1

LBNL‐5021E

    Performance of Charcoal Cookstoves for Haiti, Part 1:      Results from the Water Boiling Test  

   Kayje Booker, Tae Won Han, Jessica Granderson,    Jennifer Jones, Kathleen Lask, Nina Yang, Ashok Gadgil        

        Environmental Energy  Technologies  Division      Lawrence  Berkeley  National  Laboratory    Berkeley,  CA  94720  

  

   

  June 2011 

 

 

 

              Research funding was provided by the U.S. Department of Energy under      Contract No. DE‐AC02‐05CH11231, and partially by the support of        NDSEG Fellowship. 

 

 

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DISCLAIMER 

This document was prepared as an account of work sponsored by the United States Government. While this document is believed to contain correct information, neither the United States Government nor any agency thereof, nor The Regents of the University of California, nor any of their employees, makes any warranty, express or implied, or assumes any legal responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by its trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof, or The Regents of the University of California. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof or The Regents of the University of California. 

1.INTRODUCTION

InApril2010,ateamofscientistsandengineersfromLawrenceBerkeleyNationalLab(LBNL)andUCBerkeley,withsupportfromtheDarfurStovesProject(DSP),undertookafact‐findingmissiontoHaitiinordertoassessneedsandopportunitiesforcookstoveintervention.BasedondatacollectedfrominformalinterviewswithHaitiansandNGOs,theteam,ScottSadlon,RobertCheng,andKayjeBooker,identifiedandrecommendedstovetestingandcomparisonasahighpriorityneedthatcouldbefilledbyLBNL.

Inresponsetothatrecommendation,fivecharcoalstovesweretestedattheLBNLstovetestingfacilityusingamodifiedformofversion3oftheShellFoundationHouseholdEnergyProjectWaterBoilingTest(WBT).Theoriginalprotocolisavailableonlineat:http://ehs.sph.berkeley.edu/hem/?page_id=38.Stovesweretestedfortimetoboil,thermalefficiency,specificfuelconsumption,andemissionsofCO,CO2,andtheratioofCO/CO2.Inaddition,HaitianuserfeedbackandfieldobservationsoverasubsetofthestoveswerecombinedwiththeexperiencesofthelaboratorytestingtechnicianstoevaluatetheusabilityofthestovesandtheirappropriatenessforHaitiancooking.Thelaboratoryresultsfromemissionsandefficiencytestingandconclusionsregardingusabilityofthestovesarepresentedinthisreport.

2.METHODS

2.1StovesTestedForinclusionintesting,weattemptedtoobtainstovesthatwereeitherbeingconsideredordistributionbynon‐governmentalorganizations(NGOs)operatinginHaitiorthatwerefalreadywidelyavailableinPortauPrince.Baseduponthesecriteriaaswellasavailabilityofthecookstovesfortesting,thefollowingfivestovesshowninFig.1awerechosenforinclusionintheevaluation.

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Fig.1a:Fromlefttoright:Traditional,EcoRecho,PraktiRouj,StoveTecTwo‐Door,Mirak

A. Traditionalstove:MadelocallyinHaitifromscrapmetalandwidelyavailable.Evenlydistributedholesarelocatedallaroundthesidesandthebottomofarectangularcharcoalcontainer.Thepotsitsdirectlyonthecharcoalinthechamber,andashfallsthroughtoatrayunderneath.Thisstovewaspurchasedfor150gourdesinApril2010(US$3.75)butitwassaidtheycancostupto250gourdes($6.25).Thesestovestypicallylastonlysixmonthstooneyear.

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B. EcoRecho:AmetalstovewithaceramiclinermadeinHaiti.Thepotsitsabovethecharcoalonthreetriangularmetalwedges.Adooronthefrontofthestovecanbeopenedorclosedtocontrolairflow.Thisstovecostsabout1000gourdes(US$25)toproduce,however,theyarebeingsoldatthesubsidizedpriceof450gourdesasofApril2010(US$11).

C. PraktiRouj:Insulatedmetalstove.Therectangularcharcoalchamberisthesmallestofveallstoves.Adooronthefrontofthestovecanbeadjustedtocontrolairflow.Thissto

costsUS$25.D. StoveTecTwo‐Door:Dual‐fuelwoodandcharcoalstovewithametalbodyandaclay

insulatedinterior.Thepotisplacedontopofthreemetalknobsandisnotincontactwiththecharcoal.Adooronthefrontofthestovecanbeadjustedtocontrolairflow.AccordingtotheStoveTecwebsite,thisstovecanbepurchasedforahumanitarianprojectforUS$15.

E. Mirak(copy):Alocallymade,scrapmetalcopyoftheMirakstovedesignedbyCARE,ahumanitarianorganizationfightingglobalpoverty,andwidelyavailableinPort‐au‐Prince.Thisstovewaspurchasedfor150gourdesinApril2010(US$3.75).Thecharcoalchamberishalfspherical,andthepotsitsdirectlyonthecharcoal.

Wedidnotreceiveinstructionsonusingthestovesbutdidseveralpracticerunswitheachtovepriortotesting.Eachstovewasoperatedinordertomaximizeitsefficiency,sincludingvaryingthepowerwhenpossiblebymanipulatingairflow.AlthoughtheStoveTeccomeswithaskirtthatcanbeusedforaddedefficiency,wethoughtitbettertoevaluatethestovewithouttheskirtaswewereconcernedtheskirtmaynotbecommonlyused.Theseconcernswerebasedonanecdotalevidencefromothercountries,nwhichdetachableskirtshavegenerallybeendiscarded,andobservationofncompatibilityinsizebetweentheskirtandthelargerricepotsusedinHaiti.ii2.2FuelstestedGrillmark©naturallumpcharcoalwasusedforalltesting.Charcoalsampleswereanalyzedusingstandardoven‐dryproceduresandwerefoundtohave5.9%moisturecontent.However,resultsfromthatexperimentwerenotavailableintimetoincorporateintotheefficiencyandspecificfuelcalculations,soreportedvaluesareuncorrectedforactualmoisturecontent.Theexpectedimpactofcorrectingformoisturecontentistheefficiencyforallstoveswillrisesomewherebetweenthreeandfourpercentagepoints(i.e.31.5%wouldbecome34%).Note,however,thatwhiletheoven‐drytestconfirmedtypicalule‐of‐thumbestimatesforcharcoal(approximately5%),thestandardWBTprocedurencludesmoisturecorrectionforwoodfuels,notforcharcoal.ri2.3TestSystemAlltestingwasperformedundercontrolledconditionsatLawrenceBerkeleyNationalLaboratory.Thetestsystemconsistsofastoveplatformandanexhausthoodwhichdrawsgassesupwardwheretheyaremixedandsampled(Fig.1b).BothCOandCO2emissionsweremeasuredwithaCaliforniaAnalyticalInstruments600‐seriesgasanalyzerand

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ilutionrateswerecontinuouslymonitored.Inadditiontoemissions,fuelweightandatertemperatureweremeasuredandrecordedinrealtime.

