Thermal comfort study of hospital workers in Malaysia

Transcription

1 Indoor Air 2009; 19: Printed in Singapore. All rights reserved Ó 2009 John Wiley & Sons A/S INDOOR AIR doi: /j x Thermal comfort study of hospital workers in Malaysia Abstract This article presents findings of the thermal comfort study in hospitals. A field survey was conducted to investigate the temperature range for thermal comfort in hospitals in the tropics. Thermal acceptability assessment was conducted to examine whether the hospitals in the tropics met the ASHRAE Standard-55 80% acceptability criteria. A total of 114 occupants in four hospitals were involved in the study. The results of the field study revealed that only 44% of the examined locations met the comfort criteria specified in ASHRAE Standard 55. The survey also examined the predicted percentage of dissatisfied in the hospitals. The results showed that 49% of the occupants were satisfied with the thermal environments in the hospitals. The field survey analysis revealed that the neutral temperature for Malaysian hospitals was 26.4 C. The comfort temperature range that satisfied 90% of the occupants in the space was in the range of C. The results from the field study suggested that a higher comfort temperature was required for Malaysians in hospital environments compared with the temperature criteria specified in ASHRAE Standard (2003). In addition, the significant deviation between actual mean vote and predicted mean vote (PMV) strongly implied that PMV could not be applied without errors in hospitals in the tropics. Y. H. Yau, B. T. Chew Department of Mechanical Engineering, University of Malaya, Kuala Lumpur, Malaysia Key words: Malaysia; Hospital; Thermal comfort; Predicted mean vote; Actual mean vote. Y. H. Yau Department of Mechanical Engineering University of Malaya Kuala Lumpur Malaysia Tel.: Fax: , yhyau@um.edu.my Received for review 8 January Accepted for publication 20 July Ó Indoor Air (2009) Practical Implications The new findings on thermal comfort temperature range in hospitals in the tropics could be used as an important guide for building services engineers and researchers who are intending to minimize energy usage in heating, ventilating and air conditioning systems in hospitals operating in the tropics with acceptable thermal comfort level and to improve the performance and well-being of its workers. Nomenclature ACH AMV ASHRAE clo EPA HVAC HVAC&R ISO met MRT OT PMV PMV-Std SBS 500 Air Changes per Hour Actual Mean Vote American Society of Heating, Refrigerating and Air-Conditioning Engineers clothing insulation Environmental Protection Agency Heating, Ventilating and Air Conditioning Heating, Ventilating and Air Conditioning & Refrigerating International Organization for Standardisation metabolic rate Mean Radiant Temperature Operating Theatre Predicted Mean Vote Standard Predicted Mean Vote Sick Building Syndrome Introduction Thermal comfort control is a never-ending war in tropical hot and humid built environments, for instance in Malaysia and Singapore. For hospitals located in the tropics, air conditioning systems must be installed in the buildings to help in achieving minimum hygienic and comfort level for the occupants. Although the ANSI/ASHRAE Standard (2004) and ISO 7730 (2005) provide thermal comfort guidelines to the Mechanical & Electrical design engineers, the applicability of these standards has always been questioned. van Hoof (2008) discussed the predicted mean vote (PMV)-model in light of the requirements by environmental engineering practice in the 21st century to move from a PMV to comfort for all. Improved prediction of thermal comfort could be achieved through improving the validity of the PMV-model, better specification of the modelõs input parameters and accounting for outdoor thermal conditions and special groups.

