Design and Monitoring of an Innovative Geothermal System including an Underground Heat-Storage Tank

The design, the implementation, and the setup of an innovative layout for a geothermal-driven heating and cooling system using a high-efficiency heat pump is presented. Standard procedures for the sizing of geothermal wells take into account the maximum heat and cooling power need of the building according to the typical weather conditions for the site and the system performances. In common applications, there is a peak of thermal energy needed from the geothermal unit during the heating season, and similarly for energy dissipation during the cooling season, lasting for at most a few hours per day. Even in coldest or hottest days, geothermal wells exchange energy with the ground below their maximum capacity during the 24-hour cycle. The introduction of a properly-dimensioned thermal storage tank, placed just below the ground level, can provide for the needed power while requiring fewer/shorter wells. During heating (cooling) seasons, the heat is continuously pumped inside (outside) the storage tank via reduced-size geothermal wells, while the heat flows to (from) the heat-pump unit upon request. Taking into account dispersions through the tank walls, the geothermal wells can be sized according to the 24-hour energy need instead of the peak power. A pilot project has been designed and implemented for a commercial application near the city of Perugia, Italy. The system has been dimensioned on the results of the building energy-demand simulation. The design of the heat storage tank, the heat exchangers, the monitoring system, and the operation modes was carefully studied. The heating and cooling performance is monitored with a custom data acquisition system.