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Fig.1b:Above:ThestovetestingsystematLBNL.Below:Aclose‐up viewofastove(theMirak)onthetestingplatform,withthefrontdoorsoftheexhausthoodopentoviewtheset‐up.

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2.4ProtocolmodifiedformoftheShellFoundationHouseholdEnergyProjectWaterBoilingTestWB )A(

T version3.0wasusedtoevaluatethestoves.Thetestconsistsofthreephases:

1. ColdStart(highpower):Usingacoldstoveandacoldpot,2.5Lofroomtemperaturewaterisbroughttoaboil.

2. Hotstart(highpower):Immediatelyfollowingthecoldstart,thehotwaterisreplacedwithanew2.5Lofroomtemperaturewaterwhichisbroughttoaboil.

3. Simmer(lowpower):Immediatelyfollowingthehotstart,thealreadyboiledwaterismaintainedatasimmerfor45minutes.Inthisphase,thestove,pot,andwaterremainhotfromthesecondphaseofthetest.

Dataforthermalefficiencyandemissionswerecollectedforallthreetestphases.Whenentilationdoorswereavailable,wekeptthemopenforthehighpowertests(coldstartvphaseandhotstartphase),and50‐60%openduringthelowpower(simmerphase)test.Thesameflat‐bottom,15”diameter,aluminumpotpurchasedinPort‐au‐Princewasusedforallofthetests.Wetriedtoinitiallyloadallofthestoveswith250gofcharcoalattheeginningofthetests.NotethatinsomecasesthechamberofthePraktiwastoosmalltobaccommodatethewhole250g,soaslightlysmalleramountwasused.TheWBTwasdesignedforwood‐burningstovesandcannotbeexactlyappliedtocharcoal‐urningstoves.Wemadethefollowingmodificationstoaccommodatecharcoalstoves.he mbT

se odificationsareconsistentwiththepracticesobservedinHaiti.

1. Tostartthefire,apieceofhigh‐resinpinewoodwasplacedontopofthecharcoalpileandlit.Thetestersthenblewonthewoodtolightthecharcoal,aswasobservedinHaiti.

2. WhencalculatingequivalentdryfuelconsumedforallphasesoftheWBT,thewood‐burningprotocolincorporatestheenergyrequiredtoturntheleftoverwoodintochar.However,weusedcharcoalinsteadofwoodandbecausecharcoalisessentiallycharalready,weassumedtheenergycontentoftheleftovercharcoalwasthesameastheinitialcharcoal,allowingthechangeincarbon(ΔCc)toequalzero.Also,duetodifferencesintheenergycontentbetweencharcoalandwood,wereplacedthecoefficientof1.12with1.08.Thischangedtheequation1(forexampleinthecoldstartphase)from:

1Fcdistheequivalentdryfuelconsumed,Fcmisthefuelconsumed,misthemoisturecontentofthefuel,andΔCcisthenetchangeincharduringthetest.ForfurtherinformationseetheShellFoundationHouseholdEnergyProjectWBT,version3.0,foundat:http://ehs.sph.berkeley.edu/hem/?page_id=38,andAppendixBforfurtherexplanationofthechangetotheequation.

t o:

2.5AnalysisForeachmetric,wereportstoveperformanceoftheWBTasawhole,averagedorsummedoverallthreephases,aswellastheaverageperformanceofthesimmerphase.BecauseHaitiancookingoftenrequireslongperiodsofsimmering,sometimesformanyhours,performanceduringthatphaseisparticularlyimportant.Withthatinmind,wehaveisolatedandpresentedtheresultsofthesimmerphaseinadditiontopresentationofresultsfromallphasesoftheWBTcombined.Thispresentationwillenablereaderstoseehoweachstoveperformsspecificallyduringthesimmerphaseaswellasovertheentiretest.

Whenpresentinggraphsoftheresultsforeachstoveperformancemetric,weincludeerrorbarsequaltothe±95%confidenceintervalssocomparisonbetweenstovesisclearlyvisible.Duetolargevariabilityandthesmallnumberoftests,theconfidenceintervalsweresometimesquitelarge.Whenconfidenceintervalsarelarge,oftentheresultsaren’tstatisticallysignificant.Evenso,observeddifferencesfromtheexperimentsmaybepracticallysignificantforreal‐worldperformanceinthefield.Additionally,theWaterBoilingTestswillbefollowedupwithControlledCookingTeststomoresimilarlyrepresentthecookingpracticesinHaiti.

Toaccountforthesmallsamplesizes,wecalculatedthestandarddeviationandthestandarderror,andusingtheStudent’st‐distribution,wecalculatedthe±95%confidenceintervals(seeAppendixCfordetailsofthesecalculations).Wealsoconductedhypothesistestingtoidentifywhetherdifferencesbetweenstoveswerestatisticallysignificantatthep=0.05level.Whensignificantdifferenceswerefoundatthegrouplevelfromthe2‐factorANOVAhypothesistest,wefollowedupwithpair‐wiseanalysisusingaTukeyHSDtesttoidentifywhichpairsofstovesweresignificantlydifferentatthe0.05level.2

3.RESULTSResultsaregroupedintothreecategories:

Efficiency:timetoboil,thermalefficiency,andtemperature‐correctedspecificfuel

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consumption2Forthosenotfamiliarwithhypothesistesting,thesetestsaredonebyfirstposinga‘nullhypothesis’,proposingthatstoveperformanceisactuallyidenticalandtheobserveddifferencesaretheresultofrandomvariation.Statisticalanalysisisthenconducted,andthehypothesisisonlydisproved,meaningtheresultsaresignificantiftheanalysisshowstheobserveddifferenceinperformancecouldoccurfromrandomvariationalonelessthan5%ofthetime.

s:CO,CO2,andCO/CO2ratio Emission

Usability:observationsofeaseofstoveusefromstovetestersatLBNL

EquationsforthevariousmetricsarenotpresentedherebutcanbefoundintheShellFoundationHouseholdEnergyProjectWaterBoilingTest(WBT),version3.0.Theprotocolisavailableonlineat:http://ehs.sph.berkeley.edu/hem/?page_id=38.

