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Energy and Buildings 42 (2010) 273281

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Contents lists available at ScienceDirect

Energy and

journa l homepage: www.e ls1. Introduction

Current literature on thermal comfort, features research fromthe West, Australia, Asia and a few developing countries in Africa[17] but has very little reported from India [8,9]. The aspect ofthermal comfort is very important to the designer as it affects theenergy program of a building. Moreover, poor indoor thermalcomfort has several adverse effects on the user [10]. Thermalcomfort standards specied in Indian codes are based on ASHRAEstandards rather than on empirical data collected from localregions. TheNational BuildingCodeof India [11] advocates theuseof two narrow ranges of temperatures for, winter (2123 8C) andsummer (2326 8C). These are meant for air-conditioned build-ings of any type in any climatic zone in India [11,12]. ASHRAE-Std55 [13] followed by Indian codes was criticized for its systematicdiscrepancies due to the straightforward application of Fangersheat balance equation [14]. Adopting these uniform standardswas deplored by the research community [1518], especially inthe wake of the Kyoto Protocol [19] and anthropogenic climate

change [20]. The energy consumption in Indian residentialbuildings is the highest among all the Asia Pacic Partnership(APP) counties [21]. Moreover, the country is undergoing aparadigm shift in energy consumption [22]. About 73% of theenergy consumed in Indian residential buildings is used forlighting and ventilation controls to provide thermal and visualcomfort indoors [12]. Given Indias population base and theuniform comfort standards [23], the ramications of this over usebecome clear.

The adaptive thermal comfort model is the rst step, in thedevelopment of sustainable thermal comfort standards. Itincludes various environmental, behavioural and psychologicaladaptations and thus assumes great importance. These adapta-tions are known to affect the thermal acceptance of anenvironment [15]. There are very few thermal comfort studieson Indian subjects found in the literature. Thus, a eld study inapartments in Hyderabad was conducted with an aim to under-stand the thermal sensation, neutrality, preference and accep-tance etc., of occupants living here.

Indian population is diverse with varying economic levels andenergy demands. It was evident that the expectation levels ofvarious groups of subjects were different, affecting the accept-ability of the thermal environment [7,24]. Therefore, one of theobjectives of this study was to study the effect of economic group,tenure, gender and age of the subjects, on their thermal responses.

Adaptive comfort model

Field study

Apartments in Hyderabad

Economic group

Energy

Comfort standards

Indoor air quality sensation

with thermal comfort. However, thermal acceptance of women, older subjects and owner-subjects was

higher. Economic level of the subjects showed signicant effect on the thermal sensation, preference,

acceptance and neutrality. The comfort band for lowest economic group was found to be 27.333.1 8Cwith the neutral temperature at 30.2 8C. This is way above the standard. This nding has far reachingenergy implications on building and HVAC systems design and practice. Occupants responses for other

environmental parameters often depended on their thermal sensation, often resulting in a near normal

distribution. The subjects displayed acoustic and olfactory obliviousness due to habituation, resulting in

higher satisfaction and acceptance.

2009 Elsevier B.V. All rights reserved.

* Corresponding author at: Climarc, 6-3-581, B-203, Keshav Dale Apartments,

Khairatabad, Hyderabad 500004, India. Tel.: +91 4023305233; +91 9866676586

(mobile).

E-mail address: maindraganti@gmail.com (M. Indraganti).

0378-7788/$ see front matter 2009 Elsevier B.V. All rights reserved.doi:10.1016/j.enbuild.2009.09.003Effect of age, gender, economic group anin residential buildings in hot and dry

Madhavi Indraganti *, Kavita Daryani Rao

Architecture Department, Jawaharlal Nehru Architecture and Fine Arts University, Hyd

A R T I C L E I N F O

Article history:

Received 21 May 2009

Received in revised form 3 September 2009

Accepted 4 September 2009

Keywords:

Thermal comfort

A B S T R A C T

Energy consumption in Ind

Indian standards specify c

nation. However, thermal

apartments was done in

climate. This survey invo

different groups: age, genenure on thermal comfort: A eld studymate with seasonal variations

ad, India

residential buildings is one of the highest and is increasing phenomenally.

ort temperatures between 23 and 26 8C for all types of buildings across thefort research in India is very limited. A eld study in naturally ventilated

8, during the summer and monsoon seasons in Hyderabad in composite

d over 100 subjects, giving 3962 datasets. They were analysed under

, economic group and tenure. Age, gender and tenure correlated weakly

Buildings

evier .com/ locate /enbui ld

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In addition, the occupant responses to other environmentalparameters were also investigated.

