GREEN CONCEPT OF THERMAL COMFORT DESIGN FOR SUSTAINABLE HOUSING IN THE TROPICS: Learning from Thermal Comfort in School Buildings 1 INTRODUCTION

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1 Abstract GREEN CONCEPT OF THERMAL COMFORT DESIGN FOR SUSTAINABLE HOUSING IN THE TROPICS: Learning from Thermal Comfort in School Buildings Baharuddin Hamzah Department of Architecture, Hasanuddin University, Makassar Indonesia This article aims to share the thermal comfort indicators in designing thermally comfortable buildings in the tropics. It shares the three completed studies about thermal comfort in naturally ventilated and air- conditioned educational buildings. It also shares a strategy for designing thermal comfort in naturally ventilated traditional Buginese houses. The thermal comfort studies of naturally ventilated buildings involved 1,111 of elementary school students and 1,594 secondary school students from 14 schools and 81 classrooms in Makassar. The third study is carried out in the air- conditioned classrooms in the Faculty of Engineering Hasanuddin University, Gowa Campus. The fourth study is undergoing research of doctoral student in the Department of Architecture. The measurements collected four environmental variables: air temperature, humidity, radiant temperature, and air velocity, and two personal parameters, i.e. respondents' clothing and activities. In the naturally ventilated classrooms, the air temperatures were very high and coupled with low airflow speed. While the air temperatures in the air- conditioned building were quite low. The three studies show that the actual votes (TSV and TCV) are different with the predicted mean votes (PMV) either in naturally ventilated or air- conditioned buildings. In the naturally ventilated buildings, the neutral temperature of PMV always underestimates the neutral temperature of actual votes. The solar chimney is a potential strategy to cool the traditional buildings, however, there are still several aspects should be analyzed before it can be applied. Keywords: predicted mean votes, actual votes, neutral temperature, solar chimney. 1 INTRODUCTION Sustainable housing and settlement development are becoming a hot topic in the recent decade. Many housing developers try to sell their products using the green concept as a trademark. However, most of them failed to satisfy the green concept. This is because sustainable housing involved some criteria that should be fulfilled. Sustainable housing intended to reduce the environmental problem, increase the indoor quality, health, and safety for occupants, reduce the use of non- renewable building materials, increase the efficiency of energy and water (GBCI, 2014). Most of the housing developments only satisfy greening features such as parks without concerning the other aspects of the green housing such as energy and water efficiency and indoor quality of the buildings. One of the main concern of green building as mentioned before is to improve the indoor quality. The indoor quality including air quality, thermal comfort, lighting, visual, spatial and acoustic. Thermal comfort becomes a primary concern because it affects the occupant performance and leads to the energy use in residential buildings (Kwok et al., 2017). The GREENSHIP Homes award maximum two points for the house that satisfy the thermal comfort occupants without any air conditioning (AC) (GBCI, 2014). National Board of Standard of Indonesia (BSN, 2011) specifies that the buildings should provide the indoor temperatures in the ranges of 24 o C to 27 o C for thermal comfort purposes. Thermal comfort standards such as ASHRAE Standard 55 (ASHRAE, 2004) has been widely used as a standard for designing thermal comfort in different countries including Indonesia. To measure the thermal comfort experienced by the users, then according to this standard survey using a questionnaire based on a study conducted by Fanger (1970). This questionnaire asks the sensation of thermal perceived users in seven scales, namely: hot (+3), warm (+2), slightly warm (+1), neutral (0), slightly cool (- 1), cool (- 2), and cold (- 3). However, long time before, Bedford (1936) has proposed a method of measuring thermal comfort which also consists of seven scale that is much too warm (+3), too warm (+2), comfortably warm (+1), comfortable (0), comfortably cool (- 1), too cool (- 2), and much too cool (- 3).

