Thermal comfort in educational buildings: A review article

Renewable and Sustainable Energy Reviews 59 (2016) 895–906

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Renewable and Sustainable Energy Reviews journal homepage: www.elsevier.com/locate/rser

Thermal comfort in educational buildings: A review article Zahra Sadat Zomorodian a, Mohammad Tahsildoost a,n, Mohammadreza Hafezi a a

School of Architecture and Urban Planning, Shadid Beheshti University, Tehran, Iran

art ic l e i nf o

a b s t r a c t

Article history: Received 3 July 2015 Received in revised form 12 January 2016 Accepted 13 January 2016 Available online 25 January 2016

In modern societies people spend over 90% of their time indoors. Students spending more time at school than any other building except at home highlights the importance of providing comfortable indoor thermal conditions in these buildings. Thermal comfort since has been related to productivity and wellbeing and energy conservation in schools, has gained importance in recent years. This paper presents an overview of thermal comfort field surveys in educational buildings over the last five decades. The studies are reviewed in two sections; the first covering the field study methodologies including the objective and subjective surveys, and the second reviewing study results based on the climate zone, educational stage, and the applied thermal comfort approach. Confounding parameters have been discussed to outline priorities for the future research agenda in this field. Reviewed studies have assessed the thermal environment in classrooms compared to common thermal comfort standards. Most of the studies concluded that students' thermal preferences were not in the comfort range provided in the standards. Ventilation as an essential determinant of indoor air quality and thermal comfort has been highlighted in most studies. The wide disparity in thermal neutralities underlines the need for micro-level thermal comfort studies. & 2016 Elsevier Ltd. All rights reserved.

Keywords: Thermal comfort Classroom Adaptive Rational Field survey

Contents 1. 2.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 895 Literature review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896 2.1. Field study methodology. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898 2.1.1. Objective survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898 2.1.2. Subjective survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 898 2.2. Field study results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899 2.2.1. Climate zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 899 2.2.2. Education stage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 900 2.2.3. Thermal Comfort approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 901 3. Discussion and future researches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902 3.1. Thermal comfort approaches and standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 902 3.2. Confounding parameters in thermal comfort studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903 3.2.1. Architectural and constructional characteristics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903 3.2.2. Mechanical parameters (Heating/cooling/ventilation systems) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 903 4. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 904

1. Introduction

n

Corresponding author. Tel.: +989121395045. E-mail addresses: [email protected] (Z.S. Zomorodian), [email protected] (M. Tahsildoost), [email protected] (M. Hafezi). http://dx.doi.org/10.1016/j.rser.2016.01.033 1364-0321/& 2016 Elsevier Ltd. All rights reserved.

Educational buildings, accounting for a large portion of building stock, are responsible for high energy consumption within a country's non-industrial energy usage [1]. A considerable amount of this energy is used to provide thermal comfort. Furthermore,

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when attempting to determine an energy benchmark for educational buildings indoor environmental conditions should be considered [2]. Due to high occupant density in classrooms and also the negative influence that an unsatisfactory thermal environment may have on students' learning and performance, providing comfort conditions for educational buildings has always been critical [3–5]. There are two main categories of thermal comfort models – Rational (RTC;[6]) and Adaptive (ATC;[7]). Although, Fanger's RTC model was grounded on studies conducted on college students within climate-controlled contexts, various studies argue that it could not predict the thermal comfort levels in real classroom conditions accurately [8–10]. Since the introduction of the ATC, several studies have evolved to support adaptive models in thermal comfort assessments and to establish quantitative indexes to allow the subject to enhance his/her comfort conditions [11]. This model of thermal comfort has also been assessed in classrooms and students’ adaptive behaviors have been investigated. Various comfort equations have been developed based on field studies, relating the indoor comfort temperature to the monthly mean outdoor temperature [12]. As studies are based on field surveys with limited occupancy number and differences in the climate and building characteristics, generalization of the results is not usually possible. Different thermal environment requirements due to specific occupation periods through the day and the year, difference in occupants’ activity and clothing and level of freedom for adaptive actions(i.e., changing positions, clothing, opening/closing windows and blinds) and changing temperature set points in classrooms, compared to offices and residential spaces, require specific thermal comfort studies to be carried out. Furthermore, acceptable indoor condition would not be achieved unless a holistic acceptance in air quality, thermal, acoustical, and visual comfort at the same time. And any changes in these measures leads to discomfort and productivity loss in classrooms. Current comfort standards, such as ISO 7730 [13], EN 15251 [14], and ASHRAE Standard 55 [15] determine design values for operative temperatures and comfort equations based on the rational and adaptive thermal comfort models (Table 1). These standards provide thermal comfort ranges for three categories of spaces which classrooms are considered in the second category with normal level of expectations. Currently no specific standard exists for various age-ranges. Furthermore, studies have criticized the applicability of the existing standards in classrooms. A vast literature has appeared in recent years dealing with thermal comfort field surveys especially in European and Asian countries. In

