Modelling of heat energy recovery potential from underground railways with nearby vertical ground heat exchangers in an urban environment

Ground source heat pumps (GSHPs) in urban environments can take advantage of surplus ground heat energy generated by subterranean infrastructures such as underground railways (URs). This paper describes seminal work in this area and a novel 3D numerical investigation into the heat energy recovery from URs with nearby vertical ground heat exchangers (GHEs). The investigation uses the London Underground (LU) as a case study but its results are generic worldwide. The investigation included a number of studies considering different geometrical configurations of the railway tunnels and the nearby GHE array, and the impact of that variation on the GHEs heat extraction rates. The results showed that heat extraction rates of GSHPs installed near UR tunnels can be significantly improved by up to similar to 43%. This will enhance overall GSHP system efficiencies, resulting in substantial savings in both operational costs and carbon emissions. In addition, the outcomes were used to develop a relationship which allows approximating the GHEs heat extraction improvements due to the nearby tunnel(s) heat load(s). This could give guidance to engineers working in fields where thermal interactions between URs and nearby GHEs arise.