Protection system for vertical geothermal probes

The presented invention “SPSGV" (Protection System for Vertical Geothermal Probe) was created to give a valid support to designers, probes’ installers and final users because it increases Vertical Geothermal Probes’ reliability, compared to the actual state of art.

Title of the patent Low enthalpy geothermal system and method for its installation
Thematic area Mechanical, civil and environmental engineering
Ownership Alma Mater Studiorum - Università di Bologna
Inventors Francesco Tinti, Sara Focaccia
Protection Italy, Netherlands, Germany
Licensing status Available for licensing agreement
Keywords Geothermal energy, vertical geothermal probes, protection system, energy efficiency, convective motions.
Filed on Apr 24, 2012

Background of the invention is low enthalpy geothermal energy for air conditioning of buildings: in particular it refers to the market of systems using closed loop borehole heat exchangers and specifically Vertical Geothermal Probes (VGP). Traditional geothermal system consists of the installation of closed loop tubes in the ground, within which circulates a thermo-vector fluid (water or brine). The purpose is to extract thermal energy from the ground, without fluids exchange, by means of thermal conduction. This energy is then used in several ways: heating, cooling, hot water, melting of the road-ice, swimming pool heating, maintaining the microclimate of greenhouses, etc.., often by coupling a thermal machine (heat pump) and with distribution systems to radiant technology. This market is facing some barriers to its development both technical, economical and related to insurances, that had decelerated its diffusion: this is due to the impossibility to check or replace the Probes once they are embedded in the ground. This means high insurance costs and/or high replacement costs if it breaks. After the drilling phase, the Probe is lowered in the well and then cemented here: during installation, as a result of contact with natural material, abrasion may occur on the edge of the probe, which could also lead to cuts. In this case, very complex are both maintenance and, where appropriate, probe replacement.

The invention is an innovative way to install the Probes in the ground: this becomes a valid support to designers, Probes installers and final users because it increases Vertical Geothermal Probes reliability, compared to the state of the art. Probes, in fact, are no longer being inserted directly into the ground and cemented, but are first enclosed within the Protection System, which is subsequently lowered into the hole and cemented. In the annulus between the outer wall of the protection system and the inner wall of the borehole is injected a mixture bentonite cement for the maintenance of sealing and stability of the hole, as well as to ensure thermal continuity between the Protection System and the ground. The annulus between the outer wall of the probe and the inner wall of the protection system must be filled by a suitable fluid, which has peculiar characteristics, for example it doesn’t reduce thermal conductivity because of creation of convective motions that improve heat transfer. The Protection System allows to easily inspect, maintain and, eventually, replace the probe in case of malfunction over time.

The patented Protection System allows several advantages in terms of:

- Installation: reduction of the quantity of grout injected, with costs reduction; better protection of the Probe, which is not in contact either with the unconsolidated material (during installation), nor with the cement mixture (during operation); better control of the verticality of the Probe, within the protection system.

- Energy saving: ability to create convective motions and to improve heat transfer.

- Reliability: ability to easily inspect, maintain and, eventually, replace the Probe in case of malfunction over time; better control of the overall thermal resistance of the borehole and the heat exchange between the hole and the ground.

- Environmental sustainability: decrease of possibility to release thermo-vector fluids in ground water.

Francesco Tinti, Sara Focaccia, Alberto Barbaresi: "PERFORMANCE COMPARISON BETWEEN A TYPICAL VERY SHALLOW AND AN INNOVATIVE CONFIGURATION OF GROUND HEAT EXCHANGERS" to be presented at the European Geothermal Congress which will take place in The Hague (NL), in June 2019.

 

Francesco Tinti, Sara Focaccia, Alberto Barbaresi, Emanuele Mandanici:  "Una nuova configurazione di sistema geotermico superficiale, per massimizzare il potenziale di stoccaggio di calore nel sottosuolo" delivered at Geofluid (Piacenza, Italy) in October 2018.

 

Sara Focaccia, Francesco Tinti: "An innovative Borehole Heat Exchanger configuration with improved heat transfer" published at "Geothermics" journal in 2013.