Дисертації з теми "Shallow geothermal energy system"

Shallow geothermal energy (SGE) systems are becoming increasingly popular due to both their environmental and economic value. By using the ground as a source and sink for thermal energy, SGE systems are able to more efficiently heat and cool structures. However, their utility beyond structural heating and cooling is being realized as their applications now extend to slab and pavement heating, grain and agricultural drying, and swimming pool temperature control. Relatively recently, SGE systems have been combined with deep foundations to create a dual purpose element that can provide both structural support as well as thermal energy exchange with the subsurface. These thermo-active foundations provide the benefits of SGE systems without the additional installation costs. One of the novel applications of thermo-active foundations is in bridge deck deicing. Bridge decks experience two main winter weather related problems. The first of which is preferential icing, where the bridge freezes before the adjacent roadway because the bridge undergoes hastened energy loss due to its exposed nature. The second problem is the accelerated deterioration of concrete bridge decks resulting from the application of salts and other chemicals that are used to prevent accumulation and/or melt the frozen precipitation on roads and bridges. By utilizing the foundation of a bridge as a mechanism by which to access the shallow geothermal energy of the subsurface, energy can be supplied to the deck during the winter to melt and/or prevent frozen precipitation. An experimental ground-source bridge deck deicing system was constructed and the performance is discussed. Numerical models simulating the bridge deck and subsurface system components were also created and validated using the results from the numerical tests. Furthermore, the observed loads that result in a foundation from bridge deck deicing tests are shown. In order to better design for these loads, tools were developed that can predict the temperature change in the subsurface and foundation components during operation. Mechanisms by which to improve the efficiency of these systems without increasing the size of the borehole field were explored. Ultimately this research shows that SGE can effectively be used for bridge deck deicing.
Ph. D.

Geothermal energy has become a focal point of the renewable energy revolution. Both shallow and deep types of geothermal energy have the potential to offset carbon emissions, reduce energy costs, and stimulate the economy. Before widespread geothermal exploration and exploitation can occur, both shallow and deep technologies require improvement by theoretical and experimental investigations. This thesis investigated one aspect of both shallow and deep geothermal energy technologies. First, a group of shallow geothermal energy piles was modeled numerically. The model was constructed, calibrated, and validated using available data collected from full-scale in-situ experimental energy piles. Following calibration, the model was parameterized to demonstrate the impact of construction specifications on energy pile performance and cross-sectional thermal stress distribution. The model confirmed the role of evenly spaced heat exchangers in optimal pile performance. Second, experimental methods were used to demonstrate the evolution of a fractured granite permeability as a function of mineral dissolution. Steady-state flow-through experiments were performed on artificially fractured granite cores constrained by 5 MPa pore pressure, 30 MPa confining pressure, and a 120°C temperature. Upstream pore pressures, effluent mineral concentrations, and X-Ray tomography confirmed the hypothesis that fracture asperities dissolve during the flow through experiment, resulting in fracture closure.

In the context of energy transition, geothermics play an important role for the heating and cooling supply of both residential and commercial buildings. Thereby, the increasingly and intensive utilisation of shallow geothermal resources bears the risk of over-exploitation and thus poses a future challenge to ensure the sustainability and safety of such systems. Particularly, the well-established technology of borehole heat exchanger-coupled ground source heat pumps is applied for the thermal exploitation of the shallow subsurface. Due to the complexity of the involved physical processes, numerical modelling proves to be a powerful tool to enhance process understanding as well as to aid the planning and design processes. Simulations can also support the management of thermal subsurface resources, planning and decision-making on city and regional scales. In this work, the so-called dual-continuum approach was adopted and enhanced to develop a coupled numerical model considering flow and heat transport processes in both the subsurface and borehole heat exchangers as well as the heat pumps’ performance characteristics, and including the relevant phenomena influencing the underlying processes. Beside the temperature fields, the efficiency and thus the consumption of electrical energy by the heat pump is computed, allowing for the quantification of operational costs and equivalent carbon-dioxide emissions. The model is validated and applied to a number of numerical studies. First, a comprehensive sensitivity analysis on the efficiency and sustainability of such systems is performed. Second, a method for the quantification of technically extractable shallow geothermal energy is proposed. This procedure is demonstrated by means of a case study for the city of Cologne, Germany and its implications are discussed
Im Rahmen der Energiewende nimmt die Geothermie eine besondere Rolle in der thermische Gebäudeversorgung ein. Die zunehmende, intensive Nutzung oberflächennaher geothermischer Ressourcen erhöht die Gefahr der übermäßigen thermischen Ausbeutung des Untergrundes und stellt damit eine wachsende Herausforderung für die Nachhaltigkeit und Sicherheit solcher Systeme dar. Zur Erschließung oberflächennaher geothermischer Energie wird insbesondere die etablierte Technologie Erdwärmesonden-gekoppelter Wärmepumpen eingesetzt. Aufgrund der daran beteiligten komplexen physikalischen Prozesse erweisen sich numerische Modelle als leistungsfähiges Werkzeug zur Erweiterung des Prozessverständnisses und Unterstützung des Planungs- und Auslegungsprozesses. Zudem können Simulationen zum Management thermischer Ressourcen im Untergrund sowie zur Planung und politischen Entscheidungsfindung auf städtischen und regionalen Maßstäben beitragen. Im Rahmen dieser Arbeit wurde, basierend auf dem sogenannten ”dual-continuum approach” und unter Berücksichtigung des Einflusses der Wärmepumpe, ein erweitertes gekoppeltes numerisches Modell zur Abbildung der in Erdwärmesonden und dem Untergrund stattfindenden Strömungs- und Wärmetransportprozesse entwickelt. Das Modell ist in der Lage, alle relevanten Einflussfaktoren zu berücksichtigen. Neben den Temperaturfeldern im Untergrund und der Erdwärmesonde werden die Effizienz und damit der Stromverbrauch der Wärmepumpe simuliert. Damit können sowohl die Betriebskosten als auch der äquivalente CO 2 -Ausstoß abgeschätzt werden. Das Modell wurde validiert und in einer Reihe numerischer Studien eingesetzt. Zuerst wurde eine umfassende Sensitivitätsanalyse zur Effizienz und Nachhaltigkeit entsprechender Anlagen durchgeführt. Weiterhin wird ein Verfahren zur Quantifizierung des technisch nutzbaren, oberflächennahen geothermischen Potentials vorgestellt und anhand einer Fallstudie für die Stadt Köln demonstriert, gefolgt von einer Diskussion der Ergebnisse

Ice rinks are energy intense industrial applications. A typical single sheet ice rink in Sweden uses about 1000 MWh/season. A state-of-the art ice rink systems can use less than 500 MWh/season, indicating the potential for improvements. According to several investigations CO2 refrigeration system with heat recovery has proven to be energy-efficient and cost-effective solution in ice rinks.To further improve the efficiency, geothermal function may be added feature. The objective of this study is to evaluate the geothermal function from techno-economic perspective for a typical ice rink in Sweden. Modelling of several scenarios has been performed. Obtained results suggest that CO2 refrigeration system with 2-stage heat recovery, if upgraded with geothermal function, can save between 1.7 to 6.8% of energy annually. In the best case, this study suggests the geothermal function would pay back in 16.4 years.
Ishallar är energikrävande industriella applikationer. En typisk ishall i Sverige använder cirka 1000 MWh / säsong. Ett toppmodernt ishallsystem kan använda mindre än 500 MWh / säsong, vilket indikerar stora förbättringsmöjligheter. Enligt flera undersökningar har CO2-kylsystem med värmeåtervinning visat sig vara energieffektivt och kostnadseffektivt i ishallar.För att ytterligare förbättra effektiviteten kan geotermisk funktion läggas till. Syftet med denna studie är att utvärdera den geotermiska funktionen ur ett tekno-ekonomiskt perspektiv för en typisk ishall i Sverige. En modellering av flera scenarier har utförts. Resultaten antyder att CO2-kylsystem med 2-steg värmeåtervinning, om det uppgraderas med geotermisk funktion, kan spara mellan 1,7 och 6,8% energi årligen. I bästa fall antyder denna studie att den geotermiska funktionen skulle betala tillbaka om 16,4 år.

