Adaptation and comparative study of thermal comfort in naturally ventilated classrooms and buildings in the wet tropical zones

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ContentslistsavailableatScienceDirect

Energy

and

Buildings

jo u r n al h om ep a g e :w w w . e l s e v i e r . c o m / l o c a t e / e n b u i l d

Adaptation

and

comparative

study

of

thermal

comfort

in

naturally

ventilated

classrooms

and

buildings

in

the

wet

tropical

zones

Modeste

Kameni

Nematchoua

a,∗

_,

_René

_Tchinda

b

_,

_José

_A.

_Orosa

c,∗

a_{Environmental}_Energy_Technologies_Laboratory,_University_of_Yaoundé_I,_Yaounde,_Cameroon b_LISIE,_University_Institute_of_Technology_Fotso_Victor,_University_of_Dschang,_Dschang,_Cameroon

c_Department_of_Energy_and_M._P._Escuela_Técnica_Superior_de_N._y_M,_University_of_A_Coru˜_na,_Paseo_de_Ronda_51,₁₅₀₁₁_A_Coru˜_na,_Spain

a

r

t

i

c

l

e

i

n

f

o

Articlehistory: Received15April2014

Receivedinrevisedform9September2014 Accepted15September2014

Availableonline22September2014 Keywords: Naturallyventilated Wettropical Thermalcomfort Comparativestudy Buildings

a

b

s

t

r

a

c

t

Thispaperpresentstheresultsofastudyrelatingtothermalcomfortin28buildingsandschools,inthe

coastalandcentralareasofCameroon.Thisresearchwasconductedduringthedryandrainyseasons,

employingtheadaptiveapproach,innaturallyventilatedbuildings,inaccordancewithASHRAE55/2004,

ISO7730andISO10551.Windspeed,airtemperature,relativehumidityandCO2levelsweremeasured,

and2650questionnairesweredistributedsimultaneously.Theresultsrevealedthat76.7%ofthevoters

inDoualafoundtheresultsenvironmentallyacceptable,asagainst82.6%inYaoundé.Onaverage,74.6%

oftherespondentsfoundthatthesewerewithinthecomfortrange,while25.3%wereneutral.When

thelocalthermalcomfortfactorwasanalysed,itwasfoundthatthepercentageofdissatisﬁedpersons

exceeded40%inbothcities,Yaoundéinparticular,duetoitshigheraveragetemperature.

1. Introduction

Acomfortable andhealthyenvironment is aprerequisitefor

robusthumanhealth.Theconceptofthermalcomfortisquite

com-plexandvariesaccordingtoeachsubject[1].However,although

manyinternationalstandardshavedeﬁnedtherangeofcomfort,

opinionsstillstandstillwidelydivided.Comforthasbeendeﬁned

asthestateofmindthatexpressessatisfactionwiththe

environ-ment[2].Aspeoplespendagreatpercentageoftheirtimeinindoor

ambiences[3],theindoorenvironment shouldbedesigned and

operatedtoensurethethermalcomfortandhealthofitsoccupants.

Theresultsobtainedfromvariousstudiesshowedthatpeopledo

notwhollyexpresstheirfeelingsregardingthermalpreferencesin

naturallyventilatedenvironments.Theresearchworksconducted

[4–7]revealedtheinﬂuenceexertedbythephysical,physiological

andpsychologicalfeelingsofpeoples’preferencesinanaturally

ventilatedenvironment. Different approaches were used inthe

studiesperformedoverthepastfewyearstoascertaintheoptimum

levelsofthermalcomfort. Thisproactiveapproachisa

develop-mentoftheanalyticalapproachinitiatedbyFanger[8].Itisbased

∗ Correspondingauthorsat:UniversityofYaoundéI,EnvironmentalEnergy Tech-nologiesLaboratory,Yaounde,Cameroon.Tel.:+23776965374;fax:+23722353866.

E-mailaddresses:kameni.modeste@yahoo.fr(M.K.Nematchoua), jaorosa@udc.es(J.A.Orosa).

onthecalculationofthepredictedmeanvote(PMV)andpredicted

percentage of the dissatisﬁed (PPD) fromsix main parameters

establishedbyMacpheson[9]including,clothingand metabolic

resistance, dry bulb temperature, radiant temperature, relative

humidityandwindspeed.Today,mostresearchersoptforthe

adap-tiveorproactivemodel.TheworkperformedinAustralia,besides

thoseconductedintheUSA,AfricaandEurope[10–19]highlight

theimportanceoftheadaptivemodels.Theresultsobtainedvaried

widely,dependinguponthelocationofthestudyandtheclimatic

seasonsprevalentthere.Inparticular,airtemperatureisoneofthe

elementswhichdirectlyaffectsthethermalcomfortinaroom.

