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Building and Environment 66 (2013) 42e53

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Building and Environment

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Evaluation of thermal environmental conditions and thermalperception at naturally ventilated hostels of undergraduatestudents in composite climate

Shivraj Dhaka a,b,*, Jyotirmay Mathur a, Andreas Wagner b, Ghanshyam Das Agarwal a,Vishal Garg c

aDepartment of Mechanical Engineering, Malaviya National Institute of Technology, Jaipur, Rajasthan 302017, IndiabBuilding Science Group (fbta), Karlsruhe Institute of Technology, GermanycCentre for IT in Building Science, International Institute of Information Technology, Hyderabad, India

a r t i c l e i n f o

Article history:Received 8 February 2013Received in revised form17 April 2013Accepted 18 April 2013

Keywords:Field studyThermal comfortThermal sensationNeutral temperatureBehavioural control

* Corresponding author. Department of Mechanicational Institute of Technology, Jaipur, Rajasthan9829478171; fax: þ91 141 2713211.

E-mail addresses: shivrajdhaka@gmail.com, shiv_d

0360-1323/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.buildenv.2013.04.015

a b s t r a c t

Field study of thermal comfort was conducted in six naturally ventilated hostel buildings of compositeclimate considering Class-II protocol of field measurement during summer 2011. Total 429 surveysamples of same age group (average 19.6 years) were collected including objective and subjectivemeasurements. Statistical analysis of student’s responses and measured thermal environment variableswas performed to determine existing indoor environmental conditions and priority of using behaviouralcontrols. Thermal comfort indices were also calculated and compared to the student’s perceptions.

Neutral temperature was found to be 30.15 �C through regression analysis, with an average clothing of0.41 Clo (min. 0.19 Clo, max 0.82 Clo). Results have shown a wide bandwidth of neutral temperatures(25.9e33.8 �C) for the hostel buildings which is higher than national/international standards of thermalcomfort. Acceptable air velocity and relative humidity were found to be 0.51 m/s and 36%, respectively.Analysis has shown that about 51% students felt ‘overall thermal comfortable’ at the existing environ-mental conditions in the hostel rooms and only 38% occupants were comfortable based on room airtemperature. Students from single, double and triple occupancy rooms were found thermally satisfied atneutral temperature of 30.4 �C, 30.1 �C and 29.8 �C, respectively and their thermal preferences weredifferent.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

Recently there has been a considerable growth of higher edu-cation in India which demands for multi-storey hostel buildings ineducational institutes. Government has proposed a policy toestablish national level institutes in each state and also at districtlevel to propel education system in the country [1]. About 0.35million engineers graduate every year out of total 1.4 million stu-dents and about 1 million students of same age group (17e25years) reside in the hostels in different climatic zones of the country[2,3]. Most of the existing multi-storey hostel complexes arenaturally ventilated and also do not offer even use of air coolerduring harsh summer conditions. Hostels in hot & dry, warm &

l Engineering, Malaviya Na-302017, India. Tel.: þ91

haka@yahoo.co.in (S. Dhaka).

All rights reserved.

humid, and composite climate are not appropriate from thermalcomfort point of view as per the national and international stan-dards. Situations become worse due to frequent power cuts insummer. Hence it is essential to study and propose guidelines forimproving existing thermal environment conditions and determinethe extent of comfortable temperature in the hostels.

Creating thermally comfortable environment in free runningbuildings is a crucial matter although it is possible to improve tosome extent by providing climate responsive envelope, satisfactoryventilation and behavioural controls. Thermal comfort in uncon-ditioned buildings results from a complex set of physical condi-tions, occupant sensations, preferences and behavioural controls.Thermal comfort is defined as ‘the condition of mind which ex-presses satisfaction with the thermal environment and it isassessed by subjective evaluation’ [4,5]. First thermal comfortmodel was introduced by Fanger in 1972 which was based on heatexchange between human body and its surrounding environmentby means of laboratory experiment [6]. Over the time researchers

S. Dhaka et al. / Building and Environment 66 (2013) 42e53 43

and scientists conducted field studies and developed adaptivethermal comfort models as well as standards [7e11]. The funda-mental assumption of the adaptive approach is expressed by theadaptive principle: if change occurs such as to produce discomfort,people react in ways which tends to restore comfort [7]. Occupantalters control options to achieve thermal comfort state. Based onfield findings it is observed that there is a strong linear relationshipbetween monthly mean outdoor temperature and indoor comforttemperature in the conditioned and non air-conditioned buildings[12]. Thermally comfortable conditions can be determined usingpredicted mean vote (PMV) approach or adaptive comfort model orby estimating human body exergy consumption rate [13,14].