The Mountain Home (MH) geothermal system of the western Snake River Plain (SRP) magmatic province was discovered in 2012 by the Snake River Geothermal Drilling Project. Artesian flowing water with a temperature of 150°C was encountered at a depth of 1745 m below ground surface (mbgs) and extensive mineralized fracture networks of pectolite-prehnite, calcite, and laumontite were discovered in the recovered core. The objectives of this study are to: 1) describe the thermal and compositional history of past geothermal fluids, and 2) compare these fluids to modern fluids in order to characterize the evolution of the MH geothermal system and the geothermal potential of the western SRP. Core observations, thin section petrography, X-ray diffraction, and Electron Microprobe analyses were performed in order to describe mineral parageneses of various alteration zones. Carbon and oxygen stable isotope ratios along with temperatures of homogenization from fluid inclusions in hydrothermally precipitated calcite were measured along ~100 m of basalt core from 1709-1809 mbgs. The d13CPDB values in calcite range from -7.2 to -0.43 ‰ and d18OPDB values range between -20.5 and -15.9 ‰. An anomalous zone from 1722-1725 m depth displays a range in d13CPDB and d18OPDB of -1.9 to +0.88 ‰ and -17.1 to -8.1 ‰, respectively, suggesting non-equilibrium fractionation due to boiling. Carbon isotopic ratios suggest a mixture of deep-seated mantle derived and meteoric fluids. Fluid inclusion microthermometry has identified primary inclusions with trapping temperatures ranging from 168-368°C. A calcite-water geothermometer used to calculate paleo-fluid oxygen isotopic composition (-0.43 to +7.2 ‰ SMOW) and a comparison with present-day fluid oxygen isotopic composition (-3.2 ‰ SMOW) reveals a cooling trend with potential mixing of meteoric waters and deeply derived fluid. The MH geothermal system has cooled over time and reflects potentially less, if any magmatic fluid input presently into the system as there was in the past.

In this thesis proposals for different designs of a borehole thermal energy storage (BTES) have been developed for the building DN-huset in Stockholm, Sweden. To build a BTES results in savings in energy costs by approximately 44 %, i.e. 2 million Swedish crowns annually. Furthermore, a BTES would reduce the annual environmental impact with roughly 75-157 tonnes of CO2 equivalents per year, depending on how the electricity consumption’s environmental impact is estimated. The payback period is about 11 years, including the warm-up period that is necessary before commissioning the BTES. The savings in environmental impact and operating costs are a result of energy being reused. During the summer heat is stored in the bedrock beneath the building for retrieval about half a year later in the winter, when there is a heating demand. In addition to developing proposals for different BTES designs the thesis also examines the influence of certain design parameters, conservative choices and operating conditions.

The ground source resources are becoming more and more popular and now the ground source heat pumps are frequently used for heating and cooling different types of buildings. This thesis aims at giving a contribution in the development of the thermal modelling of borehole heat storage systems. Furthermore, its objective is to investigate the possibility of implementing of a GSHP (ground source heat pump) with vertical boreholes, in order to deliver the heating and cooling demand for a passive house and to emphasize some certain advantages of this equipment even in the case of a small building (e.g. residential house). A case study is presented to a suitable modelling tool for the estimation of the thermal behaviour of these systems GSHP by combining the outcome from different modelling programs. In order to do that, a very efficient residential solar house (EFden House – a passive residential single-family house, which was projected and built in Bucharest with academic purposes) is being analysed. The numerical results are produced using the software DesignBuilder, EED (Earth Energy Designer) and a sizing method for the length of the boreholes (ASHRAE method). The idea of using 2 different modelling programs and another sizing method for the borehole heat exchanger design (ASHRAE method) is to make sure that all the calculations and results are valid and reliable when analysing such a system theoretically (in the first phases of implementing a project), before performing a geotechnical study or a thermal response test in order to assess the feasibility of such a project beforehand. The results highlight that the length of the borehole, which is the main design parameter and also a good index in estimating the cost of the system, is directly influenced by the other fundamental variables like thermal conductivity of the grout, of the soil and the heat carrier fluid. Also, some correlations between these parameters and the COP (coefficient of performance) of the system were made. The idea of sizing the length of boreholes using two different methods shows the reliability of the modelling tool. The results showed a difference of only 2.5%.  Moreover, the length of borehole is very important as it was calculated that can trigger a difference in electricity consumption of the GSHP up to 28%. It also showed the fact that the design of the whole system can be done beforehand just using modelling tools, without performing tests in-situ. The method aims at being considered as an efficient tool to estimate the length of the borehole of a GSHP system using several modelling tools.

The presentation was made via Skype due to the programme being online based

The demand for energy is increasing worldwide. All applications contributed to increase the demand of all energy industry, and therefore the effect on the environment and the rise in pollution increased significantly. This is considered a large problem, and researchers focused their research on renewable energy for reducing the cost of energy in the future. Geothermal energy has significant impact as a source of electricity generation since it will not harm the environment. There are more than twenty countries that benefit from geothermal plants, which generate more than 6000 megawatts .Three alternatives of geothermal energy technology (GHP, Direct use of Geothermal Heat, and Geothermal Electricity) can be used for supporting electrical systems in Oregon. At the same time, the success of using the geothermal energy alternatives in Oregon relies on different goals for achieving the best geothermal development. Oregon has been ranked third in the potential use of geothermal energy after Nevada and California. The objective from the research study was to develop an assessment model framework that can be used for supporting cost effective renewable energy in Oregon by the development of geothermal energy sources. This research of study was done by using the Hierarchical Decision Model (HDM) and consisted of four levels: Mission, objectives, goals, and alternative. Criteria used in this research study are based on five objectives to know what are the most important factors in the decision-making process. These objectives are: social, environmental, economical, technical, and political. The decision model connected objectives, goals, and alternative for obtaining the accurate decision. HDM used for this purpose to analyze the result of data collected from experts. Seven experts who had experience in the geothermal field participated in this research study, and they gave their judgment in the questionnaire survey link by using pair-wise comparison method. The outcome analysis of the results showed that in terms of objectives that Minimizing Environmental Impact was rated at the highest value at 0.26 with respect to the mission. Within the category of Minimizing Environmental Impact, Seismic Activity and GHG Emissions had higher values. The results show that "Geothermal Electricity," with a rating of 43%, was ranked as the most important alternative with respect to mission, objectives, and goals. "Direct Use of Geothermal Heat" was ranked as the second most important alternative with 31%. The results of this research study were discussed with the experts to get their feedback, and learn from them what requirements are necessary for improvement in the geotechnical energy sector for future research. The experts agreed that this methodology is a good approach to help reach the right decision since this methodology (HDM) divides the problem into small sets, which will make the decision process easier.

