Optimization approaches for the design and operation of open-loop shallow geothermal systems

The optimization of open-loop shallow geothermal systems, which includes both design and operational aspects, is an important research area aimed at improving their efficiency and sustainability and the effective management of groundwater as a shallow geothermal resource. This paper investigates various approaches to address optimization problems arising from such research questions. The identified optimization approaches are thoroughly analyzed based on criteria such as computational efficiency and applicability. Moreover, a novel classification scheme is introduced that categorizes the approaches according to the type of groundwater simulation model (numerical or simplified) and the optimization algorithm used (gradient-based or derivative-free). Finally, a comprehensive review of existing approaches is provided, highlighting their strengths and limitations and offering recommendations for both the use of existing approaches and the development of new ones in this field.Comment: 16 pages, 3 figures; submitted to Advances in Geoscience

TAP - Thermal aquifer Potential: A quantitative method to assess the spatial potential for the thermal use of groundwater

This paper proposes a method to assess the potential for thermal use of groundwater and its integration in spatial energy planning. The procedure can be adapted to local regulatory and operational limits, thus estimating legally and technically achievable flow rates and subsequently, the thermal power that can be exchanged with the aquifer through a well doublet. The constraints applied to flow rates are a drawdown threshold in the extraction well, a limit for the groundwater rise in the injection well and a threshold to avoid the hydraulic breakthrough between the two wells. For the spatial assessment, the hydraulic influence on neighbouring well doublets is simulated with the maximum flow rates before the hydraulic breakthrough occurs. The Thermal Aquifer Potential (TAP) method combines mathematical relations derived through non-linear regression analysis using results from numerical parameter studies. A demonstration of the TAP method is provided with the potential assessment in Munich, Germany. The results are compared with monitoring data from existing open-loop systems, which prove that conservative peak extraction estimates are achieved

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

Assessment of human immediate response capability related to tsunami threats in Indonesia at a sub-national scale

Human immediate response is contextualized into different time compartments reflecting the tsunami early warning chain. Based on the different time compartments the available response time and evacuation time is quantified. The latter incorporates accessibility of safe areas determined by a hazard assessment, as well as environmental and demographic impacts on evacuation speed properties assessed using a Cost Distance Weighting GIS approach. <br><br> Approximately 4.35 million Indonesians live in tsunami endangered areas on the southern coasts of Sumatra, Java and Bali and have between 20 and 150 min to reach a tsunami-safe area. Most endangered areas feature longer estimated-evacuation times and hence the population possesses a weak immediate response capability leaving them more vulnerable to being directly impacted by a tsunami. At a sub-national scale these hotspots were identified and include: the Mentawai islands off the Sumatra coast, various sub-districts on Sumatra and west and east Java. Based on the presented approach a temporal dynamic estimation of casualties and displacements as a function of available response time is obtained for the entire coastal area. As an example, a worst case tsunami scenario for Kuta (Bali) results in casualties of 25 000 with an optimal response time (direct evacuation when receiving a tsunami warning) and 120 000 for minimal response time (no evacuation). The estimated casualties correspond well to observed/reported values and overall model uncertainty is low with a standard error of 5%. <br><br> The results obtained allow for prioritization of intervention measures such as early warning chain, evacuation and contingency planning, awareness and preparedness strategies down to a sub-district level and can be used in tsunami early warning decision support

On the Limitations and Implications of Modeling Heat Transport in Porous Aquifers by Assuming Local Thermal Equilibrium

Heat transport in natural porous media, such as aquifers or streambeds, is generally modeled assuming local thermal equilibrium (LTE) between the fluid and solid phases. Yet, the mathematical and hydrogeological conditions and implications of this simplification have not been fully established for natural porous media. To quantify the occurrence and effects of local thermal disequilibrium during heat transport, we systematically compared thermal breakthrough curves from a LTE with those calculated using a local thermal nonequilibrium (LTNE) model, explicitly allowing for different temperatures in the fluid and solid phases. For the LTNE model, we developed a new correlation for the heat transfer coefficient representative of the conditions in natural porous aquifers using six published experimental results. By conducting an extensive parameter study (>50,000 simulations), we show that LTNE effects do not occur for grain sizes smaller than 7 mm or for groundwater flow velocities that are slower than 1.6 m day−1. The limits of LTE are likely exceeded in gravel aquifers or in the vicinity of pumped bores. For such aquifers, the use of a LTE model can lead to an underestimation of the effective thermal dispersion by a factor of up to 30 or higher, while the advective thermal velocity remains unaffected for most conditions. Based on a regression analysis of the simulation results, we provide a criterion which can be used to determine if LTNE effects are expected for particular conditions

Well layout optimization for groundwater heat pump systems using the adjoint approach

Groundwater heat pump systems cause thermal anomalies in the aquifer that can impact upon downstream systems and reduce their efficiency. Therefore, it is important to optimally position the extraction and injection wells of such systems to avoid negative interactions and maximize the thermal potential of the aquifer. This paper presents a new method to determine optimal well layouts of groundwater heat pumps using the adjoint approach, which is an efficient way to solve the underlying PDE-constrained optimization problem. An integral part of the method is the numerical groundwater simulation, which here is based on the finite element method. In addition, a multi-start initialization strategy is introduced in an attempt to better reach the global optimum. The method is applied to a real case study with 10 groundwater heat pumps, i.e. 20 wells, and two optimization scenarios with different natural groundwater temperatures. In both scenarios, the optimization method successfully determines a well layout that maximizes groundwater temperatures at all extraction wells. Comparing the results from these scenarios demonstrates that hydro-geological conditions can have a significant impact on the optimal well layout. The proposed method is equally applicable to systems with multiple extraction and injection wells and can be extended to various other shallow geothermal applications, such as combined heating and cooling systems