Sev-eralstudiesintheliteratureemphasisedtheimportanceofthermal

comfortonproductivityinbuildings,ofﬁces,classroomsandother

enclosedspaces.Therefore,HusseinandHazrin[20]headedacase

studyinahealthcliniclocatedinsouthernMalaysia.Theirresults

showedthatover80%oftherespondentsvotedthethermal

condi-tionstobeacceptableand,despitethis,thosewhowereneutral

werenotalwayssatisﬁedwiththethermalconditions.

Further-more,Hens[21],usingtwopracticalcasestudiesofthermalcomfort

duringworkinghours,foundaPMVofzeroandaPPDgreaterthan

5%,incleardisagreementwiththeactualstandards.Consequently,

newmodels,likelocalthermalcomfortindices,mustbeanalysed

undersuchconditions.

Ontheotherhand,inaﬁeldsurveyperformedinJos(Nigeria)

developed byOgbonna [22], therangeof acceptableconditions

in tropicalclassrooms hasbeenrecommended. Furthermore,in

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Fig.1. Locationofthecitystudied.

theresearchdonebyZinganoinMalawi[23]theimportanceof

comfort-leveltemperaturehasbeenspeciﬁed.Finally,Miyazawa

[24]demonstratedthatduringthedifferentsleepstages,the

tem-peraturerange of thermal neutralityhoversbetween19◦C and

25◦C. Thisstudyaimstocomparetheresultsobtainedfroman

experimentalstudyof thermal comfort inthe tropicalwet and

warm (e.g., Douala) and tropical wet and cold (e.g., Yaounde)

regions.Inthepresentresearchwork,astudyispresentedonthe

thermalcomfort in 28buildings andschools in thecoastaland

centralregionsoftheCameroon,basedontheadaptiveapproach

andlocalthermalcomfortmodels.Thequestionnairemethodwas

employedandphysicalmeasurementsweretakensimultaneously

toobtaintheneutralthermalcomfortconditionsintheseregions.

Thisﬁrststudycanbethekeytodeﬁningnewstrategiestoimprove

thermalcomfortconditionsandreducethebuildingenergy

con-sumptionintheseindoorambiences.

2. Fieldstudy

2.1. Citiesanalysed

DoualaandYaoundérankamongthelargestcitiesinCentral

Africa,asseeninFig.1.DoualaistheeconomiccapitalofCameroon,

themainbusinesscentreandoneofthemajorcitiesinthecountry,

locatedontheAtlanticOceancoast,between4◦03Nand9◦42E,

coveringanareaofnearly210km2_._The_climate_in_Douala_is

tropi-calwetandhot,characterisedbytemperaturesbetween18◦Cand

34◦C,accompaniedbyheavyprecipitation,especiallyduringthe

rainyseasonfromJunetoOctober.Theairnearlyalwaysrecords

99%relativehumidityduringtherainyseasonandabout80%during

thedryseason,betweenOctoberandMay.

Thecity ofYaoundé,ontheotherhand,isthepolitical

capi-talofCameroon,locatedcentrally,atanaltitudebetween600m

and 800m and approximately 300km from the Atlantic coast.

It enjoysa sub-equatorialclimate(tropicalwet andcold),with

fourseasons,includingalongdryseason(mid-Novembertolate

March),ashortrainyseason(Apriltomid-June),ashortdryseason

(mid-Junetomid-August),andalongrainyseason(mid-Augustto

mid-November).Thecityisspreadoverseveralhills,andenjoysa

relativelyfreshclimate,muchbetterthanthatalongthecoast,with

themaximumtemperaturerangingbetween30◦Cand35◦Canda

minimumtemperatureof15◦C.

2.2. Materials

Inthisstudy,theindoorairvelocity,relativehumidity,CO2,

tem-peratureandsurroundinglightintensityweremeasuredusingthe

Thermo-AnemometerModelC.A1226,CO2MonitormodelCO200

andaLightMeterIM-1308,respectively.Theoutdoortemperature,

wind speed, and relative humidityvalues weresimultaneously

collectedfrom theNationalWeather StationSystem.The main

characteristicsofthemeasurementsystememployedinthiswork

areshowninTable1.Allequipmentwerecalibratedbeforeeach

experiment to ensure reliability and accuracy in the readings

recordedduringtheﬁeldstudies.

2.3. Methodology

The study was conducted during the summer and winter

seasonsin naturallyventilatedbuildings, adoptingtheadaptive

approach and using questionnaires to obtain quantitative data

ontheactualconditionsprevailinginthesehabitats.Toachieve

thisobjective,twodatacollectionmethodswereused,namely,a

questionnaireasthesubjectivemeasurementandaphysical

mea-surementofcertainparametersthatinﬂuencethethermalcomfort

conditionsinbuildings.Ineachbuilding,inaccordancewithprior

researchworks,samplingprocesseswereperformedbetweentwo

andﬁvedaysperseason,ineachdifferentroomorofﬁce.For

multi-storeybuildings,theofﬁceschosenwerethosethatsupporteda

greaternumber ofoccupants.Table2 showssomeofthestudy

periods.Regularlyandpriortothedistributionof the

question-naires,somequestionswereﬁlledupregardingtheoccupants,such

aspersonal data(age, sex)and micro thermalaspects (climatic

control),toelicitbetterresponsestothequestionnaires.