addition to field surveys few review articles have been published regarding different issues of thermal comfort (theoretical framework and field survey reviews). Van Hoof (2008) reviewed thermal comfort studies in the past 40 years with a focus on Fanger's theory [16]. Halawa and van Hoof (2012) reviewed the studies on adaptive thermal comfort and look critically at the foundation and underlying assumptions of the adaptive model approach and its findings [17]. Djongyang et al (2010) and de Dear et al (2013) also reviewed the progress of thermal comfort studies over the last twenty years [18,19]. Yang et al. (2014) reviewed a number of studies of thermal comfort in general and those pertinent to building energy efficiency in different parts of the world [20]. Mishra and Ramgopal (2013) reviewed field surveys in different building types and grouped them based on climate zones [12]. Rupp et al. (2015) reviewed papers published in the last 10 years that examine the various sub-areas of research related to human thermal comfort (e.i. standards; experiments in climate chamber and semi-controlled environments; field studies in educational, office, residential and other building types; productivity; human physiological models; outdoor and semi-outdoor field studies) [21] Khodakarami and Nasrollahi (2012) also reviewed the thermal comfort studies particularly in hospitals [22]. No research has reviewed thermal comfort studies in educational buildings specifically. Although educational building studies are not comparable to the studies conducted in offices and residential buildings in number, they have increased over recent years and vary mainly in the theoretical approach, climate zone, and educational level. In this paper, forty eight articles on thermal comfort field studies in classrooms, published from 1969 to 2015 in peer-reviewed scientific journals such as Building and Environment, Building and Energy, Applied Energy, ASHRAE Transactions, and Indoor Air and also those published in international conference proceedings such as Passive and Low Energy Architecture (PLEA) are categorized based on different criteria such as year of study, country, climate, ventilation type, thermal comfort approach, number of respondents, and study season. It was not meaningful to list all conclusions from each and every study included. Instead, general conclusions are summarized and discussed in different sections. To provide a better understanding of thermal comfort in classrooms and related issues, and to achieve a holistic view in this field, the key points have been extracted by comparing and contrasting the previous studies. First, studies are categorized and reviewed to provide a wide literature review (i.e., based on climate, educational stage, and the thermal comfort approach) to find the similarities and contrasts. Second, limitations of thermal comfort approaches and standards, and confounding parameters in thermal comfort studies (i.e., architectural, constructional, and mechanical) are discussed. Finally, recommendations for future studies on thermal comfort in classrooms are presented.

Table 1 Thermal comfort standards in classrooms. Standard

Thermal comfort approach

ISO 7730 (2005)

Rational
0.5 o PMVo þ 0.5 PPD o 10% ASHRAE 55 Rational (2004)
0.5 o PMVo þ 0.5 PPD o 10% EN- 15521 Adaptive (2007) ASHRAE 55 Adaptive (2010) TRMT: Running Mean Temperature. TO: Outdoor Temperature. Tn ¼ Neutral Temperature. PMV: Predicted Mean Vote.

Operative temperature winter (°C)

Operative temperature summer (°C)

20–24

23–26

20.5–25.5

24.5–28.0

Tn ¼0.302TRMT þ 19.39; TRMT4 10 Tn ¼22:88; TRMT r 10 Tn ¼ 0.31TO þ17.8

2. Literature review In this paper, the reviewed studies are limited to those focusing on thermal comfort field surveys in typical classrooms. These studies have been classified based on three main parameters: climate zone, educational stage, and the thermal comfort approach, and also sub parameters including year of study, country, continent, ventilation type, number of respondents, and the season of study (Table 2). Similarities and contrasts among the studies, and the relationships between the above mentioned parameters have been extracted by statistical analysis, presented in percentage and graphs. However due to the limited number of studies and the variety of study conditions, building a precise meta-analysis model was not possible. Thermal comfort field studies in classrooms were reported first in 1969, by Auliciem and vastly presented over the last decade. Indeed

Table 2 Summary of reviewed papers. Level

Primary

Year

Continent Climate Ventilation type

[45] [57]

1975 1972

Australia USA

Australia America

A C

[50] [68] [40] [8]

1977 2009 2009 2011

UK Malaysia Netherlands Netherlands

Europe Asia Europe Europe

[66]

2012

Taiwan

[9] [72]

2012 2013

[56]

Season

Thermal comfort model

Lower limit

Neutral

Higher limit

– 21.5 22 24 26 – –

24,2 – – – 28.4 – –

– 25 23 26 30.7 – –

Model Compatibility ATC

RTC

Rational Rational

– –

– –

–

Lower

– Underestimated Underestimated Underestimated

–

Adaptive Rational Rational Rational and Adaptive Adaptive

Higher

Underestimated

26.4 –

Adaptive Rational

–

–

summer winter winter Whole year

Asia

C

NV

Whole year

1614

Italy Iran

Europe Asia

C B

NV NV

614 794

21 –

2013

UK

Europe

C

NV

230

–

20.5

–

Rational

Lower

Underestimated

[51]

2014

Chile

America

C

NV

2100

–

Adaptive

Lower

–

2015 1998

Greece USA

Europe America

C A

NV NV

18 22

25 29.5

Europe

C

–

[23] [69] [63]

2000 Brazil 2003 Singapore 2003 Japan

America Asia Asia

C A C

NV AC NV NV NV

Whole year Summer summer

28 493 74

20.7 27.3 –

22.9 28.8 –

25.2 29.3 –

[64]

2009 Taiwan

Asia

C

NV

1614

17.6

22.7/29.1

30

[53]

2009 Kuwait

Asia

B

AC

Mid-season and Winter Mid-season

336

19

21.5

23.5

[47]

2009 Italy

Europe

C

NV

440

23.3

–

27.4

[43] [44] [30]

2011 2012 2013

Iran Ghana Italy

Asia Africa Europe

B A C

NV NV NV

45 116 4000

– – –

– – 20

– – –

Rational Rational and Adaptive Rational and Adaptive Rational Rational Rational and Adaptive Rational and Adaptive Rational and Adaptive Rational and Adaptive Adaptive Adaptive Rational

– Underestimated compatible Underestimated

UK

193 NV:2181 AC:1363 624

16.7 21.1 22.31 26.8 27.4 17.1

–

[35] [67]

Mid-season Mid-season and Winter Mid-season and summer Winter summer Spring Winter and summer winter

22.4 29.2 – –

[48]

2015

Australia

Australia

B

AC-EC-NV

2129

19.5

22.5

26.6

[39] [112] [80] [37]

2014 1990 2002 2006

Portugal Hong Kong Japan Italy

Europe Asia Asia Europe

C C C C

NV AC AC NV

52 136 40 959

22.1 22.2 – 20.24

– 24.9 25.5 –

25.2 25.2 – 23.56

Rational and Adaptive Rational Rational Rational Rational

[113]

2006 china

Asia

C

NV

[58] [34]

2007 china 2008 Nigeria

Asia Africa

C A

[24] [31]

2009 china 2010 china

Asia Asia

[70]

2010

Asia

Mid-season and Winter spring Winter Winter and summer summer

–

186

18.4

22

26.1

Rational

NV NV

Mid-season Winter and spring whole year Mid-season and Winter Winter and Autumn Spring summer

