechnology,P.O.Box513,5600MBEindhoven,Netherlands,m.vesely@tue.nl2DepartmentofBuiltEnvironment,EindhovenUniversityofTechnology,P.O.Box513,5600MBEindhoven,Netherlands

AbstractPersonalized conditioning systems represent one of promising solutions for twomajor problems in currentindoor environment – high energy consumption and unsatisfactory thermal comfort. As personalizedconditioning focusesona small spacearounda singleperson, it canbetter andmoreeffectively satisfy theindividualneedsforthermalcomfortthanatraditionalHVACsystem.Personalizedconditioningsystemsthathavebeentestedrelymostlyoncontrolbyuserinteraction,i.e.theusershavetodecideonthelevelofcoolingorheating.Thiscan leadtodecreasedcomfortor increasedenergyconsumptiondueto incorrectuseofthesystem. This paper presents a novel method of process control of personalized heating based on humanthermophysiology. The new control method is compared with user interaction and fixed setting ofpersonalizedheatingsystemconsistingofheatedchairandheateddeskandfloormats.Differentcontrolstrategiesforpersonalizedheatingweretestedwith13humansubjectsinaclimatechamberunderoperativetemperatureof18°Cfor90minutes.Thetestsubjectsevaluatedtheirthermalcomfortevery15minutesviaacomputerbasedquestionnaire.Asskintemperatureofthehandswaspreviouslyidentifiedasagoodpredictorofcooldiscomfortunderuniformconditions,itwastestedinthisstudyasacontrolsignalforpersonalizedheating.Thermalcomfortandenergyusewithpersonalizedheatingarecomparedintheresultssection.Personalizedheating improved thermal comfort in all test cases. No significant difference was observed between userinteraction,fixedsetting,andautomaticcontrol.

Keywords: Control, Human subjects, Personalized heating, Thermal comfort,Thermophysiology

1 IntroductionThebuildingsectornowadaysaccounts for40%of theprimaryenergyconsumption inEUandUS(Pérez-Lombardetal.2008).Mostofthisenergyisspentonprovidingacomfortableindoorenvironmentbyheating,ventilationandairconditioning(HVAC).CurrentstandardsfordesigningtheindoorenvironmentsuchasISOEN15251(2007)prescribecontrollingtheindoor environment in a narrow range in order to ensure thermal comfort. However,narrowing range of indoor air temperatures is energy demanding and does not lead tohigherthermalsatisfaction(Arensetal.2010).

Especially in theoffice environment PersonalizedConditioning System (PCS) is oneof thepromising ways how to improve thermal comfort and meanwhile reduce energyconsumption.PCSbringsventilation,heating,andcoolingcloser to theuserandallowstoadjustthemicroenvironmenttosuit individualneeds.Meanwhile,energy isdeployedonlyat the place of actual need and the background environment can be controlled inmore

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relaxedmanner. Thisway, energy can be saveddue to higher effectiveness of thewholeconditioningsystem.

AnumberofPCShavebeenrecentlydevelopedandtested.Muchmoreattentionhasbeenpaidtopersonalizedventilationandcoolingratherthantopersonalizedheating (Veselý&Zeiler2014).Nevertheless,somestudieshavealreadyproventhatpersonalizedheatingcanimprove thermal comfort (Melikov & Knudsen 2007;Watanabe et al. 2010; Zhang et al.2010;Pasutetal.2014)andalsohaspotentialtoreducetheoverallheatingdemand(Zhangetal.2010;Foda&Sirén2012;Verhaartetal.2015).

MostoftheresearchedPCSwerecontrolledsolelybyuserinteraction,whichcanpotentiallyleadtoproblemswiththermalcomfort,suchasovershootsordelayedreactions,aswellasworse energy performance due to inefficient operation. As the hand and finger skintemperature relates to thermal comfort in cool environment, it seems to be a promisingcontrolsignal foranautomatedcontrol.Thestudy investigatessuchanautomationofthecontrolprocessandtestsitalongsidewithuserinteraction.

2 Methods2.1 PersonalizedHeatingSystemThetestedpersonalizedheatingsystemconsistsofaheatedchair,aheateddeskmat,andaheated floormat (Figure1). Theeffectivenessof theseheaterswas tested inanother yetunpublished study (Veselý et al. 2016). Themaximumpowerof theheaters is as follows,heatedchair:36W,heateddeskmat:80W,andheatedfloormat:100W.

Figure1Heatedchair(left),heateddeskmat(middle)andheatedfloormat(right)

Personalizedheatingsysteminsomeofthetestcaseswasusercontrolled(Figure2)andthesettingswereloggedwithanintervalof2seconds.

Figure2Usercontroloverpersonalizedheatingsystem

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2.2 ClimateChamberandEnvironmentalConditionsExperimentswereconductedinaclimatechamberofUnitofBuildingPhysicsandServices,Eindhoven University of Technology, The Netherlands. The climate chamber is a wellthermallyinsulatedroomofdimensions3.6x5.7x2.7m3.Itallowsforaprecisecontrolofthe indoor environment, namely airmovement, air temperature, and temperatures of allsurroundingsurfaces.

