Field evaluation of thermal comfort and indoor environment quality for a hospital in a hot and humid climate.
Another well-known international standard, ISO 7730 (ISO 2005), provides methods for predicting the thermal sensation and thermal dissatisfaction of personnel. Calculation of the predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) associated with other environmental conditions enables the analytical investigation and interpretation of thermal comfort. ANSI/ASHRAE Standard 62.1 (ASHRAE 2007) specifies minimum acceptable ventilation rates and indoor air quality (IAQ) for human occupants in buildings. Appendix E of this standard lists the specific outdoor air requirements for ventilation of health care facilities. ANSI/ASHRAE Standard 187 (ASHRAE 2008) demonstrates the guidelines of ventilation specific for health care facilities. In 2008, Zhang and Zhao investigated overall thermal sensation, acceptability, and comfort under uniform and non-uniform conditions. Airaksinen et al. (2008) also conducted research to calculate local and overall human body thermal sensations using time-dependent and non-uniform methods. Despite advanced development and international recognition of the international standards, and research relating to indoor thermal environment and IAQ for building design, there are special considerations (lifestyle, outdoor climate, economy) for which the revision of existing standards
is required (Olesen 2004).
In 2009, Zeiler and Boxem conducted a study on thermal comfort in 14 schools equipped with different types of HVAC systems using measurements and questionnaires. Results indicated that the effects of thermal quality in schools, like IAQ, are of great importance concerning the learning performances of students. Candido et al. (2010) investigated acceptable air movement levels inside naturally ventilated classrooms. Results indicated that occupants prefer an air velocity higher than the ASHRAE comfort limit. In another investigation, Arens et al. (2009) also reported that a large percentage of occupants prefer greater air movement than they currently have. According to thermal sensation votes, occupants prefer warm, thermally neutral, and slightly cool air movement. Extensive field experiments and numerical simulation analyses have investigated thermal comfort and IAQ in the lecture room using different HVAC systems (Noh et al. 2007). Bin and Sekhar (2007) investigated the indoor parameters of a new approach to supply fresh air, as evaluated using objective measurements and numerical simulation. Besides, the impact of air movement on perceived air quality and sick building syndrome symptoms has been studied extensively (Melikov and Kaczmarczyk 2012).
Health care buildings are complex indoor facilities requiring varying conditions for different types of occupants and healing processes. In 2007, Balaras et al. investigated HVAC and thermal conditions in hospital operating rooms. The research findings showed that the majority of indoor conditions for audited operating rooms did not conform to optimum indoor thermal conditions recommended by various guidelines and international standards. Hwang et al. (2007) also conducted a field survey on patient thermal comfort requirements in hospital environments. Results identified that patients' physical strength significantly influenced their thermal requirements. Yau and Chew (2009) conducted a thermal comfort study on hospital workers. Thermal acceptability assessments evaluated whether hospitals in tropical areas met the ASHRAE standard 80% acceptability criteria. The results revealed that hospitals in tropical environments require a higher comfort temperature compared with the criteria specified in ASHRAE standards.
Although previous studies have widely researched thermal comfort and IAQ for building indoor environments, there is little quantitative information available on the relationship between acceptable thermal sensation and IAQ, especially for occupants of a health care facility. The present study extensively investigated, using field surveys, thermal comfort and indoor environment quality of a district hospital in a hot and humid area (in Taiwan). Procedures included the analysis and comparison of thermal sensation questionnaire responses from hospital personnel, including thermal sensation and air movement preferences, and identification of the relationship between feeling of air movement and carbon dioxide (C[O.sub.2]) concentration. Mean thermal sensation votes on operative temperature are supposed to be reevaluated for thermal comfort of hospital personnel in hot and humid climates.
Hospital description and data collection
The investigated public hospital is located in hot and humid weather conditions in central Taiwan. Its floorage is approximately 49,321 [m.sup.2] (530,904 [ft.sup.2]) for the main medical building from floor B I to the 12th floor. The detailed floor plan of the hospital building is shown in Table 1. The HVAC systems are a very typical constant air volume (CAV) air handling unit (AHU) system with typical chiller application. Field evaluations were conducted during the summer season, from July to August, when the monthly mean ambient temperatures are approximately 34[degrees]C (93.2[degrees]F) with an average relative humidity of approximately 85%. On each floor, two main AHUs provide conditioned air via air ducts for all thermal comfort and healing process requirements. Survey questionnaire and field measurement data were collected simultaneously to examine the thermal requirements of working staff, including physicians, nurses, administrative, and technical personnel, and waiting patients in outpatient areas. A total of 403 hospital occupants were involved in the study assessments. The distribution of questionnaires from occupants on different floors is also listed in Table 1.