1273 200

– 24.88

21.5 26.58

– 27.66

C C

NV NV

Whole Whole

3621 3621

16 16

22.8 22.8

30 30

Rational Rational and Adaptive Rational Rational and Adaptive

B

AC

summer

500

22.4

25.23

26.6

–

–

– – Higher

Underestimated Overestimated –

Higher

–

Lower

Underestimated

Lower

Overestimated

Lower – –

– Underestimated Overestimated

Lower

Underestimated

– – – –

Overestimated – Underestimated compatible

–

–

Lower

Overestimated Overestimated

– Higher

Underestimated Overestimated

compatible –

897

C A C C

3481 NV:100 AC:66 262 335 174 79

Pakistan

winter Mid-season

Sample size Comfort band

NV NV AC NV MV þNV AC NV

[54, 55] 1969

University

Country

Z.S. Zomorodian et al. / Renewable and Sustainable Energy Reviews 59 (2016) 895–906

Secondary and High school

REF

Thermal comfort model

– –

compatible –

Overestimated Higher

– –

compatible Underestimated

Underestimated compatible Higher –

compatible compatible

Underestimated –

67

29

23.5 30.7 31.5 22 23.5 22.1 A Asia 2015 [26]

India

2014 [61]

India

NV

C Asia

Mid-season and Winter Whole year

228

24.2 66 2014 [27]

China

NV AC NV D Asia

Whole year

20.9 NV

Winter C Asia 2014 [49]

China

2015 [60]

Italy

NV C Europe

640

18.6 126

21.7

26.6

Rational and Adaptive Rational and Adaptive Rational and Adaptive Rational and Adaptive Adaptive 24.5

–

22.7 21.7 21.8 – 200 NV D Asia 2014 [29]

China

2011 2012 [62] [25]

Korea Portugal

NV NV C C Asia Europe

Mid-season and Winter Spring

25 – 17 – 205 732

20.7 26.8 – – 2011 [73]

China

AC D Asia

Winter and summer Mid-season Whole year

205

– 28 summer 2010 [70]

Thailand

NV A Asia

206

–

Rational Rational and Adaptive Rational

Rational and Adaptive Rational and Adaptive Rational Higher limit Neutral Lower limit

Sample size Comfort band Season Continent Climate Ventilation type Year

Country

about half of the addressed studies in the current paper have been conducted over the past 5 years (2011–2015), along with the raised awareness of energy efficiency issues in buildings. Studies are mainly conducted in Asia and Europe in both developed and developing countries, with climate and cultural differences. The studies are reviewed in two sections; the first covering the field study methodologies including the objective and subjective surveys and the second reviewing study results based on the climate zone, educational stage, and thermal comfort approach. 2.1. Field study methodology

REF Level

Table 2 (continued )

compatible –

ATC

RTC

Z.S. Zomorodian et al. / Renewable and Sustainable Energy Reviews 59 (2016) 895–906

Model Compatibility

898

Thermal comfort field studies use both objective and subjective surveys to assess the thermal comfort levels. In the reviewed papers these surveys have been done in accordance to ISO 7730 or the ASHRAE 55 standard regulations. The study durations vary from less than a week to the whole year [23–27]. Statistical analysis techniques such as linear regressions are used to show the interrelation between the objective and subjective data's [7]. The studied classrooms differ in architectural (e.g. room dimensions, window wall ratio, shadings), constructional (thermal envelope properties), and mechanical (heating, cooling, and ventilation system) parameters. The studied cases are mainly naturally ventilated and in a few cases air conditioned or mechanically ventilated by fans. 2.1.1. Objective survey Different physical parameters are measured based on the study's purposes. A procedure corresponding to the Class II Field experiment protocols [28] for thermal comfort has been adopted in almost all of the studies, measuring general comfort parameters including four environmental factors (i.e., air temperature, relative humidity, air velocity, and the radiant temperature) and two human parameters (i.e., clothing level and metabolic rate) for calculating thermal comfort indices i.e. the Predicted Mean Vote (PMV), Effective Temperature (ET), and Operative Temperature (Top) in one point at the sitting height (0.6–1.1 m) in the classroom. Although few studies [29–32] measured the above mentioned parameters in three heights (0.1, 0.6, 1.2) based on the Class I Field experiment protocols. In addition, illumination level on the work plane [33–35] and CO2 levels have also been measured and correlations have been made in a number of cases [9,34,36–42]. However in two studies based on the adaptive thermal comfort model only the indoor and outdoor temperature and the relative humidity have been measured in accordance to the Class III Field experiment protocols [43–45]. In addition to general comfort parameters, few studies [30,46,47] have also measured local discomfort parameters i.e., draft risk, radiant asymmetry and floor temperature. 2.1.2. Subjective survey Subjective surveys (questionnaires) are the main part of thermal comfort field studies. Over time, questionnaires have changed; early assessments only included questions on thermal sensations and preferences but currently indoor air dryness and air velocity are also been questioned. Most field surveys use descriptive scales such as the seven point ASHRAE or the Bedford scales for rating thermal sensation, the three point McIntyre scale for thermal preference, and check lists for clothing and activity [12]. Both longitudinal [26,27] and transverse surveys [45,48,49] are used. As Mishra and Ramgopal (2013) stated there is no well-defined convention when it comes to choosing how many responses to collect, or over what duration to take the survey [12]. The number of respondents in the reviewed studies differed from 28 [23] to over 4000 [30] students. The variables assessed are in accordance to ASHRAE 55 and ISO 7730 standards. However the

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questionnaires differ due to the group age, e.g. colored pictures are used for primary students and the questions are limited in some cases [36,50,51]. When designing questionnaires for primary level students, some issues should be considered in order to assure the accuracy of the data obtained. Some researchers [8] considered the ASHRAE scale to be easier for children to understand and also simplified in some researches. Haddad et al. (2012) and Fabbri (2015) proposed recommendations for designing questionnaire for children's thermal comfort assessment [42,52]. Most studies in classrooms investigated the two genders separately. Although in most cases results did not show tangible differences, but this issue is known to be important in countries with clothing restrictions for females[43, 53].

899

Table3 Neutral/comfort temperature in each climate zone. Climate vs. neutral/comfort temperature Climate

Lower limit (°C)

Neutral (°C)

Higher limit (°C)

A B C D

22 19 16 19.9

27.21 23.08 21.66 23.58

30.70 26.60 30.70 28.30

2.2. Field study results General findings of the reviewed studies are summarized and presented into the following sections: Climate zone, Educational stage, and Thermal comfort approach. 2.2.1. Climate zone The Köppen–Geiger climate classification has been used to group the above mentioned classroom thermal comfort field studies. Data reveals that most of the studies (65%) are conducted in group C in that classification; temperate/mesothermal climates; including UK [50,54–56], USA [57], China [24,31,49,58], Italy [11,30,37,47,59,60], Netherlands [8,40], India [61], South Korea [62], Japan [63], Taiwan [64–66], Portugal [39] and Greece [35]. Studies in group A, tropical/megathermal climates are the second (20%) and include studies carried out in USA [67], Australia [45], Malaysia [68], Singapore [69], Thailand [70], Nigeria [34], Ghana [44], and India [71]. The third (11%) are the studies conducted in group B; dry (semi-arid and arid) climate; in Australia [48], Iran [43,72], Kuwait [53], and Pakistan [70]. Only three studies (4%) were found in group D; the continental/microthermal climates; which were all carried out in the continental climate of China [27,29,73] and no such studies were found in group E, the polar and alpine climate. The average neutral, lower and higher comfort temperature limits obtained in each climate zone is presented in table 3 and Fig. 1. Studies were conducted in both natural ventilated (NV) and air conditioned (AC) classrooms mainly in winter and the mid-seasons, although a few studies were done through the whole year. According to Fig. 1 since studies are conducted in different seasons, the neutral temperature in terms of operative temperature varies greatly in each climate and is between 16.7–29.2 °C. The lowest neutral temperature has been reported in winter of temperate climates (i.e. Chile and UK) and the highest neutral temperature is observed in tropical climates (i.e. Thailand and Singapore). Also the widest (14 °C) [24] and narrowest (1 °C) [57] comfort band has been reported in Naturally Ventilated (NV) and Air Conditioned (AC) classrooms in the temperate climate respectively. The neutral temperature is between 24.5–28.8 °C in group A which the minimum was reported during winter in Queensland and Australia and the maximum in Singapore and Malaysia, 21.5– 25.3 °C in group B in Kuwait and Pakistan, 16.7–29.2 °C in group C in Chile and Taiwan and 20.7–26.9 °C in group D, reported in Chile and Taiwan respectively. Studies suggest that the preferred temperatures are not exactly the neutral thermal sensation of respondents and are 1.5–4 °C lower than the neutral temperature in most studies. The comfort band (higher limit-lower limit) varies between 3.7 and 7.5 in group A, 2.7 in group B, 1.0–14.0 in group C and 2.9– 5.9 in group D. A wide disparity in thermal neutralities has been observed in studies conducted in the same climate zones; since studies are conducted in different seasons and under different

Fig. 1. Neutral and comfort band in climate zones.

conditions (free running and air conditioned), comparing neutral temperatures is not reasonable. Although from the results a high level of acclimatization is observed in temperate and tropical climates and therefore the neutral temperature in spring and summer were higher than in winter. In studies carried out in group A, mainly done in naturally ventilated classrooms through winter and summer, it seems that the occupants have a higher heat tolerance and can adapt to the environment that they are used to although the thermal conditions exceeded the standards. Although the relative humidity is high in this climate studies reveal that its influence in thermal comfort is not considerable. These findings highlight the potential of passive cooling strategies in this climate for energy conservation purposes. However a recent study in this group done in Indonesia [74] indicates that the comfort temperature of students has decreased about 1.5° in the last 20 years due to the use of massive air conditioners in buildings. Studies conducted in group B are done in both naturally ventilated and air conditioned classrooms during summer and midseasons, while only one study included winter in the study [72]. The comfort range and neutral temperatures are narrower and lower in comparison to studies in group A. Thermal comfort levels above standards have also been acceptable in this climate zone. Except four studies, all carried out in group C are done in NV classrooms mainly during the midseason and winter and majorly in Italy and China. This climate zone includes a wide variety of subtypes, e.g. the humid subtropical subtype having cold winters and hot summers while the Mediterranean and oceanic subtypes are quite milder. Such a wide range of climates gives the inhabitants of group ‘C’ an equivalently broad range of adaptability [12]. Students in locations exposed to wider weather variations showing greater thermal adaptability than those in more equable weather districts [48] and even when the outdoor climatic conditions were considerably warmer than average, such as those observed in Japan [63], Singapore [69], and Taiwan [64–66], or cooler as in Italy [9,47], the students' mean thermal sensations were still within the neutral category. Moreover as reported in China [73] the lower the outdoor air temperature in winter, the worse thermal adaptability to warm environment is