3.1Efficiency

3.1.1TimetoBoil

Timetoboilwasmeasuredbeginningwhenthecharcoalwasconsideredlitandendingwhenwaterstartedboiling(atlocalatmosphericpressure).Thecharcoalwasqualitativelydeterminedtobelitwhenthetestersobservedtherewasenoughcharcoalburningtokeepthefirefromdyingout.

Thetraditionalstovebroughtwatertoaboilmorequicklythananyoftheimprovedstoves.Inthecoldstarttestphase,waterheatedonthetraditionalstoveboiledinonly36.5minutes,yetthesameamountofwatertook51.3minutestoboilinthenextfasteststove(thePrakti),adifferenceofalmost15minutes.Althoughalloftheimprovedstovesweremuchslowerthanthetraditionalstove,theyperformedsimilarlytoeachotherwithaveragesrangingfrom51.3to59.8,adifferenceof8.5minutes.

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Inthehotstarttestphase,inwhichroomtemperaturewaterisplacedonalreadyheatedcoals,theresultsaresimilar.Onceagain,thetraditionalstovewasfasterthananyimprovedstove,andtheimprovedstovesperformedsimilarlytooneanother.Onenoteonthehotstartresults:theboilingtimeofthePraktishowedalargeamountofvariationbetweentests,withboilingtimerangingfrom17to51minutes.

AverageTimeto

(minutes)

Rank(Fastesttoslowest)Boil

(± 95% CI)

0

20

40

60

80

100

Time to Boil from Cold Start 

(minutes)EcoRecho 55.2 4

Mirak 54.1 3

Prakti 51.3 2

StoveTec 59.8 5

Traditional 36.5 1

Table1:TimetoBoilfortheColdStartPhase Fig.2:TimetoBoilfortheColdStartPhase.Error

barsare±95%confidenceintervals.

TimetoBoil

(minutes)

Rank(Fastesttoslowest)

(± 95% CI)

0

20

40

60

80

100

Time to Boil from Hot Start 

(minutes)

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3.1.2ThermalEfficiency3.1.2ThermalEfficiency

Thermalefficiencyistheratiooftheheatcontentofincreasingthewatertemperatureandvaporatingthemassofwaterreleasedassteam,totheenergyconsumedbyburningood.CalculationsfordeterminingthermalefficiencycanbefoundintheWBTProtocol.

ew

Table3aboveshowsthethermalefficiencyforthesimmerphaseaswellastheaverageefficiencyoverallphasesoftheWBT.Averagethermalefficiencyresultsforthefourstoveswerebetterthanthatofthetraditionalstove.Resultsweresignificantatthe0.05levelfortheentireWBTandforthesimmerphase.Allstoves,includingthetraditionalstove,showedhigherefficiencyduringthesimmerphasethanthehotorcoldstartphases.Fig.4showstheaveragethermalefficiencyoverallphases.ThePraktiandEcoRechowerethemostefficientandthetraditionalandMirakweretheleastefficient.Inmaking

EfficiencyinSimmerPh )ase(%

EfficiencyOverthe

Ent TireWB(%)

EcoRecho 37.5 31.6

Mirak 34.1 28.6

Prakti 46.2 37.3

StoveTec 36.6 30.5

Traditional 28.5 22.2

Table3:ThermalEfficiencyoverthesimmerphaseandtheentireWBT

0%

10%

20%

30%

40%

50%

60%

Thermal Efficiency

(± 95% CI)

Fig.4:ThermalEfficiencyaveragedovertheentireWBT.Errorbarsare±95%confidenceintervals.

EcoRecho 32.1 3

Mirak 42.1 5

Prakti 33.3 4

StoveTec 29.9 2

Traditional 24.0 1

Table2:TimetoBoilfortheHotStartPhaseFig.3:TimetoBoilfortheHotStartPhase.Errorbars

are±95%confidenceintervals.

comparisonsbetweenstovesandassessingwhetherdifferencesbetweenstovesweresignificant,wefoundthePraktiandtraditionalstovestobesignificantlydifferentfromeachotheratthe0.05level.

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Whenthesimmerphaseisexaminedbyitself(Fig.5),thetraditionalstovefarestheworst.ThePraktiandtraditionalstovesweresignificantlydifferentfromeachotheratthe0.05level.

Thegraphillustratingthermalefficiencyofthesimmerphaseoverthethreesimmerphasetestsperformedforeachstove(Fig.6)isprovidedtoillustratethevariabilityinresultsbetweentests.(ThedataandstandarddeviationsarealsoincludedinAppendixA.)Forexample,consideringtheun‐averagedindividualdatapoints,theEcoRechohadthehighestefficiencyofanystoveaswellasoneofthelowest.ThePrakticonsistentlyperformedwell,whilethetraditionalconsistentlyperformedpoorly.OtherstovesvariedinperformancebutnonesomuchastheEcoRecho.Wenotethevariationcouldcomefromanumberoffactors,onlysomeofwhicharerelatedtostovedesignandactualperformance,andthatalargersamplesizewouldbeusefulforfutureanalysis.

3.1.3SpecificFuelConsumptionSpecificfuelconsumptionisdefinedinthe2007WBTas“thefuelwoodrequiredtoproduceaunitoutput”whethertheoutputisboiledwater,cookedbeans,orloavesofbread.Intheaseofthecoldstartphase,high‐powerWBT,itisameasureof"theamountofwoodcrequiredtoproduceoneliter(orkilo)ofboilingwaterstartingwithacoldstove.”Ourresultsshowthetemperature‐correctedspecificfuelconsumption,whichadjustsfordifferencesininitialwatertemperature.

