Assessment of Design Procedures for Vertical Borehole Heat Exchangers

The use of ground source energy systems is a well-established method to provide low cost heating to buildings, diversify the energy mix and help meeting increasingly stricter sustainability targets. However, considerable uncertainties remain over their efficient design, with several standards, guidelines and manuals being proposed over the last few years. This paper aims at providing insight into the implications to the design of a vertical borehole heat exchanger of the adoption of different design procedures. The hypothetical case of a typical dwelling located in London, UK, is analysed in order to highlight the impact on the final design of the chosen methodology. Moreover, a parametric study using an analytical design procedure was performed to point out the influence of various factors, such as borehole characteristics and thermal properties of the ground. It is shown that there are considerable discrepancies between design methods and that uncertainties in some input parameters, such as the thermal properties of the ground, which for relatively small systems are often selected from tables rather than measured in situ, may have a substantial influence on the length of borehole required

The Study of Soil Temperature Distribution for Very Low-Temperature Geothermal Energy Applications in Selected Locations of Temperate and Subtropical Climate

The publication presents the results of research on soil temperature distribution at a depth of 0.25–3 m in three measurement locations. Two boreholes were located in Białystok in the temperate climatic zone and one measuring well was installed in Belmez in the subtropical climatic zone. Measurements were made in homogeneous soil layers in sand (Białystok) and in clay (Białystok and Belmez). Based on the results of the measurements, a simplified model of temperature distributions as a function of depth and the number of days in a year was developed. The presented model can be used as a boundary condition to determine heat losses of district heating pipes located in the ground and to estimate the thermal efficiency of horizontal heat exchangers in very low-temperature geothermal energy applications

UNDERSTANDING LARGE-SCALE NATURAL MINE WATER-GEOLOGIC FORMATION SYSTEMS FOR GEOTHERMAL APPLICATIONS

Geothermal energy recovery from flooded mines has been gaining momentum worldwide. Numerous mines are flooded after their closure, either naturally or artificially, in which the water in the mines can be heated by the surrounding geologic formations due to geothermal gradients, leading to sizeable man-made reservoirs of warm water. Such mine water, therefore, can be treated as a renewable geothermal resource for heating/cooling buildings, which has the potential to benefit over millions of people in the United States and much more around the world. Though some real projects and/or installations launched worldwide for the use of flooded mines for geothermal applications, there are many uncertainties in the theoretical aspect of this application, in particular, the scientific understanding of the large-scale natural mine water-geologic formation system is still in a preliminary stage and thus far lags behind its application. Motived by this missing scientific linkage, the current dissertation presents an investigation with multiphysics analyses to understand the large-scale natural mine water-geologic formation system. The main objective is to provide an in-depth understanding of this system for guiding and optimizing this large-scale geothermal application from a scientific perspective. For the purpose, this dissertation presents four specific investigations. The first investigation explores a specific site with comprehensive information relevant to the natural mine water-geologic formation system for recovering geothermal energy from deep abandoned mines for heating and cooling buildings. The second investigation presents the results of field tests and multiphysics analysis of a flooded shaft for understanding the transport of heat and mass in the natural mine water-geologic formation system. The third investigation addresses a key scientific issue regarding the layering phenomenon observed in large bodies of mine water, which controls the temperature distribution and heat energy storage in the deep geothermal field for the proposed energy renovation. The fourth investigation aims to provide insights into the dominant heat and mass transport mechanisms underlying thermohaline stratifications and investigate the factors influencing thermohaline stratifications. The above four investigations presented in this dissertation provide the urgently needed scientific understanding of the natural mine water-geologic formation system for this large-scale geothermal application, which eventually offers scientific bases for the future optimal design of this unique large-scale application of recovering geothermal energy from flooded mines

Caratterizzazione dei parametri di un reservoir geotermico tramite la risoluzione del problema inverso e le simulazioni geostatistiche