The present work addresses the thermodynamic optimization of small binary-cycle geothermal power plants. The optimization process and entropy generation minimization analysis were performed to minimize the overall exergy loss of the power plant, and the irreversibilities associated with heat transfer and fluid friction caused by the system components. The effect of the geothermal resource temperature to impact on the cycle power output was studied, and it was found that the maximum cycle power output increases exponentially with the geothermal resource temperature. In addition, an optimal turbine inlet temperature was determined, and observed to increase almost linearly with the increase in the geothermal heat source. Furthermore, a coaxial geothermal heat exchanger was modeled and sized for minimum pumping power and maximum extracted heat energy. The geofluid circulation flow rate was also optimized, subject to a nearly linear increase in geothermal gradient. In both limits of the fully turbulent and laminar fully-developed flows, a nearly identical diameter ratio of the coaxial pipes was determined irrespective of the flow regime, whereas the optimal geofluid mass flow rate increased exponentially with the Reynolds number. SeveORCs were observed to yield maximum cycle power output. The addition of an IHE and/or an Oral organic Rankine Cycles were also considered as part of the study. The basic types of the FOH improved significantly the effectiveness of the conversion of the available geothermal energy into useful work, and increased the thermal efficiency of the geothermal power plant. Therefore, the regenerative ORCs were preferred for high-grade geothermal heat. In addition, a performance analysis of several organic fluids was conducted under saturation temperature and subcritical pressure operating conditions of the turbine. Organic fluids with higher boiling point temperature, such as n-pentane, were recommended for the basic type of ORCs, whereas those with lower vapour specific heat capacity, such as butane, were more suitable for the regenerative ORCs.
Dissertation (MEng)--University of Pretoria, 2013.
Mechanical and Aeronautical Engineering
unrestricted

The building stock in the European Union accounts for over 40% of final energy use, where the usage of non-residential buildings may be up to 40% higher than the residential sector. Improving building energy efficiency across all categories of buildings is one key goal of the European energy policies, made prominent by the Climate and Energy package, Energy Performance of Building Directive (EPBD) and Energy Efficiency Directive (EED). In this study, a simulation model of an office-building complex utilizing district heating was created using transient simulation software TRNSYS. The model was validated using consumption data provided by the facility owner, after which an investigation of the energy saving potential along with the economic viability of adapting a new heat- and power supply system was conducted. The system designs were comprised of a geothermal energy system in combination with a PV-system and electricity storage. It was concluded that the systems were sufficient in maintaining an adequate indoor climate. Furthermore, the investments were ascertained as profitable and resulted in a decreased building specific energy demand.

District heating and geothermal heating are in present times two established heating systems that are often compared against each other. The purpose of this work is to describe which factors influence the choice of heating system during the planning stage and what the costs are for each system. In this paper, a typical house model has been developed and used as a basis for the comparison of both systems. The comparison has been made in the form of energy calculations in the energy calculation program BV2, where heat requirements and regulatory requirements for energy performance have been compared in different geographical areas in Sweden. Furthermore, cost calculations have been carried out based on the energy calculations' results, where investment costs and annual costs have been set against each other. The result of the work shows how the measurement of energy performance differs from the actual amount of purchased energy due to geographical conditions. In the southern parts of Sweden, where the geographical correction factor is below 0, consumers are penalized by raising the primary energy number, unlike the northern parts where the primary energy number is instead lowered. Based on the cost calculations, it can be concluded that district heating, when available, is more economically advantageous in the short term. Geothermal heating on the other hand is a more profitable alternative in the long run.
Fjärrvärme och bergvärme är idag två etablerade värmesystem som ofta ställs mot varandra. Syftet med det här arbetet är att redogöra vilka faktorer som påverkar valet av värmesystem under projekteringsstadiet och vilka kostnaderna som finns för respektive system. I arbetet har en typisk husmodel tagits fram och använts som grund för jämförelsen av båda systemen. Jämförelsen har dels gjorts i form av energiberäkningar i energiberäkningsprogrammet BV2 där värmebehov och myndighetskrav på energiprestanda har jämförts i olika geografiska områden i Sverige. Vidare har kostnadsberäkningar genomförts utifrån energiberäkningarnas resultat där investeringskostnader och årliga kostnader har ställts mot varandra. Resultatet av arbetet visar hur måttet på energiprestanda skiljer sig från den faktiska mängden köpt energi på grund ut av geografiska förhållanden. I de södra delarna i Sverige där den geografiska korrigeringsfaktorn understiger 0 straffas konsumenter genom att primärenergitalet höjs, till skillnad mot de norra delarna där primärenergitalet istället sänks. Utifrån kostnadsberäkningarna kan man dra slutsatsen att fjärrvärme, när den finns tillgänglig, är mer ekonomiskt fördelaktigt på kort sikt. Bergvärme å andra sidan är ett mer lönsamt alternativ på lång sikt.

In the past two decades, a growing interest in alternative energy resources as a replacement to the non-renewable resources used now days. These alternatives include geothermal energy which can be used to generate power and reduce the demands on energy used to heat and cool buildings. Ground-coupled ventilation system is one of the many applications of the geothermal energy that have a lot of attention in the early 80â s and 90â s but all designs of the system where based on single case situations. On the other hand, computational fluid dynamics tools are used to simulate heat and fluid flow in any real life situation. They start to develop rapidly with the fast development of computers and processors. These tools provide a great opportunity to simulate and predict the outcome of most problems with minimum loss and better way to develop new designs. By using these CFD tools in GCV systems designing procedure, energy can be conserved and designs going to be improved. The main objective of this study is to find and develop a CFD modeling strategy for GCV systems. To accomplish this objective, a case study must be selected, a proper CFD tool chosen, modeling and meshing method determined, and finally running simulations and analyzing results. All factors that affect the performance of GCV should be taken under consideration in that process such as soil, backfill, and pipes thermal properties. Multiple methods of simulation were proposed and compared to determine the best modeling approach.
Master of Science

El texto completo de este trabajo no está disponible en el Repositorio Académico UPC por restricciones de la casa editorial donde ha sido publicado.
The recent climate change has forced people to live in extreme conditions, either excessive heat or cold, implying that they must adapt to survive in these situations. However, there are people who, because of their geographical condition and lack of resources, lack the means and tools to combat these climate changes. The context of this study is provided in a rural town located in the Arequipa region (Peru), whose inhabitants have to fight against frosts of up to −20 °C in an area without electricity. A viable solution to this problem is found through the design and implementation of a heating system using geothermal and photovoltaic energy, which are resources found in the area, according to a report of the Ministry of Energy and Mines. This study analyzes and researches the geographical and meteorological conditions of the region, for validating, through theory and simulations, whether the proposed system can supply the thermal energy required to maintain the indoor temperature at a minimum of 15 °C under extreme conditions. The system is designed after analyzing the best technological options and techniques currently available in the context studied for its ultimate financing and establishing guidelines and indicators for monitoring results.

Heating, Ventilating and Air Conditioning Systems (HVAC) are not only one of the most energy consuming components in buildings but also contribute to green house gas emissions. As a result often environmental design strategies are focused on the performance of these systems. New HVAC technologies such as Geothermal Heat Pump systems have relatively high performance efficiencies when compared to typical systems and therefore could be part of whole-building performance design strategies.

In collaboration with the Virginia Tech Corporate Research Center, Inc., this research studies the energy consumption and cost benefits of the Geothermal Heat Pump System that has been integrated and operated in the KnowledgeWorks I and II buildings located on the Virginia Tech campus.

