Heat loss from buildings, infrastructure and enhanced heat flow from sealed surfaces increase the temperatures of shallow groundwater often more than global warming. A worldwide analysis of thousands of wells reveals that the temperature at every second location is higher than expected, and local anthropogenic heat sources that exist for decades contribute to subsurface waste heat accumulation down to a depth of around 100 m. At some places, such as in the city centre of Cologne, heating of groundwater by several degrees of Celsius appears to have even reached a maximum. Here, long-term temperature records reveal stabilizing thermal conditions in the shallow aquifer. This also means that the geothermal potential has increased significantly, possibly to a critical level for maximum stored heat in place. Still, the natural geothermal resources together with the artificially stored resources are often overlooked. In many regions, recycling only the energy lost to the subsurface could (1) fulfil a substantial part of the heat demand of buildings, and (2) increase the efficiency of heat pumps with a more favourable thermal regime during the heating period. This resource is growing.  On the global scale, by the end of this century nearly 75% of the heat demand could be covered by recycling the heat that accumulates in the subsurface from anthropogenic heat loss and in response to climate change. Especially in densely populated areas, continued heat accumulation mitigates the risk of overexploiting the geothermal potential of shallow aquifers. Sustainable thermal management of aquifers must integrate concepts of heat recycling to avoid long-term warming of groundwater. For this, integrated spatial planning is needed. Shallow geothermal systems such as groundwater heat-pump installations have to be spatially organized in urban districts to achieve optimal use of the geothermal resource. They can maintain controlled cooling of the groundwater while benefitting from enhanced waste heat flux. As an example, we discuss the thermal interference of urban infrastructure and geothermal wells for the city of Lyon, which are spatially arranged based on hydraulic and thermal criteria to benefit from urban groundwater heating.

How to cite: Bayer, P., Attard, G., Blum, P., Hemmerle, H., Kurylyk, B. L., Menberg, K., Noethen, M., and Benz, S.: Heat accumulation in shallow aquifers: managing a growing resource, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1781, https://doi.org/10.5194/egusphere-egu23-1781, 2023.

This study presents the performance evaluation of ATES-GSHP system based on long term monitoring since 2016. It consists of two office buildings with a combined net heated floor area of 18000 m2. ATES-GSHP system is in operation since 2016. The aim evaluate the performance as well as propose KPIs that take into account both the building HVAC system and ATES long term sustainable operation. 
The system is equipped with comprehensive instrumentation in HAVC system, heatpumps and aquifer including a unique and continuous installation of high resolution distributed temperature sensing using fiber optic cables throughout the aquifer.

The system is connected to district heating and has two heat pumps with a total nominal cooling and heating capacity of 1.5 MW and 1.8MW. Allowable groundwater extraction and injection is 50 l/sec. with undisturbed groundwater temperature of 9.5 ◦C.  The monitoring period analyzed for the HVAC system is March 2019 - March 2020 (for ATES from March 2016- March 2020). For the year 2019/2020, the total heating load (including domestic hot water) and cooling load was 456 and 381 MWh respectively. The total average heating and cooling used from the ATES are 673 MWh and 743 MWh respectively during the first 3 annual storage cycles of operation. Over the first three storage cycles, the average injection and extraction temperatures in the warm and cold ATES sides range between 7.6◦C and 13.3◦C. The average temperature differences across the main heat exchanger for ATES are 4.5-2.8 K which is 4-5 degrees lower than the optimum value. The average thermal recovery efficiency over the first 3 storage cycles were 47 % and 60 % for warm and cold storages respectively. The seasonal performance factors SPF for the system ranged between 5-54 depending on the boundary levels 0, 1 and 2 according to Annex 52 boundary definition. Furthermore, it discusses possible improvements to be implemented regarding the system boundary definition and GSHP-ATES coupled operation. The data analysis indicated annual energy and hydraulic imbalances which results into undesirable thermal breakthrough between the warm and cold side of the aquifer. Despite having favorable conditions from aquifer point of view, this was mainly due to suboptimal operation of the building energy system which led to insufficient heat recovery from the warm side, and subsequently insufficient cold injection in the cold wells, despite the building heating demand and the available suitable temperatures in the ATES. The cause of the suboptimal operation is attributed to oversizing of the heat pumps. As a result, the heat pumps could not be operated during small-medium loads. Additionally, the limitations of currently used energy and thermal KPIs for ATES are discussed and additional thermal KPI named heat exchanger efficiency balance (βHEX) that connects and evaluate the optimum operational point of temperature differences from both the building and ATES prospective is proposed to contribute in providing more complete picture on the ATES-building interaction performance and highlights the losses in energy recovery from ATES are due to the subsurface processes or building energy system operation.

