A Field Study of the Thermal Environment in Residential Buildings in Harbin

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1 KC (4664) A Field Study of the Thermal Environment in Residential Buildings in Harbin Zhao-Jun Wang, Ph.D. Gang Wang Le-Ming Lian ABSTRACT This paper presents the main findings of Project HIT supported by the Scientific Research Foundation of Harbin Institute of Technology, a field study of indoor climates and occupant comfort in 66 residential buildings in Harbin, located in northeastern China. One hundred and twenty sets of questionnaire responses were provided from 120 subjects for winter, each accompanied by a full set of physical indoor climatic measurements with an indoor climate analyzer and a thermal comfort meter, which met ASHRAE Standard and ISO Standard 7726 (1985) for accuracy, duration of sample, and response time. Only 77.5% of the indoor measurements fell within the ASHRAE Standard and ISO Standard 7730 (1994) winter comfort zone of 16.5~22.5 C (corresponding to the average clothing, 1.37 clo); 91.7% of the occupants considered their thermal conditions acceptable. The operative temperature corresponding to the accepted thermal environment by 80% of the occupants is 18.0~25.5 C. Thermal neutrality, according to responses on the ASHRAE seven-point sensation scale, occurred at 21.5 C in winter. The preferred temperature is 21.9 C. Over 80% of the occupants felt dry at a relative humidity of 20%~30% in the comfort zone and over 40% at a relative humidity of 30%~55%. INTRODUCTION Current thermal comfort standards, such as ASHRAE and ISO 7730, are based almost exclusively on data from climate chamber experiments performed in mid-latitude climatic regions of North America and northern Europe. These standards are suitable for static, uniformly thermal conditions. But real people live in changeable, inconsistent environments. This poses potential problems when the standards are applied to residents living in real-world situations (McIntyre 1980; Schiller 1990; Benton et al. 1990). A large number of field studies have been performed around the world (Humphreys 1976; Dedear and Auliciems 1985; Schiller et al. 1988; Dedear and Fountain 1994; Howell and Kennedy 1979; Howell and Stramler 1981; Fishman and Pimbert 1979; Busch 1990; Xia et al. 1999; Cena and Dedear 1999; de Paula, Xavier, and Roberto 2000), but most of these were carried out in tropical and temperate climatic zones except Donnini et al. (1996), which was conducted in a cold climate in Montreal, Canada. The results of such field studies indicate that there is not perfect harmony between the expression of thermal comfort proposed by ASHRAE and ISO 7730 (ISO 1994) and the sensations that people are really feeling. This paper presents the main findings of Project HIT supported by the Scientific Research Foundation of Harbin Institute of Technology, a field study of indoor climates and occupant comfort in 66 residential buildings in Harbin, located in northeastern China. AIMS The current study was performed in Harbin, which has a cold and arid climate. The objectives of this project are as follows: To develop a database of the thermal environments and subjective responses of occupants in existing residential buildings in a cold, dry climate. To determine both the neutral and preferred operative temperature for occupancy as well as the range of thermal conditions found to be acceptable by the occupants. These findings are to be compared to the conditions required by ASHRAE and ISO To investigate the influence of relative humidity and vertical temperature difference. Zhao-Jun Wang is an associate professor, Gang Wang is a doctoral candidate, and Le-Ming Lian is a professor in the School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin, China ASHRAE. THIS PREPRINT MAY NOT BE DISTRIBUTED IN PAPER OR DIGITAL FORM IN WHOLE OR IN PART. IT IS FOR DISCUSSION PURPOSES ONLY AT THE 2003 ASHRAE ANNUAL MEETING. The archival version of this paper along with comments and author responses will be published in ASHRAE Transactions, Volume 109, Part 2. ASHRAE must receive written questions or comments regarding this paper by July 11, 2003, if they are to be included in Transactions.