2. Research methods

2.1. Location, building types and envelope characteristics

Spread over an area of 260 km2, and 540 m above the mean sealevel, Hyderabad has a population of 5.7 million [25] and is thecapital of the state of Andhra Pradesh. Hyderabad, lying on 178270Nlatitude and 788280E longitude in Deccan Plateau, has inland

M. Indraganti, K.D. Rao / Energy and Buildings 42 (2010) 273281274composite climate with four seasons: winter, summer, monsoonand post monsoon [12,26]. The research was conducted in thesummer month of May and monsoon months of June and July in2008 in Hyderabad. These seasons have extreme and high levels ofdiscomfort respectively. The subjects were studied under thetransverse survey for 1 day and in longitudinal survey for the next4 days in eachmonth. A total of 33 days were spent in surveys [27].

Five naturally ventilated apartments named KD, SA, RA, KA andRS were surveyed. They are all located in the residential areas ofcentral and eastern parts of Hyderabad. The buildings are up to sixstories high and are 530 years old. KD has 13 ats per oor; SA andRA have three each, while each of KA and RS have four ats peroor. The oor area of the ats surveyed varied between 65 and200 m2, with KD having the largest area and RS and KA thesmallest. All the buildings have plastered brick walls (115230 mm thick), except RS, which has hollow cement block walls(150 mm thick).

2.2. Subject sample

A brief description of the sample of the investigated subjects isprovided in Table 1. A total of 3962 datasets were collected fromabout 113 occupants of 45 ats in these apartment buildings. Amaximum of 33 subjects from KD, 15 from SA, 21 from RS, and 22from RA and KA each have voluntarily participated in the surveys.The sample size varied slightly in each month, as some subjectshave refused to participate in the surveys on some days. However,variation in both male and female samples in all the surveys wasnegligible, as the same subjects were retained most of the time.Therefore, the database constituted the responses of about 35malesubjects (35%) and about 64 female subjects (65%), who haveparticipated in most of the surveys. They were in the age group of1769 years with male and female average age of 40.14 years(SD = 14.0) and 42 years respectively. They were all healthyIndian nationals living in the surveyed ats for over 3 months. Allof them were assumed to be naturally acclimatised to the climateof Hyderabad.

The subjects were also grouped based on their tenure. Ownersconstituted about 55% and tenants 45% of the data collected. RS andKA constitutedmostly tenants while SA had only owners. KD had amajority of owners and a sizeable number of tenants as well. RAhad only a few tenants. There were differences in the lifestyle,economic condition etc. of the subjects living in the apartment

Table 1Sample size of investigated subjects (all data).

Age group (years) Transverse survey, n Longitudinal survey, n

Males Females Males Females

60 39 79 113 277

n, number of votes recorded.buildings investigated. These resulted in differences in theirthermal comfort perception, as also observed in Han et al.s Harbinstudy [7]. Therefore, the subjects of the ve ats were grouped intothree classes as well, to enable further analysis in this direction.Group-1 (Gr-1, higher economic class), constituted subjects fromKD, while Group-2 (Gr-2, intermediate economic group) con-stituted subjects from SA and RA, where as Group-3 (Gr-3, lowereconomic group) had subjects from KA and RS. Each group had 3235% of the total subjects.

The questionnaire had six sections namely: apartment buildingand at identication; background information; current clothing;activity level; thermal comfort responses; and adaptation meth-ods. Table 2 shows some of the scales used in this study. ASHRAEsseven-point scale of warmth, Nicols ve-point scale of preferenceand ASHRAEs scale of acceptance were used in this study. Thermalacceptance was measured directly from the response to thequestion Can you accept the present hot environment or not? Itmeasures the subjects overall satisfaction with his/her thermalenvironment [2]. In addition, the subjects sensation and pre-ference for other environmental variables were measured in alltransverse surveys using the scales shown in Table 2. Thetransverse questionnaire was prepared both in English and Telugu,the local language based on McCartney and Nicol [28]. The choiceof language of the questionnaire was left to the subject. BothTelugu and English questionnaires were tested for similarity inmeaning and semantics, prior to the actual administration. Thequestionnaires and the details of apartment buildings surveyed arepresented in Indraganti [29].

Clothing insulation was estimated based on the standardchecklists [30]. However, a near equivalent ensemble in thestandard list was not found for Indian Sari. Therefore, clothinginsulation for Indian sari was estimated based on the equation,Icl = 0.00103W 0.0253, where Icl is the clothing insulation andWis the weight of the sari in grams (g) [31]. A petticoat was alwaysworn with this outt. Therefore, to the Icl value obtained using theabove formula, 0.15 is added to account for its insulation. Theinsulation of cotton and polyester saris was found to be 0.54 and0.61 respectively. In addition, all the Icl values were added 0.04 Clofor undergarments. When the subject was seated or was foundresting, 0.15 Clo for upholstery insulation was also added to this[32]. The overall clothing insulation values varied from 0.19 to0.84 Clo in all the 3months. Metabolic rates were estimated for theactivities lled in by the subjects, using the activity databases ofASHRAE Standard 55-1992. These values ranged from 0.7 Met(sleeping) to 2.0 Met (standing working) in this survey. The bodysurface area for all the subjects was estimated (mean range = 1.671.9 m2, SD = 0.2) [33].

