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Thermal comfort study of Kerala traditional residential buildings based on questionnaire survey among occupants of traditional and modern buildings
Energy and Buildings 42 (2010) 2139–2150
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Thermal comfort study of Kerala traditional residential buildings based on questionnaire survey among occupants of traditional and modern buildings A.S. Dili a,∗ , M.A. Naseer b , T. Zacharia Varghese c a b c
Department of Architecture, TKM College of Engineering, Kollam, Kerala, India Department of Architecture, National Institute of Technology Calicut, Kerala, India Department of Civil Engineering, National Institute of Technology Calicut, Kerala, India
a r t i c l e
i n f o
Article history: Received 25 February 2010 Received in revised form 10 June 2010 Accepted 2 July 2010 Keywords: Kerala Traditional buildings Modern buildings Thermal comfort Questionnaire survey
a b s t r a c t Thermal comfort studies on traditional residential buildings of Kerala that is known for its use of natural and passive methods for a comfortable indoor environment, are under progress. Scientific analyses of the environmental parameters determining thermal comfort have already been reported. Similar studies on modern residential buildings are underway. In order to compare the results of the scientific analysis with the user responses from the residents of traditional as well as modern residential buildings, a questionnaire survey was conducted during various seasons such as winter, summer and monsoon. A questionnaire was prepared in detail to understand the effect of factors which affect thermal comfort such as temperature, humidity and air flow in the evaluation of thermal comfort. This paper is based on the compilation of responses from the conducted survey. A comparison of the study results with that of scientific analysis already reported is also incorporated at the end of this paper. This study further confirms that Kerala traditional residential buildings are very effective in providing comfortable indoor environment irrespective of various seasons. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Passive methods of achieving thermal comfort inside the buildings are the best solution to provide a healthy and energy efficient indoor environment [1–4]. This is of supreme importance for buildings in the tropics where mechanical systems with high energy consumption are used to condition the indoor environment for thermal comfort [5]. The people are forced to depend on such systems because, majority of the buildings are designed without giving adequate importance to passive methods for controlling the indoor environment. In many cases, failure to provide the required thermal conditions has resulted in discomfort, ill health and productivity loss. Presently, there is a constant need to evaluate the thermal conditions of the indoor environments to learn further and proceed with the research in passive design [6–10]. Kerala, a state in India located in the southwest coast, falls in the warm-humid climatic zone according to Bureau of Indian Standards [11]. The presence of high amount of moisture in the atmosphere, due to its geographical setting, for major part of the year causes thermal discomfort as there is less evaporation, resulting in sweating. This becomes more acute in summer when the air temperature and relative humidity become higher.
∗ Corresponding author. Tel.: +91 9447303875. E-mail addresses: [email protected], dili [email protected] (A.S. Dili). 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.07.004
Studies on passive methods of achieving thermal comfort in buildings are under progress in the form of extracting methods and techniques from traditional buildings in various countries [12–19]. In India, such studies have been reported recently from the NorthEast part where the climate is composite in nature [20–22]. The authors have conducted an investigation of traditional architecture in the context of Kerala, where the climate is warm-humid, to understand the passive environment control system. Quantitative analyses based on continuous recording and evaluation of thermal comfort parameters in traditional buildings has already been published [23–29]. A questionnaire based survey on the residents of the traditional and modern residential buildings was required to compare with the results obtained from the quantitative analyses. Thus a questionnaire survey was conducted among the residents of traditional and modern buildings through various seasons to assess the subjective response of thermal comfort. The study was conducted during various seasons such as winter, summer and rainy period of monsoon season. The questionnaire was prepared in detail to understand the effect of factors which affect thermal comfort such as temperature, humidity and air flow in the evaluation of thermal comfort. Respondents from age groups ranging from 20 to 70 years, with more or less equal representation from either sex were selected for the survey. A Summary of Experimental Investigations already Reported on Kerala Traditional Residential Buildings is included in this paper.
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A comparative analysis of the outcome of the survey with the scientific studies already reported is also incorporated. This paper also explores a comparison of thermal comfort between traditional and modern buildings through various seasons. 2. Methods 2.1. Selection of people The survey was conducted among the selected people from selected families of both traditional and modern buildings of Kerala. Fifty families each living in traditional and modern building were selected for the survey. A total number of 200 people each from traditional and modern houses were selected for the study with an average of four members from each family. The traditional houses of about 200–300 years of age, built according to the ancient principles were selected for the survey. The basic module of traditional residential building of Kerala is known as nalukettu with four blocks built around an open courtyard. They are generally rectangular or square in plan with blocks topped with a sloping roof on all four sides while the courtyard is left open to the sky for letting air and light inside. There is an internal verandah around the courtyard for protection from rain and sun. The roofs have steep slopes up to almost 45 degrees and are topped with clay tiles on wooden framework with gaps provided in between tiles to enhance ventilation and to allow the warm air to escape. Further, ventilators are provided for the ventilation of attic spaces that are formed by the wooden false ceiling (tattu) provided for the room spaces. This roof encloses a large insulated air space keeping the lower areas cooler. A detailed description on the traditional residential buildings of Kerala and its typical layout are given elsewhere [27]. Modern buildings of less than 20 years of age were selected for the survey. Modern buildings of Kerala do not have any common design principles nor do they follow a common architectural style. Most of the buildings are constructed with brick masonry walls plastered with cement mortar and topped with RCC roof. The roofs are either flat or sloping at different angles. Window openings are provided all around the buildings and they are extensively covered with glass paneled shutters. The buildings, both traditional and modern, were selected from various parts of Kerala irrespective of the micro level variations in climate and topography. A detailed description on the topography and climate of Kerala are given elsewhere [27]. People with sensible mind and keen observation skill on thermal comfort were selected for the survey. They were briefed about the scope of the survey, and were given sufficient input before the conduct of the survey on how to respond to the questionnaire.
2.3. Survey methodology The survey was conducted with the help of many interested people in this field. They were educated in detail about the relevance and objectives of the survey by the authors. The different components of the questionnaire, its meaning and the gradation were also explained in advance. The survey was conducted in the peak of each season simultaneously in different locations i.e. during the first week of January 2009 (winter peak), last week of April 2009 (summer peak) and last week of July 2009 (monsoon peak). 3. Results and analysis The subjective responses, on various thermal comfort parameters and that on the overall thermal comfort, obtained from the questionnaire survey conducted during various seasons are illustrated below. The analysis and interpretation of the results obtained from the survey is provided at the end of this section. An average vote for overall thermal comfort in an annual basis is also illustrated. 3.1. Winter season Fig. 1 shows the distribution of subjective response on temperature in winter season. While about 35% of the residents of traditional buildings voted for neutral temperature, only 26% of the residents of modern buildings voted for the same. Also, while 25% of the residents of traditional buildings voted for slightly warm temperature, 37% of the residents of modern buildings voted for the same. 19% of the residents of modern buildings believe that their buildings are warm in winter while 8% believe that it is hot. When 32% of the residents of the traditional buildings believe that their buildings are slightly cool, only 10% of the modern building residents believe the same. It is evident from the Fig. 1 that, while the votes from people of traditional buildings are balanced around the neutral condition, the same of modern buildings shows a tendency towards warm condition. The distribution of subjective response on humidity in winter season is shown in Fig. 2. From this figure, it is clear that, around 50% of the people in the traditional and modern buildings believe that their dwellings are neutral in terms of humidity in winter season. While about 31% of the residents of traditional buildings voted for slightly dry, 36% of the residents of modern buildings voted for the same. Less than 5% of people in both the buildings believe that their buildings are humid in winter season. Also, less than 10% of people
2.2. Preparation of questionnaire The questionnaire for the survey was prepared to obtain the subjective responses from the respondents on various thermal comfort parameters such as temperature, humidity and air flow along with a response on overall thermal comfort. The selection and gradation of components in the questionnaire was done by a detailed review of literature in the respective field [30–38]. The residents were asked to evaluate the environment in a condition when they are not using any of the aid – mechanical or otherwise – to improve or modify the indoor environment. The questionnaire was prepared both in English and Malayalam (regional language of Kerala) for easy conduct of the survey. Also, it was reproduced in three different colours – light blue, pink and light green – for the surveys conducted during winter, summer and rainy season respectively. The questionnaire prepared for the investigation is given in Appendix A at the end.