2 TABLE 1 Summary of the Samples of Residence Occupants Sample size 120 Gender Male 59 (49.2%) Age (year) Length of time living in Harbin (years) To investigate potential acclimation effects and the adapted measures taken by occupants. METHOD Female 61 (50.8%) Mean 46.4 Standard deviation Maximum 80.0 Minimum 14.0 Mean 33.6 Standard deviation Maximum 67.0 Minimum 0.25 Outdoor Climatic Environment Harbin is situated in the northeast of China (at the latitude of north of the equator and longitude of east). The winter climate in Harbin is very cold and dry. The current experiment was conducted during the winter of (from December 2000 to January 2001). The mean daily temperature during this period was 15.5 C to 29.5 C, which is the lowest temperature in the past 30 years. Subjects We visited 66 families in two residential districts in Harbin. The samples were chosen equally in different living conditions, such as location of floor, area of the house, as well as the gender of subjects. A total of 120 participants provided 120 sets of data and subjective responses. The subjects participating in the study were composed of 61 females (50.8%) and 59 males (49.2%). The average age of all subjects is 46.4 years with a range of 14 to 80. A summary of the background characteristics of the subjects is presented in Table 1. Measurement of Indoor Climates An indoor climate analyzer and a thermal comfort meter made in Denmark were used to collect measurements of the indoor climates. 1. The physical data include air temperature, relative humidity, radiant asymmetry, air velocity, and predicted mean vote (PMV) and predicted percentage dissatisfied (PPD) indices. These were collected in accordance with the global database presented by Dedear and Brager (1998). Air temperature and air velocity were measured at the 0.1, 0.6, and 1.1 meter heights, representing the immediate environment of the seated person s ankles, mid-body, and neck, respectively. Relative humidity, radiant asymmetry, and PMV-PPD indices were measured at the 1.1 meter height. 2. All accuracies (manufacturer s specifications and the results of the calibration in an Instruments Testing Station in Heilongjiang Province) of the instruments used in the current field study meet the ASHRAE and ISO 7726 (ISO 1985) standards for accuracy, duration of sample, and response time. The air temperature transducer is based on a platinum resistance temperature sensing element with accuracy within 0.2 C and response time of 50 s to 90% of step change in still air. The humidity transducer is a dew-point transducer. Dew-point temperature is registered by a chilled mirror with total accuracy of ±0.5 C at 25 C, and relative humidity is measured directly. Air velocity is measured on the constant temperature anemometer principle with accuracy of ±5% at ±0.05 m/s in the measurement range of 0.05 to 1.0 m/s and response time of 0.2 s to 90% of step change. The radiant temperature asymmetry transducer consists of two identical faces (A and B), which independently measure incident radiation on each plane surface with total accuracy of ±0.5 C at 15 C and response time of 60 s to 90% of step change. Questionnaires The subjective questionnaires include the following: 1. Background survey The background survey form covered name, gender, age, and length of time living in Harbin for demographic characteristics of the sample. 2. Clothing and activity checklists 3. Thermal sensation, thermal preference, and thermal acceptability survey The thermal sensation scale is the ASHRAE seven-point scale of warmth ranging from cold (-3) to hot (+3) with neutral (0) in the middle. The McIntyre scale focuses more directly on thermal satisfaction by probing the subjects judgments of whether they would prefer the conditions to be different. The subject responds to three choices: I want to be: warmer, no change, cooler (McIntyre and Gonzalez 1976). These data are then encoded as +1, 0, and -1, respectively, for subsequent analysis. The thermal acceptability scale asked on a two-point scale whether the subjects would accept the thermal environment. Possible answers are yes and no, encoded as 1 and 0, respectively. 4. Thermal comfort and air condition survey The thermal comfort scale uses a five-point scale to rate the participants immediate impressions of comfort with regard to airflow, relative humidity, and general comfort. The five-point scale is very uncomfortable ( 2), slightly 2 KC (4664)

3 TABLE 2 Statistical Summary of Physical Data Mean Standard Deviation Maximum Minimum Air temperature ( C) Relative humidity (%) Air velocity (m/s) Radiant temperature ( C) Operative temperature ( C) PMV (%) PPD (%) Clothing (clo) Figure 1 Frequency of operative temperature. Figure 2 Frequency of air velocity. uncomfortable ( 1), comfortable (0), slightly comfortable (+1), and very comfortable (+2). The air condition assessment is collected from the subjects responses to the question: The air that you feel in the room is: muggy, fresh, dry, damp. 5. Adapted measures survey The adapted measures used by the occupants include electric heater, humidifier, openable window, curtain, and others. Figure 3 Frequency of relative humidity. RESULTS Indoor Climates Table 2 provides statistical summaries of the indoor climate measurements for the winter samples in Harbin. Air temperatures (t a ) (averaged across the three heights of 0.1, 0.6, and 1.1 m) fell within 12 C and 25.6 C, with a mean of 20.1 C. Mean radiant temperature (t r ) (mean of four directions) is 21.6 C. Operative temperatures (t o ) (average of t a and t r ) ranged between 12.1 C and 29.4 C, with a mean of 20.8 C. Relative humidities (RH) ranged from 22% to 53%. Air velocities (mean of three heights) are very low in winter, with a mean of 0.06 m/s. Figure 1 to Figure 3 give the frequency of operative temperature, air velocity, and relative humidity, respectively. From Figure 1, we see that 70.0% of the operative temperature measurements ranged between 18 C and 22.5 C. From Figure 2, we find that 95.8% of the air velocities are not more than 0.15 m/s. Personal Comfort Variables The insulation of clothes (clo) is obtained from tables (ISO 1994). On average, the chair insulation increment amounts to 0.15 clo (McCullough et al. 1994). Based on activity checklists referring to the hour just prior to sitting down to fill in the questionnaire, metabolic rates (met) of the subjects are estimated to be, on average, 1.2 met (70 W/m 2 ). Thermal insulation, including the insulation of the chairs on which subjects were sitting when they completed the questionnaire, is listed in Table 2. KC (4664) 3

4 Figure 4 Frequency of thermal sensation vote. Figure 5 Calculation of neutral temperature. Thermal Sensation The frequency distribution of thermal sensation votes is given in Figure 4. The strength of association and sensitivity of thermal sensation votes to temperature variations can be quantified using linear regression techniques. The data are binned into 0.5 C intervals. Mean thermal sensation votes and predicted mean vote for each half-degree operative temperature bin have been plotted in Figure 5. The linear regression equations are fitted for these binned thermal sensations against operative temperature: Mean thermal sensation = t o (1) Predicted mean vote = t o (2) Figure 6 Calculation of preferred temperature. The regression coefficient between the mean thermal sensation and the operative temperature is The regression coefficient between predicted mean vote and the operative temperature is The neutrality is derived by solving the equation for a mean sensation of zero, and the neutral operative temperature is 21.5 C, which is about equal to the mean operative temperature. The results are in accord with the ones that Dedear and Brager gave in 1998, proving that the adaptation of occupants to thermal environments is established. Thermal Preference Preferred temperature is assessed directly according to the answers of the question: At this point in time, would you prefer to feel warmer, cooler, or no change? Separate probit models are fitted to the want warmer and want cooler percentages within each half-degree operative temperature bin. Preferred temperature is obtained from the intersection of the two fitted probit lines in Figure 6 and the value is 21.9 C. From this we know that the preferred operative temperature is higher than the neutral operative temperature in cold area. The results are in accord with the ones given by McIntyre (1980); Figure 7 Calculation of thermal acceptability. Humphreys (1976); Dedear and Fountain (1994); Dedear and Brager (1998). Thermal Acceptability Thermal acceptability can be quantified simply as the percentage of the sample of the occupants who answered acceptable to the questionnaires on whether the thermal conditions were acceptable: 91.7% of occupants considered their thermal environments to be acceptable. ASHRAE and ISO 7730 comfort zone 20~24 C is only for ~1 clo. The average clothing in this study is 1.37 clo. This corresponds to a comfort range (PPD < 10%, PMV< ±0.5) from 16.5 C to 22.5 C, and 77.5% of the thermal conditions fell within the comfort zone 16.5 ~ 22.5 C. The acceptable temperature range is determined as follows: All persons voting +3, +2, 2, 4 KC (4664)