Thermal environment conditions in hostels are not similar tothe office or residential buildings due to differences in occupancypatterns, age group, behaviour and activities. Hostels providingcontrol features satisfy practical, social and emotional needs ofapprentices. The literature study reveals that there are very fewstudies to evaluate existing thermal environment conditions in thehostels. Dahlan et al. carried out field research at undergraduatestudent hostels in Malaysia to examine the thermal neutralityconditions. Study concluded that mean value of thermal sensation(�3 cold to þ3 hot) varied from 1.3 to 1.5 when mean indoortemperature was observed between 28.9 and 30 �C. The studyfound neutral temperature as 28.8 �C in warm and humid climaticconditions. Study showed that students were more satisfied in therooms provided with personal controls and students were moreconcerned with thermal comfort than acoustic and visual comfort[15e17]. Research conclusion of another study also shows slightdifference (0.4 �C) in neutral temperature to the previous study[18].

This study evaluates existing thermal environment conditions innaturally ventilated hostel buildings for same age group (under 20years) of undergraduate students. Statistical analysis of student’sresponses based on the field survey was carried out to determinethermal preferences, priority of using behavioural controls and theeffect of occupancy level on neutral temperature. Study also in-vestigates the effect of gender on thermal perception.

2. Methodology

2.1. Description of case study

Field study was conducted in naturally ventilated hostel build-ings at Malaviya National Institute of Technology (MNIT) Jaipur(26.82� N, 75.80� E, and þ390 msl) from August 17 to November 4,2011. Weather conditions of Jaipur city vary highly from winter tosummer. Summer maximum and winter minimum temperaturesfluctuate from 45 �C to 4 �C, respectively. Hot as well as cold windblow during summer and winter whereas cold strong wind blowsduring monsoon and hazy sky is found occasionally [19].

The studied hostel buildings were constructed in late 1970s onthe outskirts of Jaipur city. The envelope of the buildings wasconstructed using locally available rock stones for walls, reinforcedconcrete slabs for roofs, and single clear glass (four thermal breaks)for windows in steel frames. Study was carried out in six hostelbuildings including two girl hostels out of total 14 hostels. Due tosocial restrictions hostels of female students were separated fromboy’s hostel. This condition allowed to investigate the genderperception in hostels. Occupants below age of 31 year have higherexpectations for temperature and ventilation than elders [20,21].Thermal environmental conditions in naturally ventilated buildingscan be improved to some extent by providing behavioural controlssuch as opening/closing of windows, doors and ventilators, switchon fan or change speed, etc. Study investigates the priority of use ofcontrols to restore thermal comfort state.

Fig. 1 shows the location of studied hostels in the institutecampus, and their exterior views. The hostels were similar in con-struction such as number of windows, doors & ventilators andhaving same occupancy pattern as shown in Table 1. A typical singleoccupancy roomin thesehostelswas equippedwitha ceiling fan andTubular Fluorescent Light (TFL) and these numbers were varied ac-cording to the occupancy (double or triple occupancy) in the room.

2.2. Development of questionnaire

Thermal environmental questionnaire (Appendix A) was pre-pared into two parts after a detailed literature review and pre-liminary field survey [2,22e24]. Both part comprised of 42questions; 23 qualitative (opinion based) questions and 19 quan-titative ones. First part of questionnaire was used to note downoccupant responses whereas second part was used to record ther-mal environmental variable as well as surrounding conditions ofthe respondent. Questions 1e12 of Part A correspond to personalinformation of occupant such as age, gender, body surface area andnative place which affect thermal comfort state, whereas questions13e21 refer to sensation and preference of room temperature,relative humidity and air velocity based on the existing environ-ment. Comfort conditions of the occupant also depend on theclothing and type of activity. Traditional (cotton and polyestersalwar kameez, dhoti, sari, blouse, etc.) and ASHRAE clothing en-sembles were offered to the occupant in the questionnaire. Part Bhas 19 questions including 91 choices related to occupant’s residingconditions in the room such as type and duration of activity,orientation of room, window to wall ratio (WWR), exposed andunexposed roof/façade conditions etc. Signature and name of oc-cupants (for female occupants) were left optional. It was observedthat female occupants were hesitant to declare their age and name.

2.3. Field study

A group of 10 students assisted the field survey carried out in thehostels. Each respondent took around 10e12 min to complete thequestionnaire and most of the students actively participated in thesurvey. The survey was prepared anonymously to keep student’sprivacy and to ensure the confidentiality of their responses. Total429 respondents participated, although three samples have beenrejected due to incomplete information. Each measurement wastaken carefully until showing stable measurement. Total 29,318information (Part A 14,888 and Part B 14,430) were gathered fromthe questionnaire.