Fig.5:ThermalEfficiencyfortheSimmerPhase.Errorbarsare±95%confidence

intervals.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

1 2 3

Thermal Efficiency

Test Number

EcoRecho

Mirak

Prakti

Stove Tec

Traditional

Fig.6:ThermalEfficiency,SimmerPhasebyTest.

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Fig.9showsspecificfuelconsumptionforthesimmerphaseseparatedbytestnumber.Thetraditionalstoveperformedmuchworsethantheimprovedstoves.Fig.9alsoshowstheimprovedstovesperformedsimilarlytoeachotherwithnostovestandingoutfromtheothers.Infact,therelativestoverankingschangedwitheachtest;forexample,theMirak

Asseeninthetableoftemperature‐correctedspecificfuelconsumption(Table5),thesimmerphaseaccountedforalargeportionofthefuelconsumedforeachstove.Allimprovedstovesusedconsiderablylessfuelthanthetraditionalstovewithmostusingalittlemorethanhalfthatofthetraditionalstove.However,specificfuelconsumptionresultsfortheentireWBT(Fig.7)andsimmerphase(Fig.8)showedsomuchvariationthatnoneofthestovesweresignificantlydifferentfromoneanotheratthe0.05levelfortheentireWBTorthesimmerphasealone.

SimmerPhase(g)

TotalWBT(g)

(± 95% CI)

0

200

400

600

800

1000

1 2 3Specific Fuel Consumption (gra

1200

ms)

rTest Numbe

EcoRecho

Mirak

Prakti

Stove Tec

Traditional

Fig.9:SpecificFuelConsumption,SimmerPhasebyTest.

0200400600800

1,0001,2001,4001,600

Specific Fuel Consumptio

(grams)

n  (±95% CI)

Fig.8:SpecificFuelConsumptionfortheSimmerPhase.Errorbarsare±95%confidenceintervals.

EcoRecho 324 479

Mirak 289 507

Prakti 378 539

StoveTec 346 572

Traditional 808 979

Table5:Temperature‐CorrectedSpecificFuelConsumptionforSimmer

PhaseandentireWBT

0200400600800

1,0001,2001,400

Specific Fuel Consumption

(grams)

Fig.7:Temperature‐CorrectedSpecificFuelConsumptionovertheentireWBT.Errorbarsare±95%confidence

intervals.

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wasrankedfirst,fourth,andsecond,intestsonethroughthree.Insummary,thetraditionalstovefaredworstoverallandineveryphaseindividually,theEcoRechohadthelowestaveragespecificfuelconsumptionintheoverallWBT,andtheMirakhadlowestveragefuelconsumptionduringthesimmerphase.However,atthe0.05level,differencesabetweenthestoveswerenotstatisticallysignificant.ThevariationintheresultsforthePraktistoveareparticularlylarge(standarddeviation305goftotalfuelconsumption539g),andtheresultsasawholeshowedmorevariationthantheothertestswithseveraloutliers.WebelievesomeoftheseresultsareanartifactofthewayspecificfuelconsumptioniscalculatedintheWBT,specificallytheaccountingforwaterboiledoff.However,becausewedonotknowexactlywhatledtotheseoutliers,wedidnotfeeljustifiedindisregardingthem.Itisworthwhiletonotethatstovesburningcharcoalaremuchmoredifficulttoregulatefortheirthermalpoweroutputthanstovesburningfuelwood.Thispoorregulationcontributestothehighvariationinspecificfuelconsumption.

3.1.4EfficiencyConclusions

Thetimenecessarytoboilwaterforbothhotandcoldstartsismuchhigherforallimprovedstovesthanforthetraditionalstove.Thisdifferenceisworrisomebecausestoveusersoftenplacegreatimportanceoncookingtime;theyarelesslikelytocontinueusingastovethatheatsslowlyandlengthenstheircookingtime.FindingsfrominformalinterviewswithwomeninHaitiduringtheLBNL/DSPtripreflectedconcernsoflengthycookingtimeandwascitedasareasonwhysomehadgivenupontheMirak.Thedifferencesintimetoboilbetweentheimprovedstoves,however,arenotlarge,soitdoesnotyetappearthatanyofthemisaclearleaderintermsoftime‐savings.

FortheaverageperformanceacrossallphasesoftheWBT,thermalefficiencywashighestforPraktiandEcoRechoandlowestforMirakandtraditional.Thermalefficiencyresultswerestatisticallysignificantatthep=0.05levelforallofthephasesoftheWBT.Atthe0.05level,thePraktiandtraditionalstovesweresignificantlydifferentfromeachotheroverallofthephasesoftheWBTandforthesimmerphasealone.

Overall,specificfuelconsumptionwaslowest/bestfortheEcoRechoandMirak,andhighest/worstfortheStoveTecandtraditional.Thefindingsforspecificfuelconsumptionhadgreateruncertaintythanthoseforthermalefficiency.SignificantdifferencesinperformancewerenotobservedforthefullWBTorforthesimmerphase.

Inconclusion,consideringthefindingsforthermalefficiencyandspecificfuelconsumptioninaggregate,thePraktiandtheEcoRechoperformedthebest.However,theywerenotsignificantlydifferentfromtheStoveTecortheMirak.

3.2Emissions

3.2.1TotalCarbonMonoxide(CO)

IneachWBTconducted,COemissionsweremonitored,recorded,andsummedforeachphaseoftheWBT.ThosesumswerethenaveragedacrossmultipleteststocalculatethetotalCOreleasedperphase.TotalCOemissionfortheentireWBT,combiningallphases,wascalculatedbysummingtheseaveragedphasetotals.Thissummingofaveragesproducesapropagationerror,whichwastakenintoaccountwhencalculatingstandarddeviationsandstandarderrors.

ResultsfortotalCOemissionforeachstoveforthesimmerphasealoneandovertheentireWBTwerenotsignificantlydifferentforallofthestovesatthep=0.05level,meaningtruedifferencesbetweenthestoves’emissionsperformancecannotbedetected.Althoughnotsignificant,totalCOemittedoverallphaseswashighestforStoveTecandEcoRechoandlowestforMirakandPrakti.ItshouldbenotedthatintermsofCOemissions,notallimprovedstovesoutperformedthetraditionalstove.

AsseenintheerrorbarsofthegraphsofCOemissions(Fig.10andFig.11)boththeStoveTecandtraditionalstovehadlargevariationintheiremissions.Itwasdifficulttoassesswhetherthestovesweresignificantlydifferentintheirperformanceatthesesamplesizes.Itmightbeeasiertodistinguishsignificantdifferencesbetweenthestoveswithmoretestsperstovetoobtainlargersamplesizes,especiallyforthesimmerphase.

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Table6:TotalCOEmissionsforSimmerPhaseandoverallPhases

TotalCO–SimmerPhase(g)

Tota AllPha g)

lCO–ses(

EcoRecho 98.6 179Mirak 59.1 134Prakti 68.7 136StoveTec 83.5 183Traditional 91.6 154

0

50

0

50

100

150

200

?CO, (grams)

(± 95% CI)

100

150

200

250

?C

(± 95% CI)

O, (grams)

Fig.11:TotalCOEmissionsoverallPhases.Errorbarsare±95%confidenceintervals.

Fig.10:TotalCOEmissionsforSimmerPhase.Errorbarsare±95%confidenceintervals.

3.2.2TotalCarbonDioxid (COe 2)

IneachWBTconducted,CO2emissionsweremonitored,recorded,andsummedforeachphaseoftheWBT.ThosesumswerethenaveragedacrossmultipleteststocalculatethetotalCO2releasedperphase.TotalCO2emissionfortheentireWBT,combiningallphases,wascalculatedbysummingtheseaveragedphasetotals.Thissummingofaveragesproducesapropagationerror,whichwastakenintoaccountwhencalculatingstandarddeviationsandstandarderrors.AscanbeseeninTable7,thesimmerphasegenerallyaccountedforabouthalfthetotalCO2emitted.

Forthesimmerphase,thePraktihadthelowestCO2emission,whilethetraditionalstovehadthehighest(Fig.12).However,resultsfortotalCO2emissionforeachstoveforthesimmerphasewerenotsignificantlydifferentforallofthestovesatthep=0.05level,meaningtruedifferencesbetweenthestoves’emissionsperformancecannotbedetected.AlthoughthetraditionalstovehadthehighestaverageCO2emissionforthesimmerphase,itsvariabilityandthesmallsamplesizemadeitimpossibletodistinguishitfromthePraktieventhoughtheaverageCO2emissionsforbothstovesisquitedifferent.

ForthefullWBT,thePrakti’sCO2emissionswerethelowestwhiletheStoveTec’swerethehighest(Fig.13).Allstoves,excepttheStoveTec,hadlowerCO2emissionsovertheentireWBTthanthetraditionalstove.SimilartotheCOresults,thetraditionalstoveshowedhighvariability,makingitdifficulttofindasignificantdifferencebetweenitsperformanceandthatoftheimprovedstoves.OvertheentireWBT,atthep=0.05level,theEcoRechoandraktistovesweresignificantlydifferentfromtheStoveTec.P

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Table7:TotalCO2EmissionsforSimmerPhaseandoverallPhases

TotalCO2 mer(g)‐Sim TotalCO2 hases(g)–AllPEcoRecho 640 1376Mirak 747 1577Prakti 542 1249StoveTec 802 1842Traditional 928 1625

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WeincludetotalCO2emissiondatabecauseitispotentiallyusefulforcarbonfinanceprojects.However,itshouldbenotedCO2emissionisarequiredoutcomefromthecombustionofhydrocarbonfuelssuchascharcoalorfuelwoodand,therefore,isnotacompletelyundesirableoutcome.Hydrocarbonfuelsarelargelymadeofcarbon,whichisreleasedprimarilyasCO2orCOwhencombusted.Therefore,whileitismoredesirabletoburnlessfueloveralltodecreasethetotalamountofemissions,foragivenamountoffuel,itisbettertohaveahigherCO2emissionthanCOemission(alowCO/CO2emissionratio).HigherCO2emissionsmeantheprocessofcombustionwasmorecompleteandreleasedlessproductsofincompletecombustionsuchastoxicgases(CObeingoneofthem)andparticulatesthatcausehealthproblems.TheratioofCOemissiontoCO2emissionispresentedinthenextsectionforthisreason.

3.2.3RatioofCO/CO2

IneachWBTconducted,theratioofCOemissiontoCO2emissionwascalculatedforeachtestphaseandforallphasesoftheWBT.AscanbeseeninTable8,forthesimmerphaseaswellasoverall,theMirakhadthelowestCO/CO2emissionratioandtheEcoRechohadthehighest.OvertheentireWBT,theMirakandEcoRechoweresignificantlydifferentfromoneanother,butmiddlerankscouldnotbedistinguishedatthep=0.05level.Forthesimmerphasealone,stoveswerenotsignificantlydifferentfromoneanotheratthep=0.05level,meaningtruedifferencesbetweenthestoves’totalCO/CO2emissionratioswerenotetected.d

0

500

1,000

1,500

2,000

2,500

?CO2, (grams)

(± 95% CI)(± 95% CI)

0

500

1,000

1,500

2,000

?CO2, (grams)

Fig.13:TotalCO2EmissionsoverallPhases.Errorbarsare±95%confidenceintervals.

Fig.12:TotalCO2EmissionsfortheSimmerPhase.Errorbarsare±95%confidence

intervals.

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Table8:CO/CO2EmissionRatioforSimmerPhaseandoverallPhases

TotalCO/CO2‐Simmer(%)

TotalCO/CO2–AllPhases(%)

EcoRecho 15.8 13.0Mirak 8.0 8.5Prakti 12.7 10.9StoveTec 10.8 9.9Traditional 10.0 9.5

0%

5%

10%

15%

20%

25%

30%

?CO/?CO2, (%)

(± 95% CI) (± 95% CI)

0%2%4%6%8%

10%12%14%16%

?CO/?CO2, (%)

Fig.14:CO/CO2EmissionRatiosfortheSimmerPhase.Errorbarsare±95%confidence

Fig.15:TotalCO/CO2EmissionRatiosoverallPhases.Errorbarsare±95%confidence

intervals.intervals.