Themean radianttemperature (Tr)was estimatedusingthe

regressionmodelshowninEq.(1)asafunctionoftheair

tempera-turemeasured(Ta)proposedbyNagano[29]underadetermination

factorof0.99.

Tr=0.99×Ta−0.01, R2=0.99 (1)

Atthesametime,theoperativetemperature(To)was

deter-mined from the air temperature measured (Ta)and the mean

radianttemperature(Tr),asseeninthefollowingequation[2]:

To=A×Ta+ (1−A) ×Tr (2)

wheretheweightingfactor(A)dependsonairvelocity(w),asthe

followingequation:

A=0_.5 for _w_<0_.2m/s

A=0.6 for 0.2<w<0.6m/s

A=0.7 for 0.6<w<1m/s

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2.3.1. Fieldmeasurementoftheenvironmentalparameters

Measurementsweretakenevery20minat aheightof1.2m

fromthegroundlevelinstrictaccordancewiththeprescriptionsof

theASHRAEStandard55[2]andISO7730Standard[25].Oncethe

deviceswereinstalled,measurementswererecordedstartingfrom

8:00AM,toenableeachunittogetadaptedtotheenvironment.

Thedatawerenotedregularlyuntil7:00PM.Thesemeasurements

providedfourofthesixparametersestablishedbyMacpheson[9]

includingthoseofairvelocity,relativehumidity,ambient

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Table1

Characteristicsofthemeasurementsystem.

Function Range Resolution Accuracy

CO2monitor(model CO200) CO2 0–9999ppm 1ppm ±(5%rdg+50ppm) Temperature –10◦_C_to₆₀◦_C _0.1◦_C _±0.6◦_C 14◦_F_to₁₄₀◦_F _0.1◦_C _±0.9◦_F Humidity 0.1%to99.9% 0.1% ±3%(10–90%) ±5%(<10%or>90%)

Digitalthermometer Temperature −20◦_C_to₀◦_C ₁◦_C _±5.0%_of_rdg_±₄_digits

0◦Cto400◦C 1◦C ±1.0%ofrdg±3digits 400◦_C_to₁₀₀₀◦_C ₁◦_C _±2.0%_of_rdg C.A1226 thermoanemometer Airvelocity 0.15–3m/s 0.01m/s ±3%R+0.1m/s 3.1–30m/s 0.1m/s ±1%R+0.2m/s Temperature −20◦_C_to₊₈₀◦_C _0.1◦_C _±0.3%_R₊_0.25◦_C

Airﬂow 0–99999m3_/h ₁_m3_/h _±3%_R_±_0.03_surf.

LightmeterIM1308 Lightmeter 40.0lx–300.0klx ±3% ±5%reading±0.5%scale

Table2 Periodsofstudy.

Cities Dryseason Rainyseason

Time Months Years Time Months Year

Douala Fourweeks Nov.–May 2011–2012 Threeweeks Jul.–Aug. 2012

Yaounde Fiveweeks Nov.–Feb. 2011–2012 Threeweeks May–Sep. 2012

usedtocalculatethePMVand PPDindices,in accordance with

Fanger’model.

Inmostcases,thermaluniformitywasdifﬁculttoachieve in

classroomsandbuildings.Hence,inthisstudy,themeasurement

oftheenvironmentalparameterswasconductedatvariouspoints

occupiedbytheoccupantswhowouldberespondingtothe

ques-tionnaires.

2.3.2. Subjectivemeasurements

The questionnairesemployed in this work were distributed

twiceaday(beforeandafternoon).Thisimpliedthat1450

ques-tionnaireswerecollectedandanalysedduringthestudy.

Thesequestionnaireswereconstructedinaccordancewiththe

ISO7730[25]andISO10551standards,asexplainedprior[26,27].

Fromthesequestionnaires,theclothingandmetabolicratewere

assessedaswellas,itwasalsopossibletoknowthesex,age,weight

andsizeofeachoccupant.Finally,asinthepreviousresearchworks,

thequestionnairesenabledtheidentiﬁcationofthethermal

sensa-tion,thermalpreferenceandacceptanceofthethermalcontrolof

airmovementandhumidityintheareasoccupied.

3. Resultsanddiscussions

Table3listssomeresultsofthephysicalmeasurementsobtained

in28buildingsandclassesstudied,locatedintwoprovinces

sit-uated in thecentral and coastalregions, as mentioned earlier.