2.4. Measurement of environmental variables

Thermal comfort is influenced by environmental variables suchas room air temperature, mean radiant temperature, air velocity,relative humidity and personal factors like clothing and activity.Thermal environment variables were recorded at the height ofw1.1m from the floor level between 9:00 a.m. and 6:00 p.m. duringthe study. Ambient air temperature was also recorded after everyfour samples. Table 2 represents the details of the measuring in-struments. Four measurements were taken for each respondentfrom front, back , left and right side. Average value of the measuredvariable was used for thermal comfort analysis.

2.5. Data compilation and data analysis

Survey data sets were analysed statistically using Social PackageStatistical Science (SPSS version 21) to find correlation betweensensation and recorded environmental variables. R Code was usedto calculate the thermal comfort index such as predicted mean vote

Fig. 1. Location plan of hostels (A), view of the hostel corridors (B), view of window and the ventilator (C), elevation of girls hostel (D), elevation of boys hostel building (E).

S. Dhaka et al. / Building and Environment 66 (2013) 42e5344

Table 1Physical characteristics of the hostels.

Physical conditions at hostels Boys hostel Girls hostel

H-1 H-2 H-3 H-7 Gargi H-B

Survey samples 131 99 36 60 85 15Total occupancy 220 224 232 108 179 170Window area (m2) 1.17 1.17 1.17 1.17 1.85 1.2Door area (m2) 1.93 1.93 1.93 1.93 2.2 1.93Door material Steel Steel Steel Steel Steel SteelRoom area (m2) Single bed 7.2 7.2 7.2 7.2 9.3 -

Double bed 11 11 11 11 e 18.5Triple bed 17.65 17.65 17.65 17.65 e e

Room volume (m3) Single bed 20.8 20.8 20.8 20.8 28.34 e

Double bed 36.0 36.0 36.0 36.0 e 40Triple bed 52.9 52.9 52.9 52.9 e e

Percentage of window operable 40 40 40 70 100 804 mm Glass Coarse Coarse Coarse Coarse Clear coarseWindow frame Steel Steel Steel Steel Aluminium SteelWindow panes Single Single Single Single Double TripleWindow to wall ratio (WWR) 18 18 18 18 22 24Ventilation Available Available Available Available Nil AvailableVentilator glass Coarse Coarse Coarse Coarse Clear CoarseRoom type single/shared Shared Shared Shared Shared Single SharedNo of fans 1/2/3 1/2/3 1/2/3 1/2/3 1 1/2Light type (55 W) TFL TFL TFL TFL TFL TFLNo of TFL 1/2/3 1/2/3 1/2/3 1/2/3 1 1/2Computer/laptop 1/2/3 1/2/3 1/2/3 1/2/3 1 1/2Exhaust fan Nil Nil Nil Nil Nil NilCorridor breadth (m) 1.2 1.2 1.2 1.2 1.25 1.2

S. Dhaka et al. / Building and Environment 66 (2013) 42e53 45

(PMV) [25]. Significance test for different variables were also per-formed to evaluate the effect of thermal environment variable onthermal comfort state.

3. Results and discussion

3.1. Physical characteristics of the respondents

Subjects of this field research were young and healthy studentsof same age group (average age 19.6 years). Physical characteristicsof the respondents such as average height, weight and age haveshown in Table 3 along with body surface area calculated using Eq.(1). The average body surface area was found to be lower than thestandard surface area of human body (1.8 m2).

S ¼ 0:202M0:425H0:725 (1)

where, S is the body surface area (m2); H, height (m), andM, weightof the occupant (kg).

Renowned thermal comfort (human heat balance) model wasdeveloped by P.O. Fanger to evaluate thermal comfort. This modelproposed indices such as predicted mean vote (PMV) and predictedpercentage discomfort (PPD) to determine the state of thermalcomfort using Eqs. (2) and (3). PMV predicts the mean value of thevotes of a large group of persons on the seven-point thermalsensation scale, whereas PPD defines percentage of people pre-dicted to be dissatisfied due to local discomfort [4,5].

Table 2Instruments used during measurements.

Parameter Instrument Make

Air temperature HT30 heat stress meter Extech InstrumenRelative humidity HT30 heat stress meter Extech InstrumenGlobe temperature HT30 heat stress meter Extech InstrumenOutdoor temperature HT30 heat stress meter Extech InstrumenAir velocity Anemometer Lutron Electronic

PMV¼ 0:303e �0:036Mð Þþ0:028h i

� M�Wð Þ�H�Ec�Cres�Eres½ �(2)

PPD ¼ 100� 95e �0:03353PMV4�0:2179PMV2ð Þ (3)

Neutral temperature was determined through regression anal-ysis between room air temperature and thermal sensation vote. Theintersection of regression line with neutral or ‘0’ thermal sensationgives neutral temperature of the studied population. Mean valuesof PMV, PPD and neutral temperature were 0.88, 21, and 30.15 �C,respectively.

