THERMAL COMFORT OF A COURTYARD IN GUANGZHOU IN SUMMER

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1 THERMAL COMFORT OF A COURTYARD IN GUANGZHOU IN SUMMER L Jin 1,*, QL Meng 1 and LH Zhao 1 1 Building Environment Energy Laboratory, South China University of Technology, Guangzhou , China Engineering college, South China Agricultural University, Guangzhou , China ABSTRACT The quality of outdoor thermal environment directly influences the indoor air quality. The improvement of the quality of the outdoor ambience is a positive way not only to improve the indoor air s quality but also to prevent the vicious cycle of deterioration of the environment--energy consuming increasing-- deterioration of the Environment. In this paper, a survey of the thermal comfort in an outdoor courtyard in Guangzhou city was recorded. Eight hundred sixty-eight pupils were questioned about their comfort level in this outdoor space while the climate factors were recorded. Basic physical factors (solar radiation, air temperature, wind speed and relative humidity) influencing the outdoor environment were analyzed by regression analysis. The design reference of outdoor environment was provided correspondingly. The relationship between thermal comfort and thermal stress index, WBGT, was discussed extendedly. INDEX TERMS Outdoor; Thermal comfort; Regression analysis; WBGT INTRODUCTION Rapid urbanization of cities in the tropics, together with a lack of climate responsive guidelines, have created a diminished quality of outdoor urban environments. These resultant climate modifications have created an increased demand on urban energy resources. The implications of re-establishing and maintaining thermally desirable outdoor ambient environments, goes well beyond the capabilities of urban design to the level of individual building design. In creating comfortable outdoor environments, the first step is to define conditions of comfort for these outdoor spaces (K.S. Ahmed 003). From this definition, we can begin to work toward achieving sustainability of our outdoor urban environments. The South China region is primarily located south of the Nan-Ling line, with its northern part cut through by the Tropic of Cancer. Wet, hot, and windy are the main climatic characteristics of this region. Guangzhou is a representative city of this area, having a mean air temperature in July of 8~9 and a maximum temperature of The average relative humidity in Guangzhou varies from 76% to 84%( Anon.). The research team obtained test subjects thermal sensation by questionnaire and recorded the micrometeorological parameters at the same time during a three months period from July to September in 004. RESEARCH METHODS Survey location The study was conducted in the courtyard of the Building Environment Energy Laboratory of South China University of Technology. There is a two-story building situated in the north area of the site, and a single-story area on the south. Both the west and east sides are constructed of cast-iron columns. The South China Agriculture University football field is on the eastern side of the courtyard, and on the western side is a campus street running south- north of South China University of Technology. The prevailing ventilation flow is in the west-east direction. In the courtyard there is a big tree with heavy leaves providing ample shade. Micrometeorological measurements and instrumentation The instruments used to record the environmental factors were WBGT index instrument, Digital Humidity * Corresponding author jinling_08@16.com 849

2 collector, Pyranometer with shadow ring. Table 1. Introduction of the Sensors Sensors Type Variable Range Precision WBGT index instrument WBGT-000 T a 10~60 ±1 T nwb 5~40 ±0.5 T g 0~10 T g =0~50 ±0.5 T g =50~10 ±1 Anemometre Electronic _ V 0~30m/s ±% Pyranometer with shadow CC11 W <000W/m ±0.% ring HOBO Relative Humidity Logger Box3450 RH 0~95% ±5% Where T a =Air Temperature; T nwb =Nature Wet-Bulb Temperature; T g =Globe Temperature; V=Wind Speed; W=Radiation; RH=Relative Humidity. Procedure The experiment methodology consisted of adopting the questionnaires about thermal sensation of subjects while measuring the hot environmental parameters at the same time. The procedure was: Set up the experimental instruments in place 0 minutes prior to starting the experiment in order to obtain more accurate readings by acclimating them to the environment. Put several chairs around the instruments for the subjects later. Invite passing students to complete a questionnaire. Explain to the student the purpose of the survey and what is expected of them on the experiment. Within 10 minutes time span, the students are to finish the questionnaire while instruments record the environment data. Thermal sensation scale The internationally recognized ASHRAE 7-point thermal sensation scale is popular for field evaluation of thermal sensation of an environment. The range of scale varies from 3 to +3, where 3 is cold, - is cool, -1 is slightly cool, 0 is neutral, +1 is slightly warm, + is warm and +3 is hot (ISO ). This scale we used at the beginning of the survey. However, it was discovered that this scale was inadequate in describing the subjects outdoor thermal sensation in Guangzhou in summer, and caused confusion to the test subjects. The description words were changed to very cold, cold, slightly cool, neutral, slightly hot, hot, very hot for the values from 3~+3, respectively. RESULTS The physical parameters of thermal environment is indeed of great importance influencing people s thermal sensation vote (TSV), but psychological adaptation is also indelible in evaluation of ambience, such as environmental stimulation, thermal history, memory effect, expectations, etc. To omit the disturbances of psychological adaptation that come from the differences in occupation and the age of test subjects, all of the subjects in this survey were undergraduates. In addition, in order to assuring all participants have similar metabolic rate, every subject walked at normal speed on the road and finished the questionnaire seated. The typical attire of undergraduate in Guangzhou is T-shirt and short pants or short skirt in summer. The average value of thermal resistance of clothing (clo) is about 0.41 clo, additionally the appendix thermal resistance of the chairs used is about 0.1clo. Therefore, the total thermal resistance is 0.51clo. (Table~3.) Table. Summary of Subjects and Datasets Collected No Total Datasets Collected Male Percent of Male(%) Female Percent of Female(%)