The purpose of this thesis is to understand the energy and cost benefits of the Geothermal Heat Pumps System when compared to the conventional package variable air volume (VAV) with hot water coil heating and air-source heat pump systems using computer simulation and statistical models. The quantitative methods of building energy performance and life-cycle cost analyses are applied to evaluate the results of simulation models, the in-situ monitoring data, and the associated documents. This understanding can be expanded to the higher level of architectural systems integration.
Master of Science

Ground-coupled ventilation (GCV) is a system that exchanges heat with the soil. Because ground temperatures are relatively higher during the cold season and lower during the hot season, the system takes advantage of this natural phenomenon. This research focused on designing a ground-coupled ventilation system evaluation tool of many factors that affect system performance. The tool predicts the performance of GCV system design based on the GCV system design parameters including the location of the system, pipe length, pipe depth, pipe diameter, soil type, number of pipes, volume flow rate, and bypass system. The tool uses regression equations created from many GCV system design simulation data using Autodesk Computational Fluid Dynamics software. As a result, this tool helps users choose the most suitable GCV system design by comparing multiple GCV systems' design performances and allows them to save time, money, and effort.
Doctor of Philosophy

Pagrindinės šiame darbe sprendžiamos problemos yra susijusios su efektyviu ilgalaikiu šilumos siurblių eksploatavimu. Šilumos siurblio sistemos kintamuoju priimamas gruntinis šilumokaitis. Tai reiškia, kad šilumos siurblio efektyvumas priklausys nuo šilumnešio temperatūros gruntiniame šilumokaityje. Pirmoje darbo dalyje pateikiama informacija apie geoterminę energiją bei jos naudojimo būdus. Apibrėžiama seklioji geoterminė energija. Pateikiamos šilumos siurblių šilumokaičių schemos. Praktinėje darbo dalyje pateikiama gruntinių šilumokaičių modeliavimo metodų analizė bei pasirenkamas metodas tolimesniam modeliavimui. Modeliuojami trijų skirtingų tipų vertikalūs gruntiniai šilumokaičiai. Modeliavimo rezultatas: šilumnešio vidutinės mėnesinės temperatūros 25 metų laikotarpiui. Pagal temperatūras nustatomas šilumos siurblio vidutinis mėnesinis efektyvumo koeficientas. Naudojant efektyvumo koeficientus apskaičiuojamas elektros energijos poreikis. Atliekama ekonominė analizė. Analizės rezultatai parodė, kad efektyviausias vertikalus gruntinis šilumokaitis, prie darbe priimtų modeliavimo sąlygų, yra viengubas gruntinis šilumokaitis su dviem U-formos vamzdžiais.
The main problems that are solved in this thesis are tailored with heat pumps longtime efficiency. The borehole heat exchanger was selected as a variable of a heat pump system. This means that efficiency of the heat pump depends from the temperature of heat carrier inside soil heat exchanger. First part of this thesis represents information about geothermal energy and ways of using it. Definition about shallow geothermal energy is made. The examples of heat pump heat exchangers are given. The practical part of the thesis contains analysis of the simulation models for soil heat exchangers. According to this analysis, selection of the simulation tool is made for further modeling. The simulations of three different heat exchangers types are made. Modeling results show heat carrier’s mean monthly temperatures during time period of 25 years. Using these temperatures the heat pump’s mean monthly coefficient of performance is defined. Using coefficients of performance the calculation of electric power demand is made. Economic analysis is made. The analysis results showed that the most efficient vertical borehole heat exchanger is one heat exchanger with two U-pipes, in terms of conditions that had been used in this thesis.

Les géostructures énergétiques consistent à établir un échange thermique direct avec le sol grâce à des systèmes intégrés dans les fondations ou les structures géotechniques. L’incorporation des échangeurs de chaleur aux géostructures provoque une variation cyclique de la température du sol adjacent. Des questions se posent sur l'impact de ces variations thermiques sur les paramètres géotechniques des sols en général, et en particulier des sols sensibles argileux. L’objectif de cette thèse est d’améliorer la compréhension et la quantification de l’impact de la variation de la température sur la capacité portante des pieux géothermiques. Actuellement, le dimensionnement des capacités portantes des fondations profondes est basé sur les résultats d’essais pénétrométriques ou pressiométriques. Des méthodes expérimentales ont été développées afin de permettre la réalisation de ces essais dans les conditions du laboratoire. Des essais mini-pénétrométriques sont réalisés sur des éprouvettes compactées à différents états initiaux et soumises à des températures variant de 1 à 70 °C. Les résultats montrent une évolution sensible des paramètres étudiés, la résistance en pointe (qc) et le frottement latéral (fs), pour un matériau illitique, lorsqu’il est compacté du côté sec de l’optimum. Les essais mini-pressiométriques, réalisés sur des massifs de sol illitique compactés en modèle réduit d’échelle métrique dans une cuve thermo-régulée, ont montré une diminution de la pression de fluage (pf) et de la pression limite (pl) avec l’augmentation de la température, tandis que la variation du module pressiométrique (EM) est moins marquée. Les résultats montrent une quasi-réversibilité des effets d’un cycle de chauffage dans la gamme de température testée alors que l’effet d’un cycle de refroidissement n’est que partiellement réversible. Pour les essais soumis à plusieurs cycles thermiques, le premier cycle induit des variations de paramètres toujours plus importantes que les cycles suivants. Une analyse approfondie de l’évolution des propriétés thermiques (la conductivité thermique (λ), la capacité thermique volumique (Cv) et la diffusivité thermique (D)) des sols en fonction de la teneur en eau, de la masse volumique sèche et de la température montre une augmentation de ces paramètres avec l’augmentation de w et ρd et une augmentation de λ des éprouvettes illitiques du côté sec de l’optimum avec l’augmentation de la température de 1 à 70 °C. En résumé, pour les pieux énergétiques, les résultats obtenus en laboratoire montrent une modification de la capacité portante due à la variation des paramètres du sol illitique sous l’effet des cycles thermiques
Energy geostructures involve providing a direct heat exchange with the ground through integrated systems in the foundations or geotechnical structures. The incorporation of heat exchangers in geostructures produces a cyclic variation of the temperature in the adjacent soil. Therefore, there are important scientific questions about the effect of temperature variations on hydro-mechanical soil parameters in general, and particularly for sensitive clay soils. The main objective of this thesis is to improve the understanding and the quantification of the impact of temperature variation on the bearing capacity of geothermal piles. Currently, the design of the bearing capacity of deep foundations is based on the results of in situ penetrometer and pressuremeter tests. Herein, experimental methods are developed to carry out these tests in laboratory conditions. Mini-penetrometer tests were carried out on samples compacted at different initial states and subjected to temperature variations ranging from 1 to 70 °C. The results showed a significant change in the studied parameters: the cone resistance (qc) and the friction sleeve resistance (fs) for an illitic material compacted on the dry side of the compaction curve. Mini-pressuremeter tests performed on the same illitic compacted soil in a thermo-regulated metric scale container, showed a decrease in creep pressure (pf) and limit pressure (pl) with increasing temperature, while the variation of pressuremeter modulus (EM) is less pronounced. The results showed a quasi-reversibility of the effect of a heating cycle through the temperature range tested, while the effect of a cooling cycle was only partially reversible. In the case of several thermal cycles, the first cycle induced more important parameter variations than the subsequent cycles, and at the end of the experimentation. Further analysis of the evolution of the thermal properties (thermal conductivity (λ), heat capacity (Cv) and thermal diffusivity (D)) within heating and cooling process as a function of soil water content and dry density showed an increase of these parameters with the increase of initial values of w and ρd, and an increase of λ in the dry side of the compaction curve with increasing temperature from 1 to 70 °C. In summary, for the energy piles driven in the clay soils, some modifications in the bearing capacity have to be taken into account due to the variation of the hydro-mechanical parameters of the soil induced by thermal cycles