Questionnaires were used to evaluate occupants' subjective responses on thermal comfort in the study hospital. The survey questionnaire was based on Appendix E--Thermal Environment Survey in ASHRAE Standard 55 (ASHRAE 2010), modified slightly to fulfill the research interests of the study and was divided into three parts. The first part of the questionnaire consisted of background information and demographic information, such as age, gender, and health condition. The clothing and activity level of each occupant were recorded and the corresponding clothing insulation values (clo) and metabolic rates (met) were evaluated by referring to the tables in ASHRAE Standard 55. The second part of the questionnaire focused on the thermal environment, including thermal sensation (using a traditional ASHRAE 7-point scale), feeling of air movement, and overall acceptability of the environment. The last part of the questionnaire highlighted the respondents' thermal sensation and air movement preferences.
While conducting the subjective questionnaire survey, the physical conditions of spaces were simultaneously measured and recorded. Climatic variables (such as temperature, relative humidity, global temperature, air velocity) and IAQ indices (such as C[O.sub.2] and total volatile organic compounds [TVOC] concentrations) were recorded in real time to evaluate the relationship between thermal comfort and IAQ parameters. The apparatus specifications for field measurements are summarized in Table 2. A multi-channel data logger (YOKOGAWA, Model MV100), with several temperature and humidity transmitters, was used to record the temperature and relative humidity in each space. Tests of temperature, to an accuracy of 0.2[degrees]C (0.36[degrees]F), and humidity, to an accuracy of 2% RH, were performed at the height of 1.1 m (3.6 ft) for standing occupants and 0.6 m (2.0 ft) for sitting occupants. Measurements were collected in triplicate at each location to improve accuracy and repeatability. Global temperatures ([T.sub.g]) and air velocity were measured by applying the thermal comfort data logger (METREL, Model MI6401), along with a hot wire anemometer, to an accuracy of 0.5[degrees]C (0.9[degrees]F) for temperature and 3% for velocity. The mean radiant temperature ([T.sub.mrt]) was calculated according to the following equation, adopted from ISO 7726 Standard (ISO 1998).
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] (1)
where V (m/s) is the air velocity, [D.sub.g] (m) is the diameter of the globe, [epsilon] is the emissivity of the globe, and [T.sub.mrt] ([degrees]C), [T.sub.g] ([degrees]C), and [T.sub.a] ([degrees]C) represent the mean radiant temperature, black globe temperature, and air temperature, respectively.
The concentrations of C[O.sub.2] and TVOC were measured by applying the IAQ meter (AreaRAE IAQ, PGM-5210) to an accuracy of 10 ppm for C[O.sub.2] and 0.1 ppm for TVOC. All instruments for field measurement were attached to a measuring cart to conduct field surveys efficiently and simultaneously. The instruments applied in this study were calibrated regularly according to the manufacturer's instructions.
Results and discussion
Of a total of 403 respondents participating in the field evaluation, 41 (10.17%) were male while 362 (89.83%) were female. Their ages ranged from 20 to 65 years. The majority of the respondents were female and between the ages of 21 and 30. Most of these were young nurses working at the hospital. Figure la presents the distribution of overall thermal sensation data as collected using questionnaires. One hundred forty-eight (36.72%) correspondents referred to the thermal sensation as "neutral" while 77 (19.11%), 18 (4.47%), and 57 (14.14%) correspondents referred to it as "slightly warm," "warm," and "hot," respectively. Two hundred fifty-five (64.28%) correspondents felt dissatisfied with the thermal comfort, despite over 80% of field measurement data falling within the ASHRAE comfort zone. This indicated that working staff might prefer lower temperatures, greater air movement, or have had their perception affected by IAQ parameters. Figure l b displays the detailed distribution of thermal sensation votes using the ASHRAE 7-point scale on different floors in the hospital. The occupants of the 1st floor (emergency care and registration), 2nd floor (outpatient clinic), 3rd floor (intensive care and operation room), 5th floor (delivery room and weird), 8th floor (psychiatric ward), and 12th floor (isolation room) had higher percentages of unfavorable responses concerning the thermal environment.
