Current status of ground source heat pumps and underground thermal energy storage in Europe

Abstract

Geothermal Heat Pumps, or Ground Coupled Heat Pumps (GCHP), are systems combining a heat pump with a ground heat exchanger (closed loop systems), or fed by ground water from a well (open loop systems). They use the earth as a heat source when operating in heating mode, with a fluid (usually water or a water-antifreeze-mixture) as the media transferring the heat from the earth to the evaporator of the heat pump, utilising that way geothermal energy. In cooling mode, they use the earth as a heat sink. With BHE geothermal heat pumps can offer both heating and cooling at virtually any location, with great flexibility to meet any demands. More than 20 years of R&D focusing on BHE in Europe resulted in a well-established concept of sustainability for this technology, as well as sound design and installation criteria. Recent developments are the Thermal Response Test, which allows in-situ-determination of ground thermal properties for design purposes, and thermally enhanced grouting materials to reduce borehole thermal resistance.
For cooling purposes, but also for the storage of solar or waste heat, the concept of underground thermal energy storage (UTES) could be proven successfully. Systems can be either open (aquifer storage) or can use BHE (borehole storage). While cold storage meanwhile is established on the market, heat storage, and in particular high temperature heat storage (>50 ?C) still is in the demonstration phase.
Despite the use of geothermal heat pumps for over 50 years now (first in USA), market penetration of this technology, is still at its infancy, with fossil fuels dominating the market of heating of buildings and air-to-air heat pumps dominating the market of cooling of buildings. In some countries, namely Germany, Switzerland, Austria, Sweden, Denmark, Norway, France and USA, already larger numbers of geothermal heat pumps are operational. In these countries meanwhile installation guidelines, quality control and contractor certification becomes a major issue.