BTES (borehole thermal energy storage)systems exchange thermal energy by conduction with the surrounding ground through borehole materials. The spatial variability of the geological properties and the space-time variability of hydrogeological conditions affect the real power rate of heat exchangers and, consequently, the amount of energy extracted from / injected into the ground. For this reason, it is not an easy task to identify the underground thermal properties to use when designing. At the current state of technology, Thermal Response Test (TRT) is the in situ test for the characterization of ground thermal properties with the higher degree of accuracy, but it doesn’t fully solve the problem of characterizing the thermal properties of a shallow geothermal reservoir, simply because it characterizes only the neighborhood of the heat exchanger at hand and only for the test duration. Different analytical and numerical models exist for the characterization of shallow geothermal reservoir, but they are still inadequate and not exhaustive: more sophisticated models must be taken into account and a geostatistical approach is needed to tackle natural variability and estimates uncertainty. The approach adopted for reservoir characterization is the “inverse problem”, typical of oil&gas field analysis. Similarly, we create different realizations of thermal properties by direct sequential simulation and we find the best one fitting real production data (fluid temperature along time). The software used to develop heat production simulation is FEFLOW 5.4 (Finite Element subsurface FLOW system). A geostatistical reservoir model has been set up based on literature thermal properties data and spatial variability hypotheses, and a real TRT has been tested. Then we analyzed and used as well two other codes (SA-Geotherm and FV-Geotherm) which are two implementation of the same numerical model of FEFLOW (Al-Khoury model)

An Analysis of the Geothermal Energy of Surface Water in Fátima do Sul, Mato Grosso do Sul, Brazil with an Emphasis on the Climatization of Buildings Environments

Investment in unrenewable energy sources has grown at a rapid pace during the beginning of the 21st century, and they may be exhausted by the middle of this century if this rhythm of consumption is maintained. Sustainable solutions have become a priority and the use of Geothermal Energy from Surface Water has attracted interest as a source of clean and renewable energy which can be used to climatize constructed environments. This article analyzes the surface water of a reservoir located in Fátima do Sul, Mato Grosso do Sul determining its temperature at depths of 0.3 to 1.5 meters (1 to 5 feet) using our own method which employs an Arduino Mega 2560 R3, a free electronic hardware prototype with a single board. The results demonstrate an inverse relationship between the variation in the water’s temperature and an increase in depth, or in other words, there are smaller variations in temperature at greater depths. This fact gives these waters the capacity to store heat, and thus it can be employed in heating and cooling constructed environments

Analysis of the thermo-physical properties of soils and rocky materials in trento area related to use of the subsoil as a thermal energy storage

The thesis analyzes the thermo-physical properties of soils and rocky materials in trento area related to use of the subsoil as a thermal energy storage. There were measured thermal conductivity, volumetric heat capacity and thermal diffusivity of 21 rock samples and 8 soil samples. This provides a first database for thermal properties in the municipality of Trent

Análisis y desarrollo de nuevas técnicas y posibilidades de utilización de energía geotérmica

Tesis por compendio de publicacionesLas energías renovables juegan un papel imprescindible en la lucha contante contra el cambio climático. La sociedad de hoy en día requiere la implementación de fuentes de energías limpias con el objeto de reducir la utilización de combustibles fósiles. Dentro del amplio espectro de energías renovables, la energía geotérmica constituye un pilar importante en el futuro desarrollo sostenible. En función de su caracterización térmica y geológica, el uso de esta energía está directamente relacionado con la producción de agua caliente sanitaria o la climatización de un determinado espacio. La generación eléctrica puede también incluirse en las aplicaciones de la energía geotérmica si las condiciones geológicas del recurso lo permiten. Existen un gran número de ventajas que definen esta clase de recurso renovable (como por ejemplo; uso continuo, emisión de gases de efecto invernadero reducida, costes operativos mínimos, independencia geológica en aplicaciones de climatización, etc.). Sin embargo, la elevada inversión inicial que estas instalaciones requieren y la carencia de conocimiento en el ámbito, limitan el uso de esta energía en ciertas ocasiones. La presente Tesis Doctoral se enmarca en el análisis y evaluación de los principales parámetros y componentes que directa o indirectamente influyen en el desarrollo de los sistemas geotérmicos de baja entalpía. En particular, el principal propósito de este trabajo es definir el esquema de funcionamiento geotérmico óptimo con el fin de contribuir a un uso más extensivo de esta tecnología renovable. Las líneas de investigación incluyen un extenso proceso de trabajo de campo y ensayos de laboratorio, así como el procesamiento y análisis de los datos experimentales y de simulación. El punto de partida del trabajo de investigación dio comienzo con la identificación de los puntos débiles de los recursos geotérmicos de baja entalpía. Tras esta primera evaluación, los esfuerzos se centraron en la realización de diferentes ensayos sobre los parámetros detectados como esenciales en la etapa anterior. El trabajo experimental se complementó con el uso de software especializado en el dimensionamiento de sistemas geotérmicos, simulación y modelado energético además de la realización de los correspondientes estudios teóricos y numéricos. Las conclusiones extraídas de todo el desarrollo práctico y teórico han permitido establecer la metodología geotérmica más adecuada. En resumen, la presente Tesis Doctoral está compuesta por información muy relevante para el campo geotérmico, que ha sido recogida en forma de artículos científicos donde se compila todo el conocimiento y experiencia adquiridos a lo largo de la etapa investigadora.[EN] Renewable energies have got an essential role in the continuous climate change mitigation. The present-day society requires the implementation of green energy sources with the principal aim of reducing the fossil’s fuels use. Within the broad spectrum of renewable energies, geothermal energy constitutes an important part for a future sustainable development. Depending on its thermal and geological characterization, the use of this energy is directly related to the generation of domestic hot water and/or heating/cooling purposes. Electricity production could be also included as a geothermal application if the geological conditions of the resource allowed it. There is a large number of advantages that define this kind of renewable source (e.g. continuous use, reduced greenhouse gases emissions, minimum operational costs, geological independence for heating and cooling uses, etc.). However, the high initial investment commonly required for domestic installations and the lack of knowledge in the field, make the use of this energy limited in certain occasions. The present Doctoral Thesis is framed within the analysis and evaluation of the principal parameters and components that, directly or indirectly, influence the development of low enthalpy geothermal systems. Specifically, the main goal of this research work is to define the most optimal schema of geothermal operation that helps to contribute in a more extensive use of this renewable technology. The research lines include extensive field work and laboratory tests, in addition to the computing processing and analysis of the experimental and simulation data. The starting point of the research work was the identification of the weaknesses that characterize low enthalpy geothermal resources. After this first evaluation, efforts were focused on the realization of different tests on the parameters detected as essential in the previous stage. Experimental work was complemented with the use of specific software on the basis of the geothermal systems dimensioning, energy simulation and modelling apart from the corresponding numerical and theoretical studies. Conclusions obtained from the whole practical and theoretical work allowed establishing the most optimal geothermal methodology. In summary, the present Doctoral Thesis contains valuable information that has been compiled in numerous scientific works in which all the know-how and expertise arising during this research stage have been compiled

Commercial Program Development for a Ground Loop Geothermal System: Energy Loads, GUI, Turbulent Flow, Heat Pump Model and Grid Study

The use of the earth\u27s thermal energy to heat and cool building space is nothing new; however, the heat transfer approximations used in modeling geothermal systems, leave uncertainty and lead to over sizing. The present work is part of a Wright State effort to improve the computer modeling tools used to simulate ground loop geothermal heating and cooling systems. The modern computer processor has equipped us with the computation speed to use a finite volume technique to solve the unsteady heat equation with hourly time steps for multi-year analyses in multiple spatial dimensions. Thus we feel there is more need to use approximate heat transfer solution techniques to model geothermal heating and cooling systems. As part of a DOE funded project Wright State has been developing a ground loop geothermal computer modeling tool that uses a detailed heat transfer model based on the governing differential energy equation. This tool is meant to be more physically detailed and accurate than current commercial ground loop geothermal computer codes. The Wright State code allows the geothermal designer to optimize the system using a number of outputs including temperature field outputs, existing fluid temperature plots, heat exchange plots, and even a histogram of the COP data. Careful attention to the algorithm speed allows for multi-year simulations with minimal computation cost. Once the thermal and heat transfer computations are complete, a payback period calculator can compare any conventional heating and cooling system to the designed geothermal system and payback periods are displayed. The work being presented as part of this thesis deals with five issues that were required to make the Wright State geothermal computer code a reality. The five aspects of this modeling tool addressed by this thesis work are: energy load calculations, GUI (graphical user interface) development, turbulence model development, heat pump model development, and two-dimensional numerical grid development. The energy load, or heating and cooling load, calculations are handled using the sophisticated DOE program called EnergyPlus. This thesis work developed a technique for coupling EnergyPlus to the Wright State geothermal code and devising a way for novice users to obtain energy loads quickly and easily, while still allowing expert users to utilize the full strength of EnergyPlus. The GUI for the Wright State computer program was developed with the novice and expert users in mind. The GUI offers ease of use while maintaining the ability for the expert users to setup unique designs for simulation. A unique way of modeling the effects of turbulent flow in the ground tube has allowed the Wright State code to maintain low computation times, while having small errors for a wide range of Reynolds numbers. To make the Wright State ground loop computer model more complete, a heat pump was developed as part of this work. The heat pump model uses the performance characteristics of commercial heat pumps to determine the performance of the geothermal system. The energy transport in the fluid is determined and used to select one of eighteen water-to-air heat pumps that calculate hourly COP\u27s for all system conditions. The calculated heat pump efficiencies are used in an energy balance with hourly building loads to calculate the next iteration\u27s bulk temperature entering the ground loop. Additional details are provided in this thesis on each of these five, important, computer modeling issues

