Impact of rainfall on the thermal performance of geothermal permeable pavement systems

Geothermal permeable pavement (GPP) systems are a nascent type of energy geo-structures. GPP combine ground-source heat pump (GSHP) systems with permeable pavements to enable the additional functionality of heating and cooling, through energy harvesting using roads alongside existing drainage controls. GPP thermal performance is relatively unknown, hence, this research focuses on the development of a detailed 3D finite element (FE) model that considers local thermal non-equilibrium (LTNE) for exploring the influence of rainfall infiltration on the thermal performance of GPPs. The 3D numerical model was successfully validated and was used to evaluate the short-term thermal response of GPPs during rainfall events in both cooling (summer) and heating (winter) demand conditions. Furthermore, the diurnal rainfall effects and the influence of raindrop temperature and rainfall duration on GPPs were also examined. Results show that rainfall can have significant impacts on the thermal performance of GPPs and the raindrop temperature is an important parameter in yield predictions. Compared to no-rainfall events, the GSHP system fluid temperature during rainfall can differ by up to 19% when in the cooling operation model (air conditioning) and 63% in heating mode. These results indicate the significantly better performance of GPPs than impervious geothermal pavements, depending on the climatic conditions and end-use.