2.3. Measurement of indoor and outdoor environmental data

The indoor environment was measured following the Class-IIprotocols for thermal comfort eld studies [30]. A set of calibrated,digital hand held instruments were used in this study. Fourenvironmental variables of thermal comfort viz: air temperature(Ti), globe temperature (Tg), relative humidity (RH) and air velocity(AV) were measured, while the subject lled in the thermalquestionnaire. Indoor air temperature and humidity were mea-sured using Sisedo Hygro therm from China. Globe temperaturewas measured using Eurolab digital thermometer. Its tempera-ture probe was kept at the centre of a black painted table tennisball [34]. Air velocity was measured using Lutron vaneAnemometer (Model: AM-4201). Indoor illumination was mea-sured using pocket type Lux meter (Model: Lutron-LX-101) with arange of 050,000 lux. The subjects act as human-meters of theirenvironment [15]. Therefore, the survey was conducted between7 am and 11 pm three times a day: morning, midday and in the

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Table

2Scalesusedto

measure

subjectiveresponse

tootherenvironmentalvariablestransversesurvey.

Scale

point(vote)

Sensationof

Preference

for

Effect

onproductivity

Airmovement

Humidity

Lightinglevel

Background

noiselevel

Airquality

Airmovement

Humidity

Lightinglevel

Noiselevel

3Very

high

Very

humid

Very

bright

Very

quiet

Excellent

2High

Humid

Bright

Quiet

Good

Much

less

air

movement

Much

drier

Much

dim

mer

Much

noisier

Much

higherthan

norm

al

1Slightlyhigh

Slightlyhumid

Slightlybright

Slightlyquiet

Slightlygood

Abitless

air

movement

Abitdrier

Abitdim

mer

Abitnoisier

Slightlyhigherthan

norm

al

0Neitherhigh

norlow

Neitherhumid

nordry

Neitherbright

nordim

Neithernoisy

norquiet

Neitherbad

norgood

Nochange

Nochange

Nochange

Nochange

Norm

al

1Slightlylow

Slightlydry

Slightlydim

Slightlynoisy

Slightlybad

Abitmore

air

movement

Abitmore

humid

Abitbrighter

Abitquieter

Slightlylowerthan

norm

al

2Low

Dry

Dim

Noisy

Bad

Much

more

air

movement

Much

more

humid

Much

brighter

Much

quieter

Much

lowerthan

norm

al

3Very

low

Very

dry

Very

dim

Very

noisy

Very

bad

M. Indraganti, K.D. Rao / Energy and Buildings 42 (2010) 273281 275evening. A minimum interval of 2 h was maintained between twoconsecutive readings. The instruments were placed at 1.1 m levelfrom the oor, on a tray, xed to a tripod stand. The survey washeld in the living/dining rooms of the ats with the subjects seatedor engaged in their everyday activities. The tripod was placed closeto the subject while taking the measurements causing leastdisturbance to the subject. Maximum and minimum outdoortemperature and outdoor humidity values for all the days of thesurvey were obtained from the local meteorological station.

3. Results and discussion

3.1. Outdoor and indoor environments

The month of May was very hot and dry with high diurnalvariation (mean diurnal range 13.1 K, SD = 0.95) in outdoortemperatures (To). There was slight variation in outdoor tempera-ture during May (mean To = 33.9 8C, SD = 0.65). The relativehumidity (RHo) was fairly low and was more variable (meanRHo = 32.6%, SD = 6.8). The maximum outdoor temperaturerecorded during the survey was 41.7 8C. The mean To in Julyremained at around 28.7 8C and varied slightly (SD = 0.6). Therelative humidity in June was fairly moderate and variable (meanRHo = 52.3%, SD = 3.2) increasing with summer showers towardsthe end of themonth. In July, it was the highest (mean RHo = 58.8%,SD = 4.1). In June and July, mean outdoor temperature was belowthe skin temperature, while the mean outdoor humidity variedbetween 50 and 70%.

