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The need to use groundwater resources for agricultural and livestock farms is a constantly growing issue, as these resources condition the socio-economic development of many areas with limited climatic regimes and surface water resources. Decisions on the location and characteristics of groundwater extraction works are based on hydrogeological studies, in which geophysical techniques are a very useful tool. In our study, the Time-Domain Electromagnetics technique (TDEM) was used, which significantly improves the precision and safety when planning to drill for water extraction in Mesozoic formations thanks to the significant resistivity contrast among its different hydrogeological units. The performance of a research campaign using TDEM allows for obtaining 2D geoelectrical profiles which define the hydrogeological structure of the study area and the materials of which it is composed, enabling the selection of a site where drilling can be carried out with the best prospects of success. This article shows the usefulness of this study methodology, applied to Mesozoic formations in a specific area located in the municipality of Liceras (Soria, Spain).

The use of low-impact energy sources is gradually growing with the aim of reducing greenhouse gases emission and air pollution. The alternatives offered by geothermal systems are one of the key solutions for a future renewable development, enabling the electrification of heating systems and the use of biofuels. This research addresses an overview of geothermal heating systems using ground source heat pumps in different European countries. Besides the traditional electrical heat pumps, gas engine heat pumps aided by natural gas or biogas are analysed in three areas. From a previous research, the technical parameters defining the geothermal system are used here to evaluate the most appropriate system in each scenario. The evaluation of different influential factors (operational costs, initial investment, environmental impact, and availability) allows defining the most recommendable systems for each area. Results of this multi-parametric study show that gas engine heat pumps aided by biogas could mean an excellent solution in all countries, also contributing to the management of waste and polluting substances. If biogas systems were not available, the electrical heat pump would be the first option for areas 1 and 3 (Italy and Sweden) but not for area 2 (United Kingdom), where natural gas is preferred.

The pig farm sector has been developing rapidly over recent decades, leading to an increase in the production of slurry and associated environmental impacts. Breeding farms require the maintenance of adequate indoor thermal environments, resulting in high energy demands that are frequently met by fossil fuels and electricity. Farm heating systems and the storage of slurry constitute considerable sources of polluting gases. There is thus a need to highlight the advantages that new green heating solutions can offer to reduce the global environmental impact of pig farming. This research presents an overview of alternative pig farm slurry technology, using geothermal heat pumps, which reduces the harmful effects of slurry and improves the energy behavior of farms. The results reflect the environmental benefits of this solution in terms of reducing carbon and hydric footprints. Reducing the temperature of slurry with the geothermal heat pump of the system also reduces the annual amount of greenhouse gases and ammonia emissions, and, via the heat pump, slurry heat is used for installation heating. Annual emissions of CO2e could be reduced by more than half, and ammonia emissions could also experience a significant reduction if the slurry technology is installed. Additional advantages confirm the positive impact that the expansion of this renewable technology could have on the global pig farm sector.

[EN] Within the installation of a shallow geothermal system, the lack of information on the subsoil frequently leads to errors in the design of the geothermal wellfield. This research presents the application of geophysics, combining 2D and 3D electrical resistivity tomography surveys and the geological information of a certain area for defining the structural distribution of the underground. Processed electrical resistivity data allow elucidating possible geological units and the thermal behavior of the in-depth materials. Two different assumptions (with different locations of the wells) are designed by using the specific geothermal software GES-CAL. Results show, that Case 1 (based on the geophysical results, so avoiding complex areas) allows the reduction of the global drilling length, and hence, the general initial investment of the system (around 20% lower). Meanwhile, Case 2 (without considering the geophysics) is less economically advantageous and could also present technical difficulties during the drilling process, as well as the possible alteration to the normal system operation. The study highlights the benefits of geophysics as an effective approach to characterize the underground and to help to understand its thermal behavior, which is, in turn, crucial for a proper geothermal design. SI

Low enthalpy geothermal resources play an essential role in climate change mitigation. When ensuring the correct future operation of ground-source heat pump systems, an accurate design is mandatory. In this sense, different methodologies can be implemented. Although using sophisticated software constitutes the most optimal solution, its implementation is sometimes inviable in certain projects (the increase of the initial investment required is not justified in small plants). This work is focused on evaluating and comparing procedures used in the design of shallow geothermal systems. Thus, the research includes a simple method based on manual calculations, the Climasoft free application, Earth Energy Designer (EED) software, and the new geothermal tool GES-CAL developed by researchers from the TIDOP Research Group (University of Salamanca). The objective is to evaluate this new software and compare the results of all the detailed methodologies. This comparison derives from applying these tools in the calculation of the same case study (a single-family house placed in Ávila, Spain). Results show that the easiest methods involve oversized well-field schemas that also mean higher initial investments. Regarding GES-CAL, it is considered an accurate and valid alternative for the design of all heat exchanger configurations, especially for those installations placed in the region of Ávila. However, EED is recommended to calculate high-power geothermal systems that require an exhaustive analysis of the ground and the heat carrier fluid behaviour.