[ES] Uno de los mayores retos para el mercado de bombas de calor geotérmicas es el alto coste asociado a la perforación de los intercambiadores de calor geotérmicos. Conseguir unos intercambiadores de calor geotérmicos más eficientes reduciría dicho coste, ya que sería necesaria una menor longitud de intercambiador para obtener las mismas temperaturas de trabajo en él (misma eficiencia de la bomba de calor). La eficiencia térmica de un intercambiador de calor geotérmico está caracterizada por su resistencia térmica. Dicha resistencia térmica depende de una serie de elementos entre los que se encuentran: propiedades y caudal del fluido que recorre el intercambiador de calor, diámetro de la perforación geotérmica, geometría y materiales de la tubería del intercambiador de calor y las propiedades del material de relleno de la perforación (grouting). Cuanto mayor sea la resistencia térmica del intercambiador de calor, menor será el calor transferido entre el fluido caloportador y el terreno, traduciéndose en una necesidad mayor de longitud de intercambiador enterrado. Por lo tanto, es necesario una reducción de este parámetro al mínimo posible. En consecuencia, el objetivo principal de esta tesis doctoral consiste en, a partir de un modelo analítico comprensivo de cuantificación del impacto de los parámetros anteriores, realizar un estudio detallado para analizar su influencia combinada en la resistencia térmica del intercambiador geotérmico, pero también examinando dicho efecto en otros planos, como costes económicos de ejecución del intercambiador y de explotación (consumo eléctrico de la bomba de calor y costes de bombeo asociados).
[CA] Un dels majors reptes per al mercat de bombes de calor geotèrmiques és l'alt cost associat a la perforació dels bescanviadors de calor geotèrmics. Aconseguir uns bescanviadors de calor geotèrmics més eficients reduiria aquest cost, ja que seria necessària una menor longitud de bescanviador per a obtenir les mateixes temperatures de treball en ell (mateixa eficiència de la bomba de calor). L'eficiència tèrmica d'un bescanviador de calor geotèrmic està caracteritzada per la seva resistència tèrmica. Aquesta resistència tèrmica depèn d'una sèrie d'elements entre els quals es troben: propietats i cabal del fluid que recorre el bescanviador de calor, diàmetre de la perforació geotèrmica, geometria i materials de la canonada del bescanviador de calor i les propietats del material de farciment de la perforació (grouting). Com més gran sigui la resistència tèrmica del bescanviador de calor, menor serà la calor transferida entre el fluid termòfor i el terreny, traduint-se en una necessitat major de longitud de bescanviador enterrat. Per tant, és necessari una reducció d'aquest paràmetre al mínim possible. En conseqüència, l'objectiu principal d'aquesta Tesi Doctoral consisteix en, a partir d'un model analític comprensiu de quantificació de l'impacte dels paràmetres anteriors, realitzar un estudi detallat per a analitzar la seva influència combinada en la resistència tèrmica del bescanviador geotèrmic, però també examinant aquest efecte en altres plans, com a costos econòmics d'execució del bescanviador i d'explotació (consum elèctric de la bomba de calor i costos de bombament).
[EN] One of the biggest challenges for the ground source heat pump market is the high cost associated with drilling geothermal borehole heat exchangers. Achieving more efficient geothermal heat exchangers would reduce this cost, since a shorter exchanger length would be required to obtain the same working temperatures in it (same efficiency of the heat pump). The thermal efficiency of a geothermal heat exchanger is characterized by its borehole thermal resistance. This borehole thermal resistance depends on a number of parameters, mainly: properties and flow rate of the working fluid that flows through the borehole heat exchanger, diameter of the geothermal borehole, geometry and materials of the heat exchanger pipe and the properties of the borehole grouting material. The higher thermal resistance of the heat exchanger, the less heat is transferred between the heat carrier fluid and the ground, resulting in an increased requirement for the length of the buried heat exchanger. Consequently, it is essential to reduce this parameter to the minimum possible. Therefore, the main objective of this Ph. Doctoral Thesis is to carry out, based on a comprehensive analytical model of quantification of the impact of the above mentioned parameters, a detailed study to analyze their combined influence on the thermal resistance of the geothermal borehole, but also exploring this effect in other less researched areas, such as economic costs of running the exchanger and operating it (electricity consumption of the heat pump and associated pumping costs).
This research has received funding from the European Union’s Horizon 2020 Research and Innovation program under grant agreement No [657982], [727583] and [792355].
Badenes Badenes, B. (2020). Optimización teórico-experimental de sondas de calor para intercambio geotérmico (SGE) según condiciones hidrogeológicas, características geométricas y propiedades de sus materiales [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/160477
TESIS

The thesis concerns of the possibility by using alternative decentralized sources of energy. The first chapter describes current energy situation in the Czech Republic and consideration of future electrical energy consumption and the coverage by the renewable sources. Another part of this chapter describes each types of renewable energy with their advantages and disadvantages related to the Czech Republic. In the second chapter are introduced inputs which are appropriate for the plan of energetic system. The following theoretical chapter deals with each types of alternative energy sources using renewable source including the possibility of the installation and plan for the building. These alternative sources are sorted out by the way of using renewable sources of energy. The theoretical-practical fourth chapter concerns of the heating by the heat pump. For the detailed description was chosen the heat pump which is currently denote as appropriate alternative source of heat in household. With appropriate plan, which the thesis deals with, is this alternative source considered as proper investment. In the last chapter was assembled programme for creating models of energetic flux and calculation for the plan of heating by the heating pump air/water. This model is taken for concrete buildings related to exact outdoor temperature from previous years in concrete locality. In the end was realized validation of the software with the real measurement in concrete building.

Systemtemperaturer i värmesystem är en debatterad fråga i Sverige. Vid projektering av ett värmesystem har valet av systemtemperatur en avgörande roll för kostnaden av värmesystemet. Frågan vilka systemtemperaturer i värmesystemen som är det mest ekonomiska är viktig för att värmesystemet ska ha en fördel jämfört med konkurrenterna på marknaden. Historiskt sett har systemtemperaturerna i de svenska värmesystemen varit 80/60 medans idag är den vanligaste temperaturerna 55/45. Under 60-talet stod Östen Sandberg som förespråkare för ett nytänkande värmesystem kallat lågflödesystem (LF). Detta värmesystem använder sig av låga flöden i rörledningarna och stora temperaturskillnader på framledningen och returledningen. Förespråkare av dessa lågflödesystem hävdar att vid rätt användning kan en omjustering av det befintliga värmesystemet från ett högflödesystem (HF) till ett lågflödesystem drastigt reducera energiförbrukningen för fastigheten och samtidigt uppnå acceptabla inomhusförhållanden. Hade ett LFsystem kunnat konkurrera mot ett HFsystem ekonomiskt? För att undersöka detta kommer ett 55/45-HFsystem att användas som ursprungsfall vid jämförelser mellan HFsystem och LFsystem med olika systemtemperaturer för att utreda om ett 55/45-HFsystem är det mest ekonomiska värmesystemet. Studien visar många fördelar med 55/45-HFsystemet. Ett 55/45-HFsystem har relativt låga investeringskostnader vid projekteringen i jämförelse med de andra värmesystemen. En annan fördel är att detta värmesystem är kompatibelt med både fjärrvärme samt bergvärme vilket gör detta system passande som ett standardiserat värmesystem. Det mest ekonomiska värmesystemet är ett 80/60-HFsystem, vilket har lägre investeringskostnader för både radiatorer samt rörkostnader. Förespråkare av LFsystem hävdar att de reducerade flödena medför reducerade elkostnader för cirkulationspumpen vilket i längden gör LFsystemet energisnålare. Denna studie visar att de reducerade flödena och dess påverkan av energiförbrukningen hos cirkulationspumpen är förhållandevis så låga i jämförelse med de totala energiförbrukningen hos värmesystemet att den möjliga vinsten är försumbar. Däremot kan de reducerade flödena minska risken för en snedfördelad värmefördelning i fastigheten. LFsystemens stora nackdel är ökade investeringskostnader jämfört med HFsystemen.
The choice of temperatures in heating systems has long been a question for debate in Sweden. For the design engineer, the choice of system temperatures in a heating system has a decisive impact on the cost and in order to stay competitive on the market it is crucial to design the heating system as cost effective as possible. Historically the system temperature in Swedish heating systems has been 80/60 but today we see that the most common temperatures are 55/45. During the 1960´s Östen Sandberg became the leading advocate for a new type of heating system using a low flow principle (LF) for heat distribution. The LF principle requires a larger temperatur difference between the supply and return temperatures for the adequate heating. Advocates of the LF principle claims that large energy savings are possible if an exsisting high flow heating system (HF) undergoes an adjustment to a LF heating system. The question is how accurate is this claim? This article shows many advantages with the nowadays common 55/45-HFsystem. A 55/45-HFsystem has relatively low investment costs in comparison with other types of heating systems. Another advantage is the fact that the 55/45-HFsystem is compatible with both district heating and geothermal heat pump heating systems which makes this radiator system suitable as a standardized system. The most economical radiator system is the 80/60-HFsystem, which has a lower investment cost for both radiators and piping in comparison with a 55/45-HFsystem. The claim that LFsystems and the associated LF principle could result in a reduced energy cost for the heating system was not supported. This article shows that the energy savings that comes from the LF principle is negligible in comparison with the heating systems total energy cost. The LF principle could however reduce the risk of an uneven heating distribution in the building due to a more unpredictable regulation of the flow through the radiators. LFsystem disadvantage is an general overall larger investment cost in comparison with a HFsystem.

