Field Study of thermal comfort of indoor fitness places in cold region

. A healthy body is the foundation of everything. The indoor environment comfort of fitness places has been paid more and more attention. However, there is a lack of relevant standards for the thermal environment of indoor sports and fitness venues in China, especially the research on the indoor thermal environment in different seasons. Therefore, in our study, physical environment parameters such as indoor temperature and humidity, black ball temperature, air flow rate and CO 2 concentration in 9 indoor fitness places in Xi 'an in different seasons were measured on site. At the same time, a subjective questionnaire survey was conducted on thermal sensation and acceptability of the people who were exercising in the fitness places. Through subjective questionnaire analysis, respondents generally have a high degree of satisfaction and acceptance of temperature, and the average thermal comfort vote is the highest when the indoor temperature is 17.9-23.9 (cid:263) . In addition, the thermal comfort of different sports in the same space also has certain differences. The fitness people indoor have lower satisfaction with air flow and air quality. Based on the study of the factors affecting indoor thermal comfort, this paper puts forward the improvement strategies for improving indoor thermal comfort, and provides scientific basis for the design and operation of fitness venues.


Instruction
Exercise is an important way to maintain people's physical and mental health and reduce the risk of disease through [1] .With the improvement of people's life quality, indoor sports activities such as leisure and fitness have gradually attracted people's attention. Related studies show that the quality of the indoor physical environment in a building has a great impact on the health of users and the efficiency of work activities [2] .
At present, most of the thermal and comfortable site research in China is mainly residential and office buildings. There are very few field investigations on the comfort of sports and fitness places. Most of the foreign scholars' related studies on sports and fitness places are related to indoor pollutants and related laboratory studies, and there are few studies on the field thermal environment and human comfort. The American School of Sports Medicine (ACSM) [3] recommends that the site temperature should be set within the range of 20-22 and the relative humidity be set no higher than 60%.Gian Marco Revel et al [4] . conducted the field research of gyms and natatorium in spring and summer, and used Fanger index for systematic error analysis. Thermal environmental parameters were obtained and found that in both environments, thermal sensation was in the neutral interval, and the higher thermal sensation may be due to psychological factors. Zhai Yongchao [5] conducted laboratory research and combined with a subjective questionnaire survey to study the impact of airflow on human comfort during exercise. Zhang Yufeng [6] found that in the gym, the thermal comfort results show that the ET*22 and ET*24 conditions were preferred, while the ET*26 condition was more uncomfortable and unacceptable to people during exercise.
Up to now, no scholar has done a lot of relevant research for four seasons, and the quality of data measurement is low, and the number of commercial gyms is small involved. some scholars conducted laboratory tests, but they did not conduct a lot of field research to confirm the accuracy of their conclusions. Therefore, it is very necessary to investigate the thermal environment of exercise and fitness places and study the thermal comfort evaluation under exercise state. In this study, field thermal environment tests were combined with human comfort to obtain the actual thermal environment parameters of exercise and fitness places.

gym and Subjects
Through the field survey of many sports and fitness venues in Xi'an city, 9 local sites were finally selected as the research objects. Personnel in the sports and fitness places were randomly selected to conduct on-site questionnaire survey, and a total of 758 questionnaires were obtained (due to the epidemic, the spring survey data were small, so combined with the autumn 2019 data as the transition season). The survey period ran from September 2019 to September 2020, covering four seasons: spring, summer, autumn and winter. The survey included measurements of the physical environment as well as subjective feelings of mall users. The respondents filled out the questionnaire simultaneously with the indoor environment test.
The relationship between pure physical quantities and comfort is usually linear, while the relationship of thermal comfort between human-related factors is usually not a single linear relationship. As one of the most intuitive form of the subjective survey, the reasonable design of the subjective questionnaire required for the survey can objectively obtain the subjective thermal feeling and psychological needs of the subjects. Moreover, a large sample of data, obtained from the study subjects, has obtained the relationship between each influencing factor and thermal comfort.

