## 3 Results and Discussion
### Field Survey Results and Analysis  
#### 3.2.1 Physical test results and analysis  
Professor [PERSON] highlighted six elements that influence the comfort level of an indoor thermal environment (mean radiation temperature, air temperature, relative humidity, air speed, clothing insulation, and metabolic rate); all six are necessary to form the Predicted Mean Vote (PMV) model [41]. Tubular space in subway station building complexes is mostly underground, so the influence of radiation temperature can be ignored and people's metabolic rates can be set to the same level of 1.5 met [41]. During the test period, the hottest period in summer in Beijing was selected, so clothing level was chosen as 0.35 clo [41]. Data from this survey were collected according to eight physical parameters: environment temperature, humidity, illuminance, air velocity, PM2.5, PM10, and the HCHO and CO\({}_{2}\) concentrations at each point. The average result values are shown in Tables 5-9. According to the current national standards and norms, the typical range of thermal comfort is defined as between 16-28 \({}^{\circ}\)C [43], humidity comfort is between 30-60% [42], illumination should be no higher than 150 lux [52], and indoor air velocity in winter should be lower than 0.15 m/s and 0.25 m/s in summer. The concentrations of PM2.5 and PM10 should be lower than 75 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\) and 150 \(\mathrm{\SIUnitSymbolMicro g}\)/m\({}^{3}\), respectively, according to the 24-hour average concentration limits of the two grades listed in the national standard [53]. The concentration of HCHO and CO\({}_{2}\) should be lower than 0.08 mg/m\({}^{3}\)[54] and 1000 ppm [55], respectively. (1) Comfort analysis  
Figures 6-9 are box diagrams of the physical test results for thermal conditions, lighting, IAQ, and ventilation in all five types of tubular space. The red zones show locations where the occupant comfort values were beyond the related comfort standard. As regards the thermal environment, tp1 was a solar corridor space with a higher temperature than the other three points, which were at the boundary of the comfort zone (the point at which the human body would no longer enjoy thermal comfort). The tube lengths of tp4 and tp8 were 150 m and 140 m, respectively, and the humidity levels of the two test points significantly exceeded the standard. The highest reached 84.7%. The temperature in the space was lower than the human comfort level standard would deem acceptable, and the excessive humidity could easily cause mildew and affect users' health. As regards the lighting environment, the illuminance levels of tp4 and tp8 in the middle tubular space were not sufficient; the values did not reach the national standard requirement and thus could be hiding potential dangers. Due to the large amount of natural light at tp1, the average illuminance could reach 990 lux without artificial lighting. A better lighting environment would also improve the quality of the indoor environment. Past research results have shown that occupants become uncomfortable and can even experience headaches and chest tightness, causing their work ability to decline, when the CO\({}_{2}\) concentration is over 1000 ppm. In the test of CO\({}_{2}\) concentration for the middle tube, the two longer tube sat tp4 and tp8 had lower air quality; the highest CO\({}_{2}\) concentration was at tp4, which reached 1931 ppm. This is over two times the standard. The maximum PM2.5 concentration at tp8 reached 121 g/m\({}^{3}\); the outdoor concentration was 74.6 g/m\({}^{3}\). Thus, the disadvantages were greatly exacerbated. Although the air velocity values at tp4 and tp11 were slightly higher than the standard, moderate ventilation in a thermal environment can lower body surface temperature, taking away the sweat that collects on the human body's surface. To sum up, the main problems as regards comfort in the middle tubular space were its high humidity, poor light environment, and low air quality.