Design and monitoring of an innovative geothermal system including an underground heat-storage tank

ABSTRACT

The design, implementation, and setup of an innovative layout for geothermal heating and cooling systems are presented. An underground heat-storage tank, used as a thermal flywheel, decouples the utility side of the system (i.e., the heat pump) from the geothermal side (i.e., the boreholes). The innovative layout allows for a more efficient exploitation of the ground energy reservoir and a sensible reduction of investment costs.

A pilot system has been realized for a commercial building near the city of Perugia, Italy. The design of the heat-storage tank, the heat exchangers, the monitoring system, and the operation modes were carefully studied. The heating performance monitoring shows that the innovative approach allows for a significant reduction of the ground heat exchangers, hence requiring for fewer and/or shorter boreholes (up to 75%) while still supplying the total energy need. The peak-power demand is covered taking advantage of the high thermal capacity of the water inside the tank, while the reduced-size geothermal boreholes are used with a higher duty cycle to independently provide the total energy need.

Keywords:

• Geothermal heat pumps
• heat storage
• heating and cooling
• renewable energy sources (RES)
• system monitoring

Acknowledgments

The paper is based on the results obtained in the framework of the SCER (the Italian acronym for Development of a new Renewable-Energy Conditioning system for commercial buildings) Project. The project was co-financed by the Italian Ministry for the Environment and coordinated by the Biomass Research Centre (CRB), University of Perugia. The authors would like to thank the partners: the Italian Ministry for the Environment, the Municipality of Perugia, and Consorzio Le Fratte. The authors also thank the following companies for the precious support during the system design, implementation, and monitoring: Baldassarri B&B; Idrotermica Frattegiani; Studio Associato Flu.Project; Studio di Ingegneria Delta.

Notes

¹ Directive 2009/28/EC of the European Parliament and of the Council of 23 April 2009 on the promotion of the use of energy from renewable sources and amending and subsequently repealing Directives 2001/77/EC and 2003/30/EC.

² The European Union climate and energy package, 2008.

³ http://www.elco.ch/i/prodotti/aquatop.html