Fig. 1. Distribution of subjective response on temperature in winter season.
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Fig. 2. Distribution of subjective response on humidity in winter season.
in both the buildings believe that their buildings are moderately dry in winter and no one voted for “very dry”. Fig. 3 shows the distribution of subjective response on air movement in winter season. More than 70% of the occupants of the traditional houses voted for acceptable air movement. The remaining people of the traditional houses voted towards still air as shown in figure. Almost 80% of the occupants of the modern buildings have difference in opinion about air movement ranging from slightly still to moderately draughty. The extreme characteristics, very still and very draughty are selected by less than 10% of the occupants of modern houses. The distribution of subjective response on overall thermal comfort in winter season is shown in Fig. 4. 73% of the occupants of the traditional buildings voted that their dwellings are very comfortable in winter. The remaining 27% voted for comfortable and slightly uncomfortable with a distribution of 25% and 2% respectively. Only 8% of the occupants of the modern buildings voted that their dwellings are very comfortable in winter. 63% from the modern buildings voted for comfortable and slightly uncomfortable with a distribution of 31% and 32% respectively. The remaining 29% of the modern buildings voted for uncomfortable and very uncomfortable with a distribution of 17% and 12% respectively as shown in Fig. 4. 3.2. Summer season Fig. 5 shows the distribution of subjective response on temperature in summer season. While about 56% of the residents of traditional buildings voted for neutral temperature, only 8% of the residents of modern buildings voted for the same. Also, while about 8% of the residents of traditional buildings voted for slightly warm
Fig. 3. Distribution of subjective response on air movement in winter season.
Fig. 4. Distribution of subjective response on overall thermal comfort in winter season.
Fig. 5. Distribution of subjective response on temperature in summer season.
temperature, 11% of the residents of modern buildings voted for the same. It is evident from this figure that no one in the modern buildings feels their dwellings are slightly cool, cool or cold. 81% of the residents of the modern buildings voted for warm and hot with a distribution of 49% and 32% respectively. The distribution of subjective response on humidity in summer season is shown in Fig. 6. From this figure, it is clear that, 61% of the people in the traditional buildings believe that their dwellings are neutral in terms of humidity in summer season. Only 11% of the residents in modern buildings believe that the condition is neu-
Fig. 6. Distribution of subjective response on humidity in summer season.
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Fig. 7. Distribution of subjective response on air movement in summer season. Fig. 9. Distribution of subjective response on temperature in rainy season.
tral. While 10% of the residents of traditional buildings voted for slightly dry, 8% of the residents of modern buildings voted for the same. 76% of the residents of the modern buildings voted for slightly humid, moderately humid and very humid with a distribution of 23%, 36% and 17% respectively. Out of 24% of the residents of the traditional buildings, only 5% believes that their dwellings are moderately humid. The remaining voted for slightly humid. While no one voted for very dry, 17% of the modern residents voted that their dwellings are very humid. Fig. 7 shows the distribution of subjective response on air movement in summer season. More than 80% of the occupants of the traditional houses voted for acceptable air movement. Most of the remaining people of the traditional houses voted towards still air as shown in figure. About 80% of the occupants of the modern buildings have difference in opinion about air movement almost equally ranging from slightly still to moderately draughty. The extreme characteristics, very still and very draughty are also reported by less than 5% of the occupants of modern houses. The distribution of subjective response on overall thermal comfort in summer season is shown in Fig. 8. 70% of the occupants of the traditional buildings voted that their dwellings are very comfortable in summer. The remaining 30% voted for comfortable and slightly uncomfortable with a distribution of 27% and 3% respectively. No one among the occupants of the modern buildings voted that their dwellings are very comfortable in summer but for 71% of the occupants feel that, their dwellings are very uncomfortable. The remaining 29% of the modern buildings voted for slightly
Fig. 8. Distribution of subjective response on overall thermal comfort in summer season.
uncomfortable and uncomfortable with a distribution of 8% and 21% respectively. 3.3. Rainy season Fig. 9 shows the distribution of subjective response on temperature in rainy season. While about 32% of the residents of traditional buildings voted for neutral condition, 37% of the residents of modern buildings voted for the same. Also, while 50% of the residents of traditional buildings voted for slightly warm temperature, only 10% of the residents of modern buildings voted for the same. Only 2% of the residents of modern buildings believe that their buildings are warm in rainy season. While 10% of the residents of the traditional buildings believe that their buildings are slightly cool, only 4% believe that the temperature is cool in rainy season. It is evident from this figure that, no one in the traditional buildings as well as modern buildings feels that their dwellings are cold or hot during rainy season. The distribution of subjective response on humidity in rainy season is shown in Fig. 10. From this figure, it is clear that, around 55% of the people in the traditional and modern buildings feel that their dwellings are neutrally humid in rainy season. While about 2% of the residents of traditional buildings voted for slightly dry, 5% of the residents of modern buildings voted for the same. Around 10% of people in both the buildings believe that their buildings are moderately humid in winter season. It is evident from this figure that, no one resides in the traditional buildings as well as modern build-
Fig. 10. Distribution of subjective response on humidity in rainy season.
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modern buildings voted for comfortable and slightly uncomfortable with a distribution of 31% and 28% respectively. The remaining 22% of the modern buildings voted for uncomfortable and very uncomfortable with a distribution of 13% and 9% respectively as shown in Fig. 12. 4. Summary of experimental investigations already reported on Kerala traditional residential buildings 4.1. Instrumentation setup
Fig. 11. Distribution of subjective response on air movement in rainy season.
An instrumentation setup called Architectural Evaluation System (AES) has been devised to continuously record the comfort parameters over a period of time. AES is a combination of electronic sensors, data logger, memory module and computer interface. Electronic sensors in AES were used to sense thermal comfort parameters such as air temperature (AT), relative humidity (RH) and air movement. A memory module was used to record data from the sensors and the computer interface is used to view and download data for analysis. The Architectural Evaluation System (AES) was suitably installed in a selected traditional residential building (Nilambur Kovilakam) to record the thermal comfort parameters. A schematic diagram of AES, selected area for investigation and photographs are given elsewhere [27]. 4.2. Investigation during winter and summer [26]
Fig. 12. Distribution of subjective response on overall thermal comfort in rainy season.
