Stormwater Vault Width<\/td> 5 m<\/td> Ratio of Private Area to Ventilate <\/td> 0.789 m2\/m3<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\nTrade-off between Station Width, Public Space, and Envelope Thermal Performance<\/strong><\/p>\n\n\n\nUnder the current comparison setup, reducing the station width decreases the relative share of the public fa\u00e7ades, for which the window-to-wall ratio (WWR) is fixed at 0.6. If all other parameters were held constant, this reduction would be expected to lower the area-weighted average U-value, as the proportion of highly glazed fa\u00e7ade area would decrease.<\/p>\n\n\n\n
However, in the presented design options, the reduction in station width occurs simultaneously with an increase in the private-side WWR (from 10% to 20% to 30%). The results show that, despite the reduction in width, the average U-value increases from 0.503 to 0.551 and further to 0.606. This indicates that, within this paired-change comparison, the increase in glazing on the dominant private fa\u00e7ades outweighs the counteracting effect of shrinking the public fa\u00e7ade area. As a result, the overall thermal performance of the building envelope deteriorates.<\/p>\n\n\n\n
At the same time, the reduction in station width leads to a substantial decrease in public-use area, from 1,440 m\u00b2 to 840 m\u00b2. Taken together, these results reveal an unfavorable trade-off: public spatial capacity is reduced while envelope thermal performance becomes weaker, reflected by a higher average U-value. In other words, the design sacrifices public space without achieving a corresponding thermal benefit, primarily because the private-side glazing strategy dominates the area-weighted envelope performance.<\/p>\n\n\n\n
To ensure a controlled and interpretable comparison, the public-side WWR is intentionally kept constant across all options. From a design perspective, public areas within a metro station are assumed to benefit from a certain degree of openness, making a fixed glazing ratio more appropriate than treating it as a free variable. In addition, wall and window U-values are set to intermediate levels, representing a neutral envelope performance baseline. This avoids bias toward either highly optimized or intentionally weak constructions and allows the analysis to focus on geometric configuration and opening ratios rather than material performance extremes. All options are further evaluated under the same number of metro lines, ensuring comparable transportation capacity and functional demand.<\/p>\n\n\n\n
Trade-off between Station Height and Financial Viability<\/strong><\/p>\n\n\n\nIn parallel to the spatial and thermal assessment, the architectural and financial viability of the station is evaluated using the\u00a0ratio of private area to ventilated volume, which relates revenue-generating surfaces to ventilation-related operational demand. Within the parametric model, private area includes both above-ground retail spaces and underground platform-related business zones, reflecting the station\u2019s cross-subsidization strategy.<\/p>\n\n\n\n
Because isolating ventilation and HVAC costs for subterranean spaces is technically complex at this stage, the model applies an aggregated average cost per square meter. Under this simplified funding structure, above-ground commercial spaces operate on a transparent billing cycle and effectively act as a financial anchor, subsidizing the energy-intensive environmental controls required for the underground station infrastructure.<\/p>\n\n\n\n
The parametric results show that increasing station height introduces a clear volume penalty. When station height increases from 10 m (Design Option 1) to 12 m (Design Option 3), the total volume of air requiring ventilation increases by approximately 20%, while the monetizable private floor area remains unchanged. This directly reduces the ratio of private area to ventilated volume, indicating that each square meter of revenue-generating space must carry a higher share of the HVAC-related operational burden. In this case, increased spatial generosity in section does not translate into increased commercial capacity, but instead weakens the financial efficiency of the station.<\/p>\n\n\n\n
Conclusion<\/strong><\/p>\n\n\n\nTaken together, the two comparisons reveal a consistent pattern across spatial, thermal, and financial dimensions. Reductions in station width and increases in station height both introduce penalties that are not compensated by corresponding gains in either envelope performance or revenue-generating capacity. In the first case, public spatial quality is reduced while thermal performance deteriorates due to the dominance of private-side glazing. In the second case, increased vertical volume leads to higher ventilation demand without increasing private area, eroding the commercial\u2013operational balance of the station.<\/p>\n\n\n\n
These results highlight the importance of coordinated geometric decision-making in early-stage metro station design. Parameters such as width, height, and fa\u00e7ade openness cannot be evaluated in isolation, as their combined effects shape not only energy performance and spatial capacity, but also the long-term architectural and financial viability of the station as an integrated urban system.<\/p>\n\n\n\n