Subsurface urban heat island and its effects on horizontal ground-source heat pump potential under climate change

Recent urban air temperature increase is attributable to the climate change and heat island effects due to urbanization. This combined effects of urbanization and global warming can penetrate into the underground and elevate the subsurface temperature. In the present study, over-100 years measurements of subsurface temperature at a remote rural site were analysed, and an increasing rate of 0.17 °C per decade at soil depth of 30 cm due to climate change was identified in the UK, but the subsurface warming in an urban site showed a much higher rate of 0.85 °C per decade at a 30 cm depth and 1.18 °C per decade at 100 cm. The subsurface urban heat island (SUHI) intensity obtained at the paired urban–rural stations in London showed an unique ‘U-shape’, i.e. lowest in summer and highest during winter. The maximum SUHII is 3.5 °C at 6:00 AM in December, and the minimum UHII is 0.2 °C at 18:00 PM in July. Finally, the effects of SUHI on the energy efficiency of the horizontal ground source heat pump (GSHP) were determined. Provided the same heat pump used, the installation at an urban site will maintain an overall higher COP compared with that at a rural site in all seasons, but the highest COP improvement can be achieved in winter