Reservoir characterization and geoexchange system design to feed an innovative CO2 heat pump

Client: Nuovo Pignone, GE
Location: Balanzano (Perugia), Italy
Date: 2012

The objective of this study was to evaluate the possibility of using a geoexchange system to satisfy the thermal energy demand for heating using a transcritical cycle heat pump (carbon dioxide as refrigerant), included in a natural gas reducing station.

 Project Goals


Transcritical heat pump cycle

  • Technical feasibility of geoexchange systems connected to a transcritical heat pump (innovative application)
  • Optimization of the system in different functioning conditions:
    • Only heat extraction (to feed the heat pump)
    • Heat extraction and re-injection (heat received from gas reducing station).

Innovative aspects

Coupling of geoexchanger and innovative transcritical cycle heat pump

Activities performed

  1. Geological and hydrogeological site characterization;
  2. Geostatistical model of the thermal conductivity of the geothermal reservoir (using GeoMS);
  3. Identification of the possible geoexchange systems and design of the geothermal field;
  4. Thermal flow simulation of the geoexchange system (using FEFLOW);
  5. Sensitivity analysis of the design hypothesis and of the examined options.

    Ground thermal conductivity

Technical data

Operating mode: heating

Thermal power at the evaporator: 332 kW

Fluid flow rate 62 m3/h

Geoexchange system inlet temperature 3°C

Geoexchange system outlet temperature 8°C


Closed loop geoexchange system consisting of 200 geothermal probes of 150 m depth, spaced 6 m one from the other.

Technical feasibility

The numerical simulation showed that the required inlet temperature of the heat pump (>= 3°C) cannot be provided during the whole functioning period.
Therefore, it was studied the alternative of a summer recharge of the ground, by injecting the residual heat of the reducing station. Such solution can lead to an increase of 0.5 ºC in the ground surrounding the heat exchanger, assuring the functioning of the heat pump for the entire winter season.

Thermal behavior for solution 2


Ground temperature after 145 days of extraction on the surface