3.2. Existing thermal environmental conditions

Thermal comfort is influenced by thermal environment vari-ables; besides these psychological, physiological and behaviouralaspects also affect thermal perception of occupants [26]. Thermalsatisfaction in naturally ventilated buildings depends on theavailability of behavioural controls such as opening/closing ofwindows, doors, ventilators or change speed of fan. Table 4 showsdescriptive statistic of measured environment variables. Meanneutral temperature (average temperature of neutral or ‘0’ sensa-tion) was obtained 29.9 �C and mean PMV was found 0.88 at thistemperature. Statistical analysis has shown that neutral tempera-ture has strong correlation (r2 ¼ 0.67) with outdoor dry bulbtemperature. Significant variation in PMV was observed due to

Range Basic accuracy

ts 0e50 �C �1.0 �Cts 0e100% �3% RHts 0e80 �C �2 �Cts 0e50 �C (40 mm diameter, 35 mm high) �1.0 �Cs 0.1e30 m/s, (resolution 0.1 m/s) �2%

Table 3Physical characteristics of the respondents.

N ¼ 426 Height(m)

Weight(kg)

Body surfacearea (m2)

Age(years)

Clothinginsulation (Clo)

Mean 1.68 58 1.65 19.6 0.41Standard

deviation8.85 9.6 0.15 1.6 0.14

Maximum 1.92 92 2.14 27 0.82Minimum 1.25 36 1.21 17 0.19

S. Dhaka et al. / Building and Environment 66 (2013) 42e5346

elevated room air velocity (0e1.93 m/s) and variety in clothinginsulation.

Table 5 illustrates descriptive summary of environmental vari-ables, thermal sensation, thermal preference, neutral temperature,and PMV on monthly basis. It was found that about 62% studentsfound thermally dissatisfied at present conditions. No correlation(r¼ 0.08) was observed between thermal sensation and PMV index.This shows that field studies predict thermal comfort better thanheat balance model. Thermal sensation vote (TSV) of 0.06 wasobserved in August with mean clo of 0.40 (0.23e0.78 clo) and 44%students felt thermally satisfied. Average clothing insulation wasfound 0.41, 0.46, 0.44 and 0.55 from August to November,respectively.

3.3. Outdoor conditions and thermal neutrality

Maximum and minimum outdoor dry bulb temperature andrelative humidity during the study period were recorded 35.7 �C &95% and 27.6 �C & 16%, respectively. Fig. 2 shows seasonal variation

Table 4Descriptive summary of measured variables and thermal comfort indices.

Descriptive statistic To (�C) Ta (�C) Tg (�C) RH (%)

Mean 31.7 29.9 29.8 53.4Min 27.60 25.90 25.28 15.93Max 35.70 34.10 34.08 95.28SD 1.91 1.62 1.71 24.1r 0.34 0.45 0.45 �0.16

r - Correlation with thermal sensation; SD, standard deviation; PMV, predicted mean vo

Table 5Descriptive summary of measured environmental variables on monthly basis.

Month (data points) Descriptive statistic To (�C) Ta (�C) Tg (�C

Aug (131) Mean 31.8 29.9 29.8Min 29.9 27.0 27.1Max 33.6 32.2 31.9SD 1.1 1.1 1.1r 0.27 0.31 0.32

Sept (105) Mean 30.9 29.4 29.3Min 27.9 26.9 26.7Max 34.2 34.1 34.1SD 1.8 1.6 1.6r 0.48 0.63 0.63

Oct (131) Mean 33.2 31.2 31.1Min 30.7 26.8 27.5Max 35.7 33.8 33.8SD 1.6 1.1 1.1r 0.14 0.32 0.32

Nov (58) Mean 29.8 27.9 27.5Min 27.6 25.9 25.3Max 32.6 30.5 30.2SD 1.5 0.9 0.9r �0.25 0.03 0.11

in outdoor dry bulb temperature and relative humidity throughoutthe year for 2011, procured from Indianmeteorological department.Variations of measured outdoor and indoor temperatures, globetemperature, and relative humidity are presented in Fig. 3.

