The model enables direct comparison of alternative design configurations to evaluate how changes in key parameters affect overall performance in terms of capacity and operational energy efficiency. The design options presented below share a common baseline of three metro lines, ensuring comparable functional demand across all cases. Within this framework, controlled variations are introduced in station box height, building width, and the window-to-wall ratio (WWR) of non-public areas serving commercial functions. This approach allows the systematic assessment of trade-offs between increased building size, spatial capacity, and envelope-related energy performance.
Design Option 1
| Design Variable (Key Parameter) | Setting | Metric | Results |
| Number of Metro Lines | 3 | Capacity | |
| Station Box Length | 100 m | Passenger Capacity | 5760 pax1 |
| Station Box Depth | 3 m | Public Using Area | 1440 m2 |
| Station Box Height | 10 m | Stormwater Vault Capacity | 4 m3/m2 |
| Building Width | 30 m | Rentable Area | 2499 m2 |
| U-Value Window | 1.20 W/(m2⋅K) | Operational Energy Efficiency | |
| U-Value Wall | 0.25 W/(m2⋅K) | Average U-Value of Building Envelope | 0.50 W/(m2⋅K) |
| Public Window-to-Wall Ratio | 0.60 | Section Box Volume to Ventilate | 5799 m3 |
| Private Window-to-Wall Ratio | 0.10 | Tunnel Volume to Ventilate | 50.26 m3/m |
| Stormwater Vault Width | 5 m | Ratio of private area to ventilate | 0.8 m2/m3 |
Design Option 2
| Design Variable (Key Parameter) | Setting | Metric | Results |
| Number of Metro Lines | 3 | Capacity | |
| Station Box Length | 100 m | Passenger Capacity | 4560 pax2 |
| Station Box Depth | 3 m | Public Using Area | 1140 m2 |
| Station Box Height | 11 m | Stormwater Vault Capacity | 5 m3/m2 |
| Building Width | 25 m | Rentable Area | 2499 m2 |
| U-Value Window | 1.20 W/(m2⋅K) | Operational Energy Efficiency | |
| U-Value Wall | 0.25 W/(m2⋅K) | Average U-Value of Building Envelope | 0.55 W/(m2⋅K) |
| Public Window-to-Wall Ratio | 0.60 | Section Box Volume to Ventilate | 6379 m3 |
| Private Window-to-Wall Ratio | 0.20 | Tunnel Volume to Ventilate | 50.26 m3/m |
| Stormwater Vault Width | 4 m | Ratio of Private Area to Ventilate | 0.794 m2/m3 |
Design Option 3
| Design Variable (Key Parameter) | Setting | Metric | Results |
| Number of Metro Lines | 3 | Capacity | |
| Station Box Length | 100 m | Passenger Capacity | 3360 pax3 |
| Station Box Depth | -10 m | Public Using Area | 840 m2 |
| Station Box Height | 10 m | Stormwater Vault Capacity | 3 m3/m2 |
| Building Width | 30 m | Rentable Area | 2499 m2 |
| U-Value Window | 1.20 W/(m2⋅K) | Operational Energy Efficiency | |
| U-Value Wall | 0.25 W/(m2⋅K) | Average U-Value of Building Envelope | 0.61 W/(m2⋅K) |
| Public Window-to-Wall Ratio | 0.60 | Section Box Volume to Ventilate | 3360 m3 |
| Private Window-to-Wall Ratio | 0.10 | Tunnel Volume to Ventilate | 50.26 m3/m |
| Stormwater Vault Width | 5 m | Ratio of Private Area to Ventilate | 0.789 m2/m3 |
Trade-off between Station Width, Public Space, and Envelope Thermal Performance
Under the current comparison setup, reducing the station width decreases the relative share of the public façades, 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 façade area would decrease.
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 façades outweighs the counteracting effect of shrinking the public façade area. As a result, the overall thermal performance of the building envelope deteriorates.
At the same time, the reduction in station width leads to a substantial decrease in public-use area, from 1,440 m² to 840 m². 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.
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.
Trade-off between Station Height and Financial Viability
In parallel to the spatial and thermal assessment, the architectural and financial viability of the station is evaluated using the ratio 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’s cross-subsidization strategy.
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.
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.
Conclusion
Taken 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–operational balance of the station.
These results highlight the importance of coordinated geometric decision-making in early-stage metro station design. Parameters such as width, height, and façade 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.