The paper illustrates the experimental and numerical study performed to assess the energy performance of a thermo-active tunnel lining. The experimental data from the real-scale energy tunnel prototype tested in the tunnel of the Turin Metro Line 1 South Extension are considered, by presenting the results of the tests performed in heating and cooling mode through both the ground and air configurations of the novel Enertun layout. Thanks to the availability of the original experimental data collected, it was possible to calibrate and corroborate a thermo-hydraulic numerical model, then used to extend the results to different ground and environmental conditions. Understanding of the role of some of the most important design parameters is illustrated in the form of parametric design charts, that update to the Enertun configuration those already existing in literature. A simple method for preliminary evaluation of the potential of energy tunnels, accounting for the investigated design parameters, is formulated. (c) 2020 Elsevier Ltd. All rights reserved.