How to cite: Abuasbeh, M.: Long term performance monitoring and KPIs’ evaluation of Large Scale ATES-GSPH system: Case study in Stockholm, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-875, https://doi.org/10.5194/egusphere-egu23-875, 2023.

Sustainability is one of the points in the design stage of the groundwater heat pump (GWHP) system. Thermal impacts on the surrounding environments should be accurately configured to ensure system sustainability. To achieve that goal, a sophisticated characterization of the target aquifer is required. So far, considering heterogeneity of subsurface environment in system design is challenging because there is lack of case studies provided high-resolution monitoring data enough to catch the heterogeneity. In this study, to detect the hydraulic and thermal responses to the GWHP operation, 12 monitoring wells were densely constructed between two geothermal wells at Eum-Seong, Republic of Korea. During the system operation, the high-resolution spatiotemporal changes in hydraulic pressure and temperature were detected by pressure sensors and fiber optic-distributed temperature sensing (FO-DTS). Monitored results were interpreted by time-series analysis to derive the thermal front velocity between monitoring wells. During the GWHP system operation, groundwater level monitoring results showed that a dynamic flow condition was generated especially near the geothermal wells up to 20 times of background flow. The estimated effective thermal velocities were comparable with the theoretically calculated velocities, but the higher velocity randomly appeared at the specific depths. From this case study, we confirmed FO-DTS was applicable to monitor the GWHP system. Those three-dimensional high-resolution monitoring data enabled to prove the existence of horizontal and vertical heterogeneity, indicating the need for accurate characterization of aquifer properties.

Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2022R1A2C1006696). This work was also supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government(MSIT) (No. 2022R1A5A1085103).

How to cite: Baek, J.-Y., Oh, H.-R., Ha, S.-W., and Lee, K.-K.: High-Resolution Spatiotemporal Monitoring Data During Groundwater Heat Pump System Operation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5558, https://doi.org/10.5194/egusphere-egu23-5558, 2023.

Ground-coupled heat pump systems can help reducing energy consumption and electrical peak power demand while contributing to reduce greenhouse gas emissions. A key element of these systems is the ground heat exchanger that links the mechanical equipments to the underground geological materials. Although most ground heat exchangers are composed of closed-loop wells, standing column wells (SCW) represent a transformative opportunity in dense urban areas where aquifer productivity is limited. Based on a decade of research conducted in the area of Montreal in Canada, this conference will illustrate the potential of SCWs, present the preliminary results of two demonstration projects, discuss the impact of hydrogeological and hydrogeochemichal conditions on system design and discuss some recent advances related to field testing and modeling of SCWs. The challenges that remain to be overcome will also be discussed.

How to cite: Pasquier, P.: Standing Column Wells: A transformative opportunity to provide heating to buildings in dense urban areas., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1318, https://doi.org/10.5194/egusphere-egu23-1318, 2023.

The interest towards standing column well (SCW) is increasing due to their higher thermal efficiency and a lower initial construction cost compared to conventional vertical ground heat exchangers. The SCW pumps and reinjects the groundwater inside the same well. They are usually coupled with an injected well to discharge a portion of the pumped groundwater, an operation called “bleed”, to increase punctually the thermal capacity of the system. Since groundwater is the heat carrier fluid, clogging issues can develop if detrimental conditions are locally present. The most common issue for hard water is calcite scaling. The impact of SCW on calcite precipitation had already been studied with a thermohydrochemical model and field experiments. However, it still lacks a reactive thermohydrochemical model calibrated with field acquired data. Once calibrated, this model could help defining the best strategy to avoid calcite precipitation.
A full-scale SCW was operated with a geothermal mobile laboratory for 70 consecutive days. A fractured zone intersects the SCW close to the surface. The operation corresponded to a heat injection with different flow rate sequences. In addition, a groundwater treatment unit installed in the laboratory was used to test different treatment sequences. During this experiment, 20 groundwater samples were collected and analyzed. Those analyses focused on the physico-chemical parameters and the major ions. A reactive thermohydrochermical model was developed in the Comsol Multiphysics environment. This model includes a complex geometry, groundwater flow, heat transfer, and reactive solute transport. The reactive solute transport is composed of two parts; the transport and kinetics model for three primary species and the chemical equilibrium of nine secondary species of calcite reaction. The calibration is achieved by imposing operational parameters as input variables for hydraulic and thermal model as well as the initial concentration.
The calibration identified the presence of CO₂ degassing. The parameter with more influence on ion calcium concentration is bleed flow. In fact, bleed operation generates a groundwater flow of native groundwater toward the SCW. During this operation, the fracture contributed up to 33 % of the total calcium flux coming to the SCW. This flux is a convective flux. The concentration of total calcium transported by the fracture is closed to the initial concentration. As a consequence, the ion calcium concentration stabilized near the initial state. Thus, the groundwater treatment performance is minimized. The saturated index of the calcite is above zero. On the opposite side, when bleed is not activated, the groundwater is recycled is the SCW. As a results, the treatment unit is responsible of the observed decreases of the ion calcium concentration. The saturated index decreases below zero after five days. Also, when the total calcium concentration decreases in the SCW, a diffusive flux emerged into the fracture.
In conclusion, this study highlights the alteration of the solute transport as a function of the bleed operation. The type of flux depends on bleed and the treatment. In addition, the treatment of groundwater is unnecessary when bleed is activated.

How to cite: Cerclet, L., Courcelles, B., and Pasquier, P.: Thermohydrochemical Model to Identify the Impact of Bleed Flow on Calcite Scaling in a Standing Column Well, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17433, https://doi.org/10.5194/egusphere-egu23-17433, 2023.

Nearly half of Europe’s total energy consumption is dedicated to buildings. Heating and cooling consist of a significant part of this consumption. Groundwater heat pumps (GWHPs) are highly efficient, environmentally friendly and low-carbon technology that can supply heating and cooling to buildings on small to large scale. Northern Gateway Heat Network is an ongoing project based on GWHP, located in Colchester, UK. The planned project will probably be the largest GWHP system using the confined chalk aquifer to date. It will provide district heating and domestic hot water to healthcare buildings, around 300 dwellings, and offices. The system is designed as part-load to cover 75% of the annual heating demand of the planned development with an 800 kW output heat pump which will benefit from the open-loop groundwater extracted at around 12.5°C.

A laboratory-scale sandbox model having external dimensions of 1.178 m × 0.721 m × 0.715 m (L × W × H) with two acrylic tubes acting as injection and abstraction wells was built to investigate the impact of GWHP operation on the system performance and sustainability. The setup was designed to perform different groundwater flow rates by changing the water levels in the hydraulic head tanks on the left and right sides of the sandbox. Several experiments were conducted considering different scenarios: heating, cooling, heating and cooling, and thermal energy storage to examine their impact on thermal plume development and system performance. The study also aims at investigating the effects of groundwater flow velocity, injection and abstraction rates on thermal plume development.

