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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.

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.

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.

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.