Results
As shown in Fig.2, the activities of interviewees when asked questions are mainly divided into two categories: aerobic activities and strength training. In addition, the number of aerobic training accounted for 49%, strength training accounted for 38%, the survey also found that aerobic training is mainly female, but strength training more men.

Fig. 2. Proportion of the type of exercise of the respondents
During the test period, the indoor environmental parameters were counted, and the results are shown in Fig.3,4,5 and 6. According to statistics, the average indoor temperature is 23.6 , winter 18.9 and summer 26.1 , and the indoor relative humidity is mainly distributed between 25% and 75%. The average indoor relative humidity was 67.5% in transition season, 29.9% in winter and 55.4% in summer. During the test period, the room was less affected by the seasonal changes, and the average wind speed was 0.08 m / s. The average concentration of CO2 was between 750 and 800 ppm, meeting the relevant criteria. To sum up, there is no significant difference between indoor thermal environment in summer and transition season, but for CO2 concentration in natural ventilation and air conditioning (AC), it is higher in air conditioning than in natural ventilation(NV). It is higher in air conditioning than in natural ventilation. exercise area and the strength training area in terms of indoor thermal environment parameters. In the course of research, the heat resistance of transition season is mainly between 0.4-0.6clo; winter is mainly between 0.6-0.8clo; summer is mainly between 0.3-0.4 clo.   As shown in Fig.7., the neutral vote is highest at 17 , and the preference for cooling gradually increases as the temperature increases . However, in terms of thermal sensation voting, the average vote of 17 , is around "+2" It is worth noting that thermal sensation does not decrease with decreasing temperature.As shown in Fig.8. The author analyzed that the difference of metabolic rate was the main reason for the difference between this result and the sedentary state. The intersection of regression curve and 20% dissatisfied percentage line is the acceptable temperature of 80% of the staff, namely, the annual acceptable temperature range of 80% of the staff in indoor sports and fitness places in cold areas is 17.9℃-23.9℃.

Discussion
Compared with the current survey results, the standard recommended temperature and humidity range is within the survey scope, but it is too general, and it does not consider different movement types and movement states [9] . This study can also verify the master's thesis of Xi' an University of Building Science and Technology 44 on the study of previous scholars, and concluded that the respondents had higher acceptability to the thermal environment in the exercise state, and the influence of temperature was less on the acceptance. Therefore, compared with the change of temperature, enhancing the exchange of airflow may have a greater impact on comfort, and be more conducive to energy saving [10] .
According to WHO and ASHRAE standards, indoor CO2 levels should not exceed 1000ppm. The results of this survey show that: in the air conditioning environment, the concentration range of carbon dioxide exceeds the standard, and indoor air dissatisfaction gradually increases with the increase of concentration. In addition, when the air conditioner is turned on, the carbon dioxide level in the gym increases significantly. It has been found that carbon dioxide concentration has a certain degree of influence on thermal comfort [11] .
Through the analysis, it is found that there are seasonal differences in the acceptability of air flow, and the acceptability in winter is significantly higher than that in other seasons. The preference for "stronger" airflow is stronger in summer and transition seasons. Therefore, we believe that in a neutral and cool environment, appropriately increasing air flow can not only make the air fresher, but also improve the satisfaction of interviewees.

Conclusions
According to statistics, the average indoor temperature is 23.6 , winter 18.9 , summer 26.1 , and indoor relative humidity is mainly distributed between 25% and 75%. There was no significant difference between transitional season and summer, and no significant difference between aerobic zone and strength training zone.
This study obtained the temperature range accepted by gyms in this area throughout the year. The acceptable range of temperature is narrower than the existing research conclusions and specifications. In addition, air indoor comfort of gym still needs to be further improved, especially the carbon dioxide problem in air-conditioned room and the increase of excessive and wind speed in summer. The subsequent research on thermal comfort of different activity levels needs to be further improved.