2 The PMV is calculated based on Fanger (1970) formula which is used four thermal variables, i.e. air temperature, air humidity, radiant temperature, and air velocity and two personal parameters, i.e. clothing and activity. The use of PMV in predicting the thermal comfort of occupants in the naturally ventilated buildings in the tropic, however, has been criticised (Wong and Khoo, 2003; Feriadi and Wong, 2004; Hamzah et al., 2016). This is because the PMV mostly overestimate the actual votes of occupants in naturally ventilated buildings. Another indicator for evaluating the thermal comfort is neutral temperature. According to Feriadi and Wong (2004), the neutral temperature is the temperature where most of the respondents vote neutral (0) category in the ASHRAE scale. The neutral temperature calculated by applying simple linear regression between the TSV and Operative Temperature (T o ) as the independent variable. Several studies that have been done to overcome the heat problem in buildings in tropical climates such as providing roof insulation, using a lighter colour of the roof, and using the chimney effect. Ong (2011) conducted experiments by applying under- roof materials to reduced temperatures in the attic area under the roof or above the ceiling. Regarding the roof surface, Al Yacouby et al. (2011) state that roof surface colour should be one of the elements to be considered in the passive design. Givoni (1994) found that a dark painted roof results in a higher ceiling temperature in comparison to a painted roof with lighter colours. Another strategy for reducing the air temperature in buildings is the solar chimney. The chimney effect occurs due to a combination of hot air with the wind pressure from the vents. The air in the chimney expands from warming from the sun and becomes relatively lighter, rising out of the chimney outlet, sucking cold air into the building. The use of solar chimney for buildings in the tropic has been tested by several researchers (Tan and Wong, 2012; Tan and Wong, 2013; Tan and Wong, 2014). Tan and Wong (2012) found that the solar chimney system is operating well in the hot and humid tropics, including cooler days. In the parameterization study (Tan & Wong, 2013) found that "Among the four input parameters, the solar chimney's stack height, depth and width have a direct relationship with the output air speed where the greater the solar chimney's stack height, depth or width, the larger the output air speed." "Simulation results show that the solar chimney's width is the most significant factor influencing the output air speed." By using three completed and one ongoing studies, the author will highlight the following issues in the present article: the usage of PMV in evaluating thermal comfort in naturally ventilated and air- conditioned buildings the neutral temperature for both naturally ventilated buildings the proposed strategy to reduce the air temperature in the building interiors. 2 PREDICTED MEAN VOTES (PMV) VERSUS ACTUAL VOTES The following section describes the comparison between the predicted mean votes (PMV) and the actual votes by thermal sensation votes (TSV) and also thermal comfort votes (TCV) for two years study. 2.1 Naturally ventilated classrooms The first study carried out in 2016, which is based on the data collected from surveys that involved 1,111 respondents from six elementary schools in Makassar. Table 1 shows the thermal environmental (microclimatic) condition of the classrooms. The average temperature of o C with maximum o C indicate that classrooms in the surveyed primary schools experiencing excessive heat. The air temperature is outside the comfort zone as specified in the national standard (BSN, 2001). Air humidity is ranging from 53% - 89% with an average of 68%, indicating that the air humidity is within the comfort zone. Most of the classes have the average airflow rate is low, which is less than 0.5 m/s. Table 1: Microclimatic conditions recorded at the surveyed classrooms of elementary schools Statistic Air Temp ( O C) RH (%) MRT ( O C) Air Velocity (m/s) Average Minimum Maximum Figure 1 illustrates the primary school students' responses to the air temperature in the classrooms based on indicators of Thermal Sensation Vote (TSV), Thermal Comfort Vote (TCV), and also the Predicted Mean Vote

3 (PMV). Based on the TSV, about 43% of respondents voted the hot regions (+2 to +3) and only 29% voted the cold region (- 1 up to - 3). The percentage of respondents who felt neutral is less than 30%. Almost 90% of respondents vote in central category (- 1, 0, +1). Despite the high temperature in the surveyed classrooms These indicate that most of the students in the surveyed classrooms felt hot (uncomfortable). More than 38% of respondents voted the hot regions (+1 to +3) and only 12% in the cold region (- 1 to - 3) in the Bedford scale (TCV). Interestingly, about 50% of respondents felt comfortable in the classrooms. This figure quite different with the ASHRAE level (TSV) was less than 30% of respondents voted neutral. These suggest that both of these indicators, despite using the same size