5 and 3 are considered as uncomfortable, while people voting 1, 0, and +1 are considered as comfortable. Percentage of dissatisfied is calculated for each half-degree operative temperature bin. The operative temperatures at which 80% of the occupants felt comfortable are the acceptable temperatures. In the current study, the acceptable temperature range is 18.0~25.5 C in Figure 7. Adaptation Measures The acceptable temperature range is very wide and it indicates that the adaptation of people to thermal environment is very important. The main measure taken by occupants is clothing adjustments. The insulation of clothes is 0.81~2.08 clo. DISCUSSION Comparisons Between Observed Comfort Data and the Standards Description of Comfort Standards ASHRAE In the winter, operative temperature and humidity limits are defined by a comfort zone on the psychrometric chart having the following coordinates: t o =19.5~23.0 C at 16.7 C T dp (dew point) and t o = 20.2~24.6 C at 1.7 C T dp. The two slanted sides are defined by the new effective temperature (ET * ). The winter limits are ET * = 20.0 and 23.6 C. The maximum limit for mean air velocity is 0.15 m/s in the winter. The vertical air temperature difference between the 0.1 and 1.7 meter levels shall not exceed 3 C. ISO The ISO standard is very similar to the ASHRAE standard with a few minor exceptions. It does not specify humidity limits, resulting in a comfort zone defined strictly in terms of operative temperature limits: t o shall be between 20~24 C in the winter. The maximum allowable air velocity is 0.15 m/s. The maximum acceptable vertical air temperature difference is the same, but it is taken between the 0.1 and 1.1 meter levels. Due to the similarity of the ASHRAE and ISO comfort standards and because the calculating of ET * is difficult, we only compare the results to the ISO standard and calculate the index of t o instead of ET *. Comparisons with Thermal Comfort Standards Humidity on Human Comfort. According to the comfort standard, the influence of relative humidities at 22% to 53% all fell within the comfort zones. But in fact, 81.1% of the occupants felt dry at relative humidity of 20% to 30%, while 18.9% people thought it acceptable. When relative humidity was 30% to 40%, 40.5% persons felt dry, 14.3% people felt damp, 42.9% occupants thought it acceptable, and the other 2.3% felt muggy. The feeling of the subjects at relative humidity of 40% to 55% was almost the same with that of ones at relative humidity of 30% to 40%. In winter, people living in northeastern China often complain that the air is too dry to feel comfortable in their throats. The comfort standard for humidity seems too wide to be applied in Harbin. Vertical Air Temperature Difference on Human Comfort. In 17.5% of the samples, people were not satisfied with ISO 7730 comfort standard on air temperature gradient. But 52.4% of the persons felt comfortable among these occupants. Only 47.6% of the people felt slightly cool at their feet when the operative temperature at the 0.1 meter level was lower than 16 C. So we think that vertical air temperature difference is not the main cause that can influence human comfort, but the operative temperature at the 0.1 meter level is the key to the question. The lowest limit of 16 C at 0.1meter level is suggested. Comparisons with Previous Thermal Comfort Field Studies Harbin subjects are as sensitive to temperature variations as the San Francisco and Pekin subjects and less sensitive to temperature variations than the Townsville and Montreal subjects. A gradient of one sensation unit per 3 C is found in the Harbin, San Francisco, and Pekin studies, while a gradient of one sensation unit per 2 C was found in both the Townsville and Montreal studies. In this study, the neutral operative temperature (21.5 C) is lower than that of Montreal (23.1 C) while higher than that of Kalgoorlie (20.3 C) in winter. The preferred operative temperature is found to be 21.9 C, which is similar to that of the Montreal study (22.0 C). Eighty percent of the occupants can accept the operative temperature range at 18.0~25.5 C, and the upper limit of accepted temperature is similar to that of the Montreal study (21.5~25.5 C) and the minimum temperature is lower than that of the Montreal study. CONCLUSION 1. According to the ASHRAE and ISO 7730 comfort standards, only 77.5% of the thermal conditions fall within the comfort zone of 16.5~22.5 C; 91.7% of the occupants considered their thermal environments to be acceptable due to adaptability measures taken by occupants. 