ings feels that their dwellings are very dry, moderately dry and very humid during rainy season. Fig. 11 shows the distribution of subjective response on air movement in rainy season. 70% of the occupants of the traditional houses voted for acceptable air movement. Most of the remaining people of the traditional houses voted towards still air as shown in figure. 60% of the occupants of the modern buildings voted for slightly draughty, moderately draughty and very draughty with a distribution of 30%, 18% and 12% respectively. 8% of the occupants of the traditional buildings voted for very still and moderately still air movement with a distribution of 5%, 3% respectively. The distribution of subjective response on overall thermal comfort in rainy season is shown in Fig. 12. 66% of the occupants of the traditional buildings voted that their dwellings are very comfortable in rainy season. The remaining 34% voted for comfortable and slightly uncomfortable with a distribution of 29% and 5% respectively. Only 19% of the occupants of the modern buildings voted that their dwellings are very comfortable in rainy season. 59% of the
An over view of the results obtained during winter and summer are presented in Table 1. The interpretations of results are explained below in brief for a better understanding. The diurnal variation of indoor air temperature is very less compared to that of outdoor ambient air temperature in both the seasons. The low diurnal variation of the indoor temperature proves the high thermal insulation property of the building envelope. There is no time lag observed between outdoor and indoor air temperatures. The absence of time lag between outdoor and indoor temperatures can be attributed to the highly insulative wall preventing conductive heat flow and to the continuous air flow maintained through the building. The reason for thermal discomfort in summer season in Kerala is not due to the increase in minimum temperature alone, but is mainly due to the increase in the moisture content in the air during that period. In such a climatic condition, the only way to achieve a comfortable indoor environment is to have a control over the air temperature supplemented by a continuous air movement that can ensure the required rate of evaporation from the body of occupants. From the investigation, it is found that, the building envelope permits a controlled and continuous air movement through the building irrespective of the seasons. The building envelope (both walls and roof) prevents the conductive heat flow into the interiors. The heat flow due to radiation is blocked by protecting the walls with roof overhangs and by providing sufficient thermal insulation for the roof. The evaluation of thermal comfort with bioclimatic chart showed that the traditional building indoors provide better comfort during winter and sum-
Table 1 Overview of the results obtained during winter and summer. Periods
Air temperature (◦ C)
Decrement factor
Outdoor
Winter Summer
Bedroom
Variation in RH (%) Outdoor
Min
Max
Variation
Min
Max
Variation
18 25
36 38
18 13
23.5 28
28 32
4.5 4
0.22 0.28
Bedroom
Min
Max
Min
Max
28 35
100 100
45 57
90 95
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Table 2 Overview of the results obtained during the various periods of rainy season [28]. Periods
Diurnal variation (◦ C)
Decrement factor
Outdoor
Beginning rain Normal rain Heavy rain Non-rainy days
Bedroom
Variation in RH (%) Outdoor
Min
Max
Variation
Min
Max
Variation
24 24 22.5 23
31 28.5 26 35.5
7 4.5 3.5 12.5
27 26.5 25 27
29 27.5 27 30.5
2 1 2 3.5
mer. The continuous air flow (around 0.5 m/s) maintained inside the building provides better comfort even at a high humidity. The PMV–PPD analysis also showed that the traditional building indoors provide the required range of thermal comfort during winter and summer. 4.3. Investigation during rainy season [28] It is observed that rainy season is the season with more fluctuations in the climatic parameters. In order to have a detailed comparative analysis, the rainy season was divided into four periods such as the beginning of rainy season, days during normal rain, days during heavy rain and non-rainy days. The results obtained during the various periods of rainy season are consolidated and presented in Table 2. The interpretations of results are explained below. The investigation has revealed that, when the outside ambient temperature is below normal, the building system tries to maintain the indoor air temperature at a higher but comfortable level and when the outside temperature is above normal, the indoor is kept at a lower but comfortable level. A continuous gentle wind flow was maintained inside the building irrespective of the wind outside. The required level of thermal comfort was thus achieved by maintaining a balanced condition of temperature and relative humidity along with the airflow. The evaluation using PMV–PPD analysis and Bioclimatic chart confirms the indoor thermal comfort of traditional buildings during the various periods of rainy season. 5. Comparison and analysis of results In this section, the results of the questionnaire survey illustrated above are compared between various seasons for analysis and better understanding. The results of the questionnaire survey are also compared with the scientific investigations on traditional buildings already reported [26–28]. Comparing Figures 1, 5 and 9, it can be seen that while more than 50% of the residents of the traditional buildings voted for neutral condition in terms of temperature in summer, 30–35% people voted for the same in other two seasons. Most of the people in traditional houses feel that their dwellings are cooler in winter and summer, and are warmer in rainy season. This observation can be substantiated by the results of the experimental investigations given in Tables 1 and 2. From Table 2, it can be seen that during heavy rain, the maximum indoor temperature (27 ◦ C) is higher than the maximum outdoor temperature (26 ◦ C). The thermal characteristics of the Kerala traditional building envelope are playing a vital role in controlling the temperature. It can also be learned from the Figures 1, 5 and 9 that, the modern buildings are warmer in winter and rainy seasons and are hotter in summer. In summer most of the residents of the modern buildings feel that their dwellings are humid as evident from Figure 6. While the residents of both traditional and modern buildings voted almost similar manner about humidity in winter and rainy season, they differ in their opinion in summer season. From Figures 2, 6 and 10,
0.32 0.22 0.50 0.28
Bedroom
Min
Max
Min
Max
70 88 80 45
100 100 100 97
80 85 80 65
90 95 93 82
it can be seen that more than 50% of the residents of the traditional buildings voted for neutral condition for humidity in all seasons. The combined effect of temperature and humidity in traditional buildings in various seasons is explained below to substantiate this point. The variation of RH along with the variation of temperature during winter and summer in traditional buildings is given in Table 1. During winter day time when the indoor temperature is high up to 28 ◦ C, the humidity is as low as 45%. This falls well within the comfort zone of the bioclimatic chart constructed by Olgyay [39]. During night, since temperature becomes low up to 18 ◦ C, the increase in humidity (up to 88%) does not really affect the indoor comfort condition. During summer day time when the indoor temperature is high up to 32 ◦ C, the humidity is as low as 57%. This falls well within the comfort region of the bioclimatic chart since the wind velocity maintained inside the building is around 0.5 m/s and it is very near to the comfort zone. During night, since temperature reduces up to 28 ◦ C, the indoors remains comfortable even though the RH is as high as 95%. The variation of RH along with the variation of temperature during rainy season in traditional buildings is given in Table 2. This shows that the day time indoor temperature is high up to 27 ◦ C and RH is 80% during the period of heavy rains. This is well within the comfort region of the bioclimatic chart with the wind velocity of 0.5 m/s maintained inside the building. In the nights, the indoor temperature and RH are 25 ◦ C and 93% respectively and is again within the comfort region of the bioclimatic chart. It can be seen from Figures 3, 7 and 11 that residents of traditional houses voted for air flow almost in a similar manner in all seasons. No one among the residents of traditional houses voted for moderately draughty and very draughty air flow and 70–80% of the same people voted for an acceptable air flow in all seasons. Reported experimental investigations on traditional buildings prove that the building system is maintaining an air flow of 0.5 m/s continuously. On the other hand, from the same figures, it can be seen that, the residents of the modern houses have a mixed opinion on the air flow ranging from very still to very draughty. On judging the overall comfort, comparing Figures 4, 8 and 12, it can be seen that around 70% of the occupants of the traditional houses voted for very comfortable condition in all seasons; while no one feels that they are uncomfortable or very uncomfortable. At the same time, it can also be seen that less than 20% of the occupants of the modern houses voted for very comfortable condition in winter and rainy seasons; while no one feels that they are very comfortable in summer season. This observation can be substantiated by the results of the experimental investigations already reported. The evaluation using PMV–PPD analysis and conformity to Bioclimatic chart proves that the traditional buildings of Kerala are comfortable in all seasons [26–28]. Fig. 13 shows the distribution of subjective response on overall thermal comfort in an annual basis. An average of 70% of the occupants of the traditional buildings feels that their dwellings are very comfortable in a year. The remaining 30% can be averaged as comfortable and slightly uncomfortable with a distribution of 27% and
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ment – are very much in agreement with their voting for the overall thermal comfort. It indicates that the selection of people for the survey is suitable for the context. The level of participation of the people involved in the survey reflects the perfection of the results. The outcome of the questionnaire survey and its analysis clearly indicate that the traditional houses of Kerala are very comfortable to live in round the year irrespective of the seasons.
6. Discussion
Fig. 13. Distribution of subjective response on annual overall thermal comfort.
3% respectively. Only 9% of the occupants of the modern buildings are found that very comfortable in all seasons. 43% of the modern buildings can be averaged annually as comfortable and slightly uncomfortable with a distribution of 21% and 22% respectively. The remaining 48% of the modern buildings are found to be uncomfortable and very uncomfortable with a distribution of 17% and 31% respectively as shown in Fig. 13. Majority of the people participated in this survey seems to have responded sensibly and their vote represents thermal comfort conditions of the houses they live in. The voting for the parameters affecting thermal comfort – temperature, humidity and air move-
There is an increasing concern over the quality of indoor environment as the standard of living improves in society [33]. The main purpose of buildings is to provide a comfortable and healthy indoor environment to its dwellers in various seasons, that is essential to perform their works effectively [40]. The atmospheric parameters – air temperature, relative humidity and air movement have an important role in providing thermally comfortable indoor environment. Researches on the aspect of thermal comfort and energy efficiency of buildings are underway throughout the world [41]. The best solution to create an energy efficient, healthy and comfortable indoor environment is to provide a passive system of ventilation in buildings. The adoption of techniques from traditional buildings is important to achieve thermal comfort indoors in a passive manner. The results of the survey at a glance reflect that the residents of the traditional houses of Kerala prefer to stay there because they are very comfortable to live in irrespective of the seasons. It is found that, the main reason for thermal discomfort in Kerala is the increase in air temperature along with the presence of
Fig. 14. Distribution of subjective response on various comfort parameters in traditional buildings during various seasons. (a) Subjective response on temperature, (b) subjective response on humidity, (c) subjective response on air movement, (d) subjective response on thermal comfort.
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Fig. 15. Distribution of subjective response on various comfort parameters in modern buildings during various seasons. (a) Subjective response on temperature, (b) subjective response on humidity, (c) subjective response on air movement, (d) subjective response on thermal comfort.
excess moisture in the atmosphere. In such a climatic condition, the thermal comfort can be achieved by providing a highly insulative building envelope while maintaining a controlled and continuous airflow through the building. The traditional buildings of Kerala have these characteristics in order to achieve the required thermal comfort condition [26]. This can be substantiated by the results obtained from the survey given in Fig. 14. The distribution of subjective response on various comfort parameters in traditional buildings during various seasons is given in Fig. 14. Fig. 14a shows that more than 50% of the occupants of the traditional buildings voted that their dwellings are slightly warm or warm. Also, no one feels that they are hot. This result is purely in agreement with the high insulative property of the building envelope. Around 75% of the people of traditional buildings feel that they get an acceptable air movement in their residences in all seasons. The percentage voted for slightly draughty air movement is less than 5% and no one voted for moderately or very draughty air movement in any season (Fig. 14c). From Fig. 14b, it can be seen that, about 55% of the people feel that their houses are neutral in humidity in all seasons. Also, no one voted for very humid. These results substantiate that the traditional buildings are perfect in maintaining a controlled and continuous airflow to provide a comfortable indoor environment by control the heat from outside and wash out the moisture inside the building. Experimental investigations already proved that the traditional residential architecture of Kerala is efficient in providing passive method of thermal comfort in all seasons [23–29]. It is evident from the Fig. 14d that the results of the investigation are in complete agreement with the occupants’ opinion.
Fig. 15 shows the distribution of subjective response on various comfort parameters in modern buildings during winter, summer and rainy seasons. It is clear from this figure that the modern buildings of Kerala are very uncomfortable for living in summer. A mixed opinion is obtained from the people in other two seasons in the case of modern buildings. From Fig. 15c, it can be seen that the people in modern building very much differ in their opinion about air movement. Only about 20% of the people feel that they get an acceptable air movement in modern buildings. It clearly shows that, the controlled and continuous air flow, that is essential for better thermal comfort in the warm-humid climate of Kerala, is nearly absent in modern buildings. It is clear from this study that energy intensive solutions are required in modern buildings to attain thermal comfort conditions in terms of cooling, and ventilation. All of the occupants of the modern houses depend on fans to survive in the uncomfortable conditions. About 20% of them in the upper middle and high income groups use air conditioning systems to get thermal comfort. This will cause severe depletion of non-renewable energy resources and environmental degradation. However, traditional buildings of Kerala are very effective in providing thermal comfort by passive methods in all seasons. The result of the survey is purely in agreement with the scientific investigation already conducted [23–29]. 7. Conclusion In this study, a detailed questionnaire survey on the subjective responses on parameters of thermal comfort along with a rating of
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overall thermal comfort was conducted in traditional and modern buildings. The analysis of the survey results confirms that Kerala traditional residential buildings are very effective in providing comfortable indoor environment irrespective of the seasons. Thus the study substantiates the quantitative investigation on Kerala traditional architecture already reported. The modern practice in architecture lacks conscious effort in using passive methods of controlling the indoor environment. Traditional residential buildings of Kerala, by virtue of their design, and materials and special methods used for construction, provide a comfortable indoor environment. It can therefore be concluded that Kerala traditional residential buildings maintains a balanced condition of temperature and humidity along with an acceptable airflow to provide the required thermal comfort through all seasons.
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Acknowledgements The authors extend sincere gratitude to Mr. C. R. Ravi Varma of Puthiya Kovilakam, Mr. Ranjith Varma of Valiya Kovilakam, Mr. Suraj Varma of Vakkaat Madham, Mr. Ranjeesh Varma of Mallisserry Kovilakam, Mr. T. R. Ravi Varma of Thulisala Kovilakam, Mr. Raman Nambidi of Vakkat Illam, Mr. K. Sasidharan of Amaravathy Kovilakam, Mr. E. K. K. Nambiar of NSS College of Engineering, Mr. Ratheesh John of Designer publications, Mr. Biju Govind of The Hindu news paper, Mr. Sreejith T. S. of EMCON and Mr. Justine Jose C. of NIT Calicut for their kind help in the conduct of the questionnaire survey. The authors are grateful to the residents of traditional and modern houses of Kerala for participating in the survey and providing the required information for the successful completion of the study.
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Appendix A.
