A method to analyze the performance of geocooling systems with borehole heat exchangers. Results in a monitored residential building in southern alps

Geothermal heat is an increasingly adopted source for satisfying all thermal purposes in buildings by reversible heat pumps (HP). However, for residential buildings located in moderate climates, geocooling, that implies the use of geothermal source for cooling buildings without the operation of HP, is an efficient alternative for space cooling not yet explored enough. Geocooling allows two main benefits: to cool the buildings by high energy efficiencies improving summer comfort; to recharge the ground if space heating is provided by HP exploiting the geothermal source (GSHP). In these cases, geocooling allows to avoid the decreasing of the performances of the GSHP for space heating over the years. To explore these issues, a method has been developed and tested on a real case: a new residential building in Lugano (southern Switzerland) coupled with 13 borehole heat exchangers. The system provides space heating in winter by a GSHP and space cooling in summer by geocooling. During a 40 months monitoring campaign, data such as temperatures, heat flows and electricity consumptions were recorded to calibrate the model and verify the benefits of such configuration. Focusing on summer operation, the efficiency of the system, after the improvements implemented, is above 30, confirming, at least in similar contexts, the feasibility of geocooling. Achieved results provides knowledge for future installations, underlining the replication potential and the possible limits.