Thermal sensation of the respondents was recorded on ASHRAEseven- point thermal sensation scale (Cold ‘e3’, Cool ‘�2’, SlightlyCool ‘�1’, Neutral ‘0’, Slightly Warm ‘1’, Warm ‘2’ and Hot ‘3’). Fig. 4shows the statistical regression analysis of occupant’s thermalsensation vote (TSV) with room air temperature. The intersection ofregression line with neutral or “0” thermal sensation gives neutraltemperature, Tn. Neutral temperature of 30.15 �C (R2 ¼ 0.22) andbandwidth of neutral temperature was found between 25.9 and33.8 �C. Linear relationship in terms of room air temperature andthermal sensation was evaluated as shown in Eq. (4). It describesthat, increase or decrease in room air temperature may causethermal dissatisfaction to occupants.

TS ¼ 0:302Ta � 9:09 (4)

Only three respondents perceived hot (Ta ¼ 32.4 �C) and 10students felt cool (Ta ¼ 28.4 �C) during the study period. Differencein the thermal perceptionwas observed between males and femalerespondents. Girls perceived neutral at slightly lower temperature(0.25 �C) than boys (30.1 �C). About 62% students’ (including bothmale and females) were thermally discomfortable at presentenvironmental conditions, i.e. Tn ¼ 30.15 �C. About 22% and 32%occupants were feeling slightly warmth and slightly coolness at thepresent environment. It was predicted that 22% and 32% occupantswhich were close to neutral sensation can be shifted towards

Va (m/s) TSV TP Tn (�C) PMV

0.45 �0.04 �0.5 29.9 0.880.0 �2.0 �2.0 25.9 0.411.93 3.00 1.00 33.80 3.340.44 0.93 0.77 1.53 0.380.14 �0.46 0.29 0.08

te.

) RH (%) Va (m/s) TSV TP Tn (�C) PMV

72.9 0.49 0.06 �0.76 29.7 2.5057.1 0.0 �2.0 �2.0 27.0 0.3190.1 1.8 3.0 1.0 31.7 3.07.4 0.4 0.9 0.6 1.1 0.5

�0.23 0.25 e �0.33 0.48 0.05

74.6 0.46 �0.29 �0.53 29.5 2.6747.8 0.0 �2.0 �2.0 27.1 1.0895.3 1.9 3.0 1.0 32.8 3.3411.1 0.5 1.0 0.8 1.3 0.3�0.62 0.11 e �0.49 �0.52 0.21

30.5 0.6 0.23 �0.61 31.2 2.4617.2 0.0 �2.0 �2.0 28.2 1.3446.2 1.9 2.0 1.0 33.8 2.77.2 0.4 0.8 0.7 1.0 0.2

�0.11 0.06 e �0.54 �0.16 0.04

23.1 0.06 �0.41 0.22 27.8 2.2915.9 0.0 �2.0 �1.0 25.9 0.4136.8 0.8 1.0 1.0 28.9 2.54.1 0.1 0.7 0.7 0.9 0.20.14 0.19 e �0.29 �0.55 0.18

Fig. 2. Variation of outdoor dry bulb temperature and relative humidity in Jaipur city.

y = 0.3017x - 9.0954R² = 0.2241

-3

-2

-1

0

1

2

3

24 26 28 30 32 34 36

The

rmal

Sen

satio

n V

ote

Room air temperature (oC)

Fig. 4. Regression analysis of thermal sensation vote and room air temperature.

S. Dhaka et al. / Building and Environment 66 (2013) 42e53 47

neutral condition by the adoption of behavioural controls availablein the rooms.

Difference in thermal perception was observed for single, dou-ble and triple occupied rooms. Respondents in single occupiedroomsweremore comfortable at higher temperature (30.4 �C) thandouble (30.1 �C) and triple (29.83 �C) occupied rooms because ofroom surface to volume ratio and limited means of controls.

3.4. Effect of mean radiant temperature

Radiant asymmetry results in discomfort. Warm glazing, roofand walls create radiant asymmetry but glazing is the most com-mon cause of radiant asymmetry [27]. Mean radiant temperature(MRT) was measured using wet bulb globe thermometer having38 mm ball diameter [28,29]. Fig. 5 has shown a strong relationshipbetween room air temperature and globe temperature withR2 ¼ 0.96. Observed temperature difference between room airtemperature and globe temperature was minimal (Ta � Tg < 0.5 �C)and therefore room temperature has been considered as operativetemperature. Only two data sets were deviated (2.1 �C) significantly(>2 �C, n ¼ 2). During the study, it was observed that most of thefemale students kept their doors closed most of time and thereforetheir room temperature was found slightly higher and neutraltemperature was slightly lower than male students.