The indoor temperature ranged between 26.6 and 42 8C acrossdifferent apartment buildings and ats. The lowest temperaturewas recorded during the morning, while the mid day temperaturein roof exposed (RE) (i.e., top oor) ats in KD was the highest.Extensive use of air coolers in KD, resulted in higher mean indoorhumidity and lower air temperature in the RE ats, than comparedto the other ats in the month of May (SD = 4.7). Temperaturerecorded in RE ats was found to be much higher, compared to thelower oor (LF) recordings in all the months of the survey. Meanindoor air velocity remained at around 0.4 m/s (SD = 0.10.2;range = 04 m/s) in all the months. The indoor globe temperaturecorrelated robustly with air temperature (r = 0.959), To (r = 0.771),relative humidity (r = 0.868), and ceiling temperature (r = 0.804).Therewas however, variation found in individual buildings in theirindoor climate. Details of the subject sample, indoor and outdoorenvironments recorded during the survey are presented inIndraganti [35].

3.2. Comparison between the thermal responses of various groups of

subjects

3.2.1. Effect of age

Although, both thermal sensation (TS) and overall comfort (OC)correlated rather weakly with age (r = 0.04, n = 3962 andr = 0.042, n = 1042 respectively), the relationship was found tobe signicant at 5% level (p < 0.001). Relationship of subjects agewith thermal sensation, thermal preference, thermal acceptanceand overall comfort is shown in Table 3.

These measures of thermal comfort reveal four interestingfacts:

(1) Thermal sensation of older people was slightly lower than thatof the young, with a lower mean prefernce vote.

(2) Owing to their low metabolic rates and sedentary life style,they have given a low TS vote than their younger counterparts.Older subjects were less mobile due to poor health etc., andexercise limited access to controls. This affected their TS/OCvote psychologically [30,36].

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f subjective responses on various comfort scales (all data transverse and longitudinal

Thermal acceptance Overall comfort

years

)

Age

controls has reduced. As a result, the subjects in lower economicgroups recorded lower TSm, than Gr-1 in June and July. Moreover,the indoor temperature in lower economic groups was higher in allthe months surveyed. Consequently, the globe temperature whenvoting neutral (Tgnv) in lower economic classes was much higherthan the two higher economic groups (Tgnv-Gr-3-May = 34.3 8C,SD = 1.31; Tgnv-Gr-1-May = 31.53 8C, SD = 1.83).

A similar pattern was observed in mean thermal preference(TPm) vote as well. TPm varied only slightly in the month of May. Apenchant for cooler environment was lower in lower economic

Table 5Economic group and tenure wise thermal non-acceptance (%) (all data). Owners

displayed a higher acceptance of the thermal environment in all the economic

groups.

Economic group May June July

Owners Tenants Owners Tenants Owners Tenants

Gr-1 29 45 8 11 3 7

Gr-2 32 39 4 0 3 0

Gr-3 16 28 2 4 2 3

r economic groups have a higher neutral temperature and a much higher comfort band.

Constant Neutral

temperature,

Tn (8C)

Comfort band

lower limit

Comfort band

upper limit

8.451 28.4 25.0 31.7

9.499 29.2 26.2 32.3

10.39 30.2 27.3 33.1

9.06 29.2 26.0 32.5

M. Indraganti, K.D. Rao / Energy and Buildings 42 (2010) 273281 277classes, especially in themonths of June and July. It is imperative tonote that, subjects of Gr-1 preferred much lower temperatures,even when their indoor temperatures were the lowest. Meanthermal acceptance was also higher in lower economic classes [7].Similarly, mean overall comfort vote was higher in all the monthsin the lower economic classes. The differences were more evidentin the months of moderate temperature, i.e., June and July, as therewas a lesser exposure to air-conditioned environments at home inthese months.

In addition, greater proclivity was found in Gr-1, for a non-adaptive lifestyle. Moreover, subjects in Gr-1 ats undertookclothing and behavioural adaptations less. They depended mostlyon A/Cs and coolers inMay and on fans inmonsoon. Subjects in Gr-2 undertook behavioural and clothing adaptations in addition tofans. A few have used A/Cs as well. Subjects in Gr-3, had no accessto A/Cs and have exploited behavioural, personal environmentalcontrols like doors and windows etc. better. Subjects in lowereconomic classes (Gr-2 and -3) displayed higher levels ofsatisfaction and tolerance with their thermal environment. Thisreected in a TSm close to neutrality in June and July (TSm = 0.210.42) even under higher indoor temperatures. Understandably, ahigher percentage of occupants in these groups have voted neutral.Past and immediate thermal history of the subjects affected thesephenomena also, as observed by Han et al. [7].

3.2.3.1. Neutral temperature and comfort range. The linear regres-sion of the thermal sensation on the indoor globe temperatureacross the three economic groups yielded different neutraltemperatures for each group (Table 4). The subjects in Gr-1 hadthe lowest neutral temperature while Gr-3 subjects had thehighest. This was due to high usage of air conditioners, loweradaptation levels and higher expectation levels of Gr-1 subjects.The comfort band for Gr-3 was found to be 27.333.1 8C, withneutral temperature at 30.2 8C (r = 0.75). This band is found to bemuch higher than the comfort band (2326 8C) specied in Indianstandards [11]. A neutral temperature of 29.2 8C and a comfortrange between 26.0 and 32.5 8C was obtained on all data throughlinear regression of thermal sensation (TS) on indoor temperature(Tg). The coefcient of correlation (r), obtained for the regressionline equation (y = 0.31x 9.06), is moderate at 0.65. The usage ofair conditioners and air coolers was lesser in Gr-2 and Gr-3. As aresult, TS vote followed the indoor temperature closely, resultingin robust correlation in Gr-2 (r = 0.71) and in Gr-3 (r = 0.75) than inGr-1 (r = 0.51). A detailed discussion on the adaptive modeldeveloped, can be found in Indraganti [29].

Table 4Group wise regression analysis of Tg and TS for neutral temperature (all data). Lowe

Economic group R2 Correlation

coefcient, r

Regression

slope

Group-1 0.258 0.51 0.298

Group-2 0.522 0.72 0.325

Group-3 0.56 0.75 0.344

All data 0.421 0.65 0.313.2.4. Effect of tenure

Thermal responses of subjects were analysed separately basedon their declared ownership/tenancy status. The inuence of tenure(r = 0.006) on TS and TP was very low. However, the effect ofownership on the way controls were used and as a result, thethermal acceptance (TA) vote was rather interesting. Conceivably,the subject gave TS and TP votes in response to his/her immediatethermal environment. However, TA vote indicated the subjectsoverall satisfaction with the thermal environment also. It isimperative to note that the percentage of tenants votingunacceptable on TA scale was high in all the months. Therewas a marked difference in the TA vote between owners andtenants as shown in Table 5.

This was possibly due to the fact that, thermal acceptability wasrelated to TS which was affected by several factors including theavailability of controls. Ownership and the employment ofstructural environmental controls were strongly related(r = 0.34, p < 0.001, signicant at 5%). Owners undertook greatermeasures in the form of structural controls to achieve thermalcomfort, as shown in Fig. 2(a). In addition, owners hadpsychological satisfaction with their tenement and had lesserproclivity to give a non-acceptance vote. This resulted in a higherTA vote among owners in all the months and in all the groups.Conversely, tenant occupied ats were tted with least variety andnumber of structural controls as shown in Fig. 2(b); for example,roof treatments in KA, RS and KD were not applied in tenantoccupied ats. Moreover, tenants displayed slight psychologicaldetachment with their at, which eventually affected the TA vote.

3.3. Analysis of occupant sensation and preferences for other

environmental parameters

3.3.1. Air movement sensation (AMS) and preference (AMP)

Air movement sensation and preference were evaluated basedon the responses to the questions How do you nd the airmovement and Howwould you prefer to have?. Fig. 3 presents therelationship of air movement sensation (AMS) with environmentaland other subjective variables. AMS correlated well with TS(r = 0.43) and with OC (r = 0.42). It has correlated robustly withmedian of square root of air velocity (r = 0.87) and with AMP(r = 0.71). Peoples preferences for higher air movement increasedwith increase in thermal sensation [40]. Toftum [41] found clearimpact of activity and overall thermal sensation on humansensitivity to air movement. The subjects voted the air movementlowwhen voting hot on TS scale (mean AMS vote = 1.42).When

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on structural controls employed, showing the effect of tenure (all data transverse

M. Indraganti, K.D. Rao / Energy and Buildings 42 (2010) 273281278Fig. 2. Distribution of (a) number of structural controls employed and (b) most commsurvey).the AMS vote was 1 and above the subjects preferred the airmovement to be lesser. Similarly the subjects have voted withinthe comfort range on the overall comfort scale (OC = 4, 5 and 6)when the AMS was between 0 and lower coinciding with neitherhigh nor low, high, very high sensations. Air movement sensationcorrelated positively with the thermal effect on productivity(r = 0.152). When the air movement sensation vote was low, theself declared productivity vote was also low. The air movementsensation correlated well with globe temperature (r = 0.353) andwith relative humidity (r = 0.234). June and July recorded very highrelative humidity coupled with moderate temperatures. Thisrequired the occupants to adaptively open the windows, promot-ing cross ventilation. Moreover, high humidities prompted thesubjects to use the fans more, increasing indoor air velocities. As aresult, AMS vote moved up with the relative humidity. Conversely,at high indoor temperature most of the natural cross ventilationceased, due to the adaptive closure of windows. This promptedmost of the subjects to give a low AMS vote, even when thepercentage of subjects with fan on was high. This was due to thefact that, at high levels of thermal distress, the air movementrequirements of the subjects could not be satisfactorily met by theceiling fans alone.