Very low enthalpy geothermal systems have been traditionally associated to the use of electricity as primary energy heat pumps supply. Gas engine heat pumps (GEHP) have been recently introduced in the current market. In this research, the electric heat pumps (EHP) as well as the GEHPs (considering natural gas and biogas as combustibles) have been analysed. The calculation of the ground source heat pump (GSHP) system has been made for a building placed in three different areas. Results reveal the influence of the heat pump configuration on the whole geothermal design. This research finally considers the European policies whose aim is a sustainable low-carbon economy by 2020. According to the existing Energy Efficiency Directive, energy requirements are defined for new and existing residential and non-residential buildings in the Member States. Based on these standards, the research compares the geothermal heat pump scenarios and a traditional one to determine if they would meet the regulation. Final results show that the Directive is a highly-demanding regulation that can only be respected by using EHP in one of the areas. The rest of geothermal heat pumps scenarios are much closer to meeting the energy standards than the traditional fossil heating sources.

[EN] In designing low enthalpy geothermal systems, the ideal location and length of the boreholes in the well-field is the key to improve the performance and reduce the costs of the installation. The correct assessment of the heat conductivity of the ground (λ) plays also a very important role in estimating the amount of energy that we are going to be able to obtain from the subsoil and the ideal pace of the process. In low enthalpy geothermal installations based on granite type environments is especially important to improve the information we have from the subsoil at a small scale. This is due to the great horizontal variation we can find on this kind of terrain. Electrical conductivity (C = 1/ρ, ρ = resistivity in ohm meters) can be related to thermal conductivity (λ) of many rock types (Directive (EU), 2019) (see Robertson, 1988). We show that a 3D electrical resistivity survey can be used as a proxy for λ in terrain with weathered and solid granitic rock. Knowledge of λ is essential for the design of efficient ground source heat pump systems that use vertical wells for closed-loop systems. Shorter well lengths are accomplished if wells are in solid granite with high λ. Furthermore the electrical resistivity survey identifies low density, clayey subsurface materials that may require specialized drilling methods. Project cost savings can result from shorter borehole lengths, number of holes, and correct drilling methods.

There is no widespread use of the very low-enthalpy geothermal energy in a large number of countries. The reason is often the high initial investment required by these systems. In this regard, geothermal heat pump is largely responsible for this important outlay. This research focuses on substituting this device by the integration of a set of renewable alternatives. Thus the ground contribution is complemented with a thermal and a power renewable module that provide the required remaining energy. The model was evaluated on a real study case by technical calculations of the common ground-source heat pump (GSHP) system and the one considered here. An economic feasibility study showed notable savings in the initial investment as well as in the annual costs on the part of the suggested system. In addition, the CO2 emissions were reduced by half in comparison to the traditional geothermal plant. The model represents a general improvement in relation to the conventional GSHP system: the heat pump is removed, and the total drilling length is reduced. Despite these improvements, it still depends on the external electricity supply.

Geothermal energy is becoming essential to deal with the catastrophic effect of climate change. Although the totality of the Earth’s crust allows the exploitation of shallow geothermal resources, it is important to identify those areas with higher thermal possibilities. In this sense, geophysical prospecting plays a vital role in the recognition and estimation of potential geothermal resources. This research evaluates the geothermal conditions of a certain area located in the center of Spain. The evaluation is mainly based on geological and geophysical studies and, in particular, the Time Domain Electromagnetic Method and the Electrical Resistivity Tomography. Once we analyzed the geology and the historical thermal evidence near the study area, our geophysical results were used to define the geothermal possibilities from a double perspective. In relation to anomalous heat gradient, the identification of a fault and the contact with impermeable granitic materials at the depth of 180 m denotes a potential location for the extraction of groundwater. Regarding the common ground-source heat-pump uses, the analysis has allowed the determination of the most appropriate area for the location of the geothermal well field. Finally, the importance of accurately defining the position of the drillings was confirmed by using software GES-CAL.