2 Thermal comfort study in Malaysia The study examined by Kwok (1998) in the schools showed that although the indoor thermal environment failed to meet the ASHRAE Standard 55 (2004), the occupant acceptability still found exceeded minimum requirement of 80% specified by the standard. Note that the similar findings were obtained in the research conducted by Kwok and Chun (2003) and Hwang et al. (2007). In these studies, occupants accepted thermal environments that did not meet the standard comfort criteria. In another research in Indonesia, Karyono (1994) revealed that the PMV tended to predict the occupant thermal sensation higher than the actual thermal sensation. In addition, Karyono (1994) found that the occupants accepted a higher space temperature in tropical building environments. Unfortunately, the heating, ventilating and air conditioning (HVAC) systems consume the largest part of energy use in a building for achieving desired thermal comfort level. Al-Sanea and Zedan (2008) mentioned that the energy usage for operating the air conditioning system consumed about half of the total electric energy generated in the Kingdom of Saudi Arabia. The result was in good agreement with the research performed by Karyono and Bahri (2005) where 50% of energy consumption was used for air conditioning system in office buildings located in Jakarta, Indonesia. The enormous energy consumption by air conditioning systems suggested that the decrease of building utility cost could only be achieved through effective HVAC systems. Effective air conditioning could be achieved by shifting up the temperature setting without compromising the occupantsõ thermal comfort. Karyono and Bahri (2005) conducted a research by the approach of modifying chilled water temperatures of the central air-conditioned system in 31-floor twin-towers office buildings in Jakarta, Indonesia. On average, shifting up the chilled water supply temperature by 1 K could result in a reduction of building energy consumption by 7.5% per month. In a similar research examined on the interaction between the thermal comfort and HVAC energy consumption, Alireza (2005) revealed that the commercial building energy consumption could be reduced through the increase of the range of set points. The results suggested that energy consumption could be reduced by 42% at the cost of 4% increase in the averaged occupantsõ thermal dissatisfaction. Hwang et al. (2007) investigated the comfort criteria of ANSI/ ASHRAE Standard (2004) for their applicability in hospital environments in Taiwan. The results showed that approximately 50% of the measured samples failed to meet the specifications of ASHRAE Standard (2004) comfort zone because of improper humidity control. Moreover, Hwang et al. (2007) found that the acceptability votes given by occupants exceeded the ASHRAE StandardÕs 80% criterion without taking into account whether the physical conditions were in or out of the comfort zone. Despite the aforementioned studies, there is virtually no research work on investigating the thermal comfort level in tropical hospital buildings. Therefore, this investigation is important to be carried out and the major aim is to examine the thermal comfort level as well as define the thermal comfort temperature range in the tropical hospital buildings. Research methodology The amount of heat generated and dissipated by individual bodies varies significantly with activity, age, size, and gender (McQuiston et al., 2005). The body has a complex regulating system acting to keep the deep body temperature of about 36.9 C regardless of the environmental conditions. A normal, healthy person generally feels most comfortable when the environment is at conditions where the body can simply maintain a thermal balance with the surroundings. The environmental factors that affect a personõs thermal balance and therefore influence thermal comfort conditions are the dry bulb temperature (DBT), humidity, velocity of the surrounding air of any surfaces that can directly view any part of the body and thus exchange radiation. Measurements of the globe thermometer, air temperature and air velocity can be combined as a practical way to estimate values of the mean radiant temperature (MRT) as described in equation (1) (McQuiston et al., 2005). Tmrt 4 ¼ T g 4 þ CV1=2 ðt g T a Þ ð1þ where, T mrt = mean radiant temperature, K, T g = globe temperature, K, T a = ambient air temperature, K, V = air velocity, m/s, and C ¼ 0: : Most comfort studies involve the use of the sevenpoint ASHRAE Standard scale of thermal sensation (ANSI/ASHRAE Standard (2004)). This scale links an Table 1 Summary of the hospital specifications Specification Hospitals Klang Kajang Putrajaya Private Hospital Age of hospital Since 1985 Since 1889 Since 2003 Since 2006 Location (State) Selangor Selangor Selangor Selangor Distance from West Coast (km) No. wards No. beds No. staffs interviewed Sex of staffs interviewed 4 males and 13 females 3 males and 21 females 7 males and 45 females 0 males and 21 females 501