Fig. 4 shows the distribution of AMS vote and its relationshipwith median of square root of air velocity. Understandably, as airvelocity reduced, AMS vote has also reduced indicating a need forhigher airmovement. Conversely, 27% of the subjects voted 2 and3 (low and very low), on the AMS scale even when the recorded(median) air velocities were between 0.4 and 0.7 m/s. The highestpercentage of subjects has felt the air movement to be neither high

Fig. 3. Relationship of air movement sensation (AMS) with environmenor low (38%). Similarly, Ogbonna and Harris found a weakrelationship between the actual vote and the air velocity in his Josstudy [3]. It is essential to note that, the air movement sensationrelated strongly with thermal discomfort. Only when a subject wasunder thermal distress, he/she gave a very low air movementsensation vote (3). At all other times, the majority (52%) foundthe airmovement lower, but voted in the central zone,with a skewtowards the right side of AMS scale. This was partially due to thefact that, the air movement induced by the natural ventilation insummer was less dependent and was variable. Moreover, theefcacy of the ceiling fans also varied, resulting in inconsistentlevels of satisfaction. Therefore, the subjects have always desiredcooler air movement in hot summer rather than just increased air

ntal and other subjective variables (all data transverse survey).

Fig. 4. The distribution of air movement sensation (AMS) vote and its relationshipwith median of square root of air velocity (all data transverse survey).

M. Indraganti, K.D. Rao / Energy and Buildings 42 (2010) 273281 279movement. The ceiling fans or natural wind drafts in hot weathercould not provide this. The ceiling fans re-circulated the hot airaround, causing further discomfort to the subjects.

3.3.2. Humidity sensation (HS) and preference (HP)

Humidity sensation correlated well with TS (r = 0.26) androbustly with humidity preference (r = 0.788), moderately withindoor relative humidity (r = 0.56) and indoor globe temperature(r = 0.35). TS vote hot was usually given by a subject in summer,when the indoor humidity was very low (1725%). As aconsequence, the subjects have responded with a low HS voteand a higher humidity preference (HP) vote.

However, in June the mean indoor humidity increased to about53%, with the onset of sporadic summer showers. It increased byanother 58% in July, coinciding with the lowering of indoortemperature and the TS vote moved close to neutrality. Moreover,the adverse effects of high humidity, like excessive skin moisture,loss of nutrients, and fatigue were rarely felt by the subjects, as thetemperature was lower than skin temperature.

It is very important to note that, humidity sensation of subjectswas related to their thermal comfort. Fig. 5 presents thedistribution of humidity sensation vote and the correspondingindoor relative humidity recorded. The skew in the distributionindicates that the subjects have normally felt the humidity level

Fig. 5. The distribution of humidity sensation (HS) and the corresponding indoorrelative humidity, showing most subjects voting in the central band most of the

time, despite very high or very low humidity (all data transverse survey).slightly humid and neither high nor low. A majority have voted inthe central band on HS scale most of the time [42], whencomfortable (1 TS 1), even when the humidity was high.However, it is interesting to note that, at RH above 50%, thehumidity sensation vote has changed very little with the RH. Aslow humidity in Hyderabad was associated with high temperatureand discomfort, HS vote plummeted steeply as humidity values fellfrom 50%. Thus, the subjects under discomfort quickly felt theadverse effects of low humidity, giving a low HS vote.

3.3.3. Sensation of lighting level (LLS) and preference (LLP)

Light had direct and indirect effects on thermal comfort; theradiant heat of light affected directly, discomfort glare and otherperformance and health related comfort sensations affectedindirectly. The lighting level in the surveyed environments variedsubstantially, as the survey progressed frommorning to late in theevening. The lighting level sensation (LLS) of subjects increasedsteadily with lighting level preference (LLP) (r = 0.67), while LLScorrelatedmoderatelywith TS (r = 0.23). At high TS associatedwithhigh temperature during the summer midday, the subjects havefelt the ambient lighting level, rather too bright. It resulted in ahigh LLS vote and a high LLP vote as well. Excessive light in midsummers was observed causing discomfort glare and radiant heatdiscomfort [19]. Lighting level sensation correlated well with Tg(r = 0.354) and weakly (r = 0.105) with indoor lighting level. Thereason for the weak correlation was low satisfaction levels of thesubjects, specically in residential environments.

The subjects adapted themselves to the prevailing conditionsphysically andmentally [43], giving a neutral vote on lighting levelsensation scale most of the time. Therefore, the distribution oflighting level sensation and preference show normality, despiteunsuitable indoor lighting in most cases, as shown in Fig. 6.Moreover, the subjectsmoved adaptively between various brighteror duller spaces in the room as demanded by the activity. Forexample, the subjects chose to read or sew near a window, andpreferred to take a nap on a sofa, in a darker corner of the room. Allthe subjects have accordingly put the space to exible use,resulting in complete acceptance of the luminous environment oftheir living/dining rooms.

3.3.4. Noise level sensation (NLS) and preference (NLP)

Noise and vibration can affect the health and safety, comfortand performance of individuals, and there are specic effects onthe body (e.g. vibration white nger). Sometimes aural and visualprivacy requirements conict with one another, adversely affect-ing the overall user satisfaction. Noise level sensation wasmeasured based on the response to the question How do yound the background noise level?. The noise level sensation (NLS)correlated well with noise level preference (NLP) (r = 0.657) andweakly with thermal sensation. As thermal discomfort increased,the subjects have felt the environments noisier and preferred tohave the environments much quieter. At high levels of thermaldiscomfort (TS vote 2 and 3), subjects general tolerance levels forirregularities in other environmental variables dwindled. As aresult, the subjects voted low on the NLS scale. On the other hand,they voted within the central three categories of the sensationscale when comfortable, despite very high ambient noise thatoriginated from several sources like neighbours houses, trafc orconstruction activity around.

Fig. 6. The distribution of lighting level sensation and preference showingnormality, despite poor indoor lighting in most cases.The sources of noise in all the buildingswere noted to bemostlyexternal, emanating from the construction activity nearby androad trafc. In case of RA, prolonged festivities observed in theneighbouring buildings (music from loud speakers), were also amajor source, over which the subjects had little control. Interest-ingly, the subjects have displayed an aural insensibility, and wereseldom found to be using the windows and doors adaptively, tocontrol the effects of external noise. However, the subjects haveadaptively used the windows, for visual and thermal comfort, andbore silently with the external noise. Even though, they weretolerant of a noisier environment, their preference was for a muchquieter environment. Raja et al, [44] found people doing a trade-offbetween aural and thermal discomfort when it comes to the use ofwindowas a control. Distribution of NLS andNLP are similar to that

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M. Indraganti, K.D. Rao / Energy and Buildings 42 (2010) 273281280of lighting level sensation and preference shown in Fig. 6.Understandably, the mean preference vote for noise level wastowards the quieter side of the neutrality (mean = 0.70). Thus, themajority always voted around neutrality, with a skew towardsslightly noisy sensation and a bit quieter preference.

3.3.5. Indoor air quality sensation (IAQS)

Fig. 7 presents the relationship of IAQS with thermal sensation,overall comfort and the relationship of IAQS distribution andthermal acceptance. IAQS correlated weakly with TS (r = 0.1), TA(r = 0.03) and with OC (r = 0.155). As IAQ deteriorated, the subjectshave voted slightly towards the discomfort side on both OC and TSscales. However, the subjects chose to be neutral in their IAQS vote,most of the time [42], irrespective of the prevailing air quality.Thermal acceptance was least inuenced by IAQS. This is incontrast to the earlier ndings [41,45,46] in ofce environmentsthat indoor air quality sensation (IAQS) has a strong bearing on thethermal sensation and thermal acceptability. It is imperative tolearn that, the city of Hyderabad is intertwinedwith the riverMusi,a highly polluted river, releasing obnoxious smells. These were feltin several parts of the city including the sites of the case studybuildings. Similarly, Hussain Sagar, a large polluted lake is in close

Fig. 7. Relationship of indoor air quality sensation (IAQS) with (a) thermal sensation, (bproximity to RA. Moreover, the researcher herself experienced foulsmells due to the general environmental pollution, several timesduring the surveys. However, most of the occupants of the ats,have voted in the central band of the IAQS scale. The subjectsespecially in RA and RS voted oblivious to the smells around. Thisolfactory obliviousness of the subjects, with regard to their homeenvironments can be attributed to their habituation to the usualsmells around.

4. Conclusions

The thermal environment and comfort responses of residents ofHyderabad, lying in composite climatic zone were investigated inthis study. About 113 occupants of 45 ats in ve apartmentbuildings were studied in May, June and July in the year 2008. Atotal of 3962 datasetswere collected in longitudinal and transversesurveys conducted in summer and monsoon seasons, for a total of33 days. The indoor environment was measured with calibrateddigital instruments following ASHRAE Class-II protocols for eldstudies. The comfort responses of the subject sample wereanalysed under different groups: age, gender, economic groupand tenure. The weather data was obtained from the localmeteorological station. Outdoor temperatures in May were veryhigh coupled with low humidities. In June and July moderatetemperature and high outdoor humidities, markedwith occasionalsummer showers were recorded.

Following are the conclusions:

(1) A signicant but poor correlation was observed between ageand thermal sensation and overall comfort. Thermal non-acceptance was lower in older subjects.