Ground source heat pump (GSHP) systems are becoming popular in space heating and cooling applications. Despite this fact, in most countries, the role of this energy is not as important as it should be nowadays according to its capabilities for energy generation without CO2 emissions, mainly due to the lack of technical knowledge about GSHP performance. The analysis of the physical processes that take part in the geothermal exchanges is necessary to allow the optimal exploitation of the geothermal resources. For all the above, an experimental geothermal device was built in the laboratory to control the phenomena that take place in a borehole heat exchanger (BHE). A 1-m high single-U heat exchanger was inserted in the center of a polyethylene container which also included granular material (surrounding ground) and the grouting material. Temperature sensors were situated in different positions of the experimental setup. Physical processes are evaluated to finally validate the model. Numerous applications can be developed from the experimental BHE. In this research, the determination of the thermal conductivity of the material used as medium was carried out. Results of this parameter were also compared with the ones obtained from the use of the KD2 Pro device.

District heating systems are gaining an increasing importance in the space heating and the production of Domestic Hot Water. Focusing on the geothermal energy as the energy supply of these systems, an optimal design could involve an increased number of geothermal district heating installations. This research presents two different designs of a groundwater heat pump system from the application of initial real data. Both designs differ in the heat pumps: 1 installation in scenario 1 and 3 installations in scenario 2. The procedure includes the calculation of all the required geothermal parameters in both assumptions. Optimization of the drilling schema is carried out using COMSOL Multiphysics software. Technical and economic results reveal that scenario 1 is the most suitable option for the study case here presented. Global initial investment is lower in scenario 1 the same as the annual operational costs since the coefficient of performance of the heat pumps in this scenario 1 is slightly higher than the one of each module of scenario 2.

[EN]The geothermal resources in Spain have been a source of deep research in recent years and are, in general, well-defined. However, there are some areas where the records from the National Institute for Geology and Mining show thermal activity from different sources despite no geothermal resources being registered there. This is the case of the area in the south of the Duero basin where this research was carried out. Seizing the opportunity of a deep borehole being drilled in the location, some geophysical resources were used to gather information about the geothermal properties of the area. The employed geophysical methods were time-domain electromagnetics (TDEM) and borehole logging; the first provided information about the depth of the bedrock and the general geological structure, whereas the second one gave more detail on the geological composition of the different layers and a temperature record across the whole sounding. The results allowed us to establish the geothermal gradient of the area and to discern the depth of the bedrock. Using the first 200 m of the borehole logging, the thermal conductivity of the ground for shallow geothermal systems was estimated.

Exploring and exploiting a geothermal resource has become one of the most prolific tasks for contributing to the global sustainable development. Despite this fact, several countries, such as Spain, are still far from achieving a generalized use of these renewable systems. The reason for this underuse often derives from the lack of information and characterization of the geothermal energy source. Considering this, the present research aims to provide relevant data about the geothermal potential of the Spanish region of Avila. The geological context of this province lays the foundations for considering the region as a promising site for different geothermal uses. In order to estimate the geothermal energy potential of the region, the existing geological information has been complemented with thermal surveys carried out in the study area. The experimental measuring has consisted of the register of the underground temperature in piezometers of variable depth and natural springs distributed throughout the province. The processing of these records has allowed knowing the thermal evolution of the subsoil at the different levels evaluated in the research. Results show that there are two main potential areas in the province that could be successfully used for heating purposes (maybe as part of district heating systems) and for future deeper evaluations in the sense of Hot Dry Rock (HDR) techniques. Final conclusions have also been included in an interactive and open-source tool that allows visualizing the thermal findings with the aim of planning future geothermal uses in the region.

In vertical closed-loop geothermal systems, the material used to fill the boreholes is an essential element since it facilitates the exchange of heat between holes and pipes which contain the heat transfer fluid. Therefore, the thermal conductivity of this grouting material plays a vital role in conducting heat to the installation; not only does it increase its efficiency with higher thermal conductivity values, but it also makes the reduction of the total drilling length required to cover some particular energetic needs, possible. In view of the importance of this grouting material, a series of mixtures were produced and both thermal and mechanical properties were analysed in the laboratory. The use of aluminium shavings and sulpho-aluminate cement improved the thermal conductivity of these mixtures and offered excellent mechanical properties. However, non-satisfactory results were obtained for the bentonite due to the contractile effects caused in samples of this nature.

