Environmental impact and energy performance of groundwater heat pumps in urban retrofit

Increasing efforts are addressed to improve heating, ventilation and air conditioning systems to achieve the decarbonization goal also in the building sector. But less attention is actually devoted to their impact on the urban heat island (UHI) phenomenon. Starting from the UHI assessment and its impact on building heating and cooling demand, a performance comparison is presented between groundwater heat pumps (GWHP) supplied by a district network and air source heat pumps (ASHP_1). Hybrid systems with small ASHPs and condensing boilers (ASHP_2) are also considered. An urban area, network and heat pumps were modeled for this study. In summer, the removal from the urban area of the heat dissipated by condensers thanks to GWHPs reduces the average UHI intensity with ASHPs by 45% and the relative cooling demand increment by 42.6%. A more favorable temperature of the groundwater than outside air permits a net superiority of the GWHP efficiency. At annual level, the GWHP provides energy savings of 27% and 34.5% and CO2 emission reductions of 27% and 39.5% compared to ASHP_1 and ASHP_2 respectively. The UHI mitigation to improve comfort and resilience in urban areas is an important added value for the contribution to decarbonization that a GWHP network can provide.