When examining the field evaluation data, the feeling of air movement presented one of the main reasons for dissatisfaction. As shown in Figure 2a, 165 (40.94%) correspondents felt that the air movement was "normal," while 158 (39.21%) and 54 (13.40%) correspondents referred to it as "low" and "too low," respectively. Over half (52.61%) of the occupants, therefore, expressed dissatisfaction with the air movement due to low perception of air movement. As displayed in Figure 2b, 212 (52.74%) and 13 (3.20%) correspondents expressed a preference for changing their thermal environment to "cooler" and "colder," respectively, despite approximately 36.72% of occupants responding "neutral" for thermal sensation votes (Figure la). Over half (55.94%) of occupants preferred a lower air temperature, despite 80% of the measured data falling within the comfort zone. Results also revealed that the hospital staff preferred lower temperatures than those recommended in the ASHRAE guidelines.
Poor air movement might also have affected the thermal sensation voting. In the survey questionnaire, the item of further preference after their answer was appended on overall acceptability of thermal sensation. Figure 3 displays the findings from the survey on overall acceptability of thermal sensation. One hundred ninety-five (48.36%) correspondents referred to the thermal sensation as "acceptable," while 208 (52.61%) correspondents referred to it as "unacceptable." In the unacceptable group, 51.44% and 24.52% of the correspondents felt that air movement was "low" and "very low," respectively. Even 26.15% of respondents in the "acceptable" group still felt that the air movement was "low." In the group of "unacceptable," there 75.92% (51.44% low + 24.5% very low) had the feeling of "low" in general. Air movement played a very important role in dissatisfaction with thermal comfort of occupants in the hospital. Reexamination of the velocity of air distributed by the HVAC system of the study hospital is, therefore, needed. In the acceptable group, approximately 30% of occupants preferred higher velocity air movement.
[FIGURE 1 OMITTED]
[FIGURE 2 OMITTED]
In the present study, simultaneously collected comprehensive field measurement and survey questionnaire data examined the relationship between thermal comfort and IAQ. These assessments incorporated climatic parameters (including air temperature, relative humidity, global temperature, and air velocity) and typical IAQ indices (including C[O.sub.2] and TVOC concentration). Table 3 presents the typical mean field measurement data on each floor. Calculation of mean radiant temperature ([T.sub.mrt]) and operative temperature ([T.sub.o]) and comparison of these values with mean sensation votes enabled the determination of the combination of air temperature and [T.sub.mrt], which people find thermally acceptable. As shown in Table 3, the C[O.sub.2] concentrations ranged from 520 ppm to 880 ppm, which were over the recommended value of 600 ppm from the EPA of Taiwan. This also indicated poor IAQ, in terms of higher C[O.sub.2] concentration, in most spaces of the hospital. The concentrations of TVOC on each floor provided favorable data (under 2 ppm), lower than the threshold limit of 3 ppm for hospital buildings. The temperature ranged from 23[degrees]C to 26[degrees]C (73.4[degrees]F to 78.8[degrees]F), which was acceptable and compliant with design specifications, while relative humidity was approximately 60% to 65%, with higher humidity during the summer season.
Comparisons of questionnaire votes on air movement with field measurement data on C[O.sub.2] concentrations examined the effects of IAQ parameters on air movement preferences. This included the plotting of the percentages of votes on feeling of air movement versus C[O.sub.2] concentration, as shown in Figure 4a. For occupants who responded feeling that the air movement was "normal," the regression line decreased with increasing C[O.sub.2] concentration. This indicated that poor IAQ (high C[O.sub.2] concentration) had a detrimental effect on the feeling of air movement in the indoor environment. Increasing C[O.sub.2] concentration had lesser effects on the correspondents who felt the air movement was "too strong." It also had lesser effects on the occupants who preferred "too strong" air movement. Figure 4b presents the correlations between the C[O.sub.2] concentration data on and air movement preferences of the occupants on different floors. For correspondents who preferred "more air," the percentages of correspondents feeling air movement increased as the C[O.sub.2] concentration increased. Poor IAQ (higher C[O.sub.2] concentration) caused occupants to feel "stuffy" and demand greater air movement. Increasing C[O.sub.2] concentration also had detrimental effects on thermal comfort in occupants of an indoor environment, with the percentages of correspondents who responded "do not change" decreasing accordingly. Increasing C[O.sub.2] concentration had lesser effects on the occupants who preferred "less air" movement.