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[23] A.S. Dili, M.A. Naseer, T. Zacharia Varghese, The passive environment control system of Kerala vernacular residential architecture: an experimental investigation on wind flow and thermal comfort, International Journal of Earth Science & Engineering 2 (2009) 264–271. [24] A.S. Dili, M.A. Naseer, T. Zacharia Varghese, Passive environment control system for a healthy and comfortable indoor environment: a study of Kerala vernacular residential buildings, in: Healthy Buildings 2009 International Conference, Syracuse, NY, USA, September 14th–17th, 2009 (paper no. 947). [25] A.S. Dili, M.A. Naseer, T. Zacharia Varghese, Investigation on indoor air temperature control of vernacular residential buildings of Kerala in summer, Journal of the Institution of Engineers (India)—AR 91 (2010) 17–19. [26] A.S. Dili, M.A. Naseer, T. Zacharia Varghese, Passive control methods of Kerala traditional architecture for a comfortable indoor environment: a comparative investigation during winter and summer, Building and Environment 45 (2010) 1134–1143. [27] A.S. Dili, M.A. Naseer, T. Zacharia Varghese, Passive environment control system of Kerala vernacular residential architecture for a comfortable indoor environment: a qualitative and quantitative analyses, Energy and Buildings 42 (2010) 917–927. [28] A.S. Dili, M.A. Naseer, T. Zacharia Varghese, Passive control methods of Kerala traditional architecture for a comfortable indoor environment: comparative investigation during various periods of rainy season, Building and Environment 45 (2010) 2218–2230. [29] A.S. Dili, M.A. Naseer, T. Zacharia Varghese, Climate responsive design for comfortable living in warm-humid climate: the need for a comprehensive investigation of Kerala vernacular architecture and its present status, in: Design Conference, Illinois University, Chicago, USA, February 13–15, 2010. [30] M. Fountain, G. Brager, R. de Dear, Expectations of indoor climate control, Energy and Buildings 24 (1996) 179–182. [31] S. Sharples, A. Malama, A thermal comfort field survey in the cool season of Zambia, Building and Environment 32 (1997) 237–243. [32] M.A. Ealiwa, A.H. Taki, A.T. Howarth, M.R. Seden, An investigation into thermal comfort in the summer season of Ghadames, Libya, Building and Environment 36 (2001) 231–237. [33] K.W.D. Cheong, E. Djunaedy, Y.L. Chua, K.W. Tham, S.C. Sekhar, N.H. Wong, M.B. Ullah, Thermal comfort study of an air-conditioned lecture theatre in the Tropics, Building and Environment 38 (2003) 63–73. [34] J. Zheng, L. Chen, B.-Z. Li, L. Chen, Indoor thermal comfort studies based on physiological parameter measurement and questionnaire investigation, Journal of Central South University of Technology 13 (2006) 404–407. [35] Y. Zhanga, R. Zhao, Overall thermal sensation, acceptability and comfort, Building and Environment 43 (2008) 44–50. [36] ANSI/ASHRAE Standard 55-2004, Thermal environmental conditions for human occupancy, in: American Society of Heating, Refrigerating and Air Conditioning Engineers, Atlanta, 2004. [37] ISO 7730, Ergonomics of the Thermal Environment-Analytical Determination and Interpretation of Thermal Comfort Using Calculation of the PMV and PPD Indices and Local Thermal Comfort Criteria, International Standards Organization, Geneva, Switzerland, 2005. [38] P.O. Fanger, Thermal Comfort—Analysis and Applications in Environmental Engineering, McGraw-Hill Book Company, 1970. [39] Koenigsberger, et al., Manual of Tropical Housing and Building—Climatic Design, Orient Longman Private Limited, 1975. [40] R. de Dear, Thermal comfort in practice, Indoor Air 14 (7) (2004) 32–39. [41] E. Arens, M.A. Humphreys, R. de Dear, H. Zhang, Are ‘class A’ temperature requirements realistic or desirable? Building and Environment 45 (2010) 4–10.
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Thermal comfort study of Kerala traditional residential buildings based on questionnaire survey among occupants of traditional and modern buildings A.S. Dili a,∗ , M.A. Naseer b , T. Zacharia Varghese c a b c
Department of Architecture, TKM College of Engineering, Kollam, Kerala, India Department of Architecture, National Institute of Technology Calicut, Kerala, India Department of Civil Engineering, National Institute of Technology Calicut, Kerala, India
a r t i c l e
i n f o
Article history: Received 25 February 2010 Received in revised form 10 June 2010 Accepted 2 July 2010 Keywords: Kerala Traditional buildings Modern buildings Thermal comfort Questionnaire survey
a b s t r a c t Thermal comfort studies on traditional residential buildings of Kerala that is known for its use of natural and passive methods for a comfortable indoor environment, are under progress. Scientific analyses of the environmental parameters determining thermal comfort have already been reported. Similar studies on modern residential buildings are underway. In order to compare the results of the scientific analysis with the user responses from the residents of traditional as well as modern residential buildings, a questionnaire survey was conducted during various seasons such as winter, summer and monsoon. A questionnaire was prepared in detail to understand the effect of factors which affect thermal comfort such as temperature, humidity and air flow in the evaluation of thermal comfort. This paper is based on the compilation of responses from the conducted survey. A comparison of the study results with that of scientific analysis already reported is also incorporated at the end of this paper. This study further confirms that Kerala traditional residential buildings are very effective in providing comfortable indoor environment irrespective of various seasons. © 2010 Elsevier B.V. All rights reserved.
1. Introduction Passive methods of achieving thermal comfort inside the buildings are the best solution to provide a healthy and energy efficient indoor environment [1–4]. This is of supreme importance for buildings in the tropics where mechanical systems with high energy consumption are used to condition the indoor environment for thermal comfort [5]. The people are forced to depend on such systems because, majority of the buildings are designed without giving adequate importance to passive methods for controlling the indoor environment. In many cases, failure to provide the required thermal conditions has resulted in discomfort, ill health and productivity loss. Presently, there is a constant need to evaluate the thermal conditions of the indoor environments to learn further and proceed with the research in passive design [6–10]. Kerala, a state in India located in the southwest coast, falls in the warm-humid climatic zone according to Bureau of Indian Standards [11]. The presence of high amount of moisture in the atmosphere, due to its geographical setting, for major part of the year causes thermal discomfort as there is less evaporation, resulting in sweating. This becomes more acute in summer when the air temperature and relative humidity become higher.
∗ Corresponding author. Tel.: +91 9447303875. E-mail addresses: [email protected], dili [email protected] (A.S. Dili). 0378-7788/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2010.07.004
Studies on passive methods of achieving thermal comfort in buildings are under progress in the form of extracting methods and techniques from traditional buildings in various countries [12–19]. In India, such studies have been reported recently from the NorthEast part where the climate is composite in nature [20–22]. The authors have conducted an investigation of traditional architecture in the context of Kerala, where the climate is warm-humid, to understand the passive environment control system. Quantitative analyses based on continuous recording and evaluation of thermal comfort parameters in traditional buildings has already been published [23–29]. A questionnaire based survey on the residents of the traditional and modern residential buildings was required to compare with the results obtained from the quantitative analyses. Thus a questionnaire survey was conducted among the residents of traditional and modern buildings through various seasons to assess the subjective response of thermal comfort. The study was conducted during various seasons such as winter, summer and rainy period of monsoon season. The questionnaire was prepared in detail to understand the effect of factors which affect thermal comfort such as temperature, humidity and air flow in the evaluation of thermal comfort. Respondents from age groups ranging from 20 to 70 years, with more or less equal representation from either sex were selected for the survey. A Summary of Experimental Investigations already Reported on Kerala Traditional Residential Buildings is included in this paper.
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A comparative analysis of the outcome of the survey with the scientific studies already reported is also incorporated. This paper also explores a comparison of thermal comfort between traditional and modern buildings through various seasons. 2. Methods 2.1. Selection of people The survey was conducted among the selected people from selected families of both traditional and modern buildings of Kerala. Fifty families each living in traditional and modern building were selected for the survey. A total number of 200 people each from traditional and modern houses were selected for the study with an average of four members from each family. The traditional houses of about 200–300 years of age, built according to the ancient principles were selected for the survey. The basic module of traditional residential building of Kerala is known as nalukettu with four blocks built around an open courtyard. They are generally rectangular or square in plan with blocks topped with a sloping roof on all four sides while the courtyard is left open to the sky for letting air and light inside. There is an internal verandah around the courtyard for protection from rain and sun. The roofs have steep slopes up to almost 45 degrees and are topped with clay tiles on wooden framework with gaps provided in between tiles to enhance ventilation and to allow the warm air to escape. Further, ventilators are provided for the ventilation of attic spaces that are formed by the wooden false ceiling (tattu) provided for the room spaces. This roof encloses a large insulated air space keeping the lower areas cooler. A detailed description on the traditional residential buildings of Kerala and its typical layout are given elsewhere [27]. Modern buildings of less than 20 years of age were selected for the survey. Modern buildings of Kerala do not have any common design principles nor do they follow a common architectural style. Most of the buildings are constructed with brick masonry walls plastered with cement mortar and topped with RCC roof. The roofs are either flat or sloping at different angles. Window openings are provided all around the buildings and they are extensively covered with glass paneled shutters. The buildings, both traditional and modern, were selected from various parts of Kerala irrespective of the micro level variations in climate and topography. A detailed description on the topography and climate of Kerala are given elsewhere [27]. People with sensible mind and keen observation skill on thermal comfort were selected for the survey. They were briefed about the scope of the survey, and were given sufficient input before the conduct of the survey on how to respond to the questionnaire.