The experimental results show that the thermal plume reaches the abstraction well in each scenario, causing a change in the abstraction temperature. This phenomenon, called thermal recycling, reduces the thermal energy abstraction from the groundwater. The results also illustrate that groundwater flow velocity, injection, and abstraction rates significantly impact thermal plume development. Higher injection and abstraction rates create a larger thermal plume. However, groundwater flow prevents heat development around the well by dispersing the heat in the groundwater flow direction. The results show that it is important to consider groundwater flow velocity, injection and abstraction rate when designing a GWHP system. The distance between injection and abstraction wells is another significant parameter that should be carefully considered. However, it could not be investigated in the current study as the sandbox model was not suitable for changing the distance between injection and abstraction well. Further studies need to be carried out using large-scale field test and/or numerical simulations.

How to cite: Sezer, T., Sani, A. K., Cui, L., and Singh, R. M.: Experimental Investigation of Groundwater Heat Pump Usage for District Heating and Cooling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16562, https://doi.org/10.5194/egusphere-egu23-16562, 2023.

Mine water geothermal has great potential to provide low carbon heating, cooling and energy storage. Some successful examples have shown that a flooded mine is a reliable, low carbon heat source and could contribute to a new green energy future for many European post-mining regions. To date, however, this potential has been hindered by scientific and technical challenges that have resulted in delay, cost overrun, or even abandonment of some mine water geothermal projects. Key sources of uncertainty that present challenges for developers, operators and regulators are groundwater flow behaviour and temperature distribution in abandoned mines under abstraction/reinjection cycles, the long-term sustainability of the geothermal system, and its interactions and impacts in the surrounding environment. 

The UK Geoenergy Observatory (UKGEOS) in Glasgow, Scotland, is an at-scale research facility with exceptional levels of hydrogeological and thermal characterisation and downhole instrumentation designed to monitor and quantify subsurface change and provide data to address challenges and risks associated with mine water geothermal systems design and operation. The Observatory includes four mine water boreholes connected in an open loop configuration with pumps for abstraction/reinjection, a heat pump-chiller and three different heat exchangers to enable testing of multiple modes of heat pump operation (heating and cooling) and component performance. A further two boreholes intercepting mine workings are equipped with downhole electrical resistivity tomography (ERT) and hybrid fibre-optic cables for distributed temperature sensing (Passive and Active DTS). Together with five environmental monitoring boreholes, a seismic monitoring borehole and ten hydrogeological downhole data loggers for continuous pressure, temperature, and electrical conductivity monitoring, the dedicated Observatory, which is not connected to any customers, is well equipped to examine the interaction and impacts of geothermal energy systems.

In this work we present a comprehensive set of initial hydrogeological and thermal observations collected during the construction and commissioning stages of the Observatory, including long term baseline monitoring, results of initial well pumping and heat abstraction/reinjection tests. These observations include evidence for the general groundwater flow circulation in the system, groundwater level response to recharge events, different transmissivities in different mined zones, and limited connectivity between mine workings at different depths, the surrounding aquifers and the River Clyde. We have integrated hydrogeological, thermal, and other information to develop an initial conceptual hydrogeological model of the system. Using the conceptual model and field data we have developed flow and heat numerical models to evaluate alternative scenarios of heating and cooling. Modelling results indicate variable flow paths and response times for thermal breakthrough for different geothermal operational configurations. Academic and commercial researchers are encouraged to get in touch to discuss using the Observatory’s unique capability for future mine water geothermal energy investigations, including investigating the behaviour, sustainability and impacts of groundwater flow and temperature under geothermal abstraction/reinjection cycles. 

How to cite: Gonzalez Quiros, A., Boon, D., MacAllister, D. J., MacDonald, A., Palumbo-Roe, B., Ó Dochartaigh, B., Walker-Verkuil, K., and Monaghan, A.: Monitoring responses to mine water geothermal use in a highly characterised and instrumented groundwater system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5989, https://doi.org/10.5194/egusphere-egu23-5989, 2023.

Summer periods of warm weather become longer and hotter causing “Urban Heat Islands” in large cities. Rising temperatures do not stop at the surface, but migrate into the underground, where infrastructure – such as sewage and district heating systems, buildings and shallow geothermal energy systems for cooling – amplifies the increase of groundwater temperatures. In order to be able to quantify this ongoing process and predict future temperature developments, a sound data basis is necessary. As of now, only groundwater temperature measurements have been available for different depth (one-point or multiple depth measurements) and time intervals (varying from two weeks to months) at a limited number of wells within the shallow urban aquifers in Vienna. To increase the spatial information content, the goal of this study was to measure groundwater temperature and level within the urban shallow aquifers of Vienna in two extensive field campaigns for more than 800 wells and to analyze those data statistically

To document the warmest and coldest conditions, measurements took place in one week each in October (2021) and April (2022). In total, groundwater temperatures in 1 m depth intervals and groundwater level were measured at 812 locations. Out of these ones, at 150 wells, water temperature was measured in pumped water. The average value of the profile equals best the pumped groundwater and thus represents the average aquifer temperature. According to our data analysis, the groundwater temperatures in Vienna vary between 6.9 °C and 30.6 °C. The highest temperatures were detected in close proximity to possible heat sources and a rapid drop in temperature with increasing distance could be demonstrated.

Based on the collected data, temperature maps for both measurement dates and for different depth-intervals were derived, and display the underground urban heat islands in Vienna. The temperature maps enable the estimation of the potential for sustainable heating and cooling with groundwater in the capital of Austria.

Together with historic long-term temperature data, trend analyses will be performed to allow a prognosis of thermal changes in the groundwater. The results, together with an extensive analysis of the groundwater chemistry and ecology, will feed into the development of a catalogue of measures for authorities and policymakers. Intention of the included recommendations is to counteract further groundwater warming and to ensure an efficient and sustainable use of groundwater for heating and cooling. The guidelines will therefore not only contribute to cooling the groundwater, but also to decarbonize the heating and cooling supply of Vienna.

How to cite: Steiner, C., Griebler, C., Kaminsky, E., Englisch, C., Stumpp, C., and Goetzl, G.: City-wide groundwater temperature profiles reveal underground urban heat islands in Vienna, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12110, https://doi.org/10.5194/egusphere-egu23-12110, 2023.

In 2013 we started a spatial and temporal high-resolution groundwater temperature monitoring campaign at a residential neighborhood under intensive shallow geothermal energy use in the western outskirts of the city of Cologne, Germany. The monitoring was conducted with the aim to identify effects of the intensive thermal use upon groundwater temperatures. Although individual systems sizes in the neighborhood are small, the installed 47 borehole heat exchanger systems sum up to a total borehole heat exchanger length of 11,009 m within a confined area of 0,12 km² to satisfy, together with three open systems, a total heat demand of 506 kW.

With almost ten years of groundwater temperature monitoring we created a valuable data set. Our results show a reduction of overall groundwater temperatures when comparing upstream and downstream groundwater temperatures during the first years of geothermal operation as an effect of the intensive use of shallow geothermal energy for heating and warm water provision. However, monitoring results depend on the measurement location in our study and it is known that urban subsurface and groundwater temperatures are influenced by several factors. In this contribution, the monitoring concept, results as well as pitfalls of the monitoring campaign are illustrated on our way to untangle urban groundwater temperature changes as a response to the intensive shallow geothermal energy use.

How to cite: Vienken, T.: Ten years of groundwater temperature monitoring at a residential neighborhood under intensive shallow geothermal energy use – insights and lessons learned, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13777, https://doi.org/10.5194/egusphere-egu23-13777, 2023.