Duringthisexperimentalphasetheclimatechamberwassettomaintainbothairandmeanradiant temperature at 18 °C. As mixing ventilation was used the air movement in theoccupied zone was negligible and can be assumed of up to 0.15 m/s. The subjectsperformedanofficeworkresultinginmetabolicrateof1.2metandtheywereinstructedtowearclothingensemblewith insulationof0.7clo(commonwinter indoorclothing).ThesebackgroundconditionsresultinPMVof-1.5andcorrespondingPPDof50%.

Two user desks (Figure 3) were set up in the climate chamber. Both user desks wereequippedwithacomputer screen,akeyboard,andamouse.The test subjectsconnectedtheirlaptopstotheprovidedequipmentatthebeginningofeachsession.

Figure3Oneofthetwouserdesksintheclimatechamber

2.3 SubjectsThirteen healthy university students (seven males and six females) volunteered as testsubjects.TheiranthropologicaldataarelistedinTable1.

Table1Anthropologicaldataofthe13testsubjects

Height[m] Weight[kg] Bodymassindex Age[years]

Mean 1.79 81.1 25.1 24.9

StandardDeviation 0.12 26.8 5.8 3.22.4 ProcedureFour test casesas shown inTable2were testedandall test subjectsexperiencedall testcases. The same personalized heating system was used in all test cases except for thereference.Thetestcases ‘Fixed’and ‘Auto’werebasedonresultsofapretestwith9testsubjects.Intestcase‘Fixed’theaveragesettingfromtheendofthepretestsessionwasset

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fortheentiretest.The‘Auto’casewasbasedoncorrelationofthesettingsofeachheaterwiththehandskintemperature.Thesettingsarepresentedintheresultschapter.

Table2Testcases

Testcasecode Description

Ref Referencecase(i.e.nopersonalizedheatingapplied)

Userctrl Usercontrolledpersonalizedheating

Fixed Fixedsettingsbasedonaveragesettingsfromthepretests

Auto Automaticcontrolbasedonhandskintemperature

Eachsessioncomprised30minutesofwarmaccustomization(i.e.justoutsideoftheclimatechamber) and 90 minutes of exposure. During the accustomization period the skintemperature loggerswereattached.Duringtheexposurethesubjectsperformedordinaryofficeworkonacomputer.Thesubjectswereaskedtofillinaquestionnaireregardingtheirthermalcomfortevery15minuteswithintheexposure.

2.5 Measurements–SubjectiveEvaluationDuring theexperimental sessions the subjectsevaluated their thermal comfort viaa java-basedapp (sample screenshots shown in Figure4). This app includesquestions regardingthe subjects’ clothing, thermal sensation, thermal comfort, and wellbeing. Thermalsensationandcomfortquestionsareaskedasoverallandinparticularforneck,head,arms,hands, legs,andfeet.AnASHRAE7-pointscale isusedforevaluationofthermalsensationandacomfortscale(fromclearlycomfortabletoclearlyuncomfortablewithseparationofjustcomfortable/justuncomfortableinthemiddle)forthermalcomfort.

Figure4Thermalcomfortquestionnaireapp

2.6 Measurements–EnvironmentalDataThe thermal environment in the climate chamber was continuously monitored during allexperimental sessions. This includesmeasurements of air speed and air temperature at theheights of 0.1, 0.7, and 1.1m (standard heights for a sitting person) aswell as the relativehumidityandglobetemperatureintheoccupiedzoneoftheroom.AllenvironmentaldatawereloggedwithanintervalofoneminuteandmeasuredincompliancewithISO7726(ISO1998).

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2.7 Measurements–PhysiologyIn order to investigate the effect of personalized heating on human physiology skintemperature was measured on 14 locations on the body by iButtons (van MarkenLichtenbelt et al. 2006) as shown in Figure 5. Digital thermometer DS18B20was used tomeasurethehandtemperature(location“I”inFigure5)additionallytoiButton.Thisallowedforreal-timereadingofthetemperaturethatcanbeusedinacontrolloop.

Figure5PositionsofiButtons

3 Results3.1 SettingsofpersonalizedheatingsystemApretestwith9testsubjectswasusedtoextrapolatesettingsofthepersonalizedheatingfor test cases ‘Fixed’ and ‘Auto’. Thepretest followed the sameprocedure as thenormaltestand test subjects controlled thepersonalizedheatingbyuser interaction.Anaveragesetting fromtheendof thepretestwasusedasa fixedsetting for thewholeexposureoftestcase‘Fixed’.Thesesettingswereasfollows,heatedchairsetat50%ofitsmaxpower,heateddeskmatat65%ofitsmaxpower,andheateddeskmatat70%ofitsmaxpower.

Proportional control based on hand skin temperature was used in test case ‘Auto’. Thecontrolequationwasderivedfromlinearcorrelationofthehandskintemperatureandtheuser controlledpowerof theheaters in thepretest (heateddeskmat shown inFigure6).ThiscorrelationresultedinR2valuesof0.62fortheheatedchair,0.90fortheheatedmat,and0.86fortheheatedfloormat.ThederivedcontrolcurvesareshowninFigure7.

Figure6Usercontroloverheateddeskmatinthepretest,averageof9testsubjects

R²=0.8968

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Figure7Proportionalcontroloftheheatersusedintestcase‘Auto’

3.2 ThermalsensationandcomfortTheaverageoverallthermalsensationoverthewholeexposureisshowninFigure8.Atthebeginning of the exposure the test subjects felt about neutral because of theaccustomization rightoutsideof the climate chamber. In the ‘Ref’ case thermal sensationdroppedunderslightlycoolat theend,while inother testcases itwasmaintainedaboveneutralbypersonalizedheatingsystem.

Figure8Overallthermalsensation(averageofall13testsubjects)

Figure9showsthethermalsensationandcomfortat theendofexposure.Thedifferencebetween the ‘Ref’ case and the other cases is significant (p < 0.05) for both, thermalsensationandcomfort.Theresponseto‘Fixed’seemstobemorescatteredthanfor‘Userctrl’and‘Auto’.However,nosignificantdifferencewasfoundamongthesethreetestcases.

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Heatedchair Heateddeskmat Heatedfloormat

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Figure9Thermalsensation(a)andcomfort(b)attheendofexposure(boxplotsofall13testsubjects)

Figure9showsthethermalsensationandcomfortat theendofexposure.Thedifferencebetween the ‘Ref’ case and the other cases is significant (p < 0.05) for both, thermalsensationandcomfort.Theresponseto‘Fixed’seemstobemorescatteredthanfor‘Userctrl’and‘Auto’.However,nosignificantdifferencewasfoundamongthesethreetestcases.

3.3 EnergyconsumptionFigure 10 depicts the energy consumption of the personalized heating system under thedifferent control modes. The lowest energy consumption was observed in the test case‘Userctrl’.

Figure10Energyconsumptionofpersonalizedheatingaveragedperpersonoverthewholeexposure(90minutes)

4 DiscussionThefingerandhandskintemperaturewaspreviouslyidentifiedasagoodpredictorofcooldiscomfort(Wangetal.2007).Itcouldbeexpectedthatthemomentofcooldiscomfortisthe moment when people turn on or increase the power of personalized heating whenavailable.Wangetal.(2007)reportedthatapprox.30°Coffingertiptemperatureseemstobe a threshold for a risk of cool discomfort. This is in line with our observation on therelationofhandskintemperatureandthesettingofpersonalizedheating.Thetestsubjects

0.02 0.02 0.02

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0.080.11

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Userctrl Fixed AutoEnergyco

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Heatedchair Heateddeskmat Heatedfloormat

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tendedtoturnonthesystemathandskintemperatureofabout30°Candthenincreasethepowerasthehandtemperaturewasdecreasing.

Asexpectedpersonalizedheatingclearlyimprovedthermalcomfort.However,nosignificantdifferencewas observed between the three testedmodes of control. Zhang et al. (2010)reportedthattheuserinteractionisinsomecasesapreferredoptionoverfixedsetting,butthishappensonly inmoreextremethermalconditions,whichcanexplainwhywedidnotobserveasimilartrend.

The energy consumption of the presented personalized heating system was the lowestwhenusercontrolled.However,thiswasprobablyinfluencedbyrathershortexposureandthefactthatmostofthetestweregraduallyincreasingtheheatingpowerwithinafirstthirdof the test in order to find a comfortable setting. It also has to be noted that the fixedsetting,whichappearstoperformtheworst fromenergyperspective,wouldbenefit frompresumablylowercostofthesystemanditsmaintenance.

The test subjectswere also asked for general commentsonpersonalizedheating control.Someclaimedthattheypreferreduserinteractionbecausetheywanttobeincharge,whileotherspreferautomaticcontrolbecausetheywanttofocusjustontheirwork.Thisimpliesthataflexiblesystemcombininguserinteractionwithautomaticcontrolmightbeneeded.Oneofthepossibleoptionsforsuchacombinationisshiftingthesetpointsoftheautomaticcontrolviauserinteraction.Thisisrecommendedforfurtherresearch.

5 ConclusionsThe presented personalized heating system significantly improved thermal comfort. Nosignificantdifference in termsof thermal comfortwasobservedbetween threemodesofcontrolofpersonalizedheating, i.e.betweenuser interaction, fixedsettingandautomaticcontrol.

User controlledpersonalizedheatingused slightly less energy than theother twomodes.Thefollowingissuesarerecommendedforfurtherinvestigation:

• Uniformityofthethermalenvironment,whenpersonalizedheatingisapplied.• Possibleindividualizingoftheautomaticcontrolofpersonalizedheating.• Possible combination of user interaction and automatic control of personalized

heating.

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