Overall,63.2%oftheindividualsintheseareasofexperienceagreed

toconductthisstudywiththesubjectshavinganaverageageof

20.6yearsintheclassroomsand28.0yearsinthebuildings.

3.1. Thermaladaptationoftheoccupants

Thestudyofthethermalinsulationandmetabolicrateof

occu-pantsanalysed inthisworkwillbedescribedin thissection.In

particular,itmustberememberedthateachoccupanthadadjusted

theirmannerofclothinginaccordancewiththeirthermalsensation

towardsneutrality.

3.1.1. Clothingvalue

Fig.2aandbindicatethethermalinsulationversusthemean

indooroperativetemperatureinDoualaandYaoundé.Insulation

duetoclothingisalwaysthemostdifﬁcultfactortobeestimatedin

anyﬁeldofinvestigation,duetothewidevarietyofclothingmodels

and,consequently,thiscannotbeaccuratelyestimated,in

accor-dancewiththeclothingindextabulatedbytheASHRAEandISO

standards.However,clothinginsulationwascalculatedusingthe

standardtabulationsaswellasfromtheinsulationvaluesobtained

fromtwomodelsasseeninthefollowingequations:

Icl=−0.05×Top+2.212, R=0.66 in Yaoundé (4)

Icl=−0.0685×Top+2.576, R=0.792 in Douala (5)

Fromthesemodels,itappearsthatclothinginsulationchanges

inverselywiththeoperativetemperature(see,Fig.2aandb).This

resistanceis stronglydependentuponthezonestudiedand the

y = -0.0685x + 2.576 R2 = 0.6289 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 0perave temperave (°C) Clo Douala y = -0.0505x + 2.2123 R2_{= 0.4441} 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 0perave temperave (°C) Clo Yaounde

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Fig.2. (a)ThermalinsulationversusmeanindooroperativetemperatureinDouala (b).ThermalinsulationversusmeanindooroperativetemperatureinYaoundé.

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Table3

Physicalmeasureddata.

Buildings&classrooms Operativetemperature(◦C) Meanvelocity(m/s) MeanCO2rate(ppm) Meanrelativehumidity(%) Meanluminosity(Lx)

C1 26.5 0.23 980.5 67.5 157.5 C2 25.0 0.18 805.7 62.5 322.5 C3 26.3 0.11 530.5 68.7 246.0 B1 258 0.15 979.5 66.5 146.5 B2 23.5 0.06 923.5 70.6 178.5 B3 23.8 0.09 877.5 69.5 185.5 B4 22.7 0.07 818.4 71.5 201.5 B5 26.1 0.12 457.5 65.5 196.5 B6 24.9 0.17 558.3 67.8 211.5 B7 25.3 0.14 1061.5 70.9 117.5 B8 25.5 0.18 750.9 71.0 199.7 B9 24.8 0.13 558.5 68.5 110.9 B10 25.6 0.15 597.0 71.3 172.6 B11 26.1 0.17 858.5 68.5 100.4 B12 23.6 0.21 938.5 725 209.0 B13 25.5 0.08 887.5 71.5 193.5 B14 25.9 0.29 1097.5 69.0 277.5 B15 24.8 0.10 920.0 72.7 205.6 B16 27.5 0.18 1011.0 69.0 230.5 B17 27.1 0.10 654.0 71.5 198.5 B18 26.3 0.21 967.5 71.5 254.5 B19 25.8 0.06 699.5 68.5 213.5 B20 27.8 0.27 887.5 72.5 301.5 B21 26.5 0.25 777.5 65.7 130.5 B22 24.9 0.30 1117.5 72.9 198.5 B23 27.6 0.12 548.5 59.5 205.7 C4 28.1 0.17 1039.0 67.5 159.9 C5 25.8 0.27 626.0 68.9 135.9

climatetype.Inparticular,therangevariesfrom0.36to1.45clo,

withan averageof 0.78cloforYaoundé, andbetween0.45 and

1.37clowithanaverageof0.67cloforDouala.

Fromthese results, we candeduce thatthe resistancefrom

clothingismuchgreaterinthetropicalwetcold(Yaoundé)thanin

thehothumidtropicalclimate(Douala).Onceagain,theseresults

conﬁrmtheworkofMoujalledAndaletal.[28]regardingthe

ther-malinsulationofclothing,foranaverageclovalueof0.3–0.7clo.At

thesametime,DjongyangandTchinda[16]foundthatwith

wear-ingtropicalwarmclothes,theclothinginsulationrangedfrom0.81

to0.94clo,thusenablingthemtoconcludethatclothinginsulation

ishighlydependentontheseason.Therefore,duringthedry

sea-son,thermalinsulation,especiallyformen,rangedbetween0.4clo

and0.96cloinbothcities.