3.5. Thermal preference of students

Thermal preferences (TP) of the students were recorded onNicol’s five point scale (‘�2’, much cooler; ‘�1’, a bit cooler; ‘0’, no

0

20

40

60

80

100

24

26

28

30

32

34

36

38

Mid Aug

End Aug

Start Sept

Mid Sept

End Sept

Start Oct

Mid Oct

End Oct

Start Nov

Rel

ativ

e hu

mid

ity (

%)

Tem

pera

ture

(o C)

Tout Ta Tg RH

Fig. 3. Variation of outdoor and indoor DBT, globe temperature and relative humidityduring study period.

change; ‘1’, a bit warmer and ‘20, much warmer) based on theexisting thermal environment of the hostel rooms.Much cooler or abit cooler vote was reported by the occupants when their thermalsensation vote was on hot or warm side. The mean thermal pref-erence was obtained to be �0.52. The subjects who want ‘nochange’ on the thermal preference scale were found thermallysatisfied with the existing thermal environment. Fig. 6 shows thegraphical representation of thermal sensation vote, thermal pref-erence, mean room air temperature and standard deviation at theperceived room temperature.

Mean room air temperature observed was between 25.9 �Cand 34.1 �C (AugusteNovember). Results of the study shows that26% occupants preferred to live at the existing environmentconditions and more than 50% (239) respondents preferred toshift towards slightly cooler environment, i.e. they preferred touse some means of air conditioning/air cooling. Fig. 7 shows thebox plot between thermal preference and room air temperature.Preferred temperature of the group considered in the study wasfound to be 27.4 �C (R2 ¼ 0.19, Y ¼ �0.2056X þ 5.632) which ishigher than the standard comfort temperature bandwidth ofNational Building Code [19] but lower by 2.75 �C as compared tothe neutral temperature of 30.15 �C. Preference of lower tem-perature by the group suggests that most of the students werefeeling slightly warmer and dissatisfied with the existing envi-ronmental condition in the hostels. Table 6 shows the summaryof thermal sensation and thermal preference vote at roomconditions.

Fig. 5. Relationship between room air temperature and globe temperature.

Fig. 6. Occupants’ thermal sensation, thermal preference, mean room temperature andstandard deviation at room temperature.

Fig. 7. Distribution of thermal preference and room air temperature for the studyperiod.

S. Dhaka et al. / Building and Environment 66 (2013) 42e5348

3.6. Effect of relative humidity

Sensation of relative humidity based on the recorded data hasbeen marked on seven-point scale (�3 to 3) such as very dry ‘�3’,moderately dry ‘�2’, slightly dry ‘�1’, acceptable ‘0’, slightly hu-mid ‘1’, moderately humid ‘2’, and very humid ‘3’ as shown in

Table 6Summary of sensation and preference of temperature and RH at room conditions.

Temperature

N ¼ 426 Cold Cool Slightly c

Thermal sensation vote 0 10 136

Thermal preference vote e 20 239

Mean room temperature (�C) 0 28 29

Standard deviation at mean room temp 0 1.10 1.50

Relative humidity

N ¼ 426 Very dry Moderatelydry

Slightly d

RH sensation vote 1 10 68RH preference vote e 12 173Mean room RH (%) 18.2 35 36.7Standard deviation at mean room RH 18.2 22.4 19.3

Fig. 8. Acceptable relative humidity of the group was found to be36% (R2 ¼ 0.224, Y ¼ 0.019X � 0.677) from the regression analysis.In the group of 426 students, about 37% experienced slightly hu-mid at the existing room conditions. Acceptable humidity for fe-male students was slightly higher (41%) than male occupants(37%). Fig. 9 shows the sensation of relative humidity, preferenceof RH, mean RH of the room and standard deviation at mean RH. Itwas noticed from the study that about 40% occupants preferred toreside at slightly dry conditions. About 11% students preferred toreside in slightly humid (more than 47% of RH) conditions as thesestudents were fromwarm & humid climatic regions of the countrysuch as Orissa, Chennai, Mumbai, and Goa. Table 6 shows thesummary of sensation and preference of relative humidity at roomconditions.

3.7. Effect of air velocity

The role of air movement becomes important in naturallyventilated buildings under hot and dry conditions of Jaipur city.Air velocity was measured at four points with respect to theoccupant at the height of 1.1 m from the floor level. Minimumand maximum air velocity was observed 0 m/s and 1.93 m/s,respectively. Total 209 (49%) students felt comfortable at theexisting average room air velocity of 0.45 m/s. A weak correlation(r ¼ 0.14) was found between room air velocity and thermalsensation.