Optimisation of geothermal resources in urban areas

L'abstract è presente nell'allegato / the abstract is in the attachmen

Experimental investigations and analysis of piles as heat exchangers in pyroclastic soils

Sustainability and the greenhouse gases containment are the main purpose of the world policies to combat climate change. These are certainly in contrast with the world's growing demand for energy that is still too heavily based on fossil fuels, which are the main causes of gas emissions. The European Energy policies for more than 20 years have been based on the reduction of the carbon dioxide emissions using renewable energy sources and the reducing the final energy consumption. Shallow Geothermal Energy (SGE) is a rapidly growing technology all over Europe as a support for the Renewable Energy policies and European Directives because of its low greenhouse gas emissions into the atmosphere. It is considered a renewable source on the timescales of technological/societal systems because do not require the geological times of fossil fuel reserves such as coal, oil, and gas. Low enthalpy geothermal energy is used for heating and/or cooling building by exploiting the ground heat by ground heat exchangers connected to a geothermal source heat pump (GSHP). Energy piles represents a rather innovative technology that couples the role of the structural foundation with the role of the heat exchangers for GSHP plants to satisfy the building heating and cooling needs. Compared to the traditional pile foundations, these structures are loaded both by mechanical and thermal loads, where for thermal loads is commonly intended the application of a thermal distortion. During the last years, thermal and thermomechanical behavior of energy piles has been investigated by different approaches. In this PhD thesis the main aim was to investigate on the thermomechanical behavior of energy piles contextualized in Neapolitan context both by a geotechnical and energy point of view. First of all, a general overview about the social and energy European context and about the geothermal energy, an introduction to energy piles, by both a mechanical and an energetical point of view, was reported. The research was carried out following three different approaches: numerical modelling, small-scale tests, and field scale tests. As regard the numerical modelling, two types of analyses were carried out. In the former case by an axisymmetric FEM model, the impact of different surface thermal boundary conditions on the thermomechanical behavior of a single end bearing energy pile embedded in pyroclastic multilayer soil is investigated. The latter case is about the study of the interaction factors for a couple of energy piles where only one is thermally loaded while the other is embedded as a passive element in the deformation field generated by the loaded pile. The results were obtained for different pile spacings and for different subsoil and are presented in the chapter 4. Chapter 5 is dedicated to the small-scale test carried out on an aluminum energy prototype pile embedded in Neapolitan pyroclastic dry sand. Both thermal and thermomechanical tests were carried out considering a cyclical application of the thermal loads both in heating and in cooling mode and also considering the impact of different mechanical loads. The thermal loads provided to pile was obtained from a dynamic energy simulation of a building in the city of Naples. The results showed different axial forces distribution depending on the kind and magnitude of thermal and mechanical load applied on pile. Moreover, it was observed irreversible pile displacements during the application of cyclic thermal loads. Finally, in the chapter 6 a field test was carried out in the province of Naples on a bored concrete energy pile 12 m in length and 0,60 m in diameter embedded in pyroclastic soil and equipped with a spiral heat exchanger configuration. Three heating thermal tests with different time duration were carried out. From the tests was observed that the null point of the pile was located at the same depth for all the tests. Anyway, the magnitude of the axial forces depended on the duration of the test and the magnitude of the inlet heat carrier fluid. The pile heating did not affect the surrounding soil temperatures during the tests and a high flow rate of heat power exchanged between the pile and soil was measured. The measured pile displacements ranged between the 75% and 78% of the theoretical free displacement. Moreover, a long-time monitoring of the pile and surrounding soil was carried out for about 7 months. The data collected allowed to study the site underground temperatures trend over the time and for different depth. It was also possible to find the mean value of the subsoil thermal diffusivity and consequently predict a yearly temperature trend over the time and for different depth for the site