Sustainable energy development in the farming sector is an essential strategy to respond the combined challenge of achieving a reliable and affordable solution but including mitigation and adaptation to climate change. Intensive breeding farms require maintaining an adequate indoor thermal environment that results in high energy demands, usually covered by fossil fuels and electricity. This paper addresses the application of the combined slurry technology for a particular pig farm that currently uses a diesel boiler to supply the piglet heating energy needs. The study also considers different options based on closed ground source heat pump systems. After the design of the slurry alternative and the geothermal ones, notable advantages are detected compared to the existing diesel system. Results show that the implementation of the slurry technology implies an important reduction of the operational costs, which, in turn, involves short amortization periods for this system in relation to the diesel one. Greenhouse gases emissions are also highly reduced in the slurry alternative based on the low electricity use of the heat pump. The environmental side is reinforced by the reduction of polluting substances such as methane of ammonia derived from the descent of temperature of the slurry.

A thermal conductivity map constitutes an important basis with regards to the design and performance of geothermal heat pump installations. Although the execution of a Thermal Response Test means an ideal solution as it provides the average value of the thermal conductivity over the length of the borehole drilled for the BHE, in small projects it is not possible to carry out these tests because they involve a huge increase of the total budget of the user. This study describes a systematic methodology to produce a thermal conductivity map of an area geographically placed in the center of Spain, the province of Avila. As a result, a map of thermal conductivity distribution of local rocks is proposed.

In ground source heat pump systems, the thermal properties of the ground, where the well field is planned to be located, are essential for proper geothermal design. In this regard, estimation of ground thermal conductivity has been carried out by the implementation of different techniques and laboratory tests. In this study, several methods to obtain the thermal properties of the ground are applied in order to compare them with the reference thermal response test (TRT). These methods (included in previous research works) are carried out in the same geological environment and on the same borehole, in order to make an accurate comparison. All of them provide a certain value for the thermal conductivity of the borehole. These results are compared to the one obtained from the TRT carried out in the same borehole. The conclusions of this research allow the validation of alternative solutions based on the use of a thermal conductive equipment and the application of geophysics techniques. Seismic prospecting has been proven as a highly recommendable indicator of the thermal conductivity of a borehole column, obtaining rate errors of below 1.5%.

The implementation of the very low geothermal energy is not as extended as the rest of renewable energies. The high initial investment these systems usually require makes them unaffordable for most users. In this regard, this research tries to emphasize the importance of a suitable dimensioning of the whole geothermal plant. With that aim, three different calculation methods have been presented. One of them is based on manual calculations using standard values while the two remaining assumptions consider the use of specific geothermal software. Results reveal that the most suitable method is constituted by the implementation of optimized parameters in the geothermal software. These parameters are obtained from a series of previous analysis and laboratory tests. Applying the most appropriated procedure the initial investment is considerably reduced. Additionally, the electricity consumption of the heat pump is also lower using the mentioned calculation. In this way, the present research demonstrates that and adjusted and proper calculation process can make the geothermal system more attractive for a large number of users.

Thermal characterization of soils is essential for many applications, including design of geothermal systems. Traditional devices focus on the computation of thermal conductivity, omitting the analysis of the convection effect, which is important for horizontal geothermal systems. In this paper, a procedure based on the monitoring of the surface of the soil with a thermal infrared (TIR) camera is developed for the evaluation of the global thermal imbalance on the surface and in-depth. This procedure allows for the computation of thermal conductivity and global convection heat rate, consequently constituting a complete thermal characterization of the geothermal system. The validation of the results is performed through the evaluation of the radiometric calibration of the thermal infrared camera used for the monitoring and the comparison of the thermal conductivity values obtained in-depth, with traditional methods, and for the surface of the system.