2. Eighty percent of the occupants can accept the operative temperature range at 18.0~25.5 C. It is higher than the winter comfort zone of 16.5~22.5 C. 3. Neutral operative temperature is 21.5 C. Preferred operative temperature is 21.9 C. 4. Some 81.1% of the occupants felt dry at relative humidity of 20% to 30%, while over 40% of the persons felt dry at relative humidity of 30% to 55%. The lowest limit of relative humidity shall be 30% instead of the 20% recommended in comfort standards. 5. Only 47.6% of the people felt slightly cool at their feet when the vertical air temperature difference between 1.1 and the 0.1 meter heights was over 3 C and the operative temperature at 0.1 meter level was lower than 16 C. So we think that vertical air temperature difference is not the main KC (4664) 5

6 factor influencing human comfort, but the operative temperature at 0.1 meter level is the key to the question. The lowest limit of 16 C at 0.1 meter level is suggested. REFERENCES ASHRAE ANSI/ASHRAE Standard , Thermal environmental conditions for human occupancy. Atlanta: American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc. Benton, C.C, F.S. Bauman, and M.E. Fountain A field measurement system for the study of thermal comfort. ASHRAE Transactions 96(1): Busch, J.F Thermal responses to the THAI office environment. ASHRAE Transactions 96(1): Cena, K, and R.J. Dedear Field study of occupant comfort and office thermal environments in a hot, arid climate. ASHRAE Transactions 105(2): Dedear, R.J, and A. Auliciems Validation of the predicted mean vote model of thermal comfort in six Australian field studies. ASHRAE Transactions 91(2B): Dedear, R.J, and G.S. Brager Developing an adaptive model of thermal comfort and preference. ASHRAE Transactions 104(1): Dedear, R.J, and M.E. Fountain Field experiments on occupant comfort and office thermal environments in a hot-humid climate. ASHRAE Transactions 100(2): de Paula Xavier, A.A, and L. Roberto Indices of thermal comfort developed from field survey in Brazil. ASHRAE Transactions 106(1): Donnini, G., J. Molina, C. Martello, et al Field study of occupant comfort and office thermal environments in a cold climate. ASHRAE Transactions 103(2): Fishman, D.S, and S.L. Pimbert Survey of the subjective responses to the thermal environment in offices. In Indoor climate, P.O. Fanger and O. Valbjorn, pp Copenhagen: Danish Building Research Institute. Humphreys, M.A Field studies of thermal comfort compared and applied. Building Services Engineer 44: Howell, W.C, and P.A. Kennedy Field validation of the Fanger thermal comfort model. Human Factors 21(2): Howell, W.C, and C.S. Stramler The contribution of psychological variables to the prediction of thermal comfort judgments in real world settings. ASHRAE Transactions 87(1): ISO International Standard Thermal environments Specifications relating to appliances and methods for measuring physical characteristics of the environment. Geneva: International Standard Organization. ISO International Standard Moderate thermal environment Determination of the PMV and PPD indices and the specification of conditions for thermal comfort. Geneva: International Standard Organization. McIntyre, D.A., and R.R. Gonzalez Man s thermal sensitivity during temperature changes at two levels of clothing insulation and activity. ASHRAE Transactions 82(2). McIntyre, D.A Indoor Climate. London: Applied Science Published LTD. McCullough, E.A, B.W. Olesen, and S. Hong Thermal insulation provided by chairs. ASHRAE Transactions 100(1): Schiller, G.E A comparison of measured and predicted comfort in office buildings. ASHRAE Transactions 96(1): Schiller, G.E, E.A. Arens, F.S. Bauman, et al A field study of thermal environment in office buildings. ASHRAE Transactions 94(2): Xia, Y.Z., R.Y. Zhao, and Y. Jiang Thermal comfort in naturally ventilated houses in Beijing. HV&AC 29(2): KC (4664)