3.1.2. Metabolicrate

Metabolicratewascalculatedfromthedescriptionsofthe

activ-ities of the individuals recorded in the various questionnaires,

accordingtoISO7730[25].Theresultsobtainedfromthisstudy,

showsthatinbothDoualaandYaoundétheactivitiesaresubjectto

seasonalvariations,beingmoreintenseinthedrythanintherainy

season.Furthermore,fortemperaturesbetween18.7◦Cand28.5◦C,

theaverageactivityof1.1 putsthehot humidtropics (Douala)

againstthatof1.05inthecoldtropics(Yaoundé).Thisresult

con-ﬁrmsthathumanactivityslightlydecreaseswithanincreasingair

temperature.

3.2. Thermalsensationindices

Thermalsensation(Tsens)wasobtainedfromthequestionnaires

andthedifferentvaluesthusobtainedenabledustoarriveatFig.3,

andseverallinearcorrelations,asevidentfromEqs.(6)and (7).

Severalgoodcorrelations(R2₌_0.822_and_R2₌_0.937)_between_T

sens

andindoorairtemperaturearenoted.

Tsens=0.355×Ta−8.843, R2=0.822 in Douala (6)

Tsens=0.407×Ta−9.855, R2=0.937 in Yaoundé (7)

ThedifferentTsensvaluesobtainedvaryfrom−2.03to2.05,with

theaverageinternaltemperaturesrangingfrom16.5◦Cto28.5◦C

inthetropicalwetwarmclimateofDouala,andfrom−2.53to1.98

forarangeofaverageinternaltemperaturesbetween18.8◦Cand

28.0◦CinthetropicalwetcoldclimateofYaoundé.ForTsens=0,

theaveragetemperatureofneutralityinDoualaobtainedduring

thetwo seasonswas25.0◦C, whereasin Yaoundé itwasabout

24.7◦C.Also,itwasdifﬁculttoclearlyrecognisetherainyseasonin

Yaoundé. y = 0.355x - 8.8439 R2 = 0.6764 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 29 28 27 26 25 24 23 22 21 20 19 18 17 16 16 Air temperature (°C) Tsens Douala y = 0.4079x - 9.8558 R2 = 0.8794 -3 -2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 3 29 28 27 26 25 24 23 22 21 20 19 18 17 Air temperature (°C) Tsens Yaounde

(a)

(b)

Fig.3. (a)ThermalsensationversusindoorairtemperatureinDouala.(b).Thermal sensationversusindoorairtemperatureinYaoundé.

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InDouala,therainyseasonischaracterisedbyﬂoodinginseveral

quarters.Theaveragetemperaturehoversaround26.5◦C,except

forOctober5,whentheminimumtemperaturerecordeddropped

below17.0◦C.Bycontrast,DoualaandYaoundéhavethecommon

factorofauniformtemperature(19.5◦C),whichcorrespondsto

Tsens=−1.93,betweenlateSeptemberandearlyOctober.

3.3. Thermalacceptability,comfortandpreferences

3.3.1. Thermalacceptability

Theacceptabilityandeachthermalresponsetoeachdifferent

typeofambiencewasbasedonthePMVscale:−3(cold),−2(cool),

−1(slightlycool),0(Neutral),+1(slightlywarm),+2(hot)and3

(toohot).Asthequestionnaireshadbeenbasedonthisscale,Fig.4a

andbrevealtheresultsrecordedduringthetwostudyseasons.In

Fig.4a,thedryseasonisshownforsubjectswhovotedforindices

(_−1,1);56.22%ofvoterswereacceptabletowardsthemiddlerange

inDouala,asagainst47.16%inYaoundé.Overall,76.56%ofthe

vot-ersinthehothumidtropics(Douala)wereacceptableasagainst

88.67%inthecoldhumidtropics(Yaoundé).theseresultsobtained

arenearoftheconclusionsofIbrahimHusseinduringhisﬁeldstudy

inMalaysia[20]Moreover,only12.98%ofthoseindices(−3,−2)

and(+2,+3)inDoualawerenotacceptabletowardsthemedium

range,asagainst6.63%inYaoundé.Duringtheheavyrainyseason

(Fig.4b),76.52%ofthevotersubjectsappearedamenabletowards

themiddlerangeinYaoundé,asagainst77.00%inDouala.

Atthesametime,thelocalthermalcomfortcanbeanalysed.

Overthelastfewyearsseveralempiricalequationsusedbysome

authors,likeSimonson[30],havebeenavailabletodoanindoor

airqualitystudy.Indices,suchasthepercentageofdissatisfaction

withthelocalthermalcomfort,thermalsensationandindoorair

acceptabilityweredeterminedintermsofsomesimpleparameters

likedrybulbtemperatureandrelativehumidity.Thus,thestandard

agreeduponbyANSI/ASHRAEandISO7730toestablishcomfort

boundaryconditionswasabout10%ofdissatisfaction.