[FIGURE 4 OMITTED]
According to the thermal sensation scale listed in ASHRAE Standard 55, the PMV range is between -0.5 and +0.5 for comfortable zone requirements. To provide a comfortable zone in summer, the operative temperature should be between 23.6[degrees]C and 27.9[degrees]C (74.4[degrees]F and 82.2[degrees]F). This may not necessarily apply in hospital buildings in hot and humid climates. As shown in Figure 5, the present study calculated the mean thermal sensation votes from the field survey questionnaire responses and then determined the operative temperatures from the field measurement data. The intersection of the regression line with the thermal sensation votes ranging between -0.5 and +0.5 could be used to demonstrate the neutral temperature for the occupants in this hospital. This provided a temperature range of 22.9[degrees]C to 26.3[degrees]C (73.2[degrees]F to 79.3[degrees] F), which are lower values than those listed in Standard 55. The occupants of the study hospital, therefore, preferred approximately 1.0[degrees]C (1.8[degrees]F) lower temperatures in hot and humid weather conditions. Figure 6 presents the comparisons of thermal comfort votes when simulating the ASHRAE Thermal Comfort Program (1995), assuming clothing insulation of 0.53 (clo) and metabolic rate of 1.4 (met). A greater shift in operative temperature (ranging from 21.3[degrees]C to 27.0[degrees]C [70.3[degrees]F to 80.6[degrees]F]) would be needed to obtain a comfortable zone in summer, due to higher clothing insulation and metabolic rate, according to ASHREA PMV recommendation values (0.5 clo and 1.0 met in summer). As clothing conditions and metabolic rates increase, this would increase the demand for lower temperatures and greater air movement.
[FIGURE 5 OMITTED]
[FIGURE 6 OMITTED]
Providing thermal comfort in a hospital is a complicated issue due to diverse physical condition requirements and different types of personnel demands. The present study describes the thermal sensation votes from field survey questionnaires, and simultaneously obtained field measurement data, in a hospital located in a hot and humid climate. Thermal sensation and air movement preferences influence the overall acceptability of thermal comfort in an indoor environment. Poor IAQ increases the respondents' demands for air movement and induces different air movement preferences. To establish a more comfortable temperature range for hospital occupants, specific for a hot and humid climate, the present study correlated the mean sensation votes and operative temperatures for the entire hospital building. This revealed a slight shift in operative temperatures to obtain a thermal comfort zone and demonstrated the hospital occupants' preferences for lower temperatures in tropical weather conditions.
The authors would like to express their great appreciation to the National Science Council for financial support under grant NSC- 100-2221-E-167023-MY3.
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Fujen Wang, (1),* Mengchieh Lee, (2) Tsungjung Cheng, (3) and Yuquan Law (1)
(1) Department of Refrigeration, Air Conditioning and Energy Engineering, National Chin-Yi University of Technology, Taichung 411, Taiwan
(2) Department of Interior Design, National Taichung Institute of Technology, Taiwan
(3) Department of Architecture, Feng Chia University, Taiwan
* Corresponding author e-mail. Jjwang@ncut.edu.tw.
Received March 2, 2011 ; accepted November 9, 2011
Fujen Wang, PhD, PE, Member ASHRAE, is Professor. Mengchieh Lee, PhD, Associate Member ASHRAE, is Assistant Professor. Tsungjung Cheng, PhD, PE, is Associate Professor. Yuquan Law is Graduate Student.