2.3. Survey methodology The survey was conducted with the help of many interested people in this field. They were educated in detail about the relevance and objectives of the survey by the authors. The different components of the questionnaire, its meaning and the gradation were also explained in advance. The survey was conducted in the peak of each season simultaneously in different locations i.e. during the first week of January 2009 (winter peak), last week of April 2009 (summer peak) and last week of July 2009 (monsoon peak). 3. Results and analysis The subjective responses, on various thermal comfort parameters and that on the overall thermal comfort, obtained from the questionnaire survey conducted during various seasons are illustrated below. The analysis and interpretation of the results obtained from the survey is provided at the end of this section. An average vote for overall thermal comfort in an annual basis is also illustrated. 3.1. Winter season Fig. 1 shows the distribution of subjective response on temperature in winter season. While about 35% of the residents of traditional buildings voted for neutral temperature, only 26% of the residents of modern buildings voted for the same. Also, while 25% of the residents of traditional buildings voted for slightly warm temperature, 37% of the residents of modern buildings voted for the same. 19% of the residents of modern buildings believe that their buildings are warm in winter while 8% believe that it is hot. When 32% of the residents of the traditional buildings believe that their buildings are slightly cool, only 10% of the modern building residents believe the same. It is evident from the Fig. 1 that, while the votes from people of traditional buildings are balanced around the neutral condition, the same of modern buildings shows a tendency towards warm condition. The distribution of subjective response on humidity in winter season is shown in Fig. 2. From this figure, it is clear that, around 50% of the people in the traditional and modern buildings believe that their dwellings are neutral in terms of humidity in winter season. While about 31% of the residents of traditional buildings voted for slightly dry, 36% of the residents of modern buildings voted for the same. Less than 5% of people in both the buildings believe that their buildings are humid in winter season. Also, less than 10% of people
2.2. Preparation of questionnaire The questionnaire for the survey was prepared to obtain the subjective responses from the respondents on various thermal comfort parameters such as temperature, humidity and air flow along with a response on overall thermal comfort. The selection and gradation of components in the questionnaire was done by a detailed review of literature in the respective field [30–38]. The residents were asked to evaluate the environment in a condition when they are not using any of the aid – mechanical or otherwise – to improve or modify the indoor environment. The questionnaire was prepared both in English and Malayalam (regional language of Kerala) for easy conduct of the survey. Also, it was reproduced in three different colours – light blue, pink and light green – for the surveys conducted during winter, summer and rainy season respectively. The questionnaire prepared for the investigation is given in Appendix A at the end.
Fig. 1. Distribution of subjective response on temperature in winter season.
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Fig. 2. Distribution of subjective response on humidity in winter season.
in both the buildings believe that their buildings are moderately dry in winter and no one voted for “very dry”. Fig. 3 shows the distribution of subjective response on air movement in winter season. More than 70% of the occupants of the traditional houses voted for acceptable air movement. The remaining people of the traditional houses voted towards still air as shown in figure. Almost 80% of the occupants of the modern buildings have difference in opinion about air movement ranging from slightly still to moderately draughty. The extreme characteristics, very still and very draughty are selected by less than 10% of the occupants of modern houses. The distribution of subjective response on overall thermal comfort in winter season is shown in Fig. 4. 73% of the occupants of the traditional buildings voted that their dwellings are very comfortable in winter. The remaining 27% voted for comfortable and slightly uncomfortable with a distribution of 25% and 2% respectively. Only 8% of the occupants of the modern buildings voted that their dwellings are very comfortable in winter. 63% from the modern buildings voted for comfortable and slightly uncomfortable with a distribution of 31% and 32% respectively. The remaining 29% of the modern buildings voted for uncomfortable and very uncomfortable with a distribution of 17% and 12% respectively as shown in Fig. 4. 3.2. Summer season Fig. 5 shows the distribution of subjective response on temperature in summer season. While about 56% of the residents of traditional buildings voted for neutral temperature, only 8% of the residents of modern buildings voted for the same. Also, while about 8% of the residents of traditional buildings voted for slightly warm
Fig. 3. Distribution of subjective response on air movement in winter season.
Fig. 4. Distribution of subjective response on overall thermal comfort in winter season.
Fig. 5. Distribution of subjective response on temperature in summer season.
temperature, 11% of the residents of modern buildings voted for the same. It is evident from this figure that no one in the modern buildings feels their dwellings are slightly cool, cool or cold. 81% of the residents of the modern buildings voted for warm and hot with a distribution of 49% and 32% respectively. The distribution of subjective response on humidity in summer season is shown in Fig. 6. From this figure, it is clear that, 61% of the people in the traditional buildings believe that their dwellings are neutral in terms of humidity in summer season. Only 11% of the residents in modern buildings believe that the condition is neu-
Fig. 6. Distribution of subjective response on humidity in summer season.
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Fig. 7. Distribution of subjective response on air movement in summer season. Fig. 9. Distribution of subjective response on temperature in rainy season.
tral. While 10% of the residents of traditional buildings voted for slightly dry, 8% of the residents of modern buildings voted for the same. 76% of the residents of the modern buildings voted for slightly humid, moderately humid and very humid with a distribution of 23%, 36% and 17% respectively. Out of 24% of the residents of the traditional buildings, only 5% believes that their dwellings are moderately humid. The remaining voted for slightly humid. While no one voted for very dry, 17% of the modern residents voted that their dwellings are very humid. Fig. 7 shows the distribution of subjective response on air movement in summer season. More than 80% of the occupants of the traditional houses voted for acceptable air movement. Most of the remaining people of the traditional houses voted towards still air as shown in figure. About 80% of the occupants of the modern buildings have difference in opinion about air movement almost equally ranging from slightly still to moderately draughty. The extreme characteristics, very still and very draughty are also reported by less than 5% of the occupants of modern houses. The distribution of subjective response on overall thermal comfort in summer season is shown in Fig. 8. 70% of the occupants of the traditional buildings voted that their dwellings are very comfortable in summer. The remaining 30% voted for comfortable and slightly uncomfortable with a distribution of 27% and 3% respectively. No one among the occupants of the modern buildings voted that their dwellings are very comfortable in summer but for 71% of the occupants feel that, their dwellings are very uncomfortable. The remaining 29% of the modern buildings voted for slightly
Fig. 8. Distribution of subjective response on overall thermal comfort in summer season.
uncomfortable and uncomfortable with a distribution of 8% and 21% respectively. 3.3. Rainy season Fig. 9 shows the distribution of subjective response on temperature in rainy season. While about 32% of the residents of traditional buildings voted for neutral condition, 37% of the residents of modern buildings voted for the same. Also, while 50% of the residents of traditional buildings voted for slightly warm temperature, only 10% of the residents of modern buildings voted for the same. Only 2% of the residents of modern buildings believe that their buildings are warm in rainy season. While 10% of the residents of the traditional buildings believe that their buildings are slightly cool, only 4% believe that the temperature is cool in rainy season. It is evident from this figure that, no one in the traditional buildings as well as modern buildings feels that their dwellings are cold or hot during rainy season. The distribution of subjective response on humidity in rainy season is shown in Fig. 10. From this figure, it is clear that, around 55% of the people in the traditional and modern buildings feel that their dwellings are neutrally humid in rainy season. While about 2% of the residents of traditional buildings voted for slightly dry, 5% of the residents of modern buildings voted for the same. Around 10% of people in both the buildings believe that their buildings are moderately humid in winter season. It is evident from this figure that, no one resides in the traditional buildings as well as modern build-
Fig. 10. Distribution of subjective response on humidity in rainy season.
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modern buildings voted for comfortable and slightly uncomfortable with a distribution of 31% and 28% respectively. The remaining 22% of the modern buildings voted for uncomfortable and very uncomfortable with a distribution of 13% and 9% respectively as shown in Fig. 12. 4. Summary of experimental investigations already reported on Kerala traditional residential buildings 4.1. Instrumentation setup
Fig. 11. Distribution of subjective response on air movement in rainy season.