En el país es poco común el uso de energías renovables, por ello es importante que se difundan las tecnologías asociadas al uso de este tipo de recursos. La energía geotérmica superficial es un recurso que se puede aprovechar prácticamente en toda la corteza terrestre, no proporciona una cantidad de energía elevada, pero si tiene aplicaciones que reducen la producción de CO2 (por sistemas de calefacción) y el consumo de energía. En la investigación se analizan los sistemas geotérmicos de baja entalpia, específicamente las cimentaciones termoactivas, las cuales consisten en incorporar el intercambiador de calor en la estructura de la cimentación, esto aunado a la bomba de calor y el sistema de distribución constituye un uso importante de la energía geotérmica somera en los sistemas de calefacción de edificaciones. Para desarrollar las cimentaciones termoactivas es necesario realizar estudios previos tales como, estudio de características geotécnicas y térmicas del suelo, hidrogeología y geología.
The use of renewable energies is rare in the country, so it is important that the technologies associated with the use of this type of resources be disseminated. Surface geothermal energy is a resource that can be used practically throughout the earth's crust, it does not provide a high amount of energy but it does have applications that reduce CO2 production (by heating systems) and energy consumption. The research analyzes low enthalpy geothermal systems, specifically thermoactive foundations, which consist of incorporating the heat exchanger in the foundation structure, this together with the heat pump and the distribution system constitutes an important use of shallow geothermal energy in building heating systems. To develop thermoactive foundations it is necessary to carry out previous studies such as a study of the geotechnical and thermal characteristics of the soil, hydrogeology and geology.
Tesis

La géothermie peu profonde est une énergie qui peut aider l'humanité à atteindre les objectifs du développement durable. Le système de pompe à chaleur géothermique est utilisé pour bénéficier de cette énergie. En tant qu'élément principal du système, la performance de l'échangeur de chaleur souterrain influence directement son efficacité énergétique. Les échangeurs de chaleur souterrains peu profonds sont normalement installés dans les sols, qui présentent une grande hétérogénéité des propriétés hydrothermales. L'objectif principal de ce projet est d'identifier le comportement des échangeurs de chaleur souterrains dans les sols. En résumé, les enquêtes suivantes ont été menées : la première consiste à introduire le transfert hydrothermique dans la modélisation numérique des échangeurs géothermiques installés sur un site en Alsace (France) ; la seconde enquête consiste à identifier les facteurs qui influencent la performance d'un échangeur de chaleur de forage peu profond installé dans les sols ; la troisième étude concerne l'analyse de sensibilité des essais de réponse thermique pour les échangeurs de chaleur de forage installés dans les sols ; la dernière étude traite l'identification de la différence de performance d'un modèle de simulation numérique avec les limites de Neumann et de Dirichlet à la surface du sol pour un échangeur horizontal de chaleur souterraine
Shallow geothermal energy is an energy that can help humanity to reach the goal of sustainable development. Ground-Coupled Heat Pump system is traditionally used to benefit this energy. As a main element of the system, ground heat exchanger performance directly influences its energy efficiency. The shallow ground heat exchangers are normally installed in soils, which show high heterogeneity of hydrothermal properties along the soil profiles. The main objective of this project is identifying how ground heat exchanger behaves in the soil. In summary, the following investigations were conducted: the first is introducing hydrothermal transfer in the numerical modeling of Borehole Heat Exchanger installed at a site in Alsace region (France); the second is identifying the factors influencing the performance of a shallow Borehole Heat Exchanger installed in soils; the third is conducting sensitive analysis of Thermal Response Tests for Borehole Heat Exchanger installed in soils; the fourth is identifying the performance difference of a numerical simulation model with Neumann and Dirichlet boundaries on the ground surface for a Horizontal Ground Heat Exchanger