Tomeetthestandardsoflocalthermalcomfortproducedbythe

insideair conditions,Toftumet al.[31,32]studiedtheresponse

of38 individualswho wereprovidedwithcleanair ina closed

environment.Asaresult,theequationforthepercentageoflocal

dissatisfactionwasdevelopedasshowninthefollowingequation:

PD= 100

1₊_e(−3.58+0.18×(30−t)+0.14×(42.5−0.01Pv) (8)

ASHRAErecommendsmaintainingthepercentageoflocal

dis-satisfaction below 15% and the percentage of general thermal

Fig.4.(a)Thermalsensationduringthedryseason(b).Thermalsensationduring therainyseason.

comfort dissatisfaction below 10%. As seen, this PD tends to

decrease when the temperature decreases and, consequently,

theselimitingconditionscanbeemployedtodeﬁnetheoptimal

conditionsforenergysavingintheairconditioningsystems.

Con-sequently,Fig.5showstheindoorlocalthermalcomfortconditions

inkeepingwiththepreviousindices.Whentheindoorair

temper-aturevariedbetween26.5◦Cand28.0◦C,thePD≥50%.Thisresult

showsthatthepercentageofgeneralthermalcomfort

dissatisfac-tionevolvedinthesamewayasairtemperature.

3.3.2. Thermalcomfort

In Fig.6a,an average76.10% ofthevotersopted fora

com-fortableenvironment,with71.10%forthecityofDoualaagainst

81%inYaoundéduringthedryseason.Thermalsensationsvary

between individuals in the same environment and in different

8 9 10 11 12 13 14 15 16 17 18 28 27 26 25 24 23 22 21 20 19

DRY BULB TEMPERATURE (ºC)

W (g wa te r /k gdry ai r ) PD=10% PD=30% Acc=0.2 Acc=0 PD=50% PD=70% Acc=-0.4 Acc=-0.6 PD=20% Acc=-0.2 Douala Yaounde

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-5% 0% 5% 10% 15% 20% 25% 30% 35% 3 2 1 0 -1 -2 -3 Thermal sensation Frequency of votes (%)

Comfortable (Douala) Uncomfortable (Douala) Comfortable (Yaounde) Uncomfortable (Yaounde)

-10% 0% 10% 20% 30% 40% 50% 60% 3 2 1 0 -1 -2 -3 Thermal sensation Frequency of votes (%)

Comfortable (Douala) Uncomfortable (Douala) Comfortable (Yaounde) Uncomfortable (Yaounde)

(a)

(b)

Fig.6. (a)Thermalcomfortduringthedryseason.(b)Thermalcomfortduringthe rainyseason.

regions[15,16].Ofthe38%ofthesubjectswithvotingindicesof

(−3,−2),and(+2,+3),19%foundacomfortableenvironmentfor

Douala,unlikeforYaoundéorinotherwords35%of50%foundthe

placecomfortable.In Fig.6b,itappearsthat87.0%ofthevoters

inDoualafoundacomfortableenvironmentduringtherainy

sea-son,asagainst59.4%inYaoundé.Ingeneral,duringthe23-month

study,79.5%ofthesubjectsparticipatedinthevoting,asagainst

70.1%inDoualacomparedwithYaoundé,whofounda

comfort-ableenvironment.Atotalof31.5%ofthevotersinDouala,against

19.5%ofthosewhovotedinYaoundé,foundtheirneutral

environ-ment.Wededucefromtheseresults,thatamediumneutraldoes

notnecessarilyindicateacomfortableenvironment[16–18].

3.3.3. Thermalpreference

Thermalpreferences and thermal sensations depend onthe

physical,psychologicalandphysiologicalfactors,whichare

unpre-dictable.Fig.7ashowstheresultsobtainedbythedifferentthermal

preferencesduringthedryseason.Fig.7aindicatesthat,inDouala,

74.5% of the voters desire an unchanged environment, against

59.49%forYaoundé.Also,19.84%oftheoccupantswishforacooler

environmentinYaoundé,asagainst25.97%inDouala.Forthis

fac-tor,fortherainyseason,thedatafromFig.7bshowsthat31.35%of

thevoterswishforawarmerenvironmentinYaoundé,asagainst

13.01%inDouala.Overall,duringtheentireexperimentalperiod,in

thedryandrainyseasons,moreoccupantsdesiredtheir

environ-menttoremainunchanged.Ananalysisofthesedifferentresults

showthatthermalsensationandthermalpreferencevaried

accord-ingtotypeofbuildingandalsoaccordingtoseason.Thisconclusion

conﬁrmtheresultsfoundinthelastworks[34–36].