3 Table3. Statistics of main factors in the field survey Ta V W RH N Mean Skewness Kurtosis Minmum Maximum DISCUSSION Regression analysis and neutral temperature in terms of the air temperature The usual procedure for obtaining the neutral temperature from a batch of field study observations is the application of regression analysis to thermal comfort data. The independent variable (x) is an index of the thermal environment, and the dependent variable (y) is the seven-point scale. Mean thermal sensation votes (TSV) were used as dependent variables to obtain best goodness of fit and level of significance. Table 4 shows the regression analysis in mean thermal sensation scale responses with air temperatures and radiation on two different statuses, no shading and shading. In the equation between radiation and TSV, we can obtain the upper limit of radiation in outdoor comfort zone. The predicted neutral air temperature obtained from equation at which the mean vote have been zero. The upper limit and lower limit obtained from equation at which the mean vote have been +1 and -1. Radiation Air temperature Table 4. Result of regression Status Regression formula R TSV = W TSV = W TSV = 0.38Ta TSV = 0.185Ta Wind speed and relative humidity The results of regression analysis about wind speed and relative humidity with TSV are not statistically significant. Thus, figure 1 shows the distribution of percentage of thermally acceptable varied with wind speed. The fact that the outdoor microclimate is generally assumed to be beyond architectural and mechanical control leads people to expect the conditions experienced outdoors to fall within a much wider range than the indoor climates experienced. The value between 1 ~ +1 is widely considered to be thermally acceptable (Jennifer Spagnolo 00). We deem the environment to be comfortable when the percentage of the votes ranged from 1 to +1 great than 80%. Then we obtained the minimal wind velocity is 0.3m/s and 0.6m/s varied from shading and no shading to satisfy most of people in outside thermal environment. Wind speed v>0. v>0.3 v>0.4 v>0.5 v>0.6 v>0.7 v>0.8 v> % 65.00% 70.00% 75.00% 80.00% 85.00% 90.00% 95.00% % Percentage of "acceptive" Figure 1. Distribution of percentage of thermally acceptable with different wind speed 851

4 From the result of the experiment we can see that the influence of the relative humidity to people's thermal comfort feeling is very finite under the hot and wet climate of Guangzhou. However we can still get the feasible scope of the relative humidity under this two kinds of conditions from figure. The feasible value of the relative humidity is 60% ~ 80% in sunlight and 40~60% in shading. While the diagram "in shading" also shows the vote ratio of " thermally acceptable " is higher (higher than 90%), too, when the relative humidity is above 80%. It's because of the small number of subjects at this level of relative humidity and those subjects influenced by lower air temperature more notable RH(%) Percentage of acceptive(%) RH(%) Percentage of acceptive(%) Figure. Distribution of percentage of thermally acceptable with different relatively humidity WBGT index and thermal comfort The wet bulb globe temperature (WBGT) index, one of the empirical indices representing the heat stress to which an individual is exposed, was first put forward by USA. The index WBGT has already attest anted by ISO743 (1989) because it is a preferable index to research outdoor thermal environment. Thus, we try to find the relationship between WBGT and the mean of TSV. At the same time, we obtained the reference values of thermal acceptable scaled by WBGT when the mean vote have been zero both with shading and with no shading. See Fig Mean of TSV WBGT Mean of TSV 1.5 Figure 3. Mean of TSV and WBGT with no shading 1 WBGT : y = 0.084x x R = : y = x x R = CONCLUSION AND IMPLICATIONS I. Through analysis above, we can get the hot comfort scope in outdoor environment of Guangzhou region in summer, please see the table 5. Table 5. Outdoor comfort zone of Guangzhou in summer Radiation (W/ m ) <130 <87 Air Temperature ( ) 1.8~ ~30.6 Wind Speed (m/s) >0.6 >0.3 Relative Humidity (%) 60%~80% 40%~60% 85

5 II. Under the premise that metabolic rate is at a low level (65<M<130) and the value of thermal resistance of clothing is about 0.5clo, the neutral temperature scale by air temperature is 6 without shading and 5. with shading. III. The upper limit of comfort zone is 8.06 and 7.96 separately in the sunlight and in shading scale by WBGT. The difference is too small to count, so we accounted it as 8 wholly. It is 4 lower than the upper limit of stress, value of 3, given by ISO743. REFERENCES Ahmed KS Comfort in urban spaces: defining the boundaries of outdoor thermal comfort for the tropical urban environments, Energy and Building. 35: Anonymity ISO Hot environments- Estimation of the heat stress on working man, based on the WBGT-index (wet bulb globe temperature). ISO Moderate Thermal Environment-determination of the PMV and PPD Indices and Specification of the Conditions for Thermal Comfort. Spagnolo J. and de Dear R A field study of thermal comfort in outdoor and semi-outdoor environments in subtropical Sydney Australia, Building and Environment. 38: