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1.INTRODUCTIONIn China, population aging is steadily increasing alongside urbanization. By 2040, the number of people aged over 60 years old will rise up to 402 million1. This demographic shift may result in numerous economic and social challenges. Consequently, both developed and developing countries have become increasingly concerned with the study of older age groups2. However, old people are more vulnerable to thermal risks associated with outdoor activities due to their physical fragility. Exposure to high temperatures for long time may lead to higher core temperatures for old people. Additionally, it is less likely for old people to take preventative measures to thermal environment as they exhibit low thermal sensitivity to environmental changes3. Therefore, it is necessary to evaluate the effect of environmental parameters on outdoor thermal comfort conditions of elderly. Recent research has revealed that human thermal comfort is not only influenced by climatic conditions, but also by the geothermal adaptation and cultural differences of the population. Firstly, people’s subjective thermal preferences vary according to their geographic location. Secondly, the subjective sensation of temperature and thermal comfort can also differ among different gender and age groups living in the same area. Finally, non-meteorological factors, such as the surrounding landscape, can also influence the subjective thermal sensory status of a population. In summary, these studies underscore the importance of thermal adaptation in thermal comfort research. In regions of China with similar climate characteristics to Chengdu, several studies have been conducted on thermal comfort for old people. Studies conducted in Chongqing showed that elderly tend to natural ventilation and environments instead of artificial cooling to enhance their thermal sensations4. In Shanghai, some studies found that old people have a lower perception on the outdoor environment than younger people5. A study carried out in Scotland demonstrated that older populations exhibit lower sensitivity to wet conditions in comparison to younger populations6. Another study conducted in Lhasa showed that, older age groups have a preference for higher levels of solar radiation in winter and lower wind speeds throughout the year7. Hence, in order to further develop a comprehensive understanding of the outdoor environment of the elderly in hot summer and cold winter climate zones. This study aims to investigate the outdoor thermal perception of the elderly in Chengdu. The objectives of the study are as follows: 2.MATERIALS AND METHODS2.1Study siteChengdu city, situated at the western periphery of the Sichuan Basin, has a sloping topography in the northwest- southeast direction. Chengdu located in the hot summer and cold winter climate zone (HSCW) of China. Generally, the Chengdu area experiences mild winters and high temperatures in the summer months, with relative humidity remaining high throughout the year. This study was conducted in Jinsha Binjiang Park and Xipu Binjiang Park in Chengdu. Three survey points were selected as the study site. Two measurement points in Jinsha Binjiang Park, one at the pavilion in the center of the park and the other at the riverside walkway. The third measurement point was located at the riverside in Xipu Binjiang Park (Figure 1). 2.2Data collectionThe experiment was conducted between July and December in 2021. The experiment included field thermal parameter measurements and subjective questionnaire. The thermal environment parameters measured in investigation included air temperature (°C), air relative humidity (%), wind speed (m/s), and solar radiation (w/m2). The measure equipment for these environment parameters met the standards of International Organization for Standardization (Table 1)8. The instruments were placed on both shaded and unshaded environment at test point. Table 1.The information of instrument.
The subjective questionnaire was conducted in the park. The elderly who suffer from diseases or take medicine were excluded from this study. Subjective feeling voting (i.e. thermal sensation voting (TSV), solar feeling voting, thermal comfort voting (TCV), moist feeling voting and wind feeling voting) was conducted in this study. Thermal comfort voting was assessed using the ASHRAE 4-point scale, and other factors were presented using ASHRAE 7-point scale9. The subjects who have been outside for at least 30 minutes were invited in the study and they were required to stand or sit at the test point for 5 minutes before completing the questionnaire. A total of 602 questionnaires were distributed, and 563 effective questionnaires were collected, with an effective rate of 93.52%. 2.3PET calculationPhysiologically equivalent temperature (PET) was chosen as the indicator for evaluating thermal comfort, as it was commonly used in previous studies7. The mean radiant temperature (Tmrt) is a crucial parameter for PET calculation. The calculation equation of Tmrt is as follows: where Tmrt denotes the mean radiation temperature, Tg represents the black sphere temperature, Ta represents the air temperature, Va represents the wind speed, D represents the diameter of the black sphere in meters (the standard black sphere used was a diameter of 0.15 m), and ε represents the emissivity of the black sphere (ε=0.95). Python in conjunction with IBM SPSS 25.0 was used to analysis the data. Spearman’s correlation analysis, and regression analysis were employed to process and derive the mathematical model. Then, the thermal neutral temperature and thermal comfort temperature ranges for elderly was obtained according to the model. 3.RESULTS3.1Objective meteorological parametersTable 2 displays the meteorological parameters in different seasons measured from three observation points. Overall, the meteorological characteristics of measurement points were consistent with the climatic features of Chengdu. The variation ranges of wind speed in summer and fall were much greater than in winter. The average solar radiance and its variation range was clearly greater than in fall and winter. It is worth to be noted that the range of thermal parameter of Chengdu in summer was much greater than in fall and winter. Table 2.Outdoor thermal environment parameters in different seasons.
3.2Subjective thermal response3.2.1Subjective feeling vote.The results of thermal feeling vote were compared to see whether there is a significant difference among different seasons. (Figure 2). Compared to summer and winter, the elderly were easy to get neutrality of thermal sensation, wind sensation, and solar sensation in fall. The old adults were likely to feel moist sensation neutrality in winter. To be specific, 67.7% of the elderly felt slight hot to very hot, 30% of elderly felt neutral in summer. In winter, 35.3% of elderly felt slightly cold, 60.7% of elderly felt neutral. In terms of solar feeling vote, 81.1% of the elderly felt slightly shaded to very shaded on winter. 75.1% of the elderly felt neutral to slightly sun. Overall, old adults were likely to get solar neutrality in summer, while they were likely to get thermal neutrality in winter. 3.2.2TCV and TSV.A binomial fit was employed to study the association between the thermal comfort vote (TCV) and the thermal sensation vote (TSV). According to Figure 3, a strong relationship existed between TSV and TCV. The regression model revealed that old adults in Chengdu could not achieve the state of a TCV=0. The elderly felt the minimum TCV was 1.14 in summer, corresponding to a TSV of -1.03; 0.54 in fall, corresponding to a TSV of 0.04; and 0.62 in winter, corresponding to a TSV of 0.71. Overall, old adults in Chengdu were easy to be in a comfortable state in winter than in summer. 3.3Thermal environmental parameters and TSVSpearman rank correlation coefficient was employed to analysis correlation between TSV and thermal environmental parameters (Table 3). Based on the statistical analysis, older people perceive the thermal environment more strongly in summer than in winter.To be specific, all environment factors strongly correlated with subjective thermal sensation in summer. Among these parameters, the Tmrt is the most important parameters for old adults in summer. The elderly preferred a lower Tmrt and higher wind speed in summer. In fall, humidity, air temperature, and Tmrt were correlated with thermal sensation. The Humidity is the most sensitive to thermal sensation. The elderly felt more comfortable with a higher humidity. While the association between thermal environmental parameters and thermal sensation was not significant in winter. Table 3.TSV correlation with other subjective.
Note: **means the probability of irrelevance is less than 0.01 *means the probability of irrelevance is between 0.01 and 0.05. 3.4Evaluation of thermal sensation3.4.1PET.Figure 4 displays the trend of TSV and PET for different seasons. As TSV increases, the value of PET increased and then decreased. The turning point of TSV is 2, 1, and -1 for summer, fall, and winter, respectively. Overall, the number of samples with TSV=-1 and TSV=0 increases gradually in winter and summer as the PET value increases. Therefore, as PET increases, older adults felt warmer. 3.4.2Neutral PET and comfort zone.Neutral temperature means the temperature that people feel is not too cold or too hot9. Previous processing method10 was employed for this study. The weighted mean TSV corresponding to PET at 1°C was obtained and then it was used to construct a regression model with PET. The regression equations of the TSV and PET of elderly people in different seasons are as follows: There was a strong relationship between TSV and TCV (Figure 5). From the regression model, it can be seen that TSV in summer is the best fitted to PET, with an R2 of 0.8, and the worst in winter. This may be due to the fact that the PET values in summer span up to 20°C, whereas in winter, the temperature is low throughout the day, making the winter PET span only 5°C. TSV=-0.5-0.5 represents the PET comfort range, while TSV=0 represents neutral PET. From the above equations, the comfortable PET range was 20.73–29.39°C, and neutral PET was 24.56°C in summer. In fall, the comfortable PET range was 10.15-23.28°C, and neutral PET was16.78°C. In winter, the comfortable PET range was 6.82–23.21°C, and neutral PET was 15.01°C. 4.DISCUSSIONThrough the above study, we have analyzed the characteristics of subjective heat sensation of old adults in Chengdu, including correlations between their thermal perception and meteorological conditions. Furthermore, we derived thermal neutral PET and comfortable PET range for old adults in different seasons. As presented in Table 4, the difference of neutral temperature and its range of old adults in different climatic zone was significant. The thermal neutral PET of summer and winter in Chengdu is higher than in cold area. Moreover, older adults have a wider thermal neutral range in summer and winter than in Madrid. Experiments conducted in Mianyang, which was geographically and climatically similar to Chengdu, showed that elderly in Chengdu experience higher thermal comfort in summer compared to younger people. While elderly in Chengdu experience lower thermal comfort than young in winter. Table 4.Comparison of thermal comfort for different age groups under similar climatic conditions in China.
Note: a: Climatic regionalization of China b: Koppen climate classification. 5.CONCLUSIONAn investigation of outdoor thermal sensation for elderly was conducted in Chengdu, which included field measurements of meteorological parameters and questionnaire survey. According to the statistical analyses of thermal sensory characteristics, PET and correlations between thermal environmental parameters and thermal sensation some conclusion may conclude:
ACKNOWLEDGEMENTSThis research was funded by Key Research and Development Program of Chengdu, China grant number (2022-YF05- 00595-SN) and National Key Research and Development Program of China, grant number (2022YFC3802702). REFERENCESThomas, S. A., Qiu, Z., Chapman, A., Liu, S. and Browning, C. J.,
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