The purpose of this paper is to present a new tool developed for the calculation and design of shallow closed-loop geothermal systems. Most of the available geothermal computer programs only allow to consider vertical heat exchangers configurations (i.e. single or double-U tubes), being the horizontal and helical designs excluded. As an attempt to fill this gap, GES–CAL tool, presented here, is capable of providing the complete design of all the most common configurations used in low enthalpy geothermal systems. This software was initially developed for its implementation in the region of Avila (Spain), including the most relevant results of previous author’s researches in this area. Throughout this work, the new software is deeply described and implemented in the calculation of three different study cases. Results of GES–CAL are complementary compared with the ones obtained from the most used geothermal software, EED (Earth Energy Designer). From the analysis of these results, it was possible to conclude that GES–CAL tool constitutes an optimal solution for planning a shallow geothermal system, but especially for those installations placed in the region of Avila. In this area, the well field can be designed in more precise way which results in lower drilling lengths and, hence, lower initial investments. The conclusions of this work indicate that GES–CAL offers remarkable advantages such as the automatic calculation of the space energy demand, the inclusion of all the heat exchanger configurations and an economic and environmental evaluation of the final geothermal solution.

This research work aims at a multinational study in Europe of the emissions and energy costs generated by the operation of low enthalpy geothermal systems, with heat pumps fed by different energy sources. From an economic point of view, natural gas and biogas prices are, usually, lower than electricity ones. So it may be advantageous to use these energy sources to feed the heat pumps instead of electricity. From the environmental point of view, it is intended to highlight the fact that under certain conditions of electricity production (electricity mix), more CO2 emissions are produced by electricity consumption than using other a priori less “clean” energy sources such as natural gas. To establish the countries where each of the different heat pumps may be more cost-efficient and environmentally friendly, data from multi-source geospatial databases have been collected and analyzed. The results show that in the majority of cases, the electric heat pump is the most recommendable solution. However, there are some geographic locations (such as Poland and Estonia), where the gas engine heat pump may be a better alternative.

As a renewable energy source, geothermal energy can provide base-load power supply both for electricity and direct uses, such as space heating. Regarding this last use, in the present study, district heating systems aided by geothermal energy, the so-called geothermal district heating systems, are studied. Thus, three different options of a geothermal district heating system are evaluated and compared in terms of environmental and economic aspects with a traditional fossil installation. Calculations were carried out from a particular study case, a set of buildings located Province of Leon in the north of Spain. From real data of each of the assumptions considered, an exhaustive comparison among the different scenarios studied, was thoroughly made. Results revealed the most suitable option from an economic point of view but always considering the environmental impacts of each one. In this regard, the assumption of a district heating system totally supplied by geothermal energy clearly stands out from the rest of options. Thus, the manuscript main objective is to emphasise the advantages of these systems as they constitute the ideal solution from both the economic and environmental parameters analysed.

The thermal conductivity of soils and rocks constitutes an important property for the design of geothermal energy foundations and borehole heat exchange systems. Therefore, it is interesting to find new alternatives to define this parameter involved in the calculation of very low enthalpy geothermal installations. This work presents the development of an experimental set-up for measurements of thermal conductivity of soils and rocks. The device was designed based on the principle of the Guarded Hot Plate method using as heat source a laboratory heater. The thermal conductivity of thirteen rocky and soil samples was experimentally measured. Results are finally compared with the most common thermal conductivity values for each material. In summary, the aim of the present research is suggesting a procedure to determine the thermal conductivity parameter by a simple and economic way. Thus, increases of the final price of these systems that techniques such as the “Thermal Response Test” (TRT) involvs, could be avoided. Calculations with software “Earth Energy Designer” (EED) highlighted the importance of knowing the thermal conductivity of the surrounding ground of these geothermal systems.

In vertical closed-loop systems, it is common to use single or double U-tube heat exchangers separated by longitudinal spacers. In addition, the helical-shaped pipe is another configuration that requires lower drilling lengths but it is less used. The aim of the present research is to study the influence of these components on the total efficiency of a borehole heat exchanger (BHE). Thus, the differences between using single/double U-tubes (with or without spacers) and helical pipes are analysed in terms of efficiency. Through different laboratory tests, a small vertical closed-loop system was simulated in order to analyse all these possible configurations. The grouting materials and the temperatures of the ground were modified at the same time in these tests. Regarding the heat exchange process between the ground and the heat carrier fluid, it must be highlighted that the best results were obtained for the helical-shaped pipe configuration. Some of the improvements offered by this heat exchanger typology with respect to the vertical configuration is that a lower drilling depth is required even it requires a larger diameter. This leads to significant economic savings in the performing drilling process. Finally, it is also worth noting the importance of using spacers in vertical U-tubes and that no improvements have been found regarding the use of single or double configuration of U-tubes. Thanks to the laboratory results derived from this study it is possible to establish the optimum behaviour pattern for the entire vertical closed-loop systems.