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Contemporary living, the extreme climate changes and the necessity of renewable energy sources challenge the engineers around the globe to discover advanced methods of enabling a more comfortable life. For this purpose, geothermal energy systems are used to satisfy the calorific needs for cooling and heating. Thermo-active geo-structures, as dual-function elements, offer structural improvement and simultaneously provide eco-friendly and long-term cost-friendly solutions. This contribution provides an overview of the design of geothermal piles based on geometry variations. Hence, thermo-mechanical analyses are performed for axially loaded piles based on the load transfer approach using t-z curves method. With an absence of precise regulations and standards, the aim of these analyses is to simplify the design of thermo-active piles by generating an envelope chart utilizing the results for piles with different lengths and diameters. However, keeping a more realistic ratio of the geometry is of a significant importance, so that the piles are applicable on real project solutions.

How to cite: Smiljanovska, M., Mroueh, H., Habert, J., and Josifovski, J.: Elaboration of charts based on geometry variations for the design of thermo-active piles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-584, https://doi.org/10.5194/egusphere-egu2020-584, 2020.

Shallow geothermal energy (SGE) is increasingly being regarded as a valuable solution for space heating and conditioning because of high efficiency, diffuse availability and low environmental impact. Significant growth in the number of installations is envisaged as a result of energy policies and European Directives. Indeed, the obligations in the construction sector about the share of energy supply from renewable sources is increasingly pushing the design of new and renovated buildings. On the one hand shallow geothermal energy is suitable as a sustainable and distributed energy source. On the other hand, significant installation costs related to drilling of traditional installations represent an hampering factor. Thermally activating geostructures such as piles, diaphragm wall, tunnels and anchors can allow to include these costs in the construction of the structural elements. Moreover, a large availability of operational surface is represented by new and/or existing building heritage in urban areas as most of them  have underground levels that can be equipped with heat exchangers.

This contribution introduces a novel modular very shallow geothermal exchanger as part of a Heating, Ventilation and Air Conditioning (HVAC) system. The system concept allows its application not only to new structures and buildings but also to existing ones. While the low depths interested may penalize the heat exchange rates, on the contrary, extremely low installation costs make the cost-benefit ratio of this new technology extremely interesting and promising.

A first prototype consisting of three modules was designed by the authors and installed in an office building in Torino (Italy). External deployment of pipes to the basement wall in two different arrangements was realized in order to test system efficiency. Due to the experimental nature of the tests, a large number of sensors were placed to monitor the additional stresses and strains on the wall and the thermal regime of the partially saturated ground volume involved in heat exchange.

Preliminary thermal performance tests were performed together with numerical modelling re-interpretation. On the basis of the first tests and interpretation carried out, it was demonstrated that remarkable heat exchange rates of up to 20 and 27 W/m² could be injected/extracted from the ground in summer and winter respectively. Furthermore, the monitoring records suggest that extremely low affection of ground thermal status is operated by the system with respect to analogous non thermo-active walls. This evidence is extremely promising in the perspective of wide and dense diffusion of this new shallow geothermal energy system in urban areas where thermal interferences should be limited or avoided.

How to cite: Baralis, M. and Barla, M.: Development and testing of an innovative energy wall system in Torino (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15060, https://doi.org/10.5194/egusphere-egu2020-15060, 2020.

We present the findings of a recently concluded research project, investigating the possibilities for collective heating and cooling supply of a planned, relatively small residential area (Rosborg Ø) in Ny Rosborg, Vejle, Denmark with ground source heat pumps utilising foundation pile heat exchangers (a.k.a. energy piles, EP). Individual EP foundations connect to a distribution network of uninsulated geothermal pipes, buried at shallow depth (cold district heating, CDH) from which connected consumers can supply heating with heat pumps as well as passive or active cooling.

To this end, the project has developed a geothermal screening procedure based on a combined analysis of geophysical data, borehole information, pile testing and laboratory measurements of soil thermal properties. A prototype computational temperature model of CDH networks has been developed for estimating the performance of EP based heating and cooling supply of Rosborg Ø. Finally, the project has developed a complete business (case) model for EP based CDH with a well-defined cost structure in which total fixed and variable costs can be quantified in specific projects.

The mapping of the geothermal potential demonstrates that CDH most likely can fully supply the estimated energy demand of the planned buildings in Rosborg Ø. However, recalculation of the scenario is necessary once additional information on the planned buildings become available. This conclusion is further supported by operational data from the EP foundation at the nearby Rosborg Gymnasium, demonstrating excess heating and cooling possibilities (beyond the demand of the building itself). Further analyses of the data from the Gymnasium estimates the average energy efficiency ratio to 24.8 for the passive cooling during July and early August 2018, roughly ten times higher than that of traditional Air Conditioning (AC). Moreover, the Gymnasium is able to supply its cooling needs passively 97% of the time where cooling is required, implying that the variable cost of cooling with EPs is exceptionally low.

The initial investment required for EP based CDH is higher, however, the variable costs of heating and cooling are greatly reduced relative to those of traditional District Heating (DH) and AC. Consequently, the estimated payback period for collective EP based CDH supply of Rosborg Ø is ca. 4.5 years. The relatively short payback period is due to a drastic reduction (of 80%) of the combined variable costs of heating and cooling with EPs, relative to traditional DH and AC. The contributing factors to the short payback period are the relatively low costs of electricity, the high COP of the heat pump, a relatively high, annual fixed tariff imposed by traditional DH and finally the exceptionally low costs of passive cooling/seasonal heat storage. As such, the project demonstrates a truly renewable, economically competitive heat pump technology to supply collective building heating and cooling/seasonal heat storage for the future energy supply in Denmark.

How to cite: Poulsen, S. E., Alberdi-Pagola, M., Tordrup, K. W., Cerra, D., and Andersen, T. R.: A case study of 5th generation district heating and cooling based on foundation pile heat exchangers (Vejle, Denmark), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4626, https://doi.org/10.5194/egusphere-egu2020-4626, 2020.

Standing column wells (SCWs) are efficient ground heat exchangers that use local groundwater as a heat source/sink for heating and cooling buildings. In a SCW, high heat exchange rates are achieved by recirculating groundwater in a single deep (75 m to 450 m) and uncased borehole. Discharging (“bleeding”) a small amount of the pumped water outside the SCW also allows maintaining the groundwater temperature within the heat pump’s operational range during peak demand periods. This strategy has been identified as the most significant parameter of SCW operation and is associated with reductions in total length, surface and cost of the borehole heat exchanger compared with the more common closed-loop systems.

This work aims at improving knowledge of the dynamic mass and heat transfer processes involved in SCW operation, in order to promote adoption of this energy-efficient technology and encourage good practice. To this end, data is collected using an experimental SCW system located near the city of Montreal, Canada, and made of a 215-m-deep SCW and a 150-m-deep injection well available for discharge of bleed water. The wells are also connected to a large-scale geothermal laboratory designed and equipped to mimic the heating and cooling operation of a small commercial building. First, an advanced finite-element model coupling advection-diffusion of heat and groundwater flow within a SCW and the surrounding ground is developed in the Comsol Multiphysics environment and is validated using experimental datasets collected through downhole temperature measurements, a pumping test, a thermal response test as well as 25 days of winter operation. The numerical model is then used to evaluate the impact of the pumping arrangement and bedrock fracturation on the well’s outlet temperature. Secondly, the operational parameters logged during the dynamic heat extraction test are analysed to provide insight about various operating strategies and their effect on the system’s performance.

The work conducted so far demonstrates that the proposed finite-element model reproduces the hydraulic and thermal behaviours of a SCW with satisfying accuracy. Numerical results suggest that placing the submersible pump near the top of the well avoids installation and maintenance difficulties without compromising heat pump operation compared with the usual reverse configuration. It is also shown that deep fractured zones are beneficial to heat pump operation in heating mode, whereas near-surface fracturing tends to impair the performance of the system throughout winter as it eventually favours recharge of the well with colder water. At last, analysis of the winter test data indicates the effectiveness of a three-level bleed control and on-off sequence for maintaining the groundwater temperature above the freezing point, while minimizing the volume of discharged water and allowing to reach a 160 W/m heat extraction rate.

How to cite: Beaudry, G., Pasquier, P., Marcotte, D., and Nguyen, A.: Experimental and numerical performance assessment of standing column well operating strategies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20952, https://doi.org/10.5194/egusphere-egu2020-20952, 2020.

Energy geostructures are a very cost-effective geothermal solution to produce renewable energy for the heating and cooling needs of the buildings. Their principle is to attach heat exchange pipes to the reinforcing cages of geotechnical structures (foundations, retaining walls, …). Mechanical and thermal roles are assigned to the same structures in order to reduce the economic and ecological costs.

Perturbations of the temperature field induced in the soil by this technology are propagated through conduction, diffusion and advection along the water-flow, leading to thermo-hydro-mechanical interactions between neighbouring structures. The behaviour of downstream energy geostructures is affected by the presence of upstream ones. In order to achieve a smart management of the shallow geothermal development at the city scale, it is crucial to characterize these interactions and their influence on the thermal efficiency.

For this purpose, a group of nine energy piles has been studied in Sense-City, a mini city where a specific climate can be imposed and the underground water-flow can be controlled. The piles can be thermally activated separately and are equipped with optic fibre to monitor their temperature evolution through time. Different groundwater conditions were imposed and different combinations of activated piles were studied.

To extrapolate and upscale the results, a numerical model was developed with CESAR-LCPC, a FEM software. Challenged by the experimental observations, the numerical model allowed simulating more complex boundary conditions and thermal infrastructure configurations. Furthermore, numerical modelling are able to simulate a long term experiment and to predict potential multi-year thermal shift.

Using combination of experimental and numerical experiments, observations can be made on the positive or negative consequence of energy geostructures interactions.

How to cite: Badinier, T., de Sauvage, J., Szymkiewicz, F., and Regnicoli Benitez, B.: Interactions between energy geostructures in the same aquifer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20710, https://doi.org/10.5194/egusphere-egu2020-20710, 2020.

The growth of urban populations, combined with the limited availability of above-ground space, is resulting in the increased use of underground structures as living spaces, e.g. residential basements. Such subsurface structures constitute continuous sources and sinks of heat to and from the surrounding underground environment, particularly if maintained at comfortable temperatures. In heavily populated cities and city-centres, underground temperature increases due anthropogenic heat fluxes are well-established, known as the urban underground heat island effect. Due to limited availability of long-term underground temperature data, models looking at subsurface temperature changes caused by man-made structures are difficult to calibrate. However, accurately accounting for the underground thermal climate is essential in ensuring efficient heating and cooling of underground structures as well as correctly estimating the geothermal potential in areas affected by the heat fluxes. The work to be presented explores the impact of temperature-maintained subsurface structures on the thermal climate of the shallow subsurface by developing a 3D finite element model of the Cardiff (UK) city-centre, using COMSOL Multiphysics. The model takes into account conductive and convective heat transfer between the ground and basements as well as geological features and existing hydraulic head measurements. Calibration of the model is performed using time-series temperature data, collected over several years by monitoring boreholes distributed throughout the modelled domain, provided by the British Geological Survey. This constitutes an important step towards accurately characterising the effects of underground urban heat islands and better understanding the human impact on the below ground thermal climate.

How to cite: Kreitmair, M., Bidarmaghz, A., Terrington, R., Farr, G., and Choudhary, R.: A calibrated 3D thermal model of urban heat fluxes into the shallow subsurface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22207, https://doi.org/10.5194/egusphere-egu2020-22207, 2020.

The main goal of the EU funded GEO4CIVHIC project is the development of more efficient and low-cost geothermal systems for conditioning retrofitting civil and historical buildings. In this framework, the identification of the most appropriate grout for different heat exchangers is a key factor for improving the overall efficiency of shallow geothermal systems. Therefore, a dedicated investigation was focused on the selection and optimization of the thermo-physical properties of grouting products to be used for:

• the sealing of the coaxial geothermal probes’ head characterized by different installation depths
• the sealing of the coaxial geothermal heat exchangers by filling the annular gap between the outer casing and the geological formations exposed to the wellbore

In both cases, the thermo-physical behavior of conventional and thermal enhanced grouts has been determined in laboratory for the purpose of manufacturing satisfactory cement based grouts with a real in-situ application. On the one hand, it is important to identify the grout mixtures having a suitable in situ workability, that is those satisfying specific conditions in terms of injection pressure, grout flowability, open working time and costs. On the other, it is essential to determine those providing optimal heat transfer between the probe and the surrounding ground.

Several lab experiments were performed on commercially available and enhanced selected mixtures to define (i) the workability and the flowability of the grouts; (ii) fundamental properties like mechanical strength, thermal conductivity and permeability of the hardened materials; (iii) leakage and calorimetric behavior, useful to identify sealing properties and grout setting times; (iv) viscosity and (v) density of the cement based mixture able to give information about the grout rate of descent and thus its pumpability under pressure.

Lastly, according to the lab results, few grout mixtures were selected as the best choice to be applied in situ for sealing the head of the geothermal probes’ and the annular space between the outer casing and the geological formations exposed to the wellbore. Therefore, this work attempts to address a knowledge gap of the thermo-physical properties, behavior and characterization of grouts for borehole heat exchangers (BHE), that are little studied and known.

How to cite: Garbin, E., Mascarin, L., Di Sipio, E., Artioli, G., Urchueguía, J., Mendrinos, D., Bertermann, D., Vercruysse, J., Pasquali, R., Bernardi, A., and Galgaro, A.: Assessing grouting mix thermo-physical properties for shallow geothermal systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21015, https://doi.org/10.5194/egusphere-egu2020-21015, 2020.

The thermal conductivity of the subsurface is a fundamental parameter for the design of borehole heat exchangers in shallow geothermal energy systems. An average thermal conductivity value is usually assumed. Under real conditions, however, the thermal conductivity at depth can vary considerably depending on the local petrophysical and mineralogical properties of the subsurface (e.g. porosity). Hence, the aim of this study was to compare these properties of the subsurface with the thermal conductivities measured in the laboratory and in the field and to highlight possible correlations. For this purpose, a test field was established in the northern Black Forest (Germany) by obtaining an undisturbed drilling core of about 100 m length from sandstone of the Middle to Upper Buntsandstein formation and then installing a borehole heat exchanger (BHE). Various rock parameters were determined in the laboratory on 160 selected samples of the drilling core. Among other parameters, thermal conductivities under saturated and unsaturated conditions were measured and compared with values determined by depth-resolved classical and enhanced thermal response tests in the borehole heat exchanger (TRT). Furthermore, the porosity, permeability, grain density and pore diameter as well as mineralogical composition of the sandstone were intensively studied in the laboratory. The results do not show clear correlations between thermal conductivity, permeability and density. In contrast to those reported in literature, our results indicate a moderate correlation between porosity and thermal conductivity and a more pronounced dependence on grain size.

With regard to the depth profile of the thermal conductivity, the results between laboratory and field measurements were mainly consistent. The highest thermal conductivities (4.3 W/mK in the laboratory and 4.5 W/mK in the field) confirm the suitability of the Upper and Middle Buntsandstein formation for shallow geothermal installations. Most of these rocks represent typical fluvial deposits, so that the results obtained can be easily transferred to other regions with similar sandstone deposits.

How to cite: Schindler, L., Wilke, S., Schüppler, S., Fliegauf, C., Karrer, H., Zorn, R., Steger, H., and Blum, P.: Determination of thermal conductivities in the laboratory and the field: A comparison, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21275, https://doi.org/10.5194/egusphere-egu2020-21275, 2020.

Reaching Net Zero CO₂ emissions by 2050 will require rapid and wide-scale deployment of renewable heating technologies in rural and urban areas, including open and closed loop type production wells and borehole heat exchangers, supplying individual, shared, and centralised heat pumps as part of wider district heating and cooling grids.  Ground and groundwater conditions are naturally variable and are a key factor in system viability, capital cost and long-term performance.  Engineering approaches for heating and cooling of buildings should be optimised for the local thermo-geological conditions to avoid system interference and thermal degradation.  Sustainable use of shallow geothermal systems can be achieved by adopting an environmental stewardship approach, integrating geological information within energy master plans, taking full advantage of subsurface data visualisation technology and integrated planning and modelling tools.

We present a method for creating a digital shallow geothermal opportunities map - mostly aimed at moderate- to expert-skill level geoenvironmetal and energy consultants, planners and civil engineers.  The output is a digital 1:50 000 scale equivalent thematic map, that provides a synthesis of available technical information by combining data such as 3D superficial geological model data - delimiting aquifer and non-aquifer boundaries, groundwater levels and temperatures, aquifer thickness, flow direction, possibly with inset tables summarising groundwater chemistry and key physical properties of the main geological units such typical thermal conductivity.  Built infrastructure that could constrain drilling locations, as well as potential water discharge points and open water heat source and storage opportunities, such as sewers, rivers, canals, docks, and lakes, might also be included in the map.  Local development plans and heat demand mapping data could then be integrated with the opportunities map to identify and prioritise districts that would benefit from more detailed viability studies for conversion of fossil fuel heating systems to low carbon heating and cooling technologies.

This project has received funding from the European Union’s H2020 research and innovation programme under the GeoERA MUSE project – Managing Urban Shallow Geothermal Energy.

How to cite: Boon, D., Farr, G., Williams, L., Thorpe, S., Patton, A., Kendall, R., Holden, A., Scheidegger, J., Self, S., Abesser, C., and Harcombe, G.: Concept for shallow geothermal opportunity mapping, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19146, https://doi.org/10.5194/egusphere-egu2020-19146, 2020.

The State of Geneva in Switzerland is determined to increase the share of renewable energy in its heating mix to reduce its dependence from fossil fuels and their greenhouse gas emissions. Geothermal energy from shallow and medium depths is identified as one of the new renewable energy sources to meet the high heat demand in urban areas of Geneva in combination with the district heating network. The program GEothermie 2020, led by the local utility Services industriels de Genève (SIG) and the State of Geneva, aims to understand the characteristics of the State’s subsurface to allow for sustainable use of geothermal energy, while considering the technology's environmental impacts.

In this study, the environmental impacts of different geothermal heating systems for groundwater extraction in the State of Geneva were quantified using Life-Cycle Assessment (LCA). A systematic literature review revealed that most studies of geothermal LCA until now focused either on shallow geothermal applications with heat pumps or on high-enthalpy systems for electricity production. There was a lack of LCA studies for geothermal systems involving groundwater extraction from shallow and medium depth, even if the number of these systems is growing internationally.

In the first phase of our LCA study, we built six scenarios, integrating the geothermal subsurface characteristics and the district heating designs at the surface. We built a model to simulate material and energy flows and create life-cycle inventories. Critical parameters such as temperature, flowrate, well depths, and the seasonal heating demand of residential buildings were used as the input parameters. For each scenario, we defined upper and lower limits for geothermal production and material intensity, and a reference case representative of an existing or ongoing project in Geneva.

In the second phase, we quantified the ranges of environmental impacts of the scenarios using the Ecoinvent 3.6 database and ReCiPe 2016 Midpoint characterization factors.  We performed hotspot analysis to understand the contribution of life-cycle steps to selected environment impacts. Subsequently, we introduced other heat sources such as electric heating, waste incineration with district heating, and gas boilers into the reference cases, and analyzed their impacts. We compared these impacts with those of other heat systems such as oil boilers, ground source heat pumps, waste incineration, and centralized gas boilers.

We found that all of our scenarios of shallow-to-medium geothermal heating systems were less detrimental to the environment than oil boilers and centralized gas boilers in terms of global warming, air pollution, fossil resource scarcity, and acidification impacts. The ground source heat pumps were less detrimental than our geothermal scenarios in most cases, except for acidification. The hotspot analysis identified the operation phase as the activity that contributed the most to the environmental impacts in most cases, followed by the activities for the subsurface development or heating system construction. The latter became increasingly dominant when the heat production output was higher. Lastly, we found that introducing centralized gas boilers and waste heat into the district heating system increased these impacts, whereas the opposite was true when the low-carbon Swiss electric heating was introduced instead.

How to cite: Pratiwi, A. S., Jaxa-Rozen, M., and Trutnevyte, E.: How will geothermal energy transform the environmental performance of the heating mix of the State of Geneva from a life-cycle perspective?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10980, https://doi.org/10.5194/egusphere-egu2020-10980, 2020.

The design by optimization of hybrid ground-coupled heat pump (Hy-GCHP) systems is a complex process that involves dozens of parameters, some of which cannot be known with absolute certainty. Therefore, designers face the possibility of under or oversizing Hy-GCHP systems as a result of those uncertainties. Of course, both situations are undesirable, either raising upfront costs or operating costs. The most common way designers try to evaluate their impacts and prepare the designs against unforeseen conditions is to use sensitivity analyses, an operation that can only be done after the sizing.

Traditional stochastic methods, like Markov chain Monte Carlo, can handle uncertainties during the sizing, but come at a high computational price paid for in millions of simulations. Considering that individual simulation of Hy-GCHP system operation during 10 or 20 years can range between seconds and minutes, millions of simulations are therefore not a realistic approach for design under uncertainty. Alternative stochastic design methodologies are exploited in other fields with great success that do not require nearly as many simulations. This is the case for the conditional-value-at-risk (CVaR) in the financial sector and for the net present value-at-risk (NPVaR) in civil engineering. Both financial indicators are used as objective functions in their respective fields to consider uncertainties. To do that, they involve distributions of uncertain parameters but only focus on the tail of distributions. This results in quicker optimizations but also in more conservative designs. This way, they remain profitable even when faced with extremely unfavorable conditions.

In this work, we adapt the NPVaR to make the sizing of Hy-GCHP systems under uncertainties viable. The mixed-integer non-linear optimization algorithm used jointly with the NPVaR, the Hy-GCHP simulation algorithm and the g-function assessment methods used are presented broadly, all of which are validated in this work or in referenced publications. The way in which the NPVaR is implemented is discussed, more specifically how computation time can be further reduced using a clever implementation without sacrificing its conservative property. The implications of using the NPVaR over a deterministic algorithm are investigated during a case study that revolves around the design of an Hy-GCHP system in the heating-dominated environment of Montreal (Canada). Our results show that over 1000 experiments, a design sized using the NPVaR has an average return on investment of 126,829 $ with a standard deviation of 18,499 $ while a design sized with a deterministic objective function yields 137,548 $ on average with a standard deviation of 33,150 $. Furthermore, the worst returns in both cases are respectively 35,229 $ and -32,151 $. This shows that, although slightly less profitable on average, the NPVaR is a better objective function when the concern is about avoiding losses rather than making a huge profit.

In that regard, since HVAC is usually considered a commodity rather than an investment, we believe that a more financially stable and predictable objective function is a welcome addition in the toolbox of engineers and professionals alike that deal with the design of expensive systems such as Hy-GCHP.

How to cite: Dusseault, B. and Pasquier, P.: A Net Present Value-at-Risk Objective Function for Uncertainty Mitigation in the Design of Hybrid Ground-Coupled Heat Pump Systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11511, https://doi.org/10.5194/egusphere-egu2020-11511, 2020.

We present a novel climate adaption technology – the Climate Road - that combines collective, ground source heat pump (GSHP) based heating with sustainable urban drainage of rain water (SUDS). The system utilizes the road bed simultaneously as a retarding basin for excess rain water and as the energy source for a GSHP. Surface water percolates through the permeable road paving and is retained in the gravel road bed during extreme precipitation events where the sewage system is often overloaded. Water is subsequently released once capacity is available again on the sewage network. In addition, geothermal piping is embedded in the roadbed, serving as the collector for individual GSHPs that supply connected households with heating. The primary benefit of the combined system is the saved digging costs and lost property value from establishing a separate rainwater basin and trench for the geothermal piping as the road bed is to be established under any circumstances. However, there is also a subtle yet positive effect on the performance of the GSHP, from constantly watering the geothermal piping.

We have constructed 50 m of Climate Road in Hedensted, Denmark. The road bed is 1 m deep and 8 m wide and can retain a maximum of 150 mm of precipitation, given that the catchment area is twice that of the road surface. Moreover, the road bed is hydraulically disconnected from the surrounding soil by means of bentonite mats, to prevent seepage of groundwater into the road bed. Water is discharged by drainage pipes to a nearby rainwater basin for experimental and practical purposes only. 800 m of geothermal piping is embedded in the road bed, supplying a nearby kindergarten with domestic hot water and room heating by means of a GSHP. The Climate Road is fully instrumented with temperature sensors in the road bed, flow meters to measure water discharge and energy metering on the GSHP. We present the performance of the Climate Road in terms of supplied heating and the coefficient of performance (COP) for the heat pump in addition to drained water volumes for the first year of operation.

How to cite: Andersen, T. R., Tordrup, K. W., and Poulsen, S. E.: Utilizing the road bed for combined ground source heating and sustainable rainwater drainage in Hedensted, Denmark , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7895, https://doi.org/10.5194/egusphere-egu2020-7895, 2020.

In the north of Québec (Canada), off-grid aboriginal communities rely on diesel for both space heating and electricity production. Renewable alternatives are therefore necessary to reduce the impact of burning diesel in a region with strong population growth and increasing energy needs. The main challenges are the subarctic environment (more than 8000 heating degree days), the presence of permafrost and the lack of local expertise on drilling and installation of borehole heat exchangers.

The communities of Kuujjuaq (58 °N) and Whapmagoostui-Kuujjuarapik (W-K, 55 °N) were chosen as case studies to evaluate the shallow geothermal potential and predict the long-term behaviour of ground source heat pumps (GSHP) and underground thermal energy storage systems (UTES). Local geology mainly consists of low permeable and thermally conductive crystalline bedrock (thermal conductivity of 2-4 W/mK) underlying highly permeable, frost-susceptible and poorly conductive marine sediments (thermal conductivity of 1-1.5 W/mK), generally not thicker than 30-40 m. Electrical resistivity tomography and ground penetrating radar surveys have been carried out to locally evaluate the presence of ice-rich ground that strongly depends on the local hydrogeological conditions. Average underground temperature in the first 100 m is around 1 °C in Kuujjuaq and 2 °C in W-K. Geothermal gradient and heat flux were estimated to be on average 15 °C/km and 40 mW/m², respectively.

Results of the studies carried out in these villages show that both GSHP and UTES are viable technologies to replace part of the current diesel consumption of residential buildings and drinking water facilities, with 10% to 50% primary energy saving depending on the technology. Fifty years’ life-cycle cost analyses demonstrated that the levelized cost of energy for GSHP and UTES is as low as 0.10 and 0.19 USD$/kWh, respectively, compared to the business-as-usual scenario standing at 0.21 USD$/kWh. It also turned out that the energy and drilling costs are key obstacles to a widespread deployment of these technologies in the North. A cost of 110 USD$/m has been defined as a threshold for getting interesting paybacks on the initial financial investment. UTES is also a valuable technology aiming to extend the growing season of community greenhouses in place in both Kuujjuaq and W-K. In Kuujjuaq, a coupled daily and seasonal heat storage is under study to provide renewable heat and help increase the food security in Nunavik.

Future activities aim at the set-up of a first demonstration plant to be tested in a subarctic environment with underground close to permafrost conditions. A 200-m well will be drilled in 2020 in W-K and the installation of a borehole heat exchanger will be showcased for technological transfer. Conventional thermal response tests (TRT) and a novel approach of oscillatory TRT will also be carried out to evaluate the in-situ thermal conductivity and heat capacity.

How to cite: Giordano, N., Gunawan, E., Comeau, F.-A., Miranda, M., Langevin, H., Covelli, M., Piché, P., Chicco, J., Gibout, S., Haillot, D., Casasso, A., Mandrone, G., Comina, C., Fortier, R., and Raymond, J.: Shallow geothermal technology as alternative to diesel heating of subarctic off-grid autochthonous communities in Northern Quebec (Canada), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-508, https://doi.org/10.5194/egusphere-egu2020-508, 2020.

Shallow Geothermal Energy, a Renewable Energy Source, finds application through Ground Source Heat Pumps (GSHPs) for space heating/cooling via tubes directed into the ground. There are two main categories of Ground Heat Exchanger (GHE) types: the horizontal and the vertical types. Ground Heat Exchangers (GHEs) of various configurations, extract or reject heat into the ground. Even though GSHP have higher performance in comparison to the Air Source Heat Pumps (ASHPs), the systems high initial costs and long payback period have made it unattractive as an investment. GSHP systems can also be utilized in the buildings foundation in the form of Thermo-Active Structure (TAS) systems or Energy Geo-Structures (EGS), with applications such as energy piles, barrette piles, diaphragm walls, shallow foundations, retaining walls, embankments, and tunnel linings. Energy piles are reinforced concrete foundations with geothermal pipes, whereby the buildings foundations are utilized to provide space heating and cooling. Apart from energy piles, another EGS system can be achieved by the incorporation of the building’s foundation bed as a GHE. Foundation piles are not required in all constructions, but a building’s foundation bed is mandatory. This configuration is still based on the principles of the energy pile.

Energy piles have yet to be applied in Cyprus and, thus, a preliminary assessment considered and investigated before application would be useful. The potential of the GSHP systems by utilizing the building’s foundation through energy piles is considered here, for a moderate climate such as Cyprus, towards a Zero Energy Building. Typical foundation piles geometry in Cyprus consists of a 10m depth, a 0.4m diameter and reinforced concrete as a grout material, which is used at the foundation bed of the building. A typical dwelling in Cyprus is selected to be numerically modelled in this study. It is a three-bedroom, two-storey house with a 190m² total floor area, matching the thermal characteristics of a Zero Energy Building (i.e., U-values of 0.4W/m²/K on all walls and ceiling and 2.25 W/m²/K on all doors and windows, respectively). A full-scale model is developed in COMSOL Multiphysics software, to examine the energy rejected or absorbed into the ground by taking the heating and cooling loads of the typical dwelling in Cyprus. The convection-diffusion equation for heat transfer is used with the three-dimensional conservation of heat transfer for an incompressible fluid on all domains except the pipes, where a simplified equation is used. Different months in winter and summer are accounted for the simulations and the fluid-in – fluid-out temperature difference is presented. Finally, an economic evaluation of the systems examined above is presented, in order to check its viability. It is concluded that utilizing the dwelling’s foundations can be a better investment than using GHEs in boreholes.

How to cite: Aresti, L., Christodoulides, P., and Florides, G. A.: Using buildings' foundation as a GHE in moderate climates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3684, https://doi.org/10.5194/egusphere-egu2020-3684, 2020.

The use of foundation structures (piles) coupled to a heat pump system, commonly referred to as geothermal energy pile (GEP) system, provides a renewable energy solution of achieving space heating and cooling in buildings; whilst also being utilised for the structural stability of the overlying structures. The system operates by exchanging the low-grade heat energy within the shallow earth surface with the building, via the circulation of heat carrier fluid enclosed in a high-density polyethylene plastic pipes. In summer, heat energy is extracted from the building and transferred into the ground to achieve space cooling. While in winter, the ground heat energy is harnessed and transferred to the building to achieve sustainable space heating. This paper investigates the thermal performance of the GEP system under the effects of factors such as initial soil pore water content and ground water flow.

The study utilises coupled thermo-hydraulic finite element modelling and analyses to achieve the aim of this study. It was observed that the initial pore water volume and groundwater flow are very significant factors that determine the amount of heat energy that can be harnessed using the system.

How to cite: Sani, A. K. and Singh, R. M.: Numerical investigation of the performance of geothermal energy piles under different soil moisture conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20003, https://doi.org/10.5194/egusphere-egu2020-20003, 2020.

Global demands for energy efficient heating and cooling systems coupled with rising commitments toward net zero emissions building infrastructure have resulted in wide deployment of shallow geothermal systems and in the continued growth in the global geothermal heat pump (GHP) market. With increasing deployment of these systems in urban areas, there is growing potential and risk for these systems to impact the subsurface thermal regime and to interact with each other or with nearby heat-sensitive subsurface infrastructures.

GHP systems have been studied in urban environments with respect to their effects on the subsurface thermal regime, and various modelling studies have investigated the sensitivity of their performance to key (hydro)geological and operational parameters. The focus of these studies has been on isolated systems, where flow conditions and background subsurface temperatures are assumed to be constant, impacted only by the modelled system itself during its operation. However, less attention has been paid to the effects on GHPs functional efficiency from perturbations in the wider hydrogeological and thermal regime, e.g. due to urbanization, multiple BHEs within tight (residential) clusters or competing subsurface uses requiring pumping of groundwater.

In this paper, we present three numerical modelling case studies, from the UK and Canada, which examine GHP systems response to perturbation of the wider hydrogeological and thermal regime. We investigate the influence of key parameters and different model realisations, e.g. relating to system design, unbalanced thermal ground loads and environmental conditions, on the modelled GHP system efficiencies and thermal interference. We highlight findings that are relevant from an economic point of view but also for regulations. Findings are discussed within the context of the contrasting design and operational pattern typical for the UK / Europe and Canada/ North America.

How to cite: Abesser, C., Schincariol, R., Raymond, J., Garcia Gil, A., Busby, J., Drysdale, R., Piatek, A., Giordano, N., Jaziri, N., and Molson, J.: Observations from shallow geothermal modelling case studies in Canada and the UK , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11711, https://doi.org/10.5194/egusphere-egu2020-11711, 2020.

Energy piles (EPs), consisting in piled foundations equipped with heat exchangers, have been extensively studied in recent years, both from the thermo-mechanical response and energy performance points of view. However, most research refers to typical rotary bored, CFA or precast driven, medium diameter piles. Little attention has been devoted to so-called energy micropiles (EMPs), representing an opportunity to provide at the same time energy and structural retrofitting to existing buildings. Existing studies show that EMPs overall may thermally perform differently to EPs, but they are comparable in terms of specific heat flux.

In this work, a 3D FE numerical model is employed to perform a comprehensive parametric study considering design factors that are peculiar to EMPs, to assess the most important parameters to maximise their energy performance. The parameter space is efficiently explored resorting to a statistically-based Taguchi approach. Then, the model is employed to compare the overall energy performance of realistic EP and EMP foundation solutions, under the same building and underground conditions. Finally, practical guidance is provided about the optimal choice of design factors to achieve the best thermal performance whenever EMPs  are to be used based on geotechnical/structural design.

Acknowledgement: The second author wishes to acknowledge support from the EU’s Horizon 2020 Research and Innovation programme under Grant Agreement No 810980 - ENeRAG.

How to cite: Salciarini, D. and Cecinato, F.: Numerical modelling of energy geo-structures for building retrofitting, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21366, https://doi.org/10.5194/egusphere-egu2020-21366, 2020.

Borehole thermal energy storages (BTES) have become a common implement for extracting and/or storing heat energy from and into the soil. Building these facilities is expensive, especially the drilling of boreholes, into which borehole heat exchangers are inserted. To cut costs, drilling methods, which can produce inaccuracies of varying degree, are utilized. This brings into question how much these inaccuracies could potentially affect the energy storage/extraction performance of a planned facility. To this end, we performed an uncertainty quantification for seasonally operated BTES facilities, where we studied the influence of geometries deviating from the planned layout and other sources of uncertainty, such as varying soil and material parameters.
In our research, we make use of a 3D simulation model for BTES facilities in a patch of soil with optional groundwater flow, designed as a system of partial differential equations (PDEs). The system is solved with a simulation toolkit, which was programmed as an extension for the finite element method solver KARDOS. The toolkit builds on previous work for the simulation tool BASIMO and was validated with benchmarks calculated with the commercial software FEFLOW, which specializes in heat transfer in porous media among other things. For the uncertainty quantification, we utilize an adaptive, anisotropic stochastic collocation method, which uses solutions of the PDE system as samples. We present the method and apply it to an illustrative as well as a practical example. Lastly, we discuss the results and assess the impact of deviating borehole paths on the performance of BTES facilities.

How to cite: Steinbach, P., Lang, J., Schulte, D. O., and Sass, I.: Uncertainty Quantification of Borehole Thermal Energy Storage Facilities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1953, https://doi.org/10.5194/egusphere-egu2020-1953, 2020.

The UK Government has a commitment to reach net-zero emissions by 2050. Because 70% of heating comes from direct burning of natural gas, this target cannot be achieved without decarbonising the gas network. One of the best routes to decarbonise heating is through use of ground thermal energy storage coupled with ground source heat pump systems. However, heat pump systems retain high investments costs, mainly due to the expense of drilling dedicated ground heat exchangers (GHE) such as deep boreholes. One route to reducing these costs is to use buried infrastructure for simultaneous structural function and ground heat exchange. In the past deep foundations, embedded retaining walls and trial tunnels have all been used as GHE.  However, there is increasing interest in extending this approach to other shallow buried infrastructure, such as waste and drinking water distribution networks, and green infrastructure such as sustainable urban drainage and swales. 

The UK Collabatorium for Research in Infrastructure and Cities (UKCRIC) is a consortium founded by thirteen universities to provide an integrated research capability with a mission to underpin the renewal, sustainment and improvement of infrastructure and cities in the UK and elsewhere. Under the auspices of UKCRIC, a pump priming project called PLEXUS has been carried out. One of the research challenges of PLEXUS has been to consider how much heating and cooling capacity can be obtained from using civil engineering infrastructure as GHE, and whether there are any risks to original structural function from the GHE operation.  The project has included trial experiments for (i) soil element thermo-mechanical and thermo-hydraulic behaviour, (ii) the operation of sustainable urban drainage under heat injection, (iii) heat transfer characteristics of a near full scale water pipe segment, (iv) effects of temperature change on the formation of fats, oils and greases in waste water treatment systems. This paper will present a summary of key findings from the project and identify challenges for implementation of this valuable thermal resource. 

How to cite: Loveridge, F., Shepley, P., Stirling, R., and Yildiz, A.: Harvesting Energy from Buried Infrastructure: current UKCRIC research, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19412, https://doi.org/10.5194/egusphere-egu2020-19412, 2020.

The study shows the result of a detailed analysis aimed at verifying possible application of the technology related to the exploitation of low temperature geothermal resources for direct uses, with particular reference to the heating and cooling of public and private buildings in Rome, in order to enhance and improve its building stock.

The analysis started with collection and consultation of geological, stratigraphic, hydrogeological and thermal data available from bibliography and previous studies of the area. This represented a fundamental and useful step to determine a potentially suitable sector, both for geological and thermic characteristics of the lithologies recognized in the area. Pietralata, north east of Rome, was selected as "pilot site" out of 15 areas identified on the basis of the collected information. Within this pilot site, a High School - Technical Institute was recognized a suitable public building for the test.

The entire school complex has been discretized into three blocks. The analysis was made preliminarily for block 1, which is the largest, by calculating the heating energy requirements based on the climatic zone and the structural parameters of the building using the CARAPACE software (CAlcolo Resistivo Annuale Prestazioni Assetti Climatizzazione Efficienti), developed by SSE Department of RSE.

Starting from these needs, the analysis was carried out by hypothesizing and sizing a field of closed loop probes capable to meet 30% of the total energy needs expected for the building. Results thus highlighted, were a conclusion drawn by 16 probes with an average depth of 95 m each.

The analysis and the determinations made on the bibliographic basis were then validated with the experimental data derived from a geognostic survey by drilling up to a depth of 100 m from the surface, and conditioned for a Geothermal Response Test to determine the experimental value of the thermal capacity W/(m*K) of the lithologies.

From the aforementioned, the possibility to optimize the thermal conductivity profile of the ground was derived, in respect to the λ values corresponding to the stratigraphy derived from the survey.

The results, thus arrived, confirm the worth of the preliminary estimates and demonstrate how a field of 12 probes with a depth of 100 m each is enough to satisfy 30% of the energy needs of the users considered.

It must be also the focal point that Pietralata area is not the optimum in terms of thermal conductivity of the ground and lithologies, wherein the value of lambda was found to be around 1.6 W/(m*K). Nevertheless, the results established the correctness of the preliminary hypothesis in the applicability of the geothermal technology for the heating and cooling of existing buildings in the city of Rome.

The study was an experimental activity carried out with Roma Capitale Municipality – Infrastructure Department.

How to cite: Bernardo, N. and Moia, F.: Geological and numerical modelling of Thermal Ground Potential for building’s heating and cooling, using low temperature shallow geothermal: The “Pietralata Pilot Site” (Roma Capitale Area, Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2912, https://doi.org/10.5194/egusphere-egu2020-2912, 2020.

The overall goal of the EU funded project GEO4CIVHIC is the development of more efficient and low cost geothermal systems for conditioning retrofitting civil and historical buildings.

The assessment of the most suitable drilling technology for a given geological context could be very useful from both the technical and the economic point of view. In fact, the installation costs are one of the main economical barrier for a wider application of shallow geothermal systems, and they are mainly covered by the drilling time and costs (drilling machine and labour costs).

Generally, the drilling technology suitable on a given site and the related most proper ground heat exchanger are mainly dictated by the local stratigraphy (kind of materials/rocks, state of consolidation) and the local hydrogeological conditions, also affecting the drilling times and costs by requiring the application or not of the casing.

The ‘drillability’ concept has been defined as the prediction of the most suitable drilling technique related to a given underground for a certain borehole heat exchanger type, by taking into account the estimated drilling and installation time. Therefore, a ‘drillability’ map has been conceived at European scale in order to support the preliminary design phase of new ground source heat pump systems and to provide a first evaluation of the drilling costs and time for a given location. The map is based on the European geological map released by the European Geological Data Infrastructure (EGDI), freely available in the web, that complies with the INSPIRE (INfrastructure for Spatial InfoRmation in Europe) Directive. It is an ESRI Shape (vector file), Scale 1:1.500.000, Projection ETRS 1989 LCC. The EGDI map is connected to a list that collect all the geological context that can be found all around Europe; the list contains 203 different geological settings. The association among ‘drillability’ techniques and geological sequence was conducted by considering the knowledge of the partners that are expert in drilling operations in several European countries.

The classical drilling methods are here distinct into percussing, rotating, and combined percussion-rotation methods. The proposed map compares traditional drilling methods usually applied to install vertical ground heat exchangers as the rotary drilling with tricone or chevron bit and the traditional down-hole hammer (with or without casing) with the new drilling techniques developed within the EU funded project Cheap-GSHPs and GEO4CIVHIC.

So far a first ‘drillability’ map has been released with the drilling time and costs; further development will report the regulatory constraints related to drilling in specific areas.

The ‘drillability’ map at European scale is connected to a ‘drillability’ app still under development that will provide a first assessment of the most suitable drilling technique in a specific geological context both to direct users such as designers, drillers, administrators. Depending on the local geology identified by the users, the app will help to estimate the required drilling time and related costs, providing a preliminary information to start decision making and authorization processes.

Goo4Civhic Project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 792355.

How to cite: Galgaro, A., Di Sipio, E., Dalla Santa, G., Ramos Escudero, A., Cuevas, J. M., Sanner, B., Righini, D., Pasquali, R., Vercruysse, J., Bertermann, D., Pockele, L., and Bernardi, A.: European drillability mapping for shallow geothermal applications , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8584, https://doi.org/10.5194/egusphere-egu2020-8584, 2020.

The utilization and development of renewable energy sources (RES) is currently a topic of great interest in energy field. In detail, the coupling of different RES and related technologies, as solar thermal and shallow geothermal, for heating/cooling purpose of residential buildings is a promising sector. The possibility to store the thermal energy produced by solar panels in the underground during the summer season, when the insolation is greater, and to use the heat accumulated during the coldest periods, is strictly related, among others, both to the thermo-physical properties of rocks and to the solar radiation locally available. As the ground is the invariant component of the whole system, a better knowledge of its thermal properties (i.e. thermal conductivity, volumetric heat capacity…) is fundamental to evaluate the amount of heat that can be stored.

This paper presents an innovative methodological approach combining information related to underground thermal energy exchanging and storage capacity with the solar radiation, taking also into account the location of the possible end-users, that is the distribution of the residential buildings in the territory. The Euganean Hills area, located in the Po River Plain (north-east Italy), is selected as demonstration test site. A qualitative map, created using Geographycal Information System (GIS) application, has been realized in order to represent the “Ground thermal suitability” of a territory to sensible heat storage, that is the possibility to store solar energy in the underground for a later use.

This thematic map is a really promising tool, suitable for local administrator and professionals, for planning the possible exploitation of solar thermal renewable resources available in the area.

How to cite: Di Sipio, E., Sassi, R., Buggiarin, S., Ceccato, S., and Galgaro, A.: Assessing underground heat exchange and solar heat storage capabilities based on ground thermo-physical properties: the Euganean hills demo site (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18915, https://doi.org/10.5194/egusphere-egu2020-18915, 2020.

The incorporation of heat exchangers into geostructures leads to changes in the temperature of the adjacent soil, which may affect its hydro-mechanical properties. In this study, mini-pressiometer tests were carried out in the vicinity of three experimental energy piles of 12 meters length and 0.52-meter diameter installed in saturated sandy soil. Tests were carried out in three locations and in two different depths (namely 3 and 4 meters in depth) before and after cyclic variations of their temperature. The pressuremeter parameters are the pressuremeter modulus EM, the limit pressure PL and the creep-pressure Pf. These parameters characterize the properties of the soils; some measurements were done close to the energy piles (1.25 meters from the center of the pile) using a mini-pressuremeter cell (380 mm in height and 28 mm in diameter). The comparison of the results before and after the four warming-cooling cycles (8° to 19° C) showed a thin thickening of the material at 3 meters depth. These results are coherent with in-lab measurements and with the results of the pile loading tests carried out later on the same site.

How to cite: Rosin-Paumier, S., Eslami, H., and Masrouri, F.: In situ investigation of the impact of cyclic thermal variations impact on the mechanical properties of sandy soil., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5622, https://doi.org/10.5194/egusphere-egu2020-5622, 2020.

We present first results from a newly developed monitoring station for a closed loop geothermal heat pump test installation at our campus, consisting of helix coils and plate heat exchangers, as well as an ice-store system. There are more than 40 temperature sensors and several soil moisture content sensors distributed around the system, allowing a detailed monitoring under different operating conditions.

In the view of the modern development of renewable energies along with the newly concepts known as Internet of Things and Industry 4.0 (high-tech strategy from the German government), we created a user-friendly web application, which will connect the things (sensors) with the open network (www). Besides other advantages, this allows a continuous remote monitoring of the data from the numerous sensors at an arbitrary sampling rate.

Based on the recorded data, we will also present first results from numerical simulations, taking into account all relevant heat transport processes.

The aim is to improve the understanding of these processes and their influence on the thermal behavior of shallow geothermal systems in the unsaturated zone. This will in turn facilitate the prediction of the performance of these systems and therefore yield an improvement in their dimensioning when designing a specific shallow geothermal installation.

How to cite: Duran, L., Mottaghy, D., Herrmann, U., and Groß, R.: Online ground temperature and soil moisture monitoring of a shallow geothermal system with non-conventional components, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19052, https://doi.org/10.5194/egusphere-egu2020-19052, 2020.

Low-temperature geothermal systems have shown great potential to reduce greenhouse gas emissions. One emerging solution, named standing column well, is particularly promising and is characterized by low installation costs and higher thermal efficiency compared to widespread closed-loop wells. In a standing column well, groundwater is continuously recirculated in an uncased well. As the well and the mechanical devices are prone to clogging and scaling, the occurrence of new operational conditions can have an impact on long-term performance and generate significant maintenance costs. Although current literature identifies the main causes of clogging, the impact of the operation strategy of a standing column well operation on clogging development has not yet been extensively studied.

The chemical signature of groundwater and the operation parameters of a real-size experimental standing column well were monitored during a two-year period using a geothermal mobile laboratory. This laboratory contains heat pumps, heat exchangers, pumps, monitoring devices and a water treatment unit enabling treatment of a fraction of the total pumping flow. This work highlights how the operation of a standing column well impacts the clogging rate by establishing a direct link with the observed calcium concentrations. Two specific operation schemes were found to be critical for the development of clogging.

First, the “on-off” sequences of the pump allowed for water stagnation in the mechanical devices and promoted a temperature rise since the geothermal laboratory is maintained at 20^oC, thus creating ideal conditions for precipitation. In addition, the calcium concentration in groundwater increased with shutdown duration and with a kinetic similar to the one observed in an independent batch test. This batch test conducted with demineralized water and samples of the local rock was carried out in close atmosphere at 10°C to measure the dissolution kinetics. Both the two-year monitoring and batch test confirm that groundwater slowly dissolves the carbonates in the standing column well that precipitate in the mechanical devices during the off sequences.

The second critical operation scheme was observed during cooling mode. As groundwater temperature gradually increases with the operation of the system, the calcium stability index increased, leading to precipitation in some mechanical devices. After two years of operation, some mineral deposits were recovered on the probes of two faulty flow sensors. The deposits were analyzed with a scanning electron microscope, which indicated high concentrations of calcium, oxygen, and carbon, all compatible with calcite precipitates. Further works will focus on the development of new operation strategies to hinder clogging and scaling of the mechanical equipment connected to a standing column well.

How to cite: Cerclet, L., Courcelles, B., and Pasquier, P.: The impact of Standing Column Well operation on Carbonate Scaling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19601, https://doi.org/10.5194/egusphere-egu2020-19601, 2020.

High temperature - aquifer thermal energy storage (HT-ATES) is gaining momentum as sustainable option for the (seasonal) storage of heat, where geothermal heat may be one of the sources. To maximize the impact of geothermal systems, the heat produced in the summertime, which is not directly needed, can be temporarily stored in a groundwater aquifer for use in the winter. However, HT-ATES does not come without technical complications. One potential complication is carbonate scaling of the technical installation and/or the aquifer in the vicinity of the injection well. Precipitation of carbonates may occur when carbonate-saturated groundwater becomes heated, upon which the groundwater becomes increasingly supersaturated for carbonates. As part of the GEOTHERMICA project HEATSTORE, both a sampling method and an experimental set-up were developed. This experimental procedure enables the sampling and testing of groundwater from HT-ATES sites or else to determine the likelihood of calcium carbonate scaling in a HT-ATES system and, if so, identify the nature and extent.

For the HEATSTORE project, Groundwater was sampled at a HT-ATES test well drilled in Middenmeer, the Netherlands down to 370 meter depth. The sampling was done with a double walled vessel, which made it possible to maintain pressure on the water sample to prevent degassing of natural occurring dissolved gases like methane and carbon dioxide during sampling and storage, as well as preventing atmospheric contamination of the groundwater. The experiments were performed in two stainless steel autoclaves which were kept at 85 degrees Celsius for up to 5 days. Three types of experiments were performed to mimic the different components of the HT-ATES system: addition of a plate of stainless steel, addition of calcium carbonate crystals and addition of aquifer sediment. The first experiment did not show any carbonate precipitation, although geochemical modelling suggests oversaturation of calcite for the applied conditions. Calcite precipitation and recrystallization were observed only in the experiments with calcite crystal seeds added. The experiment with the aquifer sediment added to the reaction vessel, containing shell fractions and intact shells (e.g. Foraminifera), did not show calcite precipitation, neither showed the chemical analysis of the water at the end of the experiment a reduction in calcium concentration. Isotope analysis suggests that carbon dioxide was released by thermally enhanced degradation of sedimentary organic matter, which would have lowered the supersaturation of calcite.

These results suggest that aquifers, in which calcite is already present and limited (or no reactive) organic matter is available, could face a risk of scaling and subsequent injectivity/productivity issues when HT-ATES is applied in these aquifers. A proper water treatment, such as the addition of carbon dioxide or hydrochloric acid to the groundwater abstracted prior to heating, could be required to prevent groundwater from getting supersaturated with carbonate minerals.

How to cite: Dijkstra, H. E., de Boer, C. V., Koenen, M., and Griffioen, J.: Experimental risk assessment of carbonate scaling in the operation of high temperature – aquifer thermal energy storage (HT-ATES) systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9184, https://doi.org/10.5194/egusphere-egu2020-9184, 2020.

Following the Directive 2010/31/EU on energy performance of buildings, EU state members have developed national plans for increasing the number of nearly zero energy buildings through measures that facilitate the implementation of renewable energy technologies. Due to this policies changes and also due to their incontestable advantages, energy geostructures are showing an increasing trend in number of implementations all across Europe. However, it is important that besides “good statistics”, the quality and efficiency of what is implemented to be ensured so that a real change is generated in terms of renewable energy exploitation and CO2 emissions reduction. The paper refers to challenges that are encountered in the process of implementation of energy geostructures especially on emerging markets for this technology, such as Eastern Europe, with emphasis on several case studies and evidence from Romania.

How to cite: Prodan, I., Ban, H., and Bujor, O.: Challenges in implementing energy geo-structures in developing markets: Evidence from Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20414, https://doi.org/10.5194/egusphere-egu2020-20414, 2020.