3 Yau & Chew PMV was bias toward at lower temperature has given higher thermal sensation. It is good to point out that the higher prediction on thermal sensation may affect the indoor temperature settings. The wrong prediction of the occupantõs actual feeling may lead to a lower indoor temperature setting. In turn, the wrong estimation will inevitably cause the occupants over-cooled and consequently, thermal discomfort occurs in most of the Malaysian hospitals. Thus, the comparison between PMV and AMV is vital to justify whether the PMV and ASHRAE Standard on thermal comfort are applicable in tropical hospitals. There are many factors that may contribute to the deviation between AMV and PMV. Some of the factors are occupant clo, activity level, health, expectation, preference, adaptation and cultural differences. These factors do not have a specific device to measure and are determined by estimation only leading to the inaccuracy of the predicted thermal sensation. The significant deviation between AMV and PMV implied that ASHRAE Standard (2003) could not be applied in Malaysian hospitals without some degree of error. The standard comfort criteria might tend to give a lower acceptable temperature for the occupants. The results strongly indicated that the usage of the same standard universally must be re-examined to insure the occupant thermal comfort, especially in hot and humid climates. Conclusions A field thermal comfort study was conducted in four hospitals in the tropics. The results showed that only 44% of all measured thermal environments met the ASHRAE Standard thermal comfort criteria. The overall occupantsõ satisfaction toward the thermal environment was only 49%. Klang Hospital and Kajang Hospital have higher rate of satisfaction compared with the modern hospitals such as Putrajaya Hospital and the Private Hospital. The new defined comfort temperature for Malaysian hospitals is in the range of C. The results suggested that the indoor temperature set point could be shifted to a higher temperature to satisfy 90% occupantsõ thermal comfort satisfaction. In turn, the higher indoor temperature setting could reduce the energy consumption for the HVAC systems suggested by Al-Sanea and Zedan (2008). In addition, the significant deviation between AMV and PMV strongly implied that the PMV might be not suitable for application in hospitals in the tropics, for instance, Malaysia. Acknowledgements The authors would like to thank the Ministry of Science, Technology and Innovation, Malaysia, for the full financial support provided for Research Project Science Fund Thanks are also extended to University of Malaya (MU) who awarded FRGS Grant FP049/2007C to the authors for research work to be conducted in University of Malaya. In addition, special thanks are extended to Mr. E.S. Wong, former final year student at the Department of Mechanical Engineering, University of Malaya, for his help during critical portions of the project. References Alireza, T.N. (2005) Interaction between Thermal Comfort and HVAC Energy Consumption in Commercial Buildings, Master Degree Thesis, Vancouver, University of British Columbia. Al-Sanea, S.A. and Zedan, M.F. (2008) Optimised monthly-fixed thermostatsetting scheme for maximum energy-savings and thermal comfort in air-conditioned spaces, Appl. Energy, 85, ANSI/ASHRAE Standard (2004) Thermal Environmental Conditions for Human Occupancy, Atlanta USA, American Society of Heating, Refrigerating and Air Conditioning Engineers (ANSI/ASH- RAE Standard ). ASHRAE Standard (1995) Thermal Comfort Tool CD (ASHRAE Item Code 94030), American Society of Heating, Refrigerating and Air Conditioning Engineers. ASHRAE Standard (2003) ASHRAE Handbook, Atlanta, USA, American Society of Heating, Refrigerating and Air Conditioning Engineers. Brager, G.S. and de Dear, R.J. (1998) Thermal adaptation in the built environment: a literature review, Energy Build., 27, Fanger, P.O. (1970) Thermal Comfort, Copenhagen, Denmark, Danish Technical Press. van Hoof, J. (2008) Forty years of FangerÕs model of thermal comfort: comfort for all? Indoor Air, 18, Hwang, R.L., Lin, T.P., Cheng, M.J. and Chien, J.H. (2007) Patient thermal comfort requirement for hospital environments in Taiwan, Build. Environ., 42, ISO 7730 (2005) Moderate Thermal Environments-Determination of the PMV and PPD Indices and Specifications of the Conditions for Thermal Comfort, Geneva, International Organisation for Standardisation (ISO Standard ). Karyono, T.H. (1994) Higher PMV causes higher energy consumption in airconditioned building: a case study in Jakarta, Indonesia. In: Fergus, N., Michael, H. and Oliver, S. (eds) Standards for Thermal Comfort: Indoor Air Temperature Standards for The 21st Century, United Kingdom, E & FN Spon, Karyono, T.H. and Bahri, G. (2005) Energy Efficient Strategies for JSX Building in Jakarta, Indonesia. In: Santamouris, M. (ed.) Proceedings of the International Conference on Passive and Low Energy Cooling for the Built Environment, Santorini, Heliotopos Conferences, Kwok, A.G. (1998) Thermal comfort in tropical classroom, ASHRAE Trans., 104, Kwok, A.G. and Chun, C. (2003) Thermal comfort in Japanese schools, Solar Energy, 74, McQuiston, F.C., Parker, J.D. and Spitler, J.D. (2005) Heating, Ventilating and Air Conditioning, Analysis and Design, United States of America, John Wiley and Sons. 508

4 Thermal comfort study in Malaysia Appendix 509

5 Yau & Chew 18. How would you describe the indoor condition in this area? Please tick only one box per scale. The boxes with thin edges represent the ideal point on each scale a) Air movement Still Draughty b) Air quality Fresh Stuffy Odourless Smelly Clean Dusty c) Lighting Too dark Too bright Steady Flickering No glare Too much glare Very uniform Very uneven Satisfactory overall Unsatisfactory overall d) Accustics No noise from Too much noise from ventilation system ventilation system No other noise Too much other noise Table on Clothing Ensembles Description Trousers, short-sleeve shirt Trousers, long-sleeve shirt Trousers, long-sleeve shirt plus suit jacket Trousers, long-sleeve shirt plus suit jacket, vest, T-shirt Trousers, long-sleeve shirt plus long sleeve sweater, T-shirt Trousers, long-sleeve shirt plus long sleeve sweater, T-shirt plus suit jacket, long underwear bottoms Knee-length skirt, short sleeve-shirt (sandals) Knee-length skirt, long sleeve-shirt, full slip Knee-length skirt, long sleeve-shirt, half slip, long-sleeve sweater Angle-length skirt, long-sleeve shirt, suit jacket Walking-shorts, short-sleeve shirt Long-sleeve coveralls, T-shirt Overalls, long-sleeve shirt, T-shirt Insulated coveralls, long-sleeve thermal underwear tops and bottoms Athletic sweat pants, long-sleeve sweatshirt 510