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reported, while the adaptability to cool environment would be stronger. 2.2.2. Education stage Since 1970 with the development of Fanger's theory, there has been a growth in thermal comfort field studies in educational buildings especially in the past two decades. Thermal comfort theories, both the rational and adaptive, are based on studies done with adult subjects and their application in different group ages has been vastly criticized. Since metabolic rate and clothing, two important personal factors, and freedom of adaption to overcome thermal discomfort, differ in classrooms due to the students' age, studies are classified based on this criteria into three groups: 1. Primary level, (students 7–11 years old), 2. Secondary and high school level (12–17 years old), and 3. University level (18–28 years old). The abovementioned educational stages include 25%, 34%, and 41% of studies respectively. Among the thermal comfort studies in classrooms, university level studies with the highest number are mostly conducted in Asia (31%), and primary level studies with the lowest in number are mostly done in Europe (10%). The lower and upper comfort limits and the neutral comfort temperature in different educational stages are presented in Fig. 2. Filed studies in secondary and primary schools are done much earlier (1969) than in university classrooms (1990). Early studies in primary and secondary stages recommend invariably lower temperatures for schools than those recommended for adults, which have been largely based on the theoretical grounds that the young have a greater metabolism per unit body surface than adults. Although researches indicated that the recommended temperatures are insufficient according to the school absenteeism and students productivity examinations [75]. Prominent studies on primary school are done by Catenacci et al. (1989), Donato et al. (1996), Grillo et al. (2003), and Giuli et al. (2012) in Italy; Hummphre (1975), Montazami and Nicol (2013), and Teli et al. (2013) in UK; Zeiler and Boxem (2009) and Mors et a.l (2011) in Netherlands; Hussein and Rahman (2009) in Malaysia; Liang et al. (2012) in Taiwan; Haddad et al. (2013) in Iran; Pepler (1972) in USA; Auliciems (1975) and de Dear et al. (2015) in Australia; Dorizas et al. (2015) in Greece, and Treblicock et al. (2014) in Chile. [76] Low air quality and thermal discomfort leads to dangerous situations for the health due to the high density of persons who occupy the same environment or a certain hyper-sensitivity of children to higher temperatures [30]. Most studies were conducted in naturally ventilated classrooms with students aged 7–11 in the C and A climate zone during winter and mid-seasons. The neutral temperature defined in terms of operative temperature is 16.7–29.2 °C across different climate zones. Humphreys (1977) [50] found that since children have a lower sensibility to temperature change than adults, their thermal responses are widely different. Teli et al (2013) [56,77] study also reveals a tendency of pupils towards warm thermal sensations which paradoxically is not complemented by an equally

strong preference for cooler environments. The results suggest that children are more sensitive to higher temperatures than adults with the comfort temperatures being about 4 °C and 2 °C lower than the rational and adaptive comfort model predictions respectively. The same result has been reported by Mors et al. (2011) [8] in the same climate zone. De Dear et al. [48] also estimated an indoor operative temperature of about 22.58 °C as the neutral and preferred temperature which is generally cooler than expected for adults under the same thermal environmental conditions. Treblicock (2014) [51] also indicated 3–4 °C lower comfort temperatures in comparison to adaptive models as the result of students higher metabolic rate [51]. In contrast to studies that suggested lower comfort temperatures for children in the C climate zone, Liang et al. (2012) [66] in the A climate zone reported a higher neutral temperature (29.2 °C) for students in the hottest month, which is 2.3 °C higher than the level suggested by the ASHRAE Standard 55, 26.9 °C; and reported 22.4 °C as the neutral temperature in the coldest month, which was close to the neutral temperature suggested by the ASHRAE Standard 55, 23.0. Although Hwang et al. (2009) [78] reported lower neutral temperatures for adults at offices in the hottest month (28.4 °C) and lower neutral temperature in the coldest month (20.4 °C) in the same context [46]. Possible explanations for lower comfort temperature may be the higher metabolic rate per kg body weight, the limited available adaptive opportunities in classrooms, the fact that children do not always adapt their clothing to their thermal sensation, and the influence of characteristics of their familiar indoor environments. Furthermore, the daily school schedule of children includes a lot of outdoor playing, unlike offices where occupants stay inside for most of the day. This variation of activity levels and the strong relationship with the outdoor climate may also influence children’s thermal perception [10]. In contrast to the assumption regarding children’s higher metabolic rate, Havenith (2007) presented lower metabolic rates for children explained by their body size and the larger ratio of body surface area to mass [79]. Considering different assumptions regarding children’s metabolic rate Haddad et al (2013) [51] investigated the effect of different metabolic rates on PMV predictions by comparing them to empirical data. Although results shows a better match between actual data and PMV using values given in adult based standards, they state that children’s resting metabolism, activity levels, and their implications in the heat balance equation needs more research. The higher comfort temperature likewise could be the result of students’ acclimatization to the local climate in tropical climates. The second category of thermal comfort students in educational buildings are done in secondary schools, in some countries defined as high schools. 12–18 years old students are studied in this group. The number of studies in this group shows that researchers are more willing to do investigation with this group due to their ability for giving more reliable information about their thermal sensations and preferences. In addition their ability to

Fig. 2. Lower and upper comfort limits and the neutral comfort temperature in different educational stage studies.

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adapt to the environment by behavioral actions is more and the metabolic rate differs much less from adults in comparison to primary students. The geographical dispersion of this group is more than the two other groups. Similar to the first group studies are carried out mostly in the C, A, and B climate zone. The seasonal variations of the studies are less in comparison to the first group. Most studies are done during winter and mid-seasons. Although the group age, climate, season, and ventilation type are similar in cases, there still exist differences in students’ thermal sensation. For instance, the neutral and preferred temperatures are different and varies between 17.1 °C (during winter in UK) to 29.1 °C (during autumn in Taiwan) where a wide range (22.7–29.1 °C) rather than a single value of neutral temperature, found as a result of the students’ characteristic thermal adaptation during autumn and winter. Xavier(2000) reported lower neutral temperatures in school children in comparison to conventional field studies with adult subjects in the same context [23]. The neutral temperature proposed for NV classrooms is higher than in AC classrooms, although Kwok [67] estimated the neutral temperatures for NV classrooms about 1 °C lower than AC’s. According to studies, the neutral temperature in AC classrooms, which were mainly in the B climate zone, are reported 21.5 °C and 22.5 °C in Kuwait (in spring) and Australia (in summer) respectively. The third category of educational stage consists of thermal comfort field studies in university classrooms. Fanger's studies are based on American and Danish university students in climate chambers, however field studies report discrepancy between the predicted thermal sensations and the actual ones in university classrooms. This discrepancy is reported to be the consequence of adaptive actions taken by students in classrooms. The results of studies on thermal comfort of office workers may be possible to apply to college and university students. However there are two basic reasons that contribute to a higher neutral temperature in classrooms than in offices. First is students' frequent movement from the hot outdoor environment into cool classrooms, while office workers are supposed to remain in the office for the duration of their working day. Second is related to the students’ clothing which is less than office workers’. Therefore it cannot be assumed that the requirements of college students for thermal comfort are the same as those for office workers [65,80]. In addition, since university students spend less than 2–3 h a day in classrooms, compared to the two other educational stages, their thermal perceptions are different. As mentioned earlier, the numbers of studies in university classrooms are more than the other two groups, mostly conducted in Asian countries. Similar to the other groups, most studies have been done in the C climate zone. The number of studies done in China in this group is considerable among other countries. De dear et al (2013) [18] also emphasized China as a contributor in thermal comfort research. The seasonal variation is more than the two previous groups and studies are carried out mainly through the whole year which makes the results more useful.