3.4. Internalenvironmentalparameters

Fig.8revealstheevolutionoftheaverageinternaltemperature

andrelativehumidity.InDouala,theaveragetemperaturevaries

from24.5◦Cto28.8◦C,whiletherelativehumidityvaluesrange

from49.9%to73.4%.InYaoundé,humidityrangesfrom46.8%to

73.7%,whiletheaveragetemperaturevariesfrombetween23.3◦C

and26.8◦C.Inmostcases,therelativehumidityvaluesobtained

-5% 0% 5% 10% 15% 20% 25% 30% 35% 3 2 1 0 -1 -2 -3

Thermal sensaon votes

Frequency of votes (%)

Want warmer(D) Want warmer(Y) Want cooler(D) Want cooler(Y) Want no change(D) Want no change(Y)

-10% 0% 10% 20% 30% 40% 50% 60% 3 2 1 0 -1 -2 -3

Thermal sensaon votes

Frequency of votes (%)

Want warmer(D) Want warmer(Y) Want cooler(D) Want cooler(Y) Want no change(D) Want no change(Y)

(a)

(b)

Fig.7.(a)Votesofthermalpreferenceduringthedryseason(b).Votesofthermal preferenceduringtherainyseason.

werenotinaccordancewiththeASHRAEcomfortrangeestablished

between30%and60%byCIBSE[2,3].

In Fig. 9a, the averagewind speed is 0.085m/s, alternating

between0.01m/s and 0.31m/s in Yaoundé, as against0.05m/s

and0.32m/sinDouala.OtherparameterslikeCO2concentration

andluminosityalsoexerttheirinﬂuenceontheindoorcomfort

ofabuilding.InFig.9b,indoorCO2concentrationdiffers

depend-ingonthebuildingmaterialsthathadbeenused,relevanttothe

habitatandtime.TheCO2 concentrationvariesfrom533ppmto

1168ppm,withtherecordedaveragebeing832.5ppminDouala,

asagainst887.5ppminYaoundé.ElevatedCO2rateinabuilding

affectthehealthofoccupant[33].Infact,ahighlevelofCO2can

causeheadacheandchangesinbreathrhythmsinhouses[33].The

effectofluminosityhasnotalwaysbeengoodintheofﬁces

stud-ied.Luminosityvariedfrom100.4to322.5lx,whenitisinferiorto

200lxinanofﬁce,itinﬂuencesonthehealth(seeTable3).

Differentoutdoorparameters(airtemperature,relative

humid-ityandwindspeed)alsoinﬂuenceindoorcomfort.Theseelements

havebeenstudiedandarediscussedinthenextparagraph.

(7)

0 0.1 0.2 0.3 8:00 8:20 9:00 9:20 _10:00 _10:20 _11:00 _11:20 _12:00 _12:00 1:00 1:20 2:00 2:20 3:00 3:20 4:00 4:20 5:00 5:20 6:00 6:20 7:00 7:20 Time (hours)

Indoor air speed ( m/s)

Douala Yaounde 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 8:00 8:20 9:00 9:20 _10:00 _10:20 _11:00 _11:20 _12:00 _12:00 1:00 1:20 2:00 2:20 3:00 3:20 4:00 4:20 5:00 5:20 6:00 6:20 7:00 7:20 Time (hours) CO 2 (ppm) Douala Yaounde

(a)

(b)

Fig.9. (a)Airspeedforthetwocities.(b)IndoorCO2concentrationforthetwo

cities.

3.5. Outdoorair

The relative humidity, as well as wind speed and air

tem-perature,exertsagreatinﬂuenceonthethermalsensationsand

preferenceswithinabuilding.InFig.10,themonthlyaveragesof

differentoutdoortemperatureshavebeenrecordedforthemonth

ofOctober2010leadinguptoSeptember2012.InDoualacity,the

temperaturesareabove26.0◦C, exceptfor themonthofAugust

2011,whereitis25.6◦C.Moreover,inYaoundé,theexternal

tem-peraturevariesfrom23.3◦C(correspondingtoOctober2010)to

25.9◦C (November 2011). Relative humidity is not predictable

becauseitisnonlinear.Byanalysingtherelativehumidityvaluesof

thedatarecordedfor24successivemonthsinFig.11,weobserve

thatitvariesfrom77.0%to90.0%forDoualawithanaveragevalueof

86%,whileinYaoundé,thevaluesrangebetween71.0%and85.0%,

andaverageat73.7%.Weconcludethattherelativehumidityis

muchgreaterinDoualathaninYaoundé.ThelocationofDouala

iscertainlyoneofthemaincausesforthisincrease inthe

rela-tivehumidityinthehumidwarmtropics.FromAugust2011to

February2012,thehumiditydecreasedconsiderablyinboththe

cities. 22 23 24 25 26 27 28 29 30

Oct(10) Nov(10 Dec(10) Jan(11) Feb(11) Mar(11 Apr(11) May(11 Jun(11) Jul(11) _Aug(11) _Sep(11) _Oct(11) Nov(11 Dec(11) Jan(12) Feb(12) Mar(12 Apr(12) May(12 Jun(12) Jul(12) _Aug(12) _Sep(12) Months (Years)

Average outdoor air temperature (°C)

Douala Yaounde

Fig.10.Outdooraverageairtemperatureforthetwocities.

