Thermal Comfort Assessment of a Classroom in Tropical Climate Conditions

Transcription

1 Thermal Comfort Assessment of a Classroom in Tropical Climate Conditions KHADIJAH KAMARUZZAMAN 1 and AZIMIN SAMSUL BIN MOHD TAZILAN 1,2 1 Department of Architecture Faculty of Engineering and Build Environment Universiti Kebangsaan Malaysia, 43600, Bangi, Selangor. MALAYSIA 2 Solar Energy Research Institute Universiti Kebangsaan Malaysia, 43600, Bangi, Selangor. MALAYSIA kaydee_kamaroz@yahoo.com, azimintazilan@gmail.com Abstract: - Thermal comfort is the study of indoor comfort level feel by the occupant in a room. This paper presents the study of thermal comfort that had been carried out in a classroom on the second floor at a local school in Bandar Baru Bangi, Selangor, Malaysia. The study was made in 5 days from 2 pm to 6 pm. This study was carried out to assess their thermal conditions during the students lesson hours. Thermal comfort variables were measured during lesson hours too. Objective data analysis showed that none of the classes had thermal conditions falling within the comfort zone of ASHRAE standard 55. The result shows the environmental condition of the class is warm to hot in 7-point ASHRAE scale. The linear regression between Predicted Mean Vote and Operative Temperature reveals that the maximum acceptable temperature in this field of study is 26.5ºC. Key-Words: - Thermal Comfort, Field Study, PMV. PPD, Classroom, Tropical Climate 1 Introduction Thermal comfort is defined by ASHRAE as that condition of mind which expresses satisfaction with the thermal environment and is assessed by subjective evaluation [1]. The subjective evaluation of thermal comfort is influenced by the thermal environment and personal factors influencing the heat transfer with this environment, but also by psychological factors influencing the condition of mind directly [2]. All these factors in thermal comfort can be altered by behavioral, physiological or psychological adaptation. Thermal comfort is a key component of quality of indoor environments and environmental elements such as heat from electrical lighting, lack of adequate ventilation, high humidity levels, and poorly performing building envelopes can contribute to poor thermal comfort. Previous studies indicated that thermal comfort does affect the productivity and learning [3-10]. A student s perception of thermal comfort is affected by air temperature in classroom, air movement or velocity in the classroom, humidity in classroom, the clothing they worn to lecture, amount of physical work activity done in classroom, mean radiant temperature, such as radiant temperature of the walls, floor, windows and so on. The mean radiant temperature is a significant factor, especially in buildings whose envelopes were exposed to a strong solar radiation. Cold walls or windows may cause a person to feel cold even though the surrounding air may be at a comfortable level. Likewise, warm surfaces may cause a person to feel warmer than the surrounding air temperature would indicate. Several studies in the tropics have been conducted by various researchers using the Malaysian climate conditions as case studies. A field study on the environmental conditions and occupant comfort was carried out in two schools, which is a primary and secondary school, and in a public waiting area in a health clinic in Johor Bahru, located in the southern region of Malaysia showed that more than 80% of the respondents found that their indoor thermal conditions acceptable even though the thermal sensation votes (TSV) exceeded those specified by ASHRAE Standard 55 and the environmental assessments exceeded the standard. ISBN:

2 The neutral temperature and comfort range were obtained through linear regression analysis of TSV and in the Fanger's PMV model [11]. From the subjective assessment, it was found that the occupants can accept the thermal range beyond the ASHRAE comfort zon indicated that the occupants in the tropic environment such as Malaysia have a higher heat tolerance and can adapt to the environment [11]. Another study has been conducted to evaluate the comfort level of an air-conditioned classroom at the School of Manufacturing Engineering campus using objective measurement, subjective assessment [12]. The results obtained showed that measured temperature and relative humidity were within the standard comfort condition by ISO EN7730 (1994) while air velocity exceeded the standard limit by ISO EN7730 (1994). The overall comfort vote, Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD) indices shows that occupants are comfortable and satisfied with the classroom comfort level [12]. The primary objectives of this study is to explore the indoor climate in mechanically ventilated buildings in Malaysia such as in classrooms of schools and to investigate occupants level of indoor thermal comfort in a tropical region. This paper reports the procedures, data and results obtained from this study. 2 Methodology 2.1 Field study description Sekolah Kebangsaan Jalan 3 was opened on the first of July in Located about 10 km from Bandar Kajang, the total gross area of this school is 4.75 acres or 38,000 square meters. The school name was taken from where the school site is located which is in a residential area of Section 3, Bandar Baru Bangi. Currently there are 55 classes, 1969 students, 95 teachers and 8 employees in this school. Fig. 1 shows the location map of SK Jalan Data collection The physical data for the indoor environment of the classroom were measured by the Thermal Comfort Equipment as shown in Fig. 2. This equipment can measure ambient temperature, air velocity, radiant men temperature, relative humidity, noise, illuminating and CO2. Fig. 2 shows the equipment designed by the Solar Energy Research Institute (SERI). Fig. 2. Thermal comfort equipment in class 2 Lili 2.3 Clothing insulation value and activity rate. Clothing insulation is the thermal insulation provided by clothing. The insulation of clothes are often measured with the unit "Clo", where 1 Clo = m2k/w. Based on the ASHRAE Standard 55, there is a method for estimating the personal parameters. By observing the occupants in the class, the clothing and metabolic rate were estimated based on the observation made during the survey. Table 1 shows estimated clothing insulation value and activity rate for class 2 Lili students. It is compulsory to all students in this school to wear the school uniform which were white sleeve shirts and straight long dark blue trousers for male, and dark blue pinafore or baju kurung (light blouse) and dark blue a-line skirts and hijab for female. Fig. 3 illustrates the standard school uniform in Malaysia. Table 1. Estimated clothing insulation value and activity rate Clo Met Estimated value baesd on ASHRAE Fig. 1. Location map of SK Jalan 3. ISBN:

3 Fig. 3. Standard school uniform in Malaysia 3 Classroom setup The field study was carried out for a week from Monday, May 7 th 2012 to Friday, May 11 th 2012 the equipment was setup in class 2 Lily that was located on the second floor. The classroom is located on a 3-storey building and the building was also designed for naturally ventilation and each classroom is also mechanically ventilated by three ceiling fans. The measuring instruments were read at about 1 meter above the floor level and were set at the back of the class in order to prevent from disturbing the pupils in class. The structure, design and measurement of all classes in block C are the same. This also applies to the types of furniture inside the classrooms. Each class is equipped with wooden tables and chairs. However, the amount and arrangement of furniture in each class are different. Fig. 4 shows the students in class 2 Lili located on the second floor of block C. Fig. 5 shows the layout plan of classroom and location of the Thermal Comfort equipment. Fig. 5. Layout plan of class 2 Lili 4 Results and discussions The environmental data was collected for about 5 to 6 hours a day for 5 days straight. Fig. 6 represents the calculated Predicted Mean Vote (PMV) from 2pm to 6pm over 5 days in a week. The PMV in all days were above 2. Fig. 6 Predicted mean vote for 5 days Fig. 7 illustrates calculated PMV versus Percentage of Predicted Dissatisfied (PPD). According to 7- point ASHRAE scale, the environment of the classroom is from warm to hot while 80% to 100% of occupants feel dissatisfied. Fig. 4. Field study in class 2 Lili ISBN:

4 Fig. 7. PPD versus PMV Fig. 8 shows the trend of PMV versus Operative Temperature (OP). The maximum acceptable temperature is 26.5ºC where the PMV is 1. Fig. 8. PMV trend versus OP for 5 Days 5 Conclusions According to the direct measurement of thermal comfort at classrooms, most classrooms do not provide a thermal comfort environment and satisfaction for teachers and students. The study field concludes that the environment of class 2 Lili is from warm to hot in 7-point ASHRAE scale. Hence, the improvements of thermal environment at this classroom have to be carried out. The air ventilation systems of the classroom have to be improved. Based on the layout plan of the class, the seats in of classroom also have to be modified. Due to over capacity of pupils, the arrangement of desk and chairs are too close together. It is recommended that the class only have around 30 pupils per class. Human body provides heat transfer or heat loss. If the seats are too close or too near with each other, the pupils will feel more discomfort or hot. References: [1] ASHRAE Standard , Thermal environmental conditions for human occupancy, American Society of Heating, Refrigerating and Air-conditioning Engineers,2004. [2] P. O. Fanger, Thermal Comfort. Analysis and applicationsin Environmental Engineering, McGraw Hill, [3] J. Van Hoof, M. Mazej, J. L. M. Hensen, Thermal comfort: Research and practice, Frontiers in Bioscience, Vol. 15, No. 2, 2010, pp [4] EN ISO 7730:2005 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, ISO International Standardisation Organisation Geneva, [5] ANSI/ASHRAE Standard 55 - Thermal Environmental Conditions for Human Occupancy ASHRAE American Society of Heating, Refrigerating and Air-Conditioning Engineers Atlanda, [6] EN 15251:2007 Indoor Environmental Input Parameters for Design and Assessment of Energy Performance of Buildings Addressing Indoor Air Quality, Thermal Environment, Lighting and Acoustics, [7] D. Teli, M. F. Jentsch, P. A. B. James, Naturally ventilated classrooms: An assessment of existing comfort models for predicting the thermal sensation and preference of primary school children, Energy and Buildings, Vol. 53, 2012, pp [8] Z. Li and J. Yao, An investigation of thermal and visual comfort in classrooms in Ningbo, Advances in Intelligent and Soft Computing, Vol. 159, No. 1, 2012, pp [9] C. Nitatwichit, Y. Khunatorn, C. Tantakitti, N. Tippayawong, Journal of the Chinese Institute of Engineers, Transactions of the Chinese Institute of Engineers,Series A/Chung-kuo Kung Ch'eng Hsuch K'an, Vol. 35, No. 1, 2012, pp [10] Nguyen, A.T., Singh, M.K., Reiter, S, 2012, An adaptive thermal comfort model for hot humid South-East Asia Building and Environment, 56, 2012, pp [11] Hussein, I., Rahman, M.H.A Field study on thermal comfort in Malaysia, European Journal of Scientific Research, Vol. 37, No. 1, 2009, pp ISBN:

5 [12] Z. A. Zailani, R. Hamidon, M. S. Hussin, M. F. M. A. Hamzas and H. Hadi, 2012, Classroom comfort ability assessment: A case study, International Review of Mechanical Engineering, Vol. 6, No. 3, 2012, pp ISBN: