Abstract
Thermo-active road systems (TARS) provide a dual-function solution for pavement thermal regulation and renewable energy harvesting. While the concept is established, the efficiency of shallow-embedded systems, governed by coupled heat harvesting, transfer, and storage processes, remains underexplored. Current numerical models rely on field trials, where stochastic surface conditions require empirical correlations, reducing model fidelity. This study presents the first TARS fully instrumented laboratory investigation under controlled conditions, providing a rigorous benchmark for model validation. This laboratory testing quantified the effects of inlet temperature and flow rate. Laminar flow (0.05 m/s) produced outlet temperatures approximately 47 °C but modest heat harvest, while reducing inlet temperature or increasing flow enhanced harvested power. Under turbulent flow (1.0–1.5 m/s), surface temperatures decreased more rapidly, while lower flows retained warmer outlet fluid due to longer residence time. The experimental dataset validated a fully coupled 3D finite-element model, enabling the development of a system efficiency framework. Harvesting efficiency was dominated by Reynolds number and pipe spacing, whereas storage efficiency depended on soil thermal diffusivity, exceeding 70% in high-diffusivity soils. These findings define the critical interaction between hydraulic extraction parameters and geological storage properties, delivering a rigorous evidence base required to optimise TARS for sustainable, climate-resilient urban infrastructure.