An analytical model for asymmetric heat transfer in energy tunnels with segment lining: Validation and multi-loop analysis

s Energy tunnels, which integrate underground construction with geothermal utilization, provide a promising approach for urban renewable energy development. However, in shielded energy tunnels, the asymmetry of heat exchanger arrangement and tunnel lining heat transfer conditions results in significant circumferential non-uniformity, and the heat flux dynamically varies with operating conditions, making traditional models based on constant heat flux and axisymmetric assumptions inadequate. This study proposes a segmental analytical heat transfer model for shielded energy tunnels, accounting for variable heat flux and asymmetric bidirectional heat transfer at the tunnel lining inner and outer surfaces. Under the assumption of uniform axial temperature, the model analytically predicts fluid temperature along the flow direction and the surrounding medium temperature field, and can be extended to multi-layer linings via superposition, enabling refined characterization of temperature and heat transfer in multi-ring energy tunnels. Validation against summer and winter field data shows that the root mean square errors of fluid temperature predictions are 0.40 °C in summer and 0.48 °C in winter, demonstrating high accuracy. Parametric analysis indicates that increasing inlet temperature or flow rate enhances circumferential heat flux non-uniformity and lining surface temperature differences, which may induce thermal stress. Increasing heat exchanger thermal conductivity improves overall heat transfer but has limited impact on circumferential non-uniformity. Multi-loop operation analysis shows that series operation maximizes heat transfer, achieving 1.52 % higher performance than parallel operation in summer and 2.76 % higher in winter. Parallel operation achieves higher system efficiency but limited heat transfer, while hybrid operation balances efficiency and heat transfer, offering the best overall performance. The proposed model overcomes limitations of existing analytical studies assuming constant heat flux and single-ring structures, providing a refined tool to describe circumferential non-uniformity and multi-ring effects, and offers a theoretical basis for optimizing energy tunnel design and thermo-mechanical coupling studies.