2.2.3. Thermal Comfort approach Reviewed Studies use both the RTC (50%) and ATC (15%) model and there has been a growth in the use of the adaptive approach in recent years. In addition many of the studies (35%) use both methods to assess the thermal comfort condition and compared the results with each other (Fig. 3). RTC consists of the traditional Fanger's PMV model, which provides results that are very close to the actual thermal votes in the spaces with a Heating, Ventilation, Air Conditioning system (HVAC), passive behavior of the occupants, and fixed clothing such as in offices [60]. Among the reviewed studies this method has been more used in universities’ thermal comfort assessments. However a high number of studies in the secondary and high schools used this method besides to the ATC model. The reliability of the PMV to predict the thermal sensation in non-air conditioned environments has been criticized vastly and the reviewed studies majorly show high levels of discrepancy between the predicted mean vote and the actual thermal sensation of students (under estimation or over estimation) in all climate zones(Fig. 4a and b) and educational stages (Fig. 5). However compatibility has been reported in a significant number of studies in university classrooms. Among the reviewed papers that used the RTC method, most (50.04%) reported that the model underestimates the students’ thermal sensations, 35.71% reported overestimation, and only 14.25% reported that the thermal comfort predictions are compatible with students’ actual thermal sensations. Under estimation was mainly reported in primary levels while over estimation was observed in secondary and high school levels, While compatibility was only reported in university classrooms. Also results reveal that incompatibility is extreme in the temperate and tropical climates. However the RTC model considers the most important variables affecting the thermal sensation, unlike the adaptive model, that takes into account only the outdoor temperature, researchers' stated that some specifications should be made to update this model. Fanger and Toftum,(2002) [81], Singh et al., (2011) [82] and Yao and Liu (2009) [24] realizing the difference in the expectations between people not used to occupy conditioned environments those used to, and the behavioral, physiological and psychological adaptations proposed the “ePMV”, “aPMV”, and “cPMV” indexes to

Fig. 3. The percentage of number of studies of Thermal Comfort (TC) approaches in educational stages.

Fig. 4. (a) Compatibility of AMV with ATC models in different climate zones. (b) Compatibility of AMV with RTC models in different climate zones.

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widen the use of PMV even in non-air conditioned environments, by means of an expectancy factor and an adaptive coefficient. These indexes have been applied in thermal comfort studies in classrooms and results indicate that by applying the expectancy factor and adaptive coefficient, a good agreement between predicted and subjective votes attributed to the environment has been found, both in winter and in summer conditions [30,66] [24,61]. Although Khaled al Rashid et al (2009) [53] stated that applying the expectancy factor in classroom in Kuwait improves the PMV, there still exist considerable discrepancy with the Actual Mean Vote (AMV). In classrooms, unlike offices, a greater control of conditioning plants, opening of windows, and controlling solar shadings is possible the during school time. Therefore the adaptive model of comfort could be an accurate method for thermal comfort assessments in classrooms which has been used in a number of the reviewed studies, however 14% of the papers used adaptive model and 35% of them used adaptive or rational model. And the compatibility to adaptive standards and widely used adaptive comfort equations such as Humphrey’s adaptive model has also been assessed in studies (Fig. 6). Among studies that used the adaptive model, 33% reported lower neutral and comfort levels in comparison to standards and 43% reported higher neutral temperatures, although 24% compatibility has been shown with the adaptive standards, especially in the university level. Also results reveal that the adaptive method predicts more accurately the comfort levels in the A climate zones. In some cases results showed that students were well acclimatized to the local climate, displayed adaptive behaviors like use of fans, clothing adjustment, and window operations. Although results show that human thermal sensations is related to both indoor and outdoor climates. Therefore the ATC model since uses only the external temperature for predicting the comfort temperature, may not accurately predict the thermal sensation of occupants, especially in classrooms where adaptive comfort actions are usually limited. Moreover, students’ neutral temperature was found to be approximately 4 °C lower than predicted by the rational PMV/PPD model and about 2 °C lower than that underlying the EN 15251 and ASHRAE-55 adaptive comfort limits.

3. Discussion and future researches Empirical studies show that thermal comfort, which is one of the main parameters of indoor environmental quality, affects students' performance [40,83] and the buildings energy consumption [1,84,85]. The growing interest in low energy and zeroenergy schools has increased thermal comfort studies in educational building over the world in recent years; however, they are not comparable in number to studies in offices and residential. Few of the reviewed studies investigated students’ performance

Fig. 5. Compatibility of RTC model in different educational levels.

Fig. 6. Compatibility of ATC model in different educational levels.