70 72 74 76 78 80 82 84 86 88 90 92

Oct(10) Nov(10 Dec(10) Jan(11) Feb(11) Mar(11 Apr(11) May(11 Jun(11) Jul(11) _Aug(11) Sep(11) Oct(11) Nov(11 Dec(11) Jan(12) Feb(12) Mar(12 Apr(12) May(12 Jun(12) Jul(12) _Aug(12) Sep(12) Months(Years)

Average outdoor relave humidity (%)

Douala Yaounde

Fig.11.Outdooraveragerelativehumidityforthetwocities.

0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3

Oct(10) Nov(10 Dec(10) Jan(11) Feb(11) Mar(11 Apr(11) May(11 Jun(11) Jul(11) _Aug(11) _Sep(11) _Oct(11) Nov(11 Dec(11) Jan(12) Feb(12) Mar(12 Apr(12) May(12 Jun(12) Jul(12) _Aug(12) _Sep(12) Months(Years)

Avarege outdoor wind speed (m/s)

Douala Yaounde

Fig.12.Outdooraveragewindspeedforthetwocities.

While thewind speed is higher inYaoundé than inDouala,

according to the different values obtained in accordance with

Fig.12,thewindspeedvariesfrom0.9m/sto2.2m/sand0.7m/s

to1.4m/s,respectively,forthecitiesofYaoundéandDouala.The

averageis1.4m/s,anaverageof1.0m/sinDouala,asagainstthe

1.8m/sinYaoundé.ThelocationofYaoundé,acityconsideredto

bebuiltonsevenhills,certainlyinﬂuencesthewindspeedvelocity

inthisregion.

Theresultsobtainedemphasisetheimportanceofthermal

com-fort in the areas of study and work (ofﬁces). Preferences and

thermalsensationsvaryaccordingtotheindividual,evenifthey

comefromthesameareaandaresubjecttothesametypeof

cli-mate[37].Thebuildingsconstructedwithlocalmaterials,recent

aswellasthoseover25yearsofage,arelessinformed,andless

thanpollutingestablishmentsandnewlybuiltofﬁces.Therateof

theaverageCO2concentrationismuchhigherinYaoundéthanin

Douala.Theacceptabletemperaturerangesfrom22.4◦Cto26.7◦C

inYaoundé,andfrom24.3◦Cto27.8◦CinDouala.

4. Conclusion

Inthiswork,aninvestigationintotheexperimentaland

sub-jectiveresultsofthermo-hygrometricalcomfortconductedin28

buildingsandschoolslocatedintwocitiesofthewettropical

cli-maticzoneofCameroonispresented.Atotalof1450questionnaires

wereusedforboththedryandrainyseasons,whiledifferent

exper-imentalvaluesofindoorparametersweremeasured.Also,external

environmentalparameters,suchastheaveragemonthlyoutside

temperature,windspeedandrelativehumidityinthetwocities,

werereported.Theconclusionsdrawnfromthisstudyareas

fol-lows:

• Individualsexpresstheirfeelingsandthermalpreferences

differ-ently.

• Theaveragethermalinsulationis0.78cloinYaoundé,asagainst

(8)

• ForTsens=0,theaveragetemperatureofneutralityobtainedin

Doualaduringthetwoseasonsis25.0◦Cand24.7◦CinYaoundé.

• Newlybuilthabitatsaremorepolluting.

• 76.7%ofthevotersinDoualaareenvironmentallyoriented,as

against82.6%inYaoundé.

• InDoualaandYaoundé,duringthedifferentseasons,votersdesire

theirenvironmentstoremainunchanged.

• Inbothcities,theresultsoftheanalysisofthephysical

measure-mentsaredifferentfromthosegivenbythevoters.Constructions

are haphazard and do not take into account the

majority-languagecases,separatingthemintoanaccount-planningaspect

ofmicroclimate.Localmaterialsareusedinfavourofimported

materials.Beforebeginningaconstruction,itisadvisableto

con-ductapreliminarystudyonthetypeofclimateprevailinginthe

regiontoadapttothetypeofthecorrespondingconstruction

material.Thechoiceofventilationandairconditioningsystems,

humidiﬁersandfans,ishighlyimportantastheyaretheones

thatpolluteandconsumelesselectricity.Thechoiceof

materi-als,dependingontheclimaticconstraints,canbeasolutionto

overcometheuncomfortableheat.

Acknowledgements

Theauthorsaregratefultothevariousauthoritiesofthetwo

citiesselectedfortheresearchwhoprovidedtheopportunityto

examineandstudytheinformationrelevanttotheirlocalities.The

authorsalsothanktheheadoftheNationalWeatherStationand

allthose,nearandfar,whoparticipatedinthepreparationofthis

workduringtheperiodoftheﬁeldstudy.

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