but gave a different result. It looks more respondents understand the word 'comfortable' than 'neutral'. Very different figure have resulted from the calculated of PMV. In the PMV model, all respondents were predicted to have voted in the hot region (1 to 3). This figure indicates that the PMV model overestimated the actual votes of those surveyed. According to this PMV model, no students will feel neutral or comfortable in these surveyed classrooms. The results gathered using PMV method were very different with the actual votes either by TSV or TCV, where about 28% and 50% respondents felt neutral and comfortable, respectively. This indication might not be appropriate to use PMV to estimate the thermal comfort of respondents in naturally ventilated rooms in the tropic. Figure 1: Comparison of PMV, TSV, and TCV of primary school students The second study was conducted in 2017, which is based on the response of 1,594 students from eight secondary schools. Table 2 shows the thermal environmental conditions in the surveyed classrooms. The average air temperature of o C and the maximum of o C indicate that the classrooms experienced high temperature during the day. The temperatures are outside the comfort zone as specified in the national standard (BSN, 2001). The relative humidity (RH) ranging from 53% - 89% with an average of 68%, indicating that most of the air humidity has already in the comfort zone. The Indonesian national standard (SNI) 6390:2011 specify that the thermal comfort zone for the comfortable room is within o C with RH 70-80%. Even for the comfortably warm, the air temperatures in the classrooms were not satisfied the SNI which specify the comfortably warm zone within o C with RH 60-70%. Table 2: Microclimatic conditions recorded at the surveyed classrooms of secondary schools Microclimatic factors Mean Standard Deviation (SD) Minimum Maximum Air temperature (T a ) in o C Relative humidity (RH) (%) Mean radiant temperature (MRT) in o C Operative temperature (T op ) in o C Air velocity (m/s)

4 The secondary school students response to the air temperature in the classrooms is shown in Figure 2, where about 87% of respondents vote in the comfortable region (slightly cool (- 1), neutral (0), and slightly warm (+1)) and only about 12% of them chose the uncomfortable hot regions (+2 to +3). These votes confirmed that despite the high temperature in the classrooms, most of the students still felt comfortable. More than 36 of respondents voted neutral (0). Regarding the TCV, also most of the students (87%) of respondents voted the three centerline votes (- 1, 0, and +1), and only about 12% felt uncomfortably hot (+2 and +3). Very little students voted the uncomfortably cold area. The percentage of respondents who voted 0 (comfortable) is about 46%, which bigger than the respondents who voted 0 in the TSV indicator. The very different figures are observed in the predicted votes using the PMV method. In this indicator, only about 23% of respondents categorized as comfortably warm (+1), and more than 77% of respondents felt uncomfortably hot (+2 and +3). 2.2 Air- conditioned classrooms Figure 2: Comparison of PMV, TSV, and TCV of secondary school students The thermal environment conditions of classrooms during measurements are shown in Table 3. As seen in the table, the air temperature in the classrooms was in the ranges of to o C with the average of o C ( 25 o C). The relative humidity (RH) were ranging from 41 to 68% with an average 49.92% ( 50%). By using the formula of operative temperature T o = (Ta+MRT)/2, then the operative temperature was ranging from to o C (T o ) with an average o C (T o ). In general, the air temperature and the relative humidity have already laid in the thermal comfort zone according to the national standard (BSN, 2001). Table 3: Microclimatic conditions recorded at the surveyed air- conditioned classrooms Statistic Air Temp ( o C) RH (%) MRT ( o C) Airflow (m/s) Average Minimum Maximum Students' response to the air temperature in the classrooms based on indicators thermal sensation vote (TSV), thermal comfort votes (TCV), and predicted mean votes (PMV) could be seen in Figure 3. Regarding TSV, Figure 3 shows that the majority of respondents (more than 50%) vote in the cool region (- 3 to - 1) where more than 35% felt cool (- 2) and about 18% felt cold (- 3). Only about 15% of respondents felt neutral (0). These indicate that most of the students felt cool and cold. Interestingly, there were about 8% of respondents felt slightly warm (+1) or warm (+2). Regarding the TCV, the figure shows that more than 60% of respondents vote the cold regions (- 3 to - 1) and only less than 10% vote the hot region (+1 to +2). About 30% of respondents felt comfortable in these surveyed classrooms. The percentages of respondents who vote comfortable (0) in the TCV are more the percentage of respondents who vote neutral in the TSV. The very different figure is observed in PMV, where the majority of respondents (more than 70%) are predicted to have voted in the cool (- 2). Less than 15% respondents to be predicted have neutral (0) votes.

5 Figure 3: Comparison of PMV, TSV, and TCV of students to the air- conditioned classrooms 3 NEUTRAL TEMPERATURE The determination of neutral temperature based on the data gathered from elementary schools is shown in Figure 4. With most of PMV values lay in the hot regions (+1 to +3) (see Figure 1), the linear regression equation (with R , F 11,220 Sig and all coefficient values are statistically significant) between PMV and T o is as follows: PMV = 0.37T op 9.37 (1) The neutral temperature (T n ) calculated from this equation (1) is o C. This value means that the respondents would feel neither warm nor cool at o C (T o ). This value is lower than the average temperature of classrooms, which were ranging from 28.5 o C up to 34 o C. Therefore according to this PMV, no one will be predicted to have neutral (0) votes in these classrooms. Figure 4: Regression between the operative temperature (T o ) with PMV, TSV, and TCV

6 The very different number is found in the relation between TSV and T o. The linear regression (with R , F Sig and all coefficient values are statistically significant) is shown in the following equation: TSV = 0.22T o 6.64 (2) The T n obtained from the equation (2) is 30,20 o C, which means that the respondents would feel neutral at a temperature of 30,20 o C (T o ). This temperature value is far higher than the neutral temperature using the PMV method. The relationship between the TCV and T o is similar to the relationship between the TSV and T o and also very different with PMV. The linear regression (with R , F Sig and all coefficient values are statistically significant) gives the equation as follows: TCV = 0.20T o 5.91 (3) The T n obtained from this equation is o C, which means that the respondents would feel neutral at a temperature of o C (T op ). This temperature value is higher than the temperature of the neutral using the PMV and slightly lower than the neutral temperature using TSV. The determination of neutral temperature based on the data gathered from secondary schools is shown in Figure 5. Figure 5 demonstrates the relationship between the operative temperature (T o ) with a value of PMV, TSV and TCV, respectively. The statistical values of the two variables (PMV and T o ) are R and R with the Sig indicated that the relationship between the two variables is statistically very significant. These give the relationship equation as follows: PMV = 0.339T o (4) The neutral temperature (T n ) from equation (4) is o C. This means that the respondents would feel neutral at an operative temperature of 25.0 o C. This value is very low if compared with the operative temperature of classrooms, which were ranging from 28.2 o C up to 33.6 o C. Therefore, the use of this PMV formula to predict the thermal comfort of the respondent might be incorrect, because then there will be no respondents who feel neutral (comfortable). Figure 5: Regression between the operative temperature (T o ) with PMV, TSV, and TCV for secondary students responses The statistical values of the regression between TSV and T o are R and R with the Sig indicated that the relationship between the two variables is statistically significant. These give the relationship equation as follows: TSV = 0.175T o (5)

7 This equation produces the neutral temperature of o C. This means that the respondents would feel neutral at an operative temperature of 25.0 o C. This value must be very low if compared with the operative temperature of classrooms ranging from 28.2 o C up to 33.6 o C. The statistical values of the regression between TCV and T o give R and R with the Sig indicated that the relationship between the two variables is statistically very significant. These give the relationship equation as follows: TCV = 0.204T o (6) The neutral temperature (T n ) obtained when the operative temperature is 28.5 o C. This means that the respondents would feel comfortable at an operative temperature of 25.0 o C. This value must be very low if compared with the operative temperature of classrooms ranging from 28.2 o C up to 33.6 o C. 4 PROPOSED STRATEGY FOR REDUCING AIR TEMPERATURE A preliminary field survey has been conducted to verify the issue that the interior of Buginese house is hot during the day. Measurements were made at 19 houses (two sample houses are seen in Figure 6) in several districts in South Sulawesi Province, i.e., Makassar, Maros, Pangkep, Barru, Pare- pare and Pinrang. The measurement results show the average air temperature in the living room of 19 Buginese house from CIT (Central Indonesia Time) C with a maximum temperature of C and a minimum of C. The relative humidity of air is 66,34%, RH maximum 79,26% and minimum 51,12%. Measurements were made on October 30 - November 1, In addition to that, a survey to collect the thermal conditions in the attic area and family room has been carried out at a traditional house in Makassar. The measurement shows that the temperature under the roof (attic room) this house was very hot. The average temperature of C with a maximum of C was recorded at 11:00. The average temperature in the family room was C with a maximum of C. The measurements were conducted on August 26, Figure 6: Traditional Buginese house (photographed by Sahabuddin Latif) As mentioned before, one of the strategies for cooling the interior space can be done by draining the air to transport hot air out of the interior space by exploiting the heat of solar radiation (stack effect). The following section presents the use of stack effect (solar chimney) for cooling the traditional house. Figure 7 illustrates a bedroom with 3m length, 3m width, and 2.55m height which is combined with the under roof 15cm deep- solar chimney. The inlet is under the window and the outlet at the top of the chimney. The roof and the wall of the model made of zinc, which is in contact with the solar radiation. The chimney parts: a) contact window with outer space; b) chimney inlet; c) aperture and d) chimney outlet.

8 Figure 7: Solar chimney construction in the bedroom Figure 8 shows the simulation results of the solar chimney model connected to the chamber. Climatic parameter inputted is climatic conditions on August 26, at the location of Makassar city at WITA, sunny weather condition with outside temperature was 28 C. The simulation is a free convection simulation that does not take into account the wind velocity of the environment. Figure 8: Contour plot of A) air velocity and B) Temperature of bedroom with chimney effect Figure 9 shows the simulated results of the solar chimney model being closed or restricting the airflow of the output. Climatic parameter inputted is climatic conditions on August 26, at the location of Makassar city at WITA, sunny weather condition with outside temperature is 28 C. This simulation does not take into account the wind velocity of the environment.

9 Figure 9: Contour plot of A) air velocity and B) Temperature of bedroom without chimney effect The cooling strategy of interior space with the application of solar chimney integrated with interior space can improve the distribution of airflow in the room while reducing the room temperature. The first experiment shown in Figure 8 shows the distribution of air temperature rising at about ± 1 C compared to outside temperature with an airflow distribution reaching 0.4m/s. Compared to the simulation without using the chimney effect shown in Figure 9, the lowest temperature distribution in the room is above 29 C above the floor level, the higher the temperature rises. Likewise, the distribution of indoor air velocity is very minimal only occur around the window. 5 CONCLUSION The survey and measurements of thermal comfort in the naturally ventilated classrooms of primary and secondary schools in Makassar show very high temperature during the day. Except for air humidity, most of the thermal environment aspects do not satisfy the Indonesian standard. However, a lot of some students felt comfortable (comfortably cool, comfortable, and comfortably warm). In fact, more than 80% of students accepted the thermal environment of the classrooms. The predicted mean votes (PMV) do not fit with the actual votes, either by thermal sensation votes (TSV) or by thermal comfort votes (TCV). The PMV always overestimates the thermal sensation of respondents. For the air- conditioned buildings, there is no much difference between the PMV, TSV, and TCV. This indicates that the PMV is more suitable for air- conditioned buildings than for naturally ventilated buildings. The neutral temperature found in the naturally ventilated buildings based on the PMV always smaller than the neutral temperature gathered from TSV and TCV. This result also shows that the PMV may be incorrect to predict the neutral temperature of respondents in naturally ventilated buildings. Stack effect by solar chimney is a promising strategy to reduce the air temperature. However, its application in the naturally ventilated Buginese traditional houses should be further investigated from different aspects.