2013/2014
La domanda alla base di questa ricerca è stata se il metodo della gravimetria satellitare possa essere utilizzato per seguire le unità geologiche anche in luoghi difficilmente accessibili. L’obiettivo di questa ricerca è di verificare se le missioni satellitari di nuova generazione permettano di identificare la più grande delle province ignee della Terra (Bertrand et al., 2013), nota come CAMP (Central Atlantic Magmatic Province) in Africa nord-occidentale. Oltre alle motivazioni scientifiche, una possibile applicazione è l’esplorazione di risorse minerarie e lo sfruttamento di energia geotermica. Tale provincia ignea è una LIP (Large Igneous Province) che si estende in Nord e Sud America, Atlantico, Europa ed Africa (istituita in Marzoli et al. 1999). Essa si è sviluppata a seguito della frammentazione del super-continente Pangea al limite Triassico-Giurassico, ca. 200 Ma fa. A causa probabilmente del riscaldamento globale del mantello e/o dalla convezione dello stesso innescata da dislivelli di blocchi litosferici, dai dicchi-sorgente si produssero i cosiddetti basalti da flusso e si verificò un intenso vulcanismo con imponenti colate laviche tali da suggerire a taluni ricercatori che gli elementi volatili presenti nel magma abbiano contribuito ad aumentare i gas serra con conseguenze nel clima globale e nelle estinzioni di massa. I depositi in esame sono costituiti da lave, tholeiti continentali, doleriti, basalti e gabbri. Ciò che rimane di questa attività vulcanica sono dicchi singoli o in sciami, batoliti, sill, colate laviche e plateau basaltici (nei fondali oceanici). L’Africa nord-occidentale è costituita principalmente da un cratone composto da rocce molto antiche dell’Archeano (3000-2500 Ma). Esso emerge a nord nello scudo Reguibat e, a sud, la dorsale dell’Uomo o del Leone (Lucazeau et al., 1991). Il cratone è circondato dalle zone di geosutura (greenstone e cinture mobili) associate al cosiddetto evento termo-tettonico Pan-Africano, verificatosi ca. 650 Ma fa con l’assemblaggio del continente africano da blocchi crostali più piccoli. Nelle Mauritanidi affiora il basamento ercinico (ca. 350 Ma) mentre negli Atlas e nelle Magrebidi prevalgono rocce più recenti connesse all’orogenesi alpina (0-150 Ma). Al centro del cratone si trova il bacino paleozoico Taoudenni che riempie una vasta area depressa. Tutto il territorio in esame è caratterizzato da una forte presenza di rocce metamorfiche dense e magmatiche di ogni età, con presenza di più di un “punto caldo” che potrebbe essere definito un terreno igneo (Bryan et al. (2008) con più LIP spesso sovrapposte o limitrofe. Mediamente, tutte queste rocce magmatiche e metamorfiche hanno una densità di 3000 kg/m3 (Kröner, 1977 ), maggiore di quella della crosta standard e dei sedimenti. Particolare attenzione è stata dedicata ad un lineamento tettonico noto come Pelusium Megashare System (PMS) che attraversa tutta l’Africa nord-occidentale (Neev et al., 1982) chiaramente visibile in tutte le immagini satellitari di Google Earth ma che è riportato solo in pochissime pubblicazioni. Per la prima volta in questa tesi si ipotizza un collegamento tra la CAMP e PMS. La gravimetria satellitare consente di rilevare variazioni di densità nella crosta terrestre. Ove vi sono rocce più dense, il segnale rilevato (detto anomalia gravimetrica) è positivo e viceversa. La gravimetria da satellite si è rivelata un valido strumento per identificare le aree con surplus di massa. La risposta all’interrogativo iniziale è dunque affermativa anche se, da quanto esposto, risulta difficile o impossibile associare ad un certo segnale positivo una data LIP. L’elaborazione dei segnali è avvenuta partendo dai dati del satellite GOCE (ultima generazione, a un’orbita di 250 km ma già ammarato) e GRACE (obsoleto ma tuttora in orbita a ca. 450 km). I dati utilizzati sono dei modelli del campo di gravità terrestre che contengono i coefficienti di Stokes per lo sviluppo in armoniche sferiche del potenziale. I modelli utilizzati sono l’EGM2008 (comprendente anche dati di terra, con risoluzione massima 10 km se sviluppato al massimo ordine di 2159) e GOCO TIM R4 (con una risoluzione massima di 80 km, la migliore mai ottenuta da dati satellitari globali). Il modello EGM2008 è stato sviluppato fino all’ordine e grado 720 per eliminare dati spuri (Pavlis, 2012) e, in tal modo, ha permesso di raggiungere una risoluzione di ca. 27 km se si considera metà lunghezza d’onda. Dopo il controllo della qualità dei dati, essi sono stati elaborati nel seguente modo, come esposto nei capitoli 2, 3 e 4. Ai dati grezzi sono state applicate tre riduzioni per sottrarre gli effetti di gravità indesiderati che mascherano il segnale cercato più debole. È stato sottratto l’effetto di gravità della topografia, dei sedimenti e dell’interfaccia crosta-mantello (ICM). Partendo dall’anomalia “in aria libera” (FA), è stata quindi ottenuta l’anomalia di Bouguer (BA) e la BA corretta per i sedimenti. Poi, calcolata la Moho (ICM) isostatica, si è prodotto il residuo isostatico corretto per i sedimenti. I campi elaborati sono la gravità gz (espressa in milli Gal, mGal) ed il gradiente Tzz (misurato in Eötvös, E). Sono state usate le risoluzioni di 0.5° e di 0.05°, computati ad una quota di 4000 m s.l. m perché maggiore del più altro rilievo montuoso dell’area. Dopo aver modellato dei casi a geometria semplice (cap. 6) si è passati alla modellizzazione di tre casi reali. I tre siti scelti per l’approfondimento sono: Tindouf (Algeria), Taoudenni (Mali), Timbuktu (Mali). Nel bacino di Tindouf un sill doleritico CAMP è annesso al suo probabile dicco-sorgente reso evidente dalla gravimetria che identifica bene anche una vicina miniera di Ferro. Nel bacino Taoudenni, le due anomalie principali suggeriscono la presenza di cumuliti magmatici spessi una dozzina di chilometri e connessi con la superficie attraverso dicchi obliqui. Il sito presso Timbuktu è trattato nel dettaglio perché al di sotto del vicino lago Faguibine è stata rivelata un’intrusione magmatica lunga ca. 250 km. In superficie vi sono evidenze di magmatismo (per es. fumarole) tali da preoccupare le popolazioni locali (El Abbass et al., 1993). Tra i risultati inaspettati, si ricorda il forte segnale gravimetrico generato dalle peridotiti in Marocco ed un’importante anomalia (80 mGal) nel Grand Erg Occidental (Algeria) al di sotto del Sahara che sembrerebbe essere causata da un corpo denso lungo ca. 600 km.
The question behind this research was whether the method of satellite gravimetry can be used to follow the geological units even in inaccessible places. The goal of this research is to verify if the new generation of satellite missions serve to identify the largest of the Earth's igneous provinces (Bertrand et al., 2013), known as CAMP (Central Atlantic Magmatic Province) in Northwest Africa . Besides the scientific reasons, a possible application is the exploration of mineral resources and the exploitation of geothermal energy. This is an igneous province (LIP Large Igneous Provinces) that extends throughout North and South America, the Atlantic Ocean, Europe and Africa (established in Marzoli et al. 1999). It developed as a result of the fragmentation of the super-continent Pangea at Triassic-Jurassic limit, ca. 200 My ago. Probably because of mantel global warming and/or its convection triggered by differences in thickness of lithospheric blocks, from source-dikes were produced the so-called continental flow basalts (CFB) and there was an intense volcanism with massive lava flows that this would suggest to certain researchers volatile elements present in the magma have contributed to increasing greenhouse gases with consequences in the global climate and mass extinctions. The deposits in question consist of lavas, tholeites continental dolerites, basalts and gabbros. What remains of this volcanic activity are individual dykes or in swarms, batholiths, sills, lava flows and basaltic plateau (in the ocean). The north-western Africa consists mainly of a craton made of most ancient rocks dell'Archean (3000-2500 Ma). It emerges in the shield Reguibat north and on the south, the Man or the Lion shield (Lucazeau et al., 1991). The craton is surrounded by areas of geosutura (greenstone belts and mobile belts) associated with the so-called Pan-African thermo-tectonic event, occurred ca. 650 Ma ago with the assembly of the African continent by smaller crustal blocks. Mauritanides emerges in the Hercynian basement (ca. 350 Ma) while in the Atlas and Magrebides prevail younger rocks (Alpine orogenesis, 0-150 Ma). At the center of the craton is the Paleozoic basin Taoudenni that fills a large area depressed. All the territory concerned is characterized by a strong presence of dense magmatic and metamorphic rocks of all ages, with the presence of more than a "hot spot" that could be called “igneous terrane” (Bryan et al. (2008) with more LIPs overlapping or adjacent. On average, these igneous and metamorphic rocks have a density of 3000 kg / m3 (Kröner, 1977), greater than that of the standard crust and the sediments. Particular attention was dedicated to a tectonic lineament known as Pelusium Megashare System (PMS) that runs through the north-western Africa (Neev et al., 1982) clearly visible in all the satellite images of Google Earth but is reported only in very few publications. For the first time this thesis suggests a link between CAMP and PMS. Satellite gravimetry can detect density variations in the Earth's crust. Where there are rocks denser, the detected signal (called gravity anomaly) is positive and vice versa. The gravimetry by satellite has proved a valuable tool to identify areas with surplus Mass. The initial response to the question is therefore affirmative although, from the above, it is difficult or impossible to associate a positive signal a date LIP. Signals processing occurred from the data of the GOCE satellite (last generation, in an orbit of 250 km, mission already finished) and GRACE (obsolete but still in orbit at ca. 450 km). The data used are the models of the Earth's gravity field containing the coefficients of Stokes for the development of potential in spherical harmonics. The models used are the EGM2008 (also including land data, with a maximum resolution 10 km if developed to the maximum order of 2159) and TIM GOCO R4 (with a maximum resolution of 80 km, the best ever obtained by global satellite data). The model EGM2008 has been developed up to the order and degree 720 to remove spurious data (Pavlis, 2012) and, thus, allowed to reach a resolution of ca. 27 km considering half wavelength. After quality control of the data, they were processed in the following flowchart, as discussed in Chapters 2, 3 and 4. Raw data were processed applying three reductions to subtract the effects of gravity that mask the signal. It was reduced by the effect of gravity of the topography, sediment and crust-mantle interface (CMI). Starting by the anomaly "free air" (FA), was thus obtained the Bouguer anomaly (BA) and BA correct for sediment. Then, once calculated the isostatic Moho (CMI), has produced the sediment-corrected-isostatic residual. The fields processed are gravity gz (in milli Gal, mGal) and gradient tzz (measured in Eötvös, E). It has been used the resolutions of 0.5 ° and 0.05 °, computed at an altitude of 4000 m a.s.l., higher of mountains in the area. After mng cases with simple geometry (ch. 6) we moved to the modeling of three real case histories. The three sites chosen for the study are: Tindouf (Algeria), Taoudenni (Mali), Timbuktu (Mali). In the basin of Tindouf a CAMP doleritic sill is attached to its likely source source-dyke evident by gravimetry that identifies well a nearby mine of Iron. In the Taoudenni basin, the two main anomalies suggest the presence of magmatic cumulites a dozen kilometers thick and connected with the surface through oblique dikes. The site at Timbuktu is discussed in detail because in the nearby lake Faguibine was revealed a magmatic intrusion long ca. 250 km. On the surface there is evidence of magmatism (e.g. Fumaroles) such that worry local populations (El Abbass et al., 1993) .Among the unexpected results, please note the strong signal generated by gravimetric peridotites in Morocco and a major anomaly (80 mGal) in the Grand Erg Occidental (Algeria) below the Sahara that would seem to be caused by a dense body ca. 600 km long.
XXVI Ciclo
1972