(2) Thermal sensation and gender correlated poorly, but sig-nicant at 5% condence level. Women expressed slightlyhigher thermal sensation, with a preference for a warmerenvironment. Thermal acceptance in women was higher.

(3) A higher percentage of people voting on the warmest side ofdiscomfort were always from the higher economic groups.Thermal acceptance was high in lower economic classes.Mean thermal sensation of the lowest economic group waslowest among all the groups studied.

(4) Linear regression of thermal sensation and globe temperatureyielded higher neutral temperature and comfort band forlowest economic group. The comfort band for Gr-3 was foundto be 27.333.1 8C with neutral temperature at 30.2 8C

verall comfort and the relationship of (c) IAQS distribution and thermal acceptance.(r = 0.75). This band was found to be much higher than thecomfort band (2326 8C) specied in Indian standards. Theneutral temperature of subjects of lower economic class wasfound to be about 2 K higher than the higher class subjects.Expectations, thermal history, use of environmental controls,exposure to A/C and satisfaction levels were found to be thereasons. This nding has far reaching energy implications inthe building design and HVAC systems design and practice.

(5) Tenurewas found to be affecting the thermal acceptance vote.The ownership status encouraged the subjects to undertakeseveral structural adaptations to the tenement, better thantenants. Thus, the owners expressed higher thermal accep-tance in all the groups studied.

(6) Air movement sensation and preference depended on thethermal sensation of the subject, than on the actual airvelocity. Majority of the subjects have voted in the centralband of the scale, displaying a penchant for higher airmovement always.

(7) A similar relationship and distribution of humidity sensationandpreferencevoteswerenoted.Voting inthenon-centralbandof humidity sensation scale occurred only when a subject wasunder thermal discomfort, irrespective of the humidity level.

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(8) Distribution of lighting level sensation (LLS) and preferencehave shown normality despite having highly varying lumi-nous environments. LLS correlatedwell with temperature and

[15] J.F. Nicol, Thermal Comfort: A Handbook for Field Studies Toward an AdaptiveModel, University of East London, London, 1993.

[16] R.J. de Dear, Thermal comfort in practice, Indoor Air 14 (Suppl. 7) (2004) 3239.[17] M.A. Humphreys, Thermal comfort temperatures and the habits of Hobbits, in: F.J.

Nicol, M. Humphreys, S. Roaf, O. Sykes (Eds.), Standards for Thermal Comfort:Indoor Air Temperature Standards, Taylor and Francis, 1995, pp. 313.

M. Indraganti, K.D. Rao / Energy and Buildings 42 (2010) 273281 281thermal sensation and weakly with indoor lighting level. Thesubjects have put the space to exible use, resulting incomplete acceptance of the luminous environment of theirhomes.

(9) The subjects have voted their acoustic environment slightlynoisy most of the time, with a preference to be a bit quietermost of the time, despite heavy road and construction noisesaround.

(10) Indoor air quality sensation (IAQS) correlated poorly withthermal comfort and overall comfort, in contrast to thendings from ofce buildings [41,45,46]. The subjects votedneutral on the IAQS scale most of the time, despite thecornucopia of foul smells pervading some buildings. Thisolfactory obliviousness of the subjects, with regard to theirhome environments was attributed to their habituation tothe usual smells around.

Acknowledgements

Wewish to profoundly thankDr. HomBahadur Rijal, of Instituteof Industrial Science, University of Tokyo, Dr. Fergus Nicol ofLondon Metropolitan University and Dr. Michael Humphreys ofOxford Brooks University, UKwho have advised, guided exchangede-mails, and have generously sent papers and books to the authors.Our sincere thanks are due to Ar. Venugopal Pulipaka, of TheDesign Concern, Hyderabad for helping us in the manuscriptpreparation. We are very grateful to Mr. VS Prasad Indraganti, Ms.Lahari and Baby Millie of Hyderabad for all the help renderedduring the research and eld survey.We also thank all our subjectswho have participated in the eld surveys.

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Effect of age, gender, economic group and tenure on thermal comfort: A field study in residential buildings in hot and dry climate with seasonal variationsIntroductionResearch methodsLocation, building types and envelope characteristicsSubject sampleMeasurement of indoor and outdoor environmental data

Results and discussionOutdoor and indoor environmentsComparison between the thermal responses of various groups of subjectsEffect of ageEffect of genderEconomic levelNeutral temperature and comfort range

Effect of tenure

Analysis of occupant sensation and preferences for other environmental parametersAir movement sensation (AMS) and preference (AMP)Humidity sensation (HS) and preference (HP)Sensation of lighting level (LLS) and preference (LLP)Noise level sensation (NLS) and preference (NLP)Indoor air quality sensation (IAQS)

ConclusionsAcknowledgementsReferences