3D numerical modelling and analysis of heat harvesting and pavement temperature regulation of a thermo-active road

Thermo-active roads are a relatively new and underdeveloped type of energy geostructures. It involves two sets of horizontally placed pipes at different depths to exchange heat between the pavement surface and the ground. Thereby, thermal energy can be stored into the ground beneath the road in summer and can be extracted and used to heat up the road surface in winter to reduce freeze-thaw cycles. This research focuses on the development of a detailed three-dimensional (3D) finite-element (FE) model in COMSOL Multiphysics to explore the thermal performance of a thermo-active road. The 3D FE model developed was extensively validated against the experimental data from a full-scale field test undertaken in Toddington, UK. The validated model is further employed to analyse the effects of soil thermal conductivity, embedded depth of pipes, fluid flow rate and insulation layer on energy harvesting and extracting efficiency of the geothermal system. System optimisation is proposed based on the analysis. Results show that the embedded depth of storage pipes influences the energy harvesting efficiency the most, with energy storage increasing by 1.75 times when the embedded depth of storage pipes increased by 1.6 m. Higher soil thermal conductivity led to a higher energy harvesting efficiency of the system as well. The energy storage value increases from 0.56 to 0.86 MWh when soil thermal conductivity increased from 0.4 to 2.0 W⁄(m∙K). This research study indicates that this system can regulate road temperature, thereby potentially preventing road rutting in summer and freeze-thaw cycles in winter and extending its lifespan.