Table 1. Floor plan of the investigated hospital and questionnaires distribution. Floor Medical building description Occupants B1 Car park/ Cafeteria/ Medicine 8 storage 1st Clinic/ Emergency Care/ 34 Radiology/ Pharmacy/Cashier and Registration 2nd Outpatient Clinic/ Waiting Area 28 3rd Intensive Care Unit/ Burn 86 Center/ Respiratory Center/ Operation Room 4th Facility Center 12 5th Ward/ Delivery Room/ Baby 31 Room/ Open air Garden 6th General Ward/ Child Intensive 26 Care unit 7th Surgery Ward 19 8th Psychiatric ward/ Nursing 42 Department 9th Internal Medicine Ward 60 10th Thoracic Ward 29 11th Family Medicine Ward/ Health 11 Examination Center 12th Negative Air Pressure Isolation 17 Ward/ Conference Room Table 2. Apparatus for field measurement. Apparatus model Probe TSI-9555-P Hot-wire anemometer YOKOGAWA-MV100 PT 100 sensor humidity sensor Area Rae IAQ TVOC sensor (PGM-5210) CO2 sensor METREL Poly Hot-wire anemometer (MI-6401) Dry-bulb sensor Global sensor Apparatus model Operative range TSI-9555-P 0.1-30 m/s (20-5906 fpm) YOKOGAWA-MV100 0-100[degrees]C (32-212[degrees]F) 0-100% RH Area Rae IAQ 0-500 (ppm) (PGM-5210) 0-2000 (ppm) METREL Poly 0.1-9.99 m/s (20-1967 fpm) (MI-6401) -20-60[degrees]C (-4-140[degrees]F) -10-120[degrees]C (14-248[degrees]F) Apparatus model Accuracy TSI-9555-P 0.02 m/s (3.9 fpm) YOKOGAWA-MV100 0.2[degrees]C (0.36[degrees]F) 2% RE Area Rae IAQ 0.1 ppm (PGM-5210) 10 ppm METREL Poly 0.05 m/s (9.8 fpm) (MI-6401) 0.5[degrees]C (0.9[degrees]F) 1.0[degrees]C (1.8[degrees]F) Table 3. Field measurement data for different floors. Floor T,[degrees]C([degrees]F) RH, (%) V, m/s(fpm) B1 22.1 (71.7) 61.0 0.15 (29.5) 1 27.6 (81.6) 62.2 0.12 (23.6) 2 24.9 (76.8) 59.4 0.12 (23.6) 3 24.7 (76.4) 63.1 0.14 (27.5) 4 24.0 (75.2) 65.2 0.11 (21.6) 5 24.8 (76.6) 68.6 0.12 (23.6) 6 23.8 (74.8) 69.2 0.13 (25.5) 7 24.9 (76.8) 68.7 0.11 (21.6) 8 24.1 (75.3) 63.6 0.12 (23.6) 9 23.3 (73.9) 69.2 0.12 (23.6) 10 23.5 (74.3) 68.0 0.14 (27.5) 11 24.1 (75.3) 68.5 0.14 (27.5) 12 24.0 (75.2) 63.2 0.12 (23.6) [T.sub.mrt], Floor C[O.sub.2](ppm) TVOC (ppm) [degrees]C([degrees]F) B1 562 0.73 24.4 (75.9) 1 690 0.82 28.1 (82.5) 2 876 1.87 26.9 (80.4) 3 725 1.03 27.0 (80.6) 4 820 0.89 25.3 (77.5) 5 521 0.54 27.9 (82.2) 6 598 0.72 26.4 (79.5) 7 650 0.93 27.4 (81.3) 8 605 0.85 26.4 (79.5) 9 595 1.25 26.5 (79.7) 10 625 1.03 25.5 (77.9) 11 570 0.87 26.0 (78.8) 12 610 1.30 25.8 (78.4) [T.sub.o], Floor [degrees]C([degrees]F) B1 23.3 (73.9) 1 27.8 (82.0) 2 26.0 (78.8) 3 25.8 (78.4) 4 24.7 (76.4) 5 25.7 (78.2) 6 24.6 (76.2) 7 25.7 (78.2) 8 24.8 (76.6) 9 24.3 (75.7) 10 24.8 (76.6) 11 24.9 (76.8) 12 24.9 (76.8) Figure 3. Comparisons of feeling of air movement according to acceptability of thermal sensation. Acceptable (48.39% 195 occupants) Normal 66.67% Low 26.15% Very Low 1.54% Strong 5.64% Unacceptable (52.61% 208 occupants) Low 51.44% Very Low 24.52% Very Strong 0.96% Strong 6.25% Normal 16.83% Percentage of air movement sensation(%) Note: Table made from pie chart.
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|Author:||Wang, Fujen; Lee, Mengchieh; Cheng, Tsungjung; Law, Yuquan|
|Publication:||HVAC & R Research|
|Date:||Aug 1, 2012|
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