Optimization Strategy for Thermal Comfort in Railway Stations above Ground Level in Beijing

Abstract

Urban rail transit, a convenient and fast public transportation mode with rapid construction and development, occupies fewer land resources and accommodates large passenger volumes. However, thermal comfort should be given more attention. Stations above ground level experience poor thermal comfort on the platforms, especially in hot summers. This study combines field research with a simulation analysis to propose a strategy for improving thermal comfort on above-ground urban rail transit platforms. This study analyzed the effects of the skylight opening rate, side window opening rate, design of transparent maintenance structure shading, and the platform profile shape on the thermal comfort of above-ground stations using field research, comparative experiments, and a simulation analysis with the PHOENICS (Command Prompt) software. The results indicate that adding longitudinal sunshade louvers to the skylight of the station platform is a cost-effective method to reduce the average temperature and PMV value, thereby improving thermal comfort. Increasing the skylight opening rate can result in a temperature rise. Adjusting the opening rate of the side windows to 20% and adding sun-shading louvers can also significantly enhance the station’s thermal comfort. Taking Wudaokou Station on Beijing Line 13 as an example, the simultaneous installation of additional longitudinal skylight shading and side window shading and increasing the side window opening rate to 20% on the platform resulted in a 2.6 °C decrease in the average temperature, a 4.7% increase in the average wind speed, and a 0.62 decrease in the PMV value, significantly enhancing thermal comfort for passengers. This study confirms that optimizing shading and ventilation systems can significantly reduce the platform temperature and improve passengers’ thermal comfort. This study provides theoretical support and innovative methods for optimizing thermal environments in similar environments.

1. Introduction

In recent years, subway systems have increasingly become the preferred mode of transportation for many people due to their high speed, large passenger capacity, and low environmental impact. However, more and more attention has been paid to the issue of thermal comfort in subway stations, especially for those above ground. Compared to underground stations, above-ground stations are constrained by existing architecture and planning but offer advantages such as lower costs, shorter construction periods, and reduced operating expenses, making them popular in subway planning and design. Above-ground stations, typically constructed using lightweight materials, are less resistant to temperature fluctuations. In the design of station platforms, above-ground platforms are directly exposed to the outdoors and primarily rely on natural ventilation. In hot summer and cold winter regions, extended periods of high temperatures and humidity contribute to poor thermal comfort. Additionally, factors such as the architectural form of the station platform, roof skylight openings, shading facilities, and side window openings significantly impact the thermal comfort of the station platform. Therefore, implementing effective technologies and optimized retrofit solutions is crucial for enhancing the thermal environment of above-ground stations.

Thermal comfort is a key indicator of satisfaction with the indoor thermal environment. Research on indoor thermal environments and human thermal comfort has predominantly focused on civil buildings, particularly residences and offices. Studies on the relationship between human thermal comfort and the thermal environment started in the early 20th century. Currently, ASHRAE 55-1992 [1] and ISO 7730 [2] are the most widely used international standards for evaluating and predicting thermal comfort levels in indoor environments. When the air temperature rises, sweat glands become active, so evaporation becomes the main method of heat dissipation. When the air temperature is above 33 °C, sweating becomes the only way for humans to dissipate heat [3]. In 1914, Leonard Hill proposed the first thermal comfort index, which involves using the heat loss of the large temperature packet thermometer to calculate the cooling capacity of the environment [4]. In 1919, the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) set up the world’s first indoor climate laboratory in Pittsburgh, and through the study of the effect of humidity on human thermal comfort in the laboratory, they established a new thermal comfort indicator, the effective temperature, denoted as t. We successively organized four large-scale field studies on thermal comfort, of which the effective temperature, t, was used in all three cases as the indicator of thermal comfort. The statistical results have a good correlation [5].

However, there is a lack of research on thermal comfort in urban rail stations. Most of the studies that have been conducted on rail transit stations focus on the internal environment of underground stations or train cars [6,7]. In 2004, Ampofo et al. [8] analyzed the characteristics of the hot and humid environment in a London subway line, concluding that the subway environment significantly differs from ground-level offices in terms of thermal comfort; then, they proposed the “Acceptable Thermal Comfort Evaluation Criteria”. Mortada et al. [9] utilized software to model a typical subway station in London, simulating the ventilation efficiency, passenger flow, and other factors. The model was calibrated using temperature sensors on platforms and tunnels, identifying heat sources and the extent of heat penetration as key factors affecting the thermal environment. The results indicate that reducing tunnel wall temperatures can significantly improve the subway station’s thermal environment.

Due to the similar operation between elevated and underground lines, research findings on indoor thermal environments, ventilation, and lighting in underground stations can also support studies on above-ground stations. However, there is a relative lack of studies on thermal comfort in above-ground stations. To save energy, above-ground stations typically only have air conditioning at the concourse level, with the platforms relying on natural ventilation. To enhance the thermal environment of station platforms during the summer, both domestic and international researchers studied ventilation and airflow organization, window opening designs, and shading techniques. Han [10] studied an above-ground station on a subway line in South China, quantitatively evaluating the thermal comfort of three different air supply schemes. The study concluded that, in summer, an air supply system on the platform is unnecessary, and extending natural ventilation is sufficient. A study of an above-ground station on Xi’an Metro Line 3 found that a direct evaporative cooling treatment lowered the air temperature in the platform’s public area by 6.5 °C compared to the outdoor air before the treatment [11]. Although the thermal environment was effectively improved, it was less effective in high-temperature and high-humidity indoor environments. The human feels comfortable with an airflow rate in the range of 1.0–1.2 m/s when the temperature range is between 28 and 32 °C and the relative humidity is between 70 and 90%. Therefore, maintaining airflow within the abovementioned range can satisfy passengers’ thermal comfort [12].

Cui et al. [13], through PHOENICS modeling on a Beijing Metro station, found that areas crowded with passengers increased the temperature in the middle of the platform by 4 °C. The outdoor temperature played a decisive role in determining the average temperature inside the station. Liu et al. [14] systematically stated the specific contents and methods used for measuring the subway’s thermal environment, guiding practical measurement. By analyzing the air-conditioning operation control temperature and its trend with the outdoor temperature at Tianjin Metro Station, the authors examined the changes in human thermal comfort, indicated by the RWI value, during passengers’ entry and exit [15]. Additionally, some scholars have studied the thermal comfort in subway stations across different seasons, control units, and times of the day to propose control strategies [16].

ASHRAE has generated extensive data on thermal comfort through numerous experiments. Fanger [17] developed the heat balance equation for the human body by analyzing subjects’ hot and cold sensation data, proposing the well-known thermal comfort evaluation indexes: the Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfaction (PPD). The PMV index is a comprehensive evaluation metric that considers basic human heat balance equations and psychophysiological subjective thermal sensation levels. It reflects the average vote of a group on a seven-point thermal sensation scale ranging from +3 (hot) to −3 (cold). In 1962, Macpherson [18] identified six factors influencing human thermal comfort: air temperature, airflow rate, relative humidity, mean radiant temperature, metabolic rate, and clothing thermal resistance. In 2006, Abbaspour et al. [19] tested the thermal environment parameters, the current status of air-conditioning, and passenger flow in stations in different areas of Tehran by studying and analyzing 231 valid data points and found that the thermal comfort in metro stations was in the acceptable range.

Current research on subway thermal comfort primarily focuses on environmental control in underground stations and the internal thermal environment of carriages. Only a few studies have focused on the thermal environment of above-ground stations. Most previous research relied on numerical simulations and were often limited to case studies within a single city, lacking field measurements and comprehensive studies on the thermal environment of subway carriages across different climatic regions and seasonal changes. Additionally, a comprehensive set of evaluation systems and control strategies for thermal comfort in subway stations and carriages has not yet been developed.

The primary objective of this study is to enhance the thermal comfort experience of passengers by implementing the most effective and economical modifications to above-ground stations. We selected five above-ground stations on four different rail transit lines in Beijing. The factors contributing to poor thermal comfort in these stations were analyzed and summarized through field measurements. Corresponding building renovation measures and optimization schemes were then implemented to study the thermal comfort of subway passengers using on-site surveys and field measurements, focusing on temperature and humidity sensations and other aspects of the thermal environment. A satisfaction evaluation was conducted based on these factors. A building model was created using SketchUp 2019 (also known as Sketchmaster), a software for creating, sharing, and displaying 3D models. The PHOENICS (Command Prompt) software (referred as PHOENICS later) was then used to simulate the effects of changing various conditions, including skylight openings, side windows, and cross-section shapes of the above-ground stations, on the temperature, wind speed, and the PMV (Predicted Mean Vote).

2. Methods

2.1. Beijing Subway Lines and Stations

As of July 2024, the Beijing metro system consists of 27 operating rail transit lines, including 5 lines with entirely above-ground stations and 12 lines with partially above-ground stations. This study selected five above-ground stations, namely Tiantongyuan Station on Line 5, Wudaokou Station and Shangdi Station on Line 13, Guozhan Station on Line 15, and Shuangqiao Station on the Batong Line, as research subjects based on factors such as skylight form, side windows, and section form (Figure 1). Thermal comfort questionnaires for passengers were conducted, and on-site measurements of temperature, humidity, and wind speed in stations were measured from 10 to 17 July 2024. All construction-related factors for the five stations are listed in

Table 1. Factors selected for comparative analysis among stations.

Metro Line	Line 5	Line 13		Line 15	Batong Line
MRT station	Tiantongyuan	Wudaokou	Shangdi	Guozhan	Shuangqiao
Sunlight	None	Vertical Strip Casement	Vertical Strip Casement	None	None
Side window	Semi-Open Side	Enclosed Glass Curtain	Enclosed Glass Curtain	Enclosed Glass Curtain	Enclosed Glass Curtain
Section form	Rectangles	Atypical	Bins	Rectangles	Bins

.

2.2. Thermal Environmental Parameters

Thermal environment parameters, including air temperature, relative humidity, and wind speed, are key factors affecting human thermal comfort. The test equipment is shown in

Table 2. Test equipment and parameters.

Parameter	Model	Range	Resolution
Temperature	TES-1361C	−20~60 °C	0.1 °C
Relative humidity	TES-1361C	10~95% RH	0.1% RH
Wind speed	Anemometer testo405-V1	0–10 m/s	0.01 m/s

. The parameters of temperature, humidity, and wind speed were measured at five typical subway stations from 14:00 to 16:00 each day between 10 and 17 July 2024. Measurement points were located at the station entrances and exits, ticket counters, station halls, and waiting areas.

2.3. Questionnaire Survey

Healthy individuals aged 18–60 were selected as survey participants. The majority of participants were passengers waiting for trains, and the remaining were staff in subway stations. A questionnaire on thermal comfort using a heat sensation poll as an evaluation criterion was distributed to passengers waiting for trains in above-ground stations. Details of the questionnaire can be found in the Appendix A. Fifty questionnaires were distributed at each station, with 46 valid responses obtained from Wudaokou Station, 43 from Shuangqiao Station, 44 from Shangdi Station, 42 from Guozhan Station, and 45 from Tiantongyuan Station, totaling 220 valid questionnaires. In the current study, invalid questionnaires were identified based on the following criteria: participants not between 18 and 60 years old, an incomplete questionnaire, a lack of clarity or inherent logical inconsistencies in the thermal comfort polls, and obvious errors in data recording. Thermal comfort perceptions mainly include sensations of heat, humidity, and airflow. The specific subjective evaluation grading is shown in

Table 3. Grading of subjective perceptions of thermal comfort.

Thermal Comfort Grading	−3	−2	−1	0	+1	+2	+3
Heat sensation	Cold	Cool	A bit cool	Comfortable	A bit warm	Warm	Hot
Wet sensation	Very humid	Humid	A bit humid	Comfortable	A bit dry	Dry	Very dry
Wind sensation	Very stuffy	Stuffy	A bit stuffy	Comfortable	A bit windy	Windy	Very windy
Overall acceptability	Totally unacceptable	Moderately unacceptable	A bit unacceptable	/	A bit acceptable	Moderately acceptable	Totally acceptable

. The PMV index is a comprehensive evaluation index that takes into account a number of factors related to human thermal comfort, starting from the basic equations of human heat balance and psychophysiological subjective thermal sensation levels. The PMV index shows the average index of a group’s vote for six levels of thermal sensation, ranging from −3 to 3.

2.4. Building Energy Efficiency Simulation Optimization

In this study, Wudaokou Station on Line 13 was selected for simulation. PHOENICS software was used to simulate and analyze the temperature, wind speed, and PMV value of the platform. Firstly, the SketchUp model was imported into PHOENICS at a 1:1 scale, with 3–5 times the modeling area left in the X and Y directions and twice the highest building height left in the Z direction to facilitate wind flow calculations. The number and distribution of grids in the X, Y, and Z directions were manually adjusted to ensure a grid width of approximately 3 m. The average summer temperature of the study site in July was 34 °C, the average wind speed of 5.0 m/s was chosen as the input wind speed at the height of 10 m, the dominant summer wind direction of S-S-E was selected as the initial wind direction, and the solar parameters were obtained on 15 July 2024 at 2:00 pm. Then, the simulation was conducted to analyze the impact of settings for skylight openness and opening rate, side window openness and shading facilities, and building cross-section design on the thermal environment. The effects of these optimizations were analyzed to propose renovation measures to improve the thermal comfort of passengers in the above-ground station.

2.4.1. Design of Skylights

Strong solar radiation is a major contributor to the poor thermal environment in above-ground stations during the summer. Wudaokou Station’s platform features a long, longitudinal skylight that cannot be opened. The main considerations in platform skylight design include the skylight opening mode, opening rate, and sunshade design. Using the original 960 m² of skylight area as a benchmark, the ratios of the openable skylight area were set to 40% and 60% of the original area, respectively (Figure 2).

In the questionnaire, almost all passengers felt that sunlight is strong and that the environment is hot in the platform area during the summer. Despite passengers being distributed on both sides of the platform, solar radiation from the skylight continues to raise the temperature in the station, creating an uncomfortable thermal environment on the platform. Skylight is a significant factor affecting the thermal comfort of passengers in above-ground stations. In this study, we optimize the skylight sunshade design, with two forms of sunshades (horizontal shading and longitudinal shading), to make comparisons with the thermal environment in the original scheme without sunshades (Figure 3).

2.4.2. Design of the Platform’s Side Windows

Both sides of the Wudaokou Station’s platform feature closed glass windows, which do not provide ventilation but have strong solar radiation. Closed glass windows lead to high temperatures inside the station during the summer. In this study, the proportion of openable sections of the closed glass windows on both sides could be adjusted to change the air convection and heat dissipation in the station. Based on the original 2000 m² area of the side windows, the openable ratios were set to 5%, 20%, and 35%, respectively (Figure 4).

Both sides of the platform at Wudaokou Station are enclosed with glass curtains that lack shading measures, resulting in direct sunlight entering the platform interior and potentially causing high temperatures. In this study, louvers were installed on the platform’s side windows to provide shading and reduce the amount of direct sunlight (Figure 5).

2.4.3. Design of Platform Cross-Section Shape

For semi-open above-ground platforms, variations in cross-section shapes significantly impact ventilation and the thermal environment. The Wudaokou Station’s platform features a curved design with varying shapes and sizes across cross-sections. In our simulation, we modeled two common cross-section forms: rectangular and arched (Figure 6). This study compared thermal comfort before and after the optimization design based on field measurement and the simulation. It also derived a thermal comfort improvement design strategy applicable to above-ground stations in Beijing’s rail transit system. Abbreviations and their definitions in this paper are shown in

Table 4. Abbreviations and their definitions.

Abbreviation	Full Name	Description or Definition
PMV	Predicted Mean Vote	The Predicted Mean Vote is a metric used to assess human thermal comfort.
PPD	Predicted Percentage Dissatisfied	This is a prediction of the number of people in a group who are uncomfortable with a given thermal environment on an average scale of thermal sensation as a percentage of the total number of people in the group.
SU 2019	Sketch Up 2019	Models created with Sketch up, is primarily a software for creating, sharing, and presenting 3D models.
RH	Relative Humidity	The relative humidity expresses the ratio of the water vapor content of the air to the saturated water vapor content.
ASHRAE	American Society of Heating, Refrigerating and Air-Conditioning Engineers	The American Society of Heating, Refrigerating, and Air-Conditioning Engineers is an international organization with more than 50,000 members and chapters worldwide.
ISO	International Organization for Standardization	The International Organization for Standardization (ISO) is a non-governmental international standardization body formed by a multinational coalition.
ET	Effective Temperature	A new thermal comfort indicator established by studying the effect of humidity on human thermal comfort in the laboratory.

.

3. Results

3.1. Thermal Environment

The air temperature, relative humidity, and wind speed of the above-ground stations were collected (

Table 5. The thermal environmental parameters in the five stations.

Station	Temperature (°C) Average (min, max)	Relative Humidity (%) Average (min, max)	Wind Speed (m/s) Average (min, max)
Tiantongyuan	37.2 (32.2, 40.3)	45.3 (41.5, 52.6)	0.69 (0.09, 1.17)
Wudaokou	37.6 (30.5, 42.8)	48.7 (38.6, 61.6)	0.65 (0.05, 1.13)
Shangdi	38.7 (31.7, 40.9)	47.8 (41.4, 56.4)	0.64 (0.10, 1.09)
Guozhan	37.5 (31.9, 41.7)	57.8 (52.9, 64.4)	0.54 (0.06, 1.05)
Shuangqiao	36.4 (30.8, 41.6)	49.3 (37.6, 75.5)	0.56 (0.08, 0.96)

). The thermal comfort conditions in all five metro stations were bad, with the maximum and average indoor temperatures exceeding 40 °C and 36 °C, respectively. Wudaokou Station recorded the highest maximum temperature, reaching 42.8 °C. The highest relative humidity was recorded at Shuangqiao Station, reaching 75.5%. The lowest wind speed was observed at Wudaokou Station, only at 0.05 m/s.

3.2. Design for Thermal Comfort Improvement

(1)

Skylight opening rate

Figure 7 illustrates the impact of skylight opening rates on the temperature, wind speed, and PMV. Increasing the skylight opening rate has a minimal effect on the wind velocity field but raises the internal temperature of the station, which means the overall comfort levels decrease with an increasing PMV value. Furthermore, increasing the skylight opening rate during the winter can lead to cold air infiltration, reducing the temperature inside the station. In summary, the skylight opening rate should not be increased.

(2)

Sunshade

Figure 8 shows the simulation results of different forms of skylight shading on the temperature field, wind speed field, and PMV. Compared with no sunshade, the station platform skylight with horizontal sunshades showed a temperature decrease of 0.67 °C. The platform skylight with longitudinal vertical sunshades resulted in a significant overall temperature decrease of 1.05 °C and an improvement in the PMV value from 2.51 to 2.28. Therefore, adding longitudinal shading is a relatively economical and effective strategy.

(3)

Opening rate of side window

Figure 9 presents the simulation results of the temperature field, wind speed field, and PMV at different side window opening rates. A higher side window opening rate leads to a lower indoor temperature in the station during the summer. At a 20% side window opening rate, the average temperature inside the station can be reduced by 1.7 °C. Further increasing the side window opening rate cannot reduce the temperature effectively but increases the costs. Therefore, a 20% side window opening rate was suggested.

(4)

Sunshades on side windows

Figure 10 shows the impact of side windows with louvers on thermal environmental parameters. Without an impact on the wind speed, side windows with louvers can reduce the indoor temperature by 1.34 °C and the PMV by 15.9%. Therefore, side windows with louvers can effectively enhance the thermal comfort in the station.

(5)

The cross-section shape of the station

Figure 11 presents the impact of the station’s cross-section shape on the thermal environment parameters. Compared to the original design, the arch-shaped cross-section is taller and has a larger scale, a greater air intake, and a higher wind speed, which results in a low indoor temperature. In contrast, the rectangular cross-section shape shows a significant increase in temperature. Therefore, a higher cross-section shape with a larger scale is suggested to improve thermal comfort.

3.3. The Application of Design Optimization: A Case Study of Wudaokou Station

The air temperature, relative humidity, and wind speed were collected at the above-ground stations (Table 4). The thermal comfort conditions in all five metro stations were bad, with the maximum and average indoor temperatures exceeding 40 °C and 36 °C, respectively. Wudaokou Station recorded the highest maximum temperature, reaching 42.8 °C. The highest relative humidity was recorded at Shuangqiao Station, reaching 75.5%. The lowest wind speed was observed at Wudaokou Station, only at 0.05 m/s. The station concourse is located at both ends of the station. The roof is curved, and the platform skylights cannot be opened. The skylights are longitudinally oriented without any shading. The side windows of the platforms consist of enclosed glass curtains without any shading. The optimization strategy involves retaining the original curved roof, adding longitudinal internal skylight shading and platform side window shading, and increasing the opening rate of the side windows to 20% (Figure 12). Following optimization, the average summer station temperature decreased by 2.56 °C, the average wind speed increased by 4.7%, and the PMV value decreased by 0.62 (Figure 13), indicating a significant improvement in thermal comfort. However, the overall improvement in wind speed remains limited and may not fully meet the comfort needs of passengers in extremely hot weather conditions.

4. Discussion

This paper proposes a series of optimization strategies to enhance the thermal comfort of above-ground rail transit stations in Beijing based on questionnaires, field measurements, and simulation analyses. The station structure, shading pattern, and designs of side windows and skylights on the platforms were considered. Taking Wudaokou Station on Line 13 as an example, the effectiveness of these strategies was quantitatively evaluated.

Many studies focused on thermal comfort in above-ground stations analyzed skylight and side window opening ratios as well as sunshade designs in various climatic regions, including hot summer and warm winter regions, hot summer and cold winter regions, cold regions, and mild regions. Increasing the skylight opening ratio tends to raise the indoor temperature of the station, necessitating proper sunshading facilities, such as blinds or sunshades. The side window opening rate significantly impacts the thermal comfort within the station. A study conducted in hot summer and warm winter regions concluded that the most critical factor affecting the thermal environment of the station platform is the side wall opening area ratio. Thermal comfort could be effectively improved if the side wall opening area ratio increases from 40% to 60%; however, further increases ranging from 60% to 80% result in low effectiveness [20]. Generally, increasing the side window opening rate could improve the thermal environment of the station platform, but further increases beyond a threshold will limit its effectiveness. Conclusions may vary based on geographic location and building type. The maintenance structure of Wudaokou Station consists of an enclosed glass curtain wall. From an economic and energy-saving perspective, the station’s thermal environment can be effectively improved by increasing the opening rate of the side windows, thereby enhancing the wind speed within the station. Our study showed that the side window opening rate should be controlled at around 20%.

Studies suggested reducing the solar heat gain of glass curtain walls by implementing shading measures such as sunshade louvers or a double-layer glass curtain wall. There are openings on the outer glass curtain wall for fresh air to enter the cavity between the two exterior walls and openable windows on the inner glass curtain wall; additionally, sunshade louvers could be placed between the layers not only to protect against wind and rain, but also to provide shading and heat reflection [21]. In general, the adoption of appropriate shading facilities can significantly improve the thermal comfort of the platform and surrounding areas.

Building shading and local evaporation caused by green plants not only reduce solar radiation heat but also provide cool wind. Therefore, in above-ground stations, green plants can be strategically placed to reduce the indoor temperature and improve thermal comfort through transpiration and shading effects in the station. Akira [22] empirically measured the cooling and shading effects of various types of greenery on the thermal environment of a single building. Many researchers conducted experimental studies and mathematical simulations on the heat transfer of rooftop lawns [23,24,25,26], and the evapotranspiration effect of indoor greenery was also measured [27]. Additionally, green plants can enhance passengers’ moods, even in urban settings, and “natural” scenes were proven to be much better for human health than “urban” or “architectural” scenes [28].

Many passengers express a strong preference for introducing air-conditioning systems in stations. To provide a comfortable waiting experience while saving energy, air-conditioned waiting areas within stations for passengers can be established. However, maintaining airtightness is challenging due to the frequent opening and closing of doors and the high passenger flow. Some studies suggested the use of full-height screen door systems in the summer, which significantly enhance platform enclosure. Such platforms are conducive to air-conditioning systems, which can directly reduce indoor temperatures during the summer, though at a higher cost.

From an economic and energy-saving perspective, the introduction of air-conditioning systems can significantly improve the station’s thermal environment, but it is expensive, time-consuming, and energy-intensive. Many measures can improve the thermal comfort of above-ground stations. Economically, adding skylights and side window shading facilities and planning greenery are low-cost and highly effective strategies. Increasing the side window opening rate can further improve ventilation and thermal comfort. Finally, additional air-conditioned waiting rooms can be established to provide passengers with a comfortable waiting experience, albeit at a high retrofitting cost.

While this paper has provided some insights into improving the thermal comfort in the above-ground stations of Beijing rail transit, there are some limitations. First, this study only focused on Wudaokou Station on Line 13 in Beijing; thus, these results may not fully represent the actual situation of all stations. Secondly, there is a lack of investigation into the thermal environment of above-ground stations across different seasons and regions. Thirdly, the influence of green plants, building materials, and other factors on the thermal comfort of above-ground stations was not considered. In the future, more above-ground stations from different regions should be considered to enhance the generalizability and applicability of the findings and to gain a more comprehensive understanding of thermal comfort issues. Additionally, a long-term follow-up study has been planned to monitor the sustained effects of the optimization strategies with an intelligent control system.

5. Conclusions

The overall thermal comfort of the above-ground stations of Beijing Metro is poor, with the passenger satisfaction rate being lower than 12%. The main conclusions of this study are as follows:

• The installation of sunshading louvers to station skylights can improve thermal comfort. Adding longitudinal louvers to sunshading facilities can reduce the average temperature inside the station by 1.05 °C and decrease the PMV value by 0.23, effectively improving thermal comfort. Adding longitudinal louvers to the skylight is a low-cost and effective measure. However, increasing the skylight opening rate raises the average temperature inside the station, which is not conducive to maintaining thermal comfort.
• The effect is significant when the opening rate of the enclosed glass curtain of the platform side window is set to 20%: the average wind speed increases by 2.8%, the average temperature decreases by 1.14 °C, and the PMV value decreases by 0.23. Further increasing the opening rate is not efficient. Therefore, maintaining a reasonable opening rate of the side windows can effectively improve thermal comfort. Adding louver shading to the side windows further decreases the average temperature by 1.34 °C and the PMV value by 0.4, which also enhances thermal comfort.
• The platform cross-section shape affects thermal comfort. The wind speed is higher and the temperature is lower if the platform profile is arched, high, and large. In the winter, lowering the roof height can reduce air intake and help maintain the temperature inside the station.
• Installing additional longitudinal inner skylight shading facilities and platform side window shading facilities and increasing the opening rate of side windows to 20% can effectively improve thermal comfort. After optimization, the average indoor temperature in the station could be decreased by 2.56 °C, the average wind speed could be increased by 4.7%, and the PMV value could be decreased by 0.62.