3.8. Overall comfort conditions

During the study occupants were asked to judge the ‘overallthermal comfort’ based on their experience of room temperature,RH and air velocity [30]. The recorded perception was analysed onfive-point thermal acceptance scale as presented in Fig. 10. It wasobserved that about half of the students (51%) of this group feltcomfortable and 42% were slightly comfortable at present roomconditions. As the overall thermal satisfaction state shifts fromcomfortable state to slightly comfortable state and then todiscomfortable state the number of students perceiving neutralstate decreases and feeling of slightly warm state increases. Most ofthe students use available behavioural controls such as opening ofwindows, door and louvers of the ventilator, switch on fan toachieve better comfortable conditions. There are fewer votes onvery discomfortable and very comfortable state.

ool Neutral Slightly warm Warm Hot

164 95 18 3

112 55 0 e

30 31 31 32

1.50 1.40 1.00 2.30

ry Acceptable Slightly humid Moderately humid Very humid

154 157 30 6192 48 1 e

46.24 65 68.5 78.723.4 20 16.5 11.3

Fig. 8. Regression analysis of relative humidity sensation and relative humidity.Fig. 10. Assessment of indoor environment based on overall thermal comfort.

S. Dhaka et al. / Building and Environment 66 (2013) 42e53 49

3.9. Adaptive opportunities and thermal comfort conditions

Adaptive comfort models predict thermal perception and ther-mal comfort of occupants in a better way than models associatedwith fixed thermal environment variables. Personal controls(clothing and activity) along with behavioural room controls affectthermal sensation and thermal comfort of occupants greatly innaturally ventilated buildings.

Clothing affects heat exchange between occupant body andsurrounding environment, therefore occupant clothing insulationis used to estimate the specific environmental conditions needed toachieve thermal comfort at different activity levels. Occupantsprefer to wear lighter clothes during summer in naturally venti-lated buildings for making themselves comfortable. It was observedthat female used to wear similar clothes and clothing insulationwas higher than males clothing insulation because of socially andculturally acceptable clothing practices for Indian females. Twenty-four clothing insulation choices have been considered in the studyranging from 0.02 Clo (inner garment) to 0.61 Clo (polyester sari &blouse). Many of the students were found wearing casual T-shirtsand shorts (0.20 Clo) with an average clothing resistance of 0.41 Clo(min. 0.19 Clo andmax. 0.82 Clo). Average activity level of the groupwas found to be 1.03 met although students were observed to beeither lying down (0.7 met) or sitting passively (1 met) or sittingand working (1.2 met).

Fig. 11 shows preferences to use control features to restorethermal comfort state. It was observed during the study that due tolack of routine maintenance many of the windows were found with

Fig. 9. Sensations of RH, RH preference, mean RH at room conditions and standarddeviation at mean RH.

limited accessibility. Louvers of the ventilators located above thewindowwere either closed or found partially open. Occupants useddifferent means such as window opening, ventilator opening, dooropening, use of fan, change of fan speed, taking bath, hanging ofwet clothes and spray of water on the exposed outer walls formaking themselves comfortable. Less than 1% students were foundwith desert coolers for getting rid of thermal discomfort.

It was observed that window opening (321) was the first pref-erence of the students followed by use of fan/change fan speed(296) and lastly door opening. Some students preferred to take bathor spray water on outer exposed walls or use of wet clothes on theirwindows for comfortable environment. Some students also com-plained about local discomfort due to excessive sweating on neckand head. In hostel B and hostel 3, there were steel screens on thewindows therefore occupants preferred to use fan/change fanspeed instead of window opening. Results have shown that 74% of164 students feeling neutral were due to either window opening orwindow opening and door opening both.

Neutral temperature equation describes the relationship be-tween outdoor temperature and room air temperature [31]. Sta-tistical relationship between neutral temperature and outdoortemperature was obtained in the study as shown by Eq. (5).

Tn ¼ 0:6478To þ 9:368 (5)

It was observed that this comfort equation predicts/estimatesneutral temperature for naturally ventilated hostel buildings incomposite climate. This equation was compared to other modelsproposed for hostel buildings, office and residential buildings as

0

20

40

60

80

100

Hos

tel 1

Hos

tel 2

Hos

tel 3

Hos

tel 7

Hos

tel B

Gan

ga

Hos

tel

Res

pond

ent

all

Per

cent

tage

res

pond

ents

Open window Open door Switch on/Off ACSwitch on Fan Room Cooler-on Others

Fig. 11. Priorities of use of behavioural control options for different hostel buildings.

Table 7Comparison of comfort temperature for different building types.

Sr. no. Hostel buildings Office building Residential buildings

Present paper Dahlan [17] De dear and Brager [9] Indraganti [21]

Equation Tcomf ¼ 0.302Ta � 9.09 Tcomf ¼ 0.421To � 13 Tcomf ¼ 0.31Ta þ 17.6 Tn ¼ 0.31Tg � 9.1Neutral temperature (�C) 30.15 �C 29.8 �C e 29.oCOutside temperature (�C) 27e36 23.4e32.6 e 27e40RH (%) 16e95 49e80 50 14e76Air velocity (m/s) 0e1.93 0.2e1.6 0.25 0e4Activity (met) 0.7e2.0 1.0 1.3 0.7e2.0Clothing (clo) 0.19e0.82 0.22e0.56 0.5(average) 0.19e0.84

S. Dhaka et al. / Building and Environment 66 (2013) 42e5350

shown in Table 7. It is important to notice that the thermal comfortcondition of non air-conditioned hostel building is quite differentfrom naturally ventilated office and residential buildings.Comfortable temperature was found higher in the present studycompared to other hostel studies.

4. Conclusion

Field study of thermal comfort was carried out in six naturallyventilated hostel buildings of composite climate considering Class-II protocol of field measurement during summer & monsoon sea-son. Present study evaluated the effect of existing thermal envi-ronmental conditions on a group of 429 students (average age of19.6 years) in the hostels. A questionnaire based survey was con-ducted in order to collect subjective and objective information ofthe occupants. Collected data were analysed statistically for ascer-taining neutral temperature of the group as well as for female andmale students. The effects of personal controls such as window anddoor opening, opening of ventilator louvers, change of fan speed,etc. have been determined on the neutral temperature. The role ofroom occupancy has also been studied.

Neutral temperature of the group was obtained to be 30.15 �Cfrom the statistical analysis for average clothing of 0.41 Clo, activitylevel of 1.03 met when average air velocity in the room andacceptable relative humidity was 0.45 m/s and 36%, respectively.

Following are the key conclusions of the study:

- Neutral temperature of the group was found between 25.9 �Cand 33.8 �C which is higher than (23e26 �C) the nationalbuilding code of India although the preferred temperature was2.75 �C lesser than the comfortable temperature of 30.15 �C.

- Neutral temperature for female students was slightly lower(29.9 �C) than male students (30.1 �C). On the contrary femalestudents preferred higher humidity (46%) than male students.

- Single, double and triple occupancy respondents were ther-mally satisfied at neutral temperature of 30.4 �C, 30.1 �C and29.8 �C, respectively and their thermal preferences were alsodifferent.

- Thermal comfort index e PMV of the group was found to be0.88 which is higher than the standard value of �0.5.

- Regression analysis has shown that the overall thermal comfortwas found statistically significant with thermal sensation(r < 0.05) and RH sensation (r < 0.05). It was observed thatcomfortable temperature has a strong correlation (r ¼ 0.67)with outdoor dry bulb temperature.

- Students were from different domicile and climatic zones.Students from warm and humid climates preferred higherhumidity. These students were not comfortable with theexisting environmental conditions of the hostels and some-times preferred to take bath or spray water on outer exposed

walls or use of wet clothes on their windows for makingthemselves comfortable.

- Adaptive thermal comfort model developed for naturallyventilated student hostels differs from the adaptive models ofthermal comfort evaluated for office and residential buildingsdue to different occupancy patterns, age group, activities,behaviour and lifestyle of students.

- Overall thermal comfort level of female students were foundbetter than male students in the existing environment of nonair-conditioned hostel building although their clothing insu-lation level were little higher.

- First preference of the students was window opening (321,N ¼ 426) followed by use of fan/change fan speed (296) andlastly door opening to restore comfort state.

Thus, study concludes that availability of behavioural controlsand implementation of building code can improve thermalenvironmental conditions in naturally ventilated hostel buildingsand thermal dissatisfaction can also be reduced upto a largeextent.

Acknowledgement

Author would like to thank DAAD (German Academic ExchangeService, Bonn Germany) for providing financial assistance andfellowship to carry out the present research in the group of Prof.Andreas Wagner, Building Science Group (fbta), Karlsruhe Instituteof Technology (KIT) Germany.

Nomenclature

To, Tout Outdoor air temperature (�C)Tg Globe temperature (�C)Va Air velocity (m/s)Clo Clothing insulation, 1 Clo ¼ 0.155 m2-�C/WR2 Coefficient of determinationTP Thermal preferencePMV Predicted mean voteTSV Thermal sensation voteASHRAE American Society of Heating Refrigerating and Air

conditioning EngineersTa Room air temperature (�C)RH Relative humidity (%)NV Naturally ventilatedMet Metabolic rate, 1 met ¼ 58.2 W/m2

r Coefficient of varianceTSS Thermal sensation scalePPD Predicted percentage dissatisfiedTS Thermal sensation

S. Dhaka et al. / Building and Environment 66 (2013) 42e53 51

Appendix A. Part A and Part B of the questionnaire

S. Dhaka et al. / Building and Environment 66 (2013) 42e5352

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