and energy consumption in relation to thermal comfort. Moreover, uncertainty in the comfort temperature for design purposes due to applying different thermal comfort approaches and standards has resulted in ambiguity of conclusions. Further discussions on the reviewed studies and recommendations for future researches are presented in two main sections: thermal comfort approaches and standards, and confounding parameters in thermal comfort field studies. 3.1. Thermal comfort approaches and standards Both adaptive and rational models have been used in the reviewed studies to evaluate thermal comfort. Although the support for the latter is larger, despite a few, studies reveal that neither approaches individually predicted students' thermal comfort levels accurately. Halawaa and Van Hoof (2012) [16] indicate that in order to improve the validity of the RTC model in NV buildings, better specification of the model’s input parameters, particularly clothing and activity levels, should be taken into account. Unlike office workers, student's adaptive mechanisms in educational spaces significantly influence their thermal preferences based on changes in activity and clothing level. Based on behavioral adaptations, the ATC is an approach for comfort that people make in order to stay comfortable by making changes to their clothing insulation, postures, activities, and by actions such as opening the windows, adjusting blinds, and adjusting the heating or cooling devices. The underlying assumption of this model is the control of the individual which is sometimes limited in classrooms. As mentioned in some studies [9] the classroom conditions strongly depend on teachers’ preferences, which prevents the use of adaptive models in classrooms, especially in lower educational stages. However, the underlying assumption of this model is the control of the individual. Also, thermal background has been seen to affect thermal preferences [51,74]. Enhancement of living standards and comfort levels in homes has raised students’ expectations in classrooms. Reviewed studies show that the comfort/neutral temperature in classrooms has increased since the past 65 years (Building Bulletin No. 2 (1950): 16.6°, even lower in 1930–1947 (12.7–15.5 °C)) [74] that is obviously the result of higher temperatures in homes due to the extensive use of heating systems. Also 1.5 °C reduction in comfort temperature over the last two decades in warm seasons [51] is the consequence of using air conditioners in households in hot and humid climates which could be the main reason for the reported discomfort in naturally ventilated classrooms [64]. Such findings from adaptive field studies could be used to improve the applicability of Fanger's RTC. As Brager and de Dear (1998) claim, both thermal comfort approaches are complementary rather than contradictory [28]. Fanger's original heat balance equation needs to be revised; the existing coefficients of this formula, originally developed from limited experimental results, can be modified using field survey findings [17]. Assessing the classrooms, thermal condition in accordance to thermal comfort standards has been one of the main purposes of

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most of the reviewed field studies. Results mainly indicated that the standards, both RTC and ATC (Table 1), are not applicable for thermal comfort evaluations in classrooms in different climates and educational stages. According to Olesen and Parsons (2002) for a standard to be truly international, a co-ordination of countries and a process of common consent is required [86]. Therefore thermal comfort researchers worldwide should collect and analyze new databases of thermal comfort field studies in different climate zones and educational stages individually, considering cultural and technological differences, in order to revise standards and provide reliable comfort temperatures by applying meta-analysis. Adaptive standards could support energy efficient design in schools. Energy savings could be achieved by adjusting comfort temperatures [29]. Although, the thermal comfort zone has been extended by the adaptive model, it has been pushed to critical boundaries [17]; moreover, Nicol and Humphreys [3] have also warned that ‘a “low energy” standard which increases discomfort may be no more sustainable than one which encourages energy use’. Regarding thermal comfort indices, almost all studies used either rational (PMV) or direct indices (TOP, (Equivalent temperature) ET) for assessing student's thermal responses. More recently, a new type of indices have been proposed which aim at the long-term evaluation of general thermal comfort conditions in a building. In contrast to the above-mentioned indices that focus on comfort parameters at a certain time and position in space, long-term comfort indexes aim at assessing thermal comfort quality of a building over a span of time and considering all the building zones [87]. Chartered Institution of Building Services Engineers CIBSE 2006 considers a fixed temperature as a benchmark for evaluating overheating in a classroom, which allowed up to 80 occupied hours in a year above this temperature, normally in the non-heating period of May–September. This is a useful index in case of assessing discomfort, although it does not give information about the severity of the uncomfortable conditions. Montazami and Nicol (2013) compared the former overheating guideline, based on RTC with recent criteria's that is in line with adaptive temperature limits in the European Standard ( i.e., BS EN 15251) for schools in the UK, by comparing classroom temperatures with occupants thermal sensation. It was found that the old guidelines were too tolerant and allowed overheating, while the new guideline is more rigid, but needs further development to reflect occupants’ perceptions more accurately [88]. Introducing long term assessment indices for schools in different climate zones could help designers achieve a holistic view of thermal comfort levels over the entire year. In addition to temporal discomfort indices (percentage of likely discomfort hours with respect to the total number of occupied hours) which are useful for understanding the best or worst case scenarios, spatial indices (percentage of space subjected to local discomfort) could assist designers in detailed design evaluations. Future research in the thermal comfort field could develop such metrics to evaluate thermal comfort levels spatially over the occupation time. Although recent standards have considered hours of exceedance from the comfort temperature, adding spatial limitations could be useful for design evaluations especially in classrooms, where students are subjected to sit in a fixed position during class time. 3.2. Confounding parameters in thermal comfort studies As mentioned in the literature review, the studied classrooms differed in architectural, constructional, and mechanical (i.e. heating, cooling, and ventilation) characteristics. These items since directly affect the indoor thermal environment in classrooms, are further discussed in the following.

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3.2.1. Architectural and constructional characteristics The thermal condition inside a building directly relates to the buildings’ architectural and constructional characteristics including layout, space dimensions (as well as height), window wall ratios, external shadings, and building thermal envelope properties ( e.g., U values of building fabrics), therefore thermal comfort should be studied in relation to the above mentioned parameters. Limited surveys have investigated the effects of architectural and constructional characteristics on thermal comfort level in classrooms by field studies. However, various researches using simulation [89,90] and experimental studies [91–97], have predicted occupants’ thermal comfort in classrooms with different constructional properties, without considering their actual thermal votes. The literature review reveals that the architectural and thermal properties of the case studies are almost not considered in the field studies and except some researches ( [66,98–100]) no relation has been developed between the students’ thermal perceptions and the classroom architectural and constructional characteristics. Although a few studies have pointed out the influence of classroom geometry on the thermal conditions [60]. The different constructional parameters of buildings make comparison between different thermal comfort field studies inconsistent, even in the similar building, where zones in different orientations with unlike openings are assessed. Most studies considered classrooms as uniform thermal zones, in which the measurement are done in one point in the center of the classroom. However the classroom layout could result in non-uniform thermal zones due to solar radiation, diverse thermal radiant fields caused by cold/hot surfaces (windows, walls, and radiators), and drafts (windows, ventilation systems). Therefore, local discomfort evaluations in relationship to subjects’ position in classroom are necessary. Among the reviewed field studies, Teli et al. (2014) focused on two type of the school buildings (light weight and medium weight construction) [98] and Liang et al. (2012) focused on window configurations, especially glass properties, and illustrated how the level of thermal comfort in a classroom changed as a function of AWSG (Average Window Solar Gain) [66]. In addition the dynamic characteristics of the building envelope and the application of solar films to control the solar gain on the classrooms thermal conditions, has been evaluated only by physical measurements [92,95]. Local discomfort, resulted by solar direct radiation, is an important issue in classrooms. Overheating due to the solar gains through large windows, as the result of providing daylight in classrooms, are the main causes of thermal diversity and discomfort in these spaces. Although using window shadings (e.g. blinds and curtains) are adaptive behaviors to overcome this problem, they are energy consuming, since they usually cause daylight obstructions and require artificial lighting usage. Consequently, detailed investigations in thermal comfort levels in classrooms are necessary. Recent studies have developed models for considering the solar radiation in thermal comfort evaluations [101,102]. These models should be tested in field surveys in order to assess the effect of different window configurations on thermal comfort levels in classrooms and compare them to student’s actual thermal votes. 3.2.2. Mechanical parameters (Heating/cooling/ventilation systems) Indoor thermal comfort evaluation is essential to the heating, ventilation, and air-conditioning industry for proper installation, and general acceptance of the conditions experienced within the building [103]. Thermal comfort in relation to different heating, cooling, and ventilation systems has been an interesting issue for researchers in recent years. The difference in students' thermal comfort levels has been assessed in classroom with different heating systems [40] and ventilation strategies [41,70,104,105]. There have also been studies comparing students thermal comfort

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levels in NV and AC classrooms [71,106,107]. Recently, there has been a trend in designing NV classrooms for energy efficiency over different climate zones. Moreover, it was verified that running on naturally ventilation mode, CO2 concentration limits were highly exceeded [9,39,107–109]. Results indicate that classroom ventilation rates do not often meet building standards, and poor indoor air quality is thought to influence students’ health and performance, especially in lower ages. In the ASHRAE comfort database, the mean indoor air velocity associated with 90% thermal acceptability was relatively low, rarely exceeding 0.3 m/s. Post hoc studies of this database showed that occupants prefer for more air movement and suggest the potential to shift thermal acceptability to even higher operative temperature values, if higher air speeds were available [110]. The perceptible air movement inside buildings has been reformed in thermal comfort research over the last 20 years. Primary, air movement was considered overwhelmingly negative (draft, nuisance), but now the focus is on the positive aspects of air movement; aerodynamic pleasure, breeze, and thermal delight [18]. Regarding thermal comfort conditions of classrooms, air velocity increase is suggested as an essential phenomenon in obtaining a thermal comfort environment [38]. Installing mechanical fans instead of air-conditioning for improving the comfort of naturally ventilated buildings not only reduces the energy consumption, but also provides thermal comfort at higher temperatures by increasing the ventilation rate in classrooms. Reviewed studies reveal that classroom temperatures were controlled better when they were ventilated by mechanical system and/or by automatically operable window(s) with exhaust fan, allowing achieving cross-ventilation, compared to classrooms ventilated with manually operable windows. In the former classrooms, CO2 concentration levels were also lower, suggesting that the ventilation rates were higher, resulted in better classroom air quality [111]. Gao et al (2014) indicated that although air-conditioning systems are installed in classrooms to provide comfortable thermal conditions, a negative effect on comfort sensation might be caused without direct control of the systems by students [53]. A study in Italian university classrooms reveals that in the average air velocity of 0.10 m/s, provided by a centralized ventilation plant, 36.2% of the students evaluated the value of air velocity unacceptable and too high [60]. It is believed that the negative thermal perception could be the result of limited individual control possibilities on the thermal environment.

4. Conclusion The impact of the built environment factors on learning progress is a major new finding for schools' research. The significance of thermal comfort study is related to the relationship between the occupants’ satisfaction in the built environment, the functioning of the building, and energy consumption. Energy efficiency in educational buildings is significant for the reduction of total energy intensity. Lack of awareness and education are the most important barriers for progress in energy conservation because of their major influence on the attitude and behavior of the energy consumers. Students spend much of their time in schools, thus it is important to provide a good thermal comfort and indoor air quality levels. Thermal discomfort in educational buildings can create unsatisfactory conditions for both teachers and students. The challenge is to design buildings which will facilitate learning and overcome the state of discomfort with minimum energy consumption. Internal comfort temperature, determined in reviewed studies, is a basic metric for environmental designers and analysts of environmental comfort. The main findings of the study and recommendations for future study are summarized as follow:

 Based on research findings, currently used thermal comfort





 

standards, such as ISO 7730, EN 15251 and ASHRAE standard 55, and guides, such as CIBSE environmental Guide ‘A’, were mainly found to be inappropriate for the assessment of classroom thermal environments. A wide disparity in thermal neutralities has been observed in studies conducted in the same climate zones; which underlines the need for micro-level thermal comfort studies. In addition inconsistency in thermal neutralities between students in the same educational stage has been observed. Thermal comfort surveys are usually done in specific seasons with limited number of respondents. Studies should be done throughout the school year with more respondent to get the generalized comfort temperature ranges. In addition to general thermal comfort assessments, local discomfort evaluations in classrooms could be useful for decreasing the percentage of dissatisfied occupants. Classroom ventilation is determined as an important element of indoor air quality and thermal comfort. Also it has been observed that thermal comfort is not usually provided in NV classrooms, due to the low air velocity. The high temperature levels and low air supply rates, resulting in carbon dioxide exceedance, are mainly the result of inappropriate energy conservation actions in schools.

 The indoor and outdoor climates both have influences on  



human adaptability. Therefore, applying both approaches for thermal comfort evaluations results in more reliable outcomes. Reviewed studies showed that students prefer cooler environments and are more sensitive to warm conditions. Overheating occurs due to solar gains through large windows, as the result of providing daylight in classrooms, high levels of thermal insulation, and air sealing the building envelope; resulting in discomfort and reducing student performance. The excess heat load apparently could not be removed since windows are often closed to prevent external noise and drafts. Therefore energy conservation measures should be carefully applied in classrooms, considering the fact that saving energy is the secondary concern in educational building. Developing spatial and temporal thermal comfort metrics could be useful for design evaluations especially in classrooms, where students are subjected to sit in a fixed position during class time.

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