Built environment and thermal comfort in metro systems: A case study in South China

The unique environmental conditions of underground metro systems pose challenges for occupant comfort. This study evaluated thermal, acoustic, lighting, and air quality environments at metro station entrances and platforms in Guangzhou, China, using environmental measurements and subjective questionnaire surveys. Key findings include: (1) The neutral SET was higher at platforms (21.6 °C) than that at entrances (19.6 °C) due to transient thermal conditions. Comfortable temperatures at platforms ranged from 21.6 to 28.8 °C, exceeding operating temperatures (22.4 – 26.5 °C) and indicating potential for energy savings. (2) Noise levels at platforms (76.4 dB) and entrances (76.4 – 84.9 dB) were within acceptable ranges, and platform lighting met national standards. However, entrance illuminance was often deemed unacceptable. (3) Air quality parameters met national standards, but respondent acceptable levels for VOC (0.003 µg/m³), CH₂O (0.048 µg/m³), and PM10 (28.0 µg/m³) were significantly stricter. These findings highlight the need for region-specific environmental control to enhance the comfort and energy efficiency of subtropical metro systems. Further, our results provide guidance for the environmental design and energy efficiency retrofitting of metro stations in humid and hot regions.