3.2.4EmissionConclusions

COemissionoverallphasesoftheWBTandoverthesimmerphaseconsideredseparatelywasnotsignificantlydifferentamongthetestedstoves.So,althoughPraktiandMirakhadthelowestaverageemissions,theirresultscannotbedistinguishedfromthoseoftheotherstovesatthesignificancelevelofp=0.05.COemissionsfromthesimmerphaseaccountedforsomewhatlessthanhalfthetotalCOemissionsfromtheentireWBT.

CO2emissionsoverallphasesoftheWBTwerethelowestforthePraktiandhighestfortheStoveTec.OvertheentireWBT,atthep=0.05level,theEcoRechoandPraktistovesweresignificantlydifferentfromtheStoveTec.However,similartoCOemissions,CO2emissionsfortheseparatelyconsideredsimmerphasewerenotsignificantlydifferentamongthetestedstoves.

TheMirakhadthelowestCO/CO2emissionratioandtheEcoRechohadthehighest.OvertheentireWBT,atthep=0.05level,theCO/CO2emissionratiosoftheMirakandEcoRechoweresignificantlydifferentfromeachother,butmiddlerankscouldnotbedistinguished.CO/CO2ratiosforthesimmerphasealonewerenotsignificantlydifferentatthep=0.05level.

17

InconsideringbothCOemissionsandtheCO/CO2ratio,theMirakstoveperformedthebest,althoughthedifferencewasonlysignificantwhencomparingthebestandworsterformers:middlerankswerenotstatisticallysignificant.p

3.3Usability

Inthissection,weprovidecommentsandobservationontheeaseofusingthestove.Exceptwherenoted,thecommentsarefromtestersinthelaboratoryperformingtheWBT,sosomecommentsmaynotberelevantforHaitiancooks.WehavepreviouslydisseminatedourobservationsandinformalusercommentaryfromasingledayHaiticook‐offinwhichmostofthesestoveswereusedinthemakingofsospwabyHaitianwomeninthespringof2010.Thatreportisavailableonlineathttp://www.fuelnetwork.org/index.php?option=com_docman&task=cat_view&gid=72&Itemid=57&limit=15&limitstart=0&order=date&dir=ASC

EcoRecho:Testershadtroublewiththeholesinthecharcoalpan,whichcloggedwithashduringcooking.Thisproblemoccurrednearlyeverytimetheyusedthestoveandcausedmultiplefailedtestsasthecloggingcompletelycutofftheairflowandputoutthefire.Theholesaredifficulttounclog:testersultimatelyresortedtousingtongstoperiodicallyunclogholesduringthetest.Thedoordoesnotallowforpartialopening,sotesterskeptitcompletelyopen.Thehandlesweresolidandcouldhandledumpingashmultipletimes.TheEcoRechohadthemoststableplatform,consistingofprongsthatcouldbeliftedsothatthepotcouldbeplacedontheprongsoronthecharcoaldirectly.Theappealoftheprongswasthestabilitytheygavethepot,theabilitytofeedcharcoalintothepanwithouthavingtoliftthepot,andnotsmotheringthefirewiththepot.

Mirak:Ascharcoaldiesdown,thepotsinksintothecharcoal,cuttingoffairflow.Testerswereabletomitigatetheproblembyputtinglargepiecesofcharcoalonthesidessoitwouldallowforairflow.Becausecharcoalburnedunevenly,thepottendedtotilt.Withabiggerpanallowingthecharcoaltospreadout,testersfoundthestovedoesnotlightaswell,andtesterswereoftenafraidofsmotheringthefire.InnotingthetemperaturechangeswithMirak,ourtestersfoundthetemperature“scissoredup”asopposedtoclimbingconsistently.Thismaybebecausetestershadtoremovethepotfromthestovetoaddmorecharcoal,whichdroppedthetemperatureofthewaterslightlyeachtimetheyaddedfuel.TesterslikedthattheMirakhadadetachablepantodumptheremainingcharcoalwithouthavingtomovetheentirestove.

Prakti:Thefourprongplatformisabitunstable(notperfectlyeven)comparedtothestablethreeprongplatformofotherstoves.Thehandlesaresmallandfalldowntorestagainstthesideofthestove,makingthemhardtomaneuverandcausingthemtobecomeextremelyhot.Thedoorworkswellandiseasytouse.Thecoalswereeasytolightbecauseoftheshallowchamber.Testerslikedtheshapeandsizeofthestoveandfoundittobesturdy.Theyalsothoughttheashpanwasagood

stove.

Inadditiontocommentsofusabilityofeachstove,wenotehoweachstovecomparedtothetraditionalstove.WhencomparingtheEcoRechotothetraditionalstove,theEcoRechohadthestableprongplatform,whichisnotpresentinthetraditionalstove.However,theholesofthetraditionalstovewerelargeenoughthattheyneverpluggeduporcausedfailedtestsasintheEcoRecho.WhencomparingtheMiraktothetraditionalstove,thedetachablepanusedtodumpthecharcoalwasanadvantage,althoughthetraditionalstovewaslightenoughtolifttheentirestove.However,thepanoftheMirakwouldlimitairflowasthepotsunkintocharcoal.Thisproblemwasnotobservedinthetraditionalstovebecausethesquarepanwaslargerandtheholessurroundtheentirepan,sothepotwouldnotcovertheentiretopofthestove.WhencomparingthePraktitothetraditionalstove,thePraktihadadoorthatworkedwell,waseasytouse,andallowedforarangeofairflow.Also,theashpanwasconvenientandeffective.However,thehandlesonthePraktiaresmallandfalldowntorestagainstthesideofthestove.Thetraditionalstove’shandlesarelargerandeasiertohandle,protrudeoutawayfromthestove,andcooldownquickly.WhencomparingtheStoveTectothetraditionalstove,theStoveTechadaprongplatformthat

18

one.Theydidfind,however,thefourprongsmadeitmoredifficulttoaddcharcoalbecausetherewaslessspacethroughwhichtoaddadditionalfuel.

StoveTec:Thetestershadtroublewiththedoor,whichfelloffeasilyandwasdifficulttofitinitsgrooves.Duringhotandcoldstarts,thedoorwas85%openasfullyopeningthedoorcausedittofalloff.Thehandlessometimesfelloffwhendumpingcharcoalout.TheStoveTec’sinteriorclayslowlykeptfallingapart.Duringonefailedtest,theclayblockshiftedandsealedoffairsupply.Testersalsofounditdifficulttogetnewcoalslitwhenaddingthem.Thestoveremainedveryhotforhoursafterthetestwascompleted.

Traditional:ThetraditionalstoveiswidespreadinHaiti.Sincethestovehasbeenwidelyadopted,itisassumedtobehighlyusableandfitHaitianneedswell.Therefore,wehighlightpositiveaspectsoftheusabilityofthetraditionalstovebecausethosearethecharacteristicsthatcouldpotentiallyleadpeopletokeepusingthestoveevenifitislessefficient.Thetraditionalstovehadthebenefitofsimplicity.Thestoveisgenerallystable,hassturdylegs,andalargepanthatcansupportvariouspotsizesandshapes.Ithadnodoorswhichmadeiteasytouse,butitalsohadnowaytocontroltheairflowtocontrolthepowersettingwithouthavingtoremovethepottoaddorremovecharcoal.Anadvantageofthetraditionalstovewastheholesaroundtheentirepanofthestove;theywouldnotgetpluggedupwithchar,andtheymaintainedsufficientairflowtopreventthefirefrombeingsmotheredbythepot.Sincethepotsitsdirectlyonthecharcoal,testershadtoputbiggerpiecesontheoutercirclewithsmallerpiecesontheinsidesothatthepotwouldnottilt.Thelargepanallowedforlargeamountsofcharcoaltobeadded,andmadeitconvenienttoaddandremovecharcoal.Sometimesitwasdifficulttolightthecharcoalbecausethelargepanallowedthecharcoaltomovearoundifitwasnotcompletelyfull.Themetalhandlesaresturdyandprotrudefromthestove,increasingstoveusability.Sincethehandlesaremetaltheybecomehotduringtestingsotestershadtouseglovesorwaituntilthestovewascooltohandlethe

19

increasedthestabilityofthepot,andensuredthatthecharcoalwasn’tsmotheredbythepot,incomparisonwiththetraditionalstovewherethepotsitsdirectlyonthecharcoal.However,thetraditionalstove’susabilitywassimplerthantheStoveTec,whichtranslatedintofewerproblemsduringtesting.

4.CONCLUSION

Inregardstoefficiency,allstovesofferedimprovementoverthetraditionalstove.Thereisatradeoff,though,intimetoboil,asallimprovedstovestookmuchlongertobringwatertoaboilthanthetraditionalstove.Overall,intermsofboththermalefficiencyandspecificfuelconsumption,thePraktiandtheEcoRechoperformedthebest.However,asdescribedabove,inmanyinstances,differencesbetweentheirperformanceandtheperformanceoftheStoveTecorMirakwerenotstatisticallysignificant.

IntermsofCOemissionsandtheCO/CO2ratio,theMirakhadthelowestemissions,althoughdifferenceswerestatisticallysignificantonlywhencomparedtothestovewiththehighestemissions,theEcoRecho.

Forusability,wehaveincludedtesterobservationsandcommentsinordertoprovidefeedbacktostovedesigners,butnostoveemergedasclearlysuperiortotheothers.

TheseWBTsprovideagoodinitialcomparisonofstoveperformanceundercontrolledconditions.Inthefuture,additionaltestsperstovewouldbeusefultoincreasethesamplesizes,andpossiblyreducetheconfidenceintervals,tobebetterabletomakecomparisonsbetweenstoves.However,evenwhenresultsaren’tstatisticallysignificantduetolargeconfidenceintervals,observeddifferencesbetweenstovesmaybepracticallysignificantforreal‐worldperformanceinthefield.Also,tobetterpredicthowstoveswillperformintermsofefficiency,emissions,andusabilityunderHaitianconditions,wearecomplementingtheWBTswithControlledCookingTests(CCTs)usingaprotocolbasedonbservationsofHaitiancooking.o

Acknowledgements

ResearchfundingwasprovidedbytheU.S.DepartmentofEnergyunderContractNo.DE‐AC02‐05CH11231,andpartiallybythesupportofNDSEGFellowship.

Theauthorswouldliketothankthefollowingpeoplefortheirassistancewiththeproject:CristinaCeballos,AllenBoltz,andEthanAveyfortheirmanyhoursofstovetestingandthehighqualityoftheirwork;AndreeSoslerandDebraSteinofDarfurStovesProjectfortheirorganizationalsupportincoordinatingthetriptoHaiti,withoutwhichthisprojectcouldnothavebeendone;PhilPrice,RobertCheng,TonyKeaveny,AdamRausch,andScottSadlonforgenerouslysharingtheirtechnicalexpertise;CrispinPemberton‐Pigottforthearithmeticreasoningbehindchangingtheequivalentdryfuelequation;andTomKirchstetterandRobertChengforreviewingthedocument.WealsothankthepeopleatStoveTec,Prakti,andEcoRechoforprovidinguswiththeirstovestotestandfortheirtirelessworkonimprovingstovesforthepeopleofHaiti.

AppendixA:SummaryofDataforWBT

TableA1:NumberofTestsperPhase TableA2:TimetoBoil(mean±SD)

Cold Hot SimmerEn eW tirBT

EcoRecho 4 4 3 11Mirak 5 3 3 11Prakti 5

44

453

333

121210

StoveTecTraditional

ColdStart(minutes)

HotSta(minut

EcoRecho 55.2±24.2 32.1±Mirak 54.1±17.3 42.1±

Prakti 51.3±6.7 33.3±

StoveTec 59.8±11.636.5±16.8

29.9±24.0±Traditional

TableA3:ThermalEfficiency(mean±SD) TableA4:SpecificFuelConsumption**(mean±SD)

20

Simmer EntireWBTEcoRecho 37.5%±13.5% 31.6%±17.1%Mirak 34.1%±6.2% 28.6%±7.7%Prakti 46.2%±2.2%

36.6%±4.2%28.5%±2.1%

37.3%±8.5%30.5%±8.4%22.2%±3.1%

StoveTecTraditional

**Temperature‐orrected

Simmer Entir (grams) (gramEcoRecho 324±127 479Mirak 289±104 507 Prakti 378±302

346±91.7808±290

539 572 979

StoveTecTraditional

C

TableA5:TotalCOEmission(mean±SD) TableA6:TotalCO2Emission(mean±SD)

Simmer EntireWBT(grams) (grams)

EcoRecho 98.6±13.3 179±19.3Mirak 59.1±13.2 134±23.8Prakti 68.7±12.1

83.5±36.691.6±31.6

136±27.4183±43.1154±34.4

StoveTecTraditional

Simmer EntireWB(grams) (grams)

EcoRecho 640±140 1376 ±15Mirak 747±52.8 1577±20Prakti 542±77.0 1249±17StoveTec 802±103

928±3541842 ±191625±3Traditional 7

21

TableA7:TotalCO/CO2Emission(mean±SD)

Simmer EntireWBTEcoRecho 15.8%±3.4% 13.0%±2.0%Mirak 8.0%±2.2% 8.5%±1.9%Prakti 12.7%±1.6%

10.8%±5.8%10.0%±0.6%

10.9%±2.6%9.9%±2.6%9.5%±3.1%

StoveTecTraditional

AppendixB:ChangetoEquationinWBTProtocolTheWBTwasdesignedforwood‐burningstovesandcannotbeexactlyappliedtocharcoal‐urningstoves.WemadethefollowingmodificationintheWBTprotocolequationtobaccommodatecharcoalstoves.WhencalculatingequivalentdryfuelconsumedforallphasesoftheWBT,thewood‐burningprotocolincorporatestheenergyrequiredtoturntheleftoverwoodintochar.However,weusedcharcoalinsteadofwoodandbecausecharcoalisessentiallycharalready,weassumedtheenergycontentoftheleftovercharcoalwasthesameastheinitialcharcoal,allowingthechangeincarbon(ΔCc)toequalzero.Also,duetodifferencesintheenergycontentbetweencharcoalandwood,wereplacedthecoefficientof1.12with1.08.Thischangedtheequation(forexampleinthecoldstartphase)from:

t o:

whereFcdistheequivalentdryfuelconsumed,Fcmisthefuelconsumed,misthemoisturecontentofthefuel,andΔCcisthenetchangeincharduringthetest.

TheWBTVersion3.0approximatestheheatofvaporization ,theenergyrequiredtoevaporatewater,as2260kJ/kg.TheWBTprotocolalsoremarksthatthisvalueisapproximately12%ofthecalorificvalueofdrywood ,

Additionally,theWBTprotocolstatesthatcharhasroughly150%ofthecalorificcontentofdrywood,

Sincetheheatofvaporizationofwaterisaconstantvalue,

22

Therefore,thecoefficientintheequationforequivalentdryfuelconsumedchangedfrom1.12to1.08,

toaccountforusingcharcoal(essentiallychar)insteadofwood.

ForfurtherinformationontheWBTprotocol,seetheShellFoundationHouseholdEnergyrojectWBT,version3.0,foundat:P http://ehs.sph.berkeley.edu/hem/?page_id=38.

23

AppendixC:Statistics

Toassessthevariationintheaveragevalue overanumberofmeasurements,thesamplestandarddeviation iscalculatedby

24

where

(1)

isthenumberofmeasurementsorsamplesizeand aretheindividualmeasurementsthatareusedtocalculatetheaverage.Aconvenientwaytocalculatethesamplestandarddeviationisusingthe“STDEV”functioninExcel(the“STDEV”functionuses inthedenominator).Averagevaluesandsamplestandarddeviationsforeachperformancemetric(timetoboil,thermalefficiency,specificfuelconsumption,carbonmonoxideemission,carbondioxideemission,andtheratioofcarbonmonoxidetocarbondioxide)arepresentedinAppendixAforreference.

Toassessuncertaintyintheaverage,thestandarddeviationofthemean (alsocalledthestandarderror),iscalculatedasthestandarddeviationdividedbythesquarerootofthesamplesize,

.

Foranormaldistribution,ifavalueisreportedasthemeanplusorminusthestandarderror(

(2)

)thenthereis68%confidencethatmeasurementswillbewithinthesebounds.Itistypicaltoreportuncertaintyatthe95%confidencelevelwhich,foranormaldistribution,isapproximatelytwostandarddeviationsfromthemean( ).Whenthisuncertaintyisusedastheerrorbarsfordataplottedinbarcharts,itcanclearlybedeterminedwhetherdifferencesbetweentwopopulationmeansaresignificant,byobservingerrorbarsthatdonotoverlap.

Whenitisassumedthatthemeasurementsarenormallydistributedbutthesamplesizeissmall(<30)andthepopulationstandarddeviationisunknown,aStudent’st‐distributionisused.WhenusingtheStudent’st‐testtocalculateconfidenceintervals,andassessstatisticalsignificance,theconfidenceintervalsare

wherethecoefficient

(3)

isthevalueoftheStudent’st‐distributionatthechosenlevelofconfidence.Aselectionoft‐valuesislistedinthetablebelowasanexample.Itisrecommendedthatsamplesizes(thenumberoftestsperstove)begreaterthanfivetoeducethereporteduncertainty.Forfurtherinformation,referencesarelistedbelow.r

25

N

(SampleSize)

N‐1

(Degreesof

Freedom)

t.975(Onesided);t.95(Twosided)

1 ‐ ‐2 1 12.713 2 4.304 3 3.185 4 2.786 5 2.577 6 2.458 7 2.369 8 2.3110 9 2.26

References

nalysis,2nded.(UniversityScienceBooks,199J.R.Taylor,AnIntroductiontoErrorA 7).

M.R.Spiegel,S.Lipschutz,andJ.Liu,MathematicalHandbookofFormulasandTables,3rded.(McGraw‐Hill,2008).

ThefollowingWikipediapagesarealsousefulatexplainingtheseconcepts:http://en.wikipedia.org/wiki/1.96andhttp://en.wikipedia.org/wiki/Student%27s_t‐distribution.