An instrumentation setup called Architectural Evaluation System (AES) has been devised to continuously record the comfort parameters over a period of time. AES is a combination of electronic sensors, data logger, memory module and computer interface. Electronic sensors in AES were used to sense thermal comfort parameters such as air temperature (AT), relative humidity (RH) and air movement. A memory module was used to record data from the sensors and the computer interface is used to view and download data for analysis. The Architectural Evaluation System (AES) was suitably installed in a selected traditional residential building (Nilambur Kovilakam) to record the thermal comfort parameters. A schematic diagram of AES, selected area for investigation and photographs are given elsewhere [27]. 4.2. Investigation during winter and summer [26]
Fig. 12. Distribution of subjective response on overall thermal comfort in rainy season.
ings feels that their dwellings are very dry, moderately dry and very humid during rainy season. Fig. 11 shows the distribution of subjective response on air movement in rainy season. 70% of the occupants of the traditional houses voted for acceptable air movement. Most of the remaining people of the traditional houses voted towards still air as shown in figure. 60% of the occupants of the modern buildings voted for slightly draughty, moderately draughty and very draughty with a distribution of 30%, 18% and 12% respectively. 8% of the occupants of the traditional buildings voted for very still and moderately still air movement with a distribution of 5%, 3% respectively. The distribution of subjective response on overall thermal comfort in rainy season is shown in Fig. 12. 66% of the occupants of the traditional buildings voted that their dwellings are very comfortable in rainy season. The remaining 34% voted for comfortable and slightly uncomfortable with a distribution of 29% and 5% respectively. Only 19% of the occupants of the modern buildings voted that their dwellings are very comfortable in rainy season. 59% of the
An over view of the results obtained during winter and summer are presented in Table 1. The interpretations of results are explained below in brief for a better understanding. The diurnal variation of indoor air temperature is very less compared to that of outdoor ambient air temperature in both the seasons. The low diurnal variation of the indoor temperature proves the high thermal insulation property of the building envelope. There is no time lag observed between outdoor and indoor air temperatures. The absence of time lag between outdoor and indoor temperatures can be attributed to the highly insulative wall preventing conductive heat flow and to the continuous air flow maintained through the building. The reason for thermal discomfort in summer season in Kerala is not due to the increase in minimum temperature alone, but is mainly due to the increase in the moisture content in the air during that period. In such a climatic condition, the only way to achieve a comfortable indoor environment is to have a control over the air temperature supplemented by a continuous air movement that can ensure the required rate of evaporation from the body of occupants. From the investigation, it is found that, the building envelope permits a controlled and continuous air movement through the building irrespective of the seasons. The building envelope (both walls and roof) prevents the conductive heat flow into the interiors. The heat flow due to radiation is blocked by protecting the walls with roof overhangs and by providing sufficient thermal insulation for the roof. The evaluation of thermal comfort with bioclimatic chart showed that the traditional building indoors provide better comfort during winter and sum-
Table 1 Overview of the results obtained during winter and summer. Periods
Air temperature (◦ C)
Decrement factor
Outdoor
Winter Summer
Bedroom
Variation in RH (%) Outdoor
Min
Max
Variation
Min
Max
Variation
18 25
36 38
18 13
23.5 28
28 32
4.5 4
0.22 0.28
Bedroom
Min
Max
Min
Max
28 35
100 100
45 57
90 95
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Table 2 Overview of the results obtained during the various periods of rainy season [28]. Periods
Diurnal variation (◦ C)
Decrement factor
Outdoor
Beginning rain Normal rain Heavy rain Non-rainy days
Bedroom
Variation in RH (%) Outdoor
Min
Max
Variation
Min
Max
Variation
24 24 22.5 23
31 28.5 26 35.5
7 4.5 3.5 12.5
27 26.5 25 27
29 27.5 27 30.5
2 1 2 3.5
mer. The continuous air flow (around 0.5 m/s) maintained inside the building provides better comfort even at a high humidity. The PMV–PPD analysis also showed that the traditional building indoors provide the required range of thermal comfort during winter and summer. 4.3. Investigation during rainy season [28] It is observed that rainy season is the season with more fluctuations in the climatic parameters. In order to have a detailed comparative analysis, the rainy season was divided into four periods such as the beginning of rainy season, days during normal rain, days during heavy rain and non-rainy days. The results obtained during the various periods of rainy season are consolidated and presented in Table 2. The interpretations of results are explained below. The investigation has revealed that, when the outside ambient temperature is below normal, the building system tries to maintain the indoor air temperature at a higher but comfortable level and when the outside temperature is above normal, the indoor is kept at a lower but comfortable level. A continuous gentle wind flow was maintained inside the building irrespective of the wind outside. The required level of thermal comfort was thus achieved by maintaining a balanced condition of temperature and relative humidity along with the airflow. The evaluation using PMV–PPD analysis and Bioclimatic chart confirms the indoor thermal comfort of traditional buildings during the various periods of rainy season. 5. Comparison and analysis of results In this section, the results of the questionnaire survey illustrated above are compared between various seasons for analysis and better understanding. The results of the questionnaire survey are also compared with the scientific investigations on traditional buildings already reported [26–28]. Comparing Figures 1, 5 and 9, it can be seen that while more than 50% of the residents of the traditional buildings voted for neutral condition in terms of temperature in summer, 30–35% people voted for the same in other two seasons. Most of the people in traditional houses feel that their dwellings are cooler in winter and summer, and are warmer in rainy season. This observation can be substantiated by the results of the experimental investigations given in Tables 1 and 2. From Table 2, it can be seen that during heavy rain, the maximum indoor temperature (27 ◦ C) is higher than the maximum outdoor temperature (26 ◦ C). The thermal characteristics of the Kerala traditional building envelope are playing a vital role in controlling the temperature. It can also be learned from the Figures 1, 5 and 9 that, the modern buildings are warmer in winter and rainy seasons and are hotter in summer. In summer most of the residents of the modern buildings feel that their dwellings are humid as evident from Figure 6. While the residents of both traditional and modern buildings voted almost similar manner about humidity in winter and rainy season, they differ in their opinion in summer season. From Figures 2, 6 and 10,
0.32 0.22 0.50 0.28
Bedroom
Min
Max
Min
Max
70 88 80 45
100 100 100 97
80 85 80 65
90 95 93 82
it can be seen that more than 50% of the residents of the traditional buildings voted for neutral condition for humidity in all seasons. The combined effect of temperature and humidity in traditional buildings in various seasons is explained below to substantiate this point. The variation of RH along with the variation of temperature during winter and summer in traditional buildings is given in Table 1. During winter day time when the indoor temperature is high up to 28 ◦ C, the humidity is as low as 45%. This falls well within the comfort zone of the bioclimatic chart constructed by Olgyay [39]. During night, since temperature becomes low up to 18 ◦ C, the increase in humidity (up to 88%) does not really affect the indoor comfort condition. During summer day time when the indoor temperature is high up to 32 ◦ C, the humidity is as low as 57%. This falls well within the comfort region of the bioclimatic chart since the wind velocity maintained inside the building is around 0.5 m/s and it is very near to the comfort zone. During night, since temperature reduces up to 28 ◦ C, the indoors remains comfortable even though the RH is as high as 95%. The variation of RH along with the variation of temperature during rainy season in traditional buildings is given in Table 2. This shows that the day time indoor temperature is high up to 27 ◦ C and RH is 80% during the period of heavy rains. This is well within the comfort region of the bioclimatic chart with the wind velocity of 0.5 m/s maintained inside the building. In the nights, the indoor temperature and RH are 25 ◦ C and 93% respectively and is again within the comfort region of the bioclimatic chart. It can be seen from Figures 3, 7 and 11 that residents of traditional houses voted for air flow almost in a similar manner in all seasons. No one among the residents of traditional houses voted for moderately draughty and very draughty air flow and 70–80% of the same people voted for an acceptable air flow in all seasons. Reported experimental investigations on traditional buildings prove that the building system is maintaining an air flow of 0.5 m/s continuously. On the other hand, from the same figures, it can be seen that, the residents of the modern houses have a mixed opinion on the air flow ranging from very still to very draughty. On judging the overall comfort, comparing Figures 4, 8 and 12, it can be seen that around 70% of the occupants of the traditional houses voted for very comfortable condition in all seasons; while no one feels that they are uncomfortable or very uncomfortable. At the same time, it can also be seen that less than 20% of the occupants of the modern houses voted for very comfortable condition in winter and rainy seasons; while no one feels that they are very comfortable in summer season. This observation can be substantiated by the results of the experimental investigations already reported. The evaluation using PMV–PPD analysis and conformity to Bioclimatic chart proves that the traditional buildings of Kerala are comfortable in all seasons [26–28]. Fig. 13 shows the distribution of subjective response on overall thermal comfort in an annual basis. An average of 70% of the occupants of the traditional buildings feels that their dwellings are very comfortable in a year. The remaining 30% can be averaged as comfortable and slightly uncomfortable with a distribution of 27% and
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ment – are very much in agreement with their voting for the overall thermal comfort. It indicates that the selection of people for the survey is suitable for the context. The level of participation of the people involved in the survey reflects the perfection of the results. The outcome of the questionnaire survey and its analysis clearly indicate that the traditional houses of Kerala are very comfortable to live in round the year irrespective of the seasons.