10 ACKNOWLEDGEMENT The author would like to thank the Ministry of Research, Technology and Higher Education and the Rector of Hasanuddin University for providing the fund for the first three studies. Thanks also due to Mr Sahabuddin, a doctoral student who provide data for the initial study on the use of solar chimney to reduce air temperature in traditional Buginese houses. REFERENCES Al Yacouby, A., Khamidi, M. F., Nuruddin, M. F., Idrus, A., Farhan, S. A. and Razali, A. E. (2011) A review on thermal performance of roofing materials in Malaysia, in A. N. A. Ghani, M. A. O. Mydin and N. F. Abas (eds.),international Building and Infrastructure Technology Conference School of Housing, Building, and Planning, Universiti Sains Malaysia, Vistana Hotel, Penang, Malaysia, ASHRAE (2004) Thermal Environmental Condition for Human Occupancy (ASHRAE Standard 55), ASHRAE, Atlanta, US. Bedford, T. (1936) Warmth factor in comfort at work, Medical Res Council, Industry Health Res Board. BSN (2001) SNI : Tata cara perancangan sistem ventilasi dan pengkondisian udara pada bangunan gedung (The procedure of designing ventilation and air conditioning systems in buildings), ed., Badan Standardisasi Nasional (BSN) Indonesia, Jakarta. Fanger, P. O. (1970) Thermal comfort - Analysis and application in environmental engineering, ed., Danish Technical Press, Copenhagen. Feriadi, H. and Wong, N. H. (2004) Thermal comfort for naturally ventilated houses in Indonesia, Energy and Buildings, 36(7), GBCI (2014) GREENSHIP Home Version 1, ed., Green Building Council Indonesia, Jakarta. Givoni, B. (1994) Passive low energy cooling of buildings, ed., John Wiley & Sons, New York, US. Hamzah, B., Ishak, M. T., Beddu, S. and Osman, M. Y. (2016) Thermal comfort analyses of naturally ventilated university classrooms, Structural Survey, 34(4/5), Kwok, Y. T., Lau, K. K.- L., Lung Lai, A. K., Chan, P. W., Lavafpour, Y., Kwan Ho, J. C. and Yung Ng, E. Y. (2017) A comparative study on the indoor thermal comfort and energy consumption of typical public rental housing types under near- extreme summer conditions in Hong Kong, Energy Procedia, 122, Ong, K. S. (2011) Temperature reduction in attic and ceiling via insulation of several passive roof designs., Energy Conversion and Management, 52 (6), Tan, A. Y. K. and Wong, N. H. (2012) Natural ventilation performance of classroom with solar chimney system, Energy and Buildings, 53, Tan, A. Y. K. and Wong, N. H. (2013) Parameterization studies of solar chimneys in the tropics., Energies, 6(1), Tan, A. Y. K. and Wong, N. H. (2014) Influences of ambient air speed and internal heat load on the performance of solar chimney in the tropics, Solar Energy, 102, Wong, N. H. and Khoo, S. S. (2003) Thermal comfort in classrooms in the tropics, Energy and Buildings, 35(4),