How a sensitive analysis on the coupling geology and borehole heat exchanger characteristics can improve the efficiency and production of shallow geothermal plants

Knowledge of the thermal behaviour around and throughout borehole heat exchangers (BHEs) is essential for designing a low enthalpy geothermal plant. In particular, the type of grout used in sealing the space between BHE walls and the pipes is fundamental for optimizing the heat transfer and minimizing the thermal resistance, thereby promoting the reduction of total drilling lengths and installation costs. A comparison between grouts with different thermal conductivities coupled with common hydrogeological contexts, was modelled for a typical one-year heating for continental climates. These data have been used for a sensitivity analysis taking into account different flow rates through pipes. The results highlight that in groundwater transient conditions, porous lithologies allow for greater heat power extractions to be obtained with an increasing grout thermal conductivity than limestone or clayey silt deposits do. Moreover, increasing the inlet flow rates through the pipe greatly improves the final heat power extraction. As a result, when the underground allows for high extraction rates, the use of high performing grouts is warmly suggested ensuring greater productions

Geothermal Heating and Cooling Networks for Green and Livable Urban Transformations – Part II

As stated in part one of “how geothermal heating and cooling networks may support the green and livable urban transformation,” geothermal energy can be very efficiently used as a resource for district heating and cooling networks and can have the ability to be a key technology for a necessary heat energy transition. Compared to natural gas, the reduction of CO2-emissions using geothermal energy in an average project can be up to 88 percent (Stichting Platform Geothermie et al., 2018), hence the implementation of geothermal energy could be an important step to reach EU climate goals. In the Netherlands, for instance, it is predicted that geothermal energy can contribute 15 percent to the necessary CO2-emission reduction in the heat sector by 2030 and up to 25 percent by 2050 (Stichting Platform Geothermie et al., 2018). In contrast to that, geothermal energy only plays a minor role in the European heating and cooling sector. Hence there is a need to strengthen the role of geothermal energy and to intensify a know-how transfer about the potential of this technology. Therefore, the COST Action Geothermal-DHC wants to foster this knowledge exchange and will develop a roadmap towards a better integration of geothermally supplied heating and cooling networks in Europe in the next three years. Showcases and good practice examples offer a reliable option to exchange experiences and achieved success and can incentivize stakeholders to integrate similar solutions in their concepts and strategies. Some of such practice examples, implementing geothermal energy for heating and cooling in various European countries, are described in the following, which show a high variety of application possibilities

Alternative use of artificial quarry lakes as a source of thermal energy for greenhouses

In northern Italy, most greenhouses rely on gas or oil heaters which are sometimes subject to high operating costs. Several greenhouses are nearby quarry lakes, which are the legacy of the expansion of cities in the last decades, including Turin (NW Italy). About 20 quarry lakes were excavated close to the Po riverbed in the southern part of this urban area, along a belt of more than 30 km in length, with an overall volume exceeding 10 million m3 water. The study addresses these artificial lakes as a low enthalpy thermal energy source, potentially providing heat to surrounding agri-business buildings. Detailed temperature monitoring of a large lake quarry was conducted over two years at different depths, measuring the surrounding groundwater level as well. Two different behaviors of the lake during the winter and summer seasons enabled the definition of a quite low water mixing process between the surrounding aquifers and the lake (in the range of 2–4◦ C). An evaluation of the heat extraction potential using the lake as a heat source, depending on water temperature and its volume, and a qualitative comparison with groundwater systems are proposed. This study contributes to increasing knowledge on an overlooked resource for sustainable heating