6. Discussion
Fig. 13. Distribution of subjective response on annual overall thermal comfort.
3% respectively. Only 9% of the occupants of the modern buildings are found that very comfortable in all seasons. 43% of the modern buildings can be averaged annually as comfortable and slightly uncomfortable with a distribution of 21% and 22% respectively. The remaining 48% of the modern buildings are found to be uncomfortable and very uncomfortable with a distribution of 17% and 31% respectively as shown in Fig. 13. Majority of the people participated in this survey seems to have responded sensibly and their vote represents thermal comfort conditions of the houses they live in. The voting for the parameters affecting thermal comfort – temperature, humidity and air move-
There is an increasing concern over the quality of indoor environment as the standard of living improves in society [33]. The main purpose of buildings is to provide a comfortable and healthy indoor environment to its dwellers in various seasons, that is essential to perform their works effectively [40]. The atmospheric parameters – air temperature, relative humidity and air movement have an important role in providing thermally comfortable indoor environment. Researches on the aspect of thermal comfort and energy efficiency of buildings are underway throughout the world [41]. The best solution to create an energy efficient, healthy and comfortable indoor environment is to provide a passive system of ventilation in buildings. The adoption of techniques from traditional buildings is important to achieve thermal comfort indoors in a passive manner. The results of the survey at a glance reflect that the residents of the traditional houses of Kerala prefer to stay there because they are very comfortable to live in irrespective of the seasons. It is found that, the main reason for thermal discomfort in Kerala is the increase in air temperature along with the presence of
Fig. 14. Distribution of subjective response on various comfort parameters in traditional buildings during various seasons. (a) Subjective response on temperature, (b) subjective response on humidity, (c) subjective response on air movement, (d) subjective response on thermal comfort.
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Fig. 15. Distribution of subjective response on various comfort parameters in modern buildings during various seasons. (a) Subjective response on temperature, (b) subjective response on humidity, (c) subjective response on air movement, (d) subjective response on thermal comfort.
excess moisture in the atmosphere. In such a climatic condition, the thermal comfort can be achieved by providing a highly insulative building envelope while maintaining a controlled and continuous airflow through the building. The traditional buildings of Kerala have these characteristics in order to achieve the required thermal comfort condition [26]. This can be substantiated by the results obtained from the survey given in Fig. 14. The distribution of subjective response on various comfort parameters in traditional buildings during various seasons is given in Fig. 14. Fig. 14a shows that more than 50% of the occupants of the traditional buildings voted that their dwellings are slightly warm or warm. Also, no one feels that they are hot. This result is purely in agreement with the high insulative property of the building envelope. Around 75% of the people of traditional buildings feel that they get an acceptable air movement in their residences in all seasons. The percentage voted for slightly draughty air movement is less than 5% and no one voted for moderately or very draughty air movement in any season (Fig. 14c). From Fig. 14b, it can be seen that, about 55% of the people feel that their houses are neutral in humidity in all seasons. Also, no one voted for very humid. These results substantiate that the traditional buildings are perfect in maintaining a controlled and continuous airflow to provide a comfortable indoor environment by control the heat from outside and wash out the moisture inside the building. Experimental investigations already proved that the traditional residential architecture of Kerala is efficient in providing passive method of thermal comfort in all seasons [23–29]. It is evident from the Fig. 14d that the results of the investigation are in complete agreement with the occupants’ opinion.
Fig. 15 shows the distribution of subjective response on various comfort parameters in modern buildings during winter, summer and rainy seasons. It is clear from this figure that the modern buildings of Kerala are very uncomfortable for living in summer. A mixed opinion is obtained from the people in other two seasons in the case of modern buildings. From Fig. 15c, it can be seen that the people in modern building very much differ in their opinion about air movement. Only about 20% of the people feel that they get an acceptable air movement in modern buildings. It clearly shows that, the controlled and continuous air flow, that is essential for better thermal comfort in the warm-humid climate of Kerala, is nearly absent in modern buildings. It is clear from this study that energy intensive solutions are required in modern buildings to attain thermal comfort conditions in terms of cooling, and ventilation. All of the occupants of the modern houses depend on fans to survive in the uncomfortable conditions. About 20% of them in the upper middle and high income groups use air conditioning systems to get thermal comfort. This will cause severe depletion of non-renewable energy resources and environmental degradation. However, traditional buildings of Kerala are very effective in providing thermal comfort by passive methods in all seasons. The result of the survey is purely in agreement with the scientific investigation already conducted [23–29]. 7. Conclusion In this study, a detailed questionnaire survey on the subjective responses on parameters of thermal comfort along with a rating of
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overall thermal comfort was conducted in traditional and modern buildings. The analysis of the survey results confirms that Kerala traditional residential buildings are very effective in providing comfortable indoor environment irrespective of the seasons. Thus the study substantiates the quantitative investigation on Kerala traditional architecture already reported. The modern practice in architecture lacks conscious effort in using passive methods of controlling the indoor environment. Traditional residential buildings of Kerala, by virtue of their design, and materials and special methods used for construction, provide a comfortable indoor environment. It can therefore be concluded that Kerala traditional residential buildings maintains a balanced condition of temperature and humidity along with an acceptable airflow to provide the required thermal comfort through all seasons.
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Acknowledgements The authors extend sincere gratitude to Mr. C. R. Ravi Varma of Puthiya Kovilakam, Mr. Ranjith Varma of Valiya Kovilakam, Mr. Suraj Varma of Vakkaat Madham, Mr. Ranjeesh Varma of Mallisserry Kovilakam, Mr. T. R. Ravi Varma of Thulisala Kovilakam, Mr. Raman Nambidi of Vakkat Illam, Mr. K. Sasidharan of Amaravathy Kovilakam, Mr. E. K. K. Nambiar of NSS College of Engineering, Mr. Ratheesh John of Designer publications, Mr. Biju Govind of The Hindu news paper, Mr. Sreejith T. S. of EMCON and Mr. Justine Jose C. of NIT Calicut for their kind help in the conduct of the questionnaire survey. The authors are grateful to the residents of traditional and modern houses of Kerala for participating in the survey and providing the required information for the successful completion of the study.
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Appendix A.
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