碩士
國立臺灣大學
機械工程學研究所
105
Traditional air-conditioning cooling systems usually use cooling tower to dissipate condense heat into outdoor air. However, the outdoor temperature and humidity, which vary over time, limit the cooling performance of cooling tower. Furthermore, the use of cooling tower has many disadvantages such as noise, vibration, and also providing a proper environment for bacteria breeding. Therefore, the aim of this thesis is to replace cooling tower system with a new cooling system—the shallow geothermal cooling system. This new cooling system dissipates condense heat into the shallow ground. Because of having a relatively small temperature variation, the shallow ground can be a stable heat sink for air-conditioning cooling.In this study, we used two types of shallow geothermal cooling system: groundwater borehole and raft foundation water. According to the experiment results, the groundwater cooling system could stably cool the condenser and reached thermal equilibrium state, but the temperature of raft foundation water was continuously rising during operation. Therefore, the groundwater cooling system can be a proper alternative for replacing cooling tower system. On the other hands, the raft foundation water cooling system could be another choice through optimized operating method.

碩士
國立臺灣大學
機械工程學研究所
107
The earth air heat exchanger (EAHE) is a low-energy ventilation technique using the stable temperature of earth. In the past decade, many experimental studies deal with the performance evaluation of EAHE system worldwide; however, in Taiwan these kinds of researches are still uncommon. This research focus on the performance of soil-based EAHE and water-based EAHE using numerical methods. Soil-based EAHE includes 4 PVC air pipes each with 52.95m in length, 0.15m in diameter and buried 4.7m beneath ground surface. Its arranged ventilation is 3150 CMH, working 9 a.m. to 9 p.m. Water-based EAHE consists of 3 PVC air pipes each with 75m in length, 0.15m in diameter and buried 9.5m underground. Its arranged ventilation is 990 CMH, working 9 a.m. to 9 p.m. This research uses ANSYS Fluent for simulating various system status over time. Initial conditions are ventilation, seasonal introduced air temperatures and seasonal introduced air humidity. After simulation, EAHE system’s seasonal outlet temperature, outlet humidity, heat transfer rates, temperature distributions in raft foundation water and soil of 2 meters around air pipes can be generated. Through heat transfer rates, seasonal energy saving efficiency can be recognized, such as cooling load in summer and heating load in winter, as well as the percentage of latent heat transfer rates through the examination of humidity difference. This analysis benefits future applications for selecting suitable areas to adjust and improve the energy saving efficiency of EAHE systems. By analyzing raft foundation water temperature distribution, the range of water affected by EAHE and its most efficient operating period can be recognized to maintain stable water temperature and its heat transfer rate for preserving EAHE’s energy saving efficiency. Through analyzing surrounding soil temperature distribution, the range and extent of soil affected by EAHE can be realized. Selecting suitable soil allows soil to maintain its stable temperature, heat transfer rates and its self-recovering ability to sustain EAHE’s energy saving efficiency. From simulation results, the influence of pipe materials, such as stainless steel, copper, aluminum and PVC on the performance of EAHE can be known, thus suitable pipe materials can be determined. From temperature distribution of introduced air within air pipes, effective length for regulating can be discerned for future applications. Besides, although increasing airflow velocities promotes heat transfer rates, heat exchange time between introduced air and air pipes also decreases. Therefore, through simulation, the optimal airflow velocities are discovered. Airflow velocities of 2m/s, 5 m/s, 9 m/s and 12 m/s are considered in this research. Finally, the influence of water temperature 21℃, 23℃, 25℃ and water storage of full, 0.75-full, half-full on the performance of EAHE and recovery during shut down period is discussed. By the simulation with mentioned settings, systems’ seasonal air regulation, energy saving efficiency, efficient operating period, influence of pipe materials, effective length, affected range of surrounding soil and water, suitable soil types, appropriate airflow velocities, the influence of water temperature and water storage can be acknowledged.

碩士
國立臺灣大學
機械工程學研究所
105
A Study of Household or Commercial Heat Pump System with Shallow Geothermal Energy By Yung-Nan Chen Master Degree of Engineering, Department of Mechanical Engineering National Taiwan University July 2016 Adviser：Sih-Li Chen, Ph.D. The purpose of this study is to test a geothermal heat pump system with two apply ways, which includes raft foundation water energy and groundwater energy. For shallow geothermal energy which temperature is lower than outdoor air in summer and higher in the winter. With this property, we want to replace the traditional heating and cooling equipment by geothermal heat pump system. In the application of raft foundation water energy and groundwater energy we via six different mode to combine heat pump system with geothermal energy for heating and cooling purpose. For groundwater energy, we used Multi-U type Borehole Heat Exchangers (MUBHEs), made of PVC material tubes to exchange heat from the evaporator or condenser of heat pump. Through experiment, we want to realize the advantages and disadvantages for this two different ways in using shallow geothermal energy. At the same time, we will compare the efficiency and cost with commonly heating and cooling household equipment in Taiwan. According to the experiment, the heating mode with raft foundation water, a high efficiency in COP 4.3 is present. And the cooling mode with raft foundation water has cooling efficiency in COP 4 with providing refrigerating capacity 18 kW. Besides, the dual mode that heating and cooling simultaneously, can provide high efficiency when operating heat pump system in right situation. In the study of these experiment, we will compare two apply modes of geothermal energy and conclusion experimental analysis, find the way to improve design to reach more high efficiency. Keywords : Shallow Geothermal Energy, Heat pump, Multi-U type Borehole Heat Exchangers, raft foundation water

碩士
國立臺灣大學
機械工程學研究所
107
When the world began to promote energy conservation issues, the energy-saving benefits of air-conditioning systems are valued by many countries. The proportion of power consumption for energy dissipation is huge. Taiwan is hot in summer. The demand for air conditioning is great, which not only cost a lot, but also cause greatly environmental burden with carbon emissions. If it can directly use solar energy as a source of heat for air conditioners and use shallow geothermal energy to cooling, this way will greatly reduce power consumption and make air conditioners more energy efficient and environmentally friendly. This study use different parameters way to explore the performance of adsorption chillers combined with solar thermal energy and shallow geothermal energy . The COP of the adsorption chiller achieve 0.51 under the operating conditions, of 70 °C regenerative temperature, 22°C cooling water temperature, and 13~15 °C cold water temperature. Under the average radiation amount is about 860 W/m2, the thermal efficiency of the solar collector is about 0.6 and the overall system performance coefficient is about 0.31. It is estimated that use shallow geothermal energy instead of cooling tower system can save 44.6 m3 of water in summer. And it uses less 1.08 kW than cooling tower system.

碩士
國立臺灣大學
機械工程學研究所
103
Plant factory refers to a closed or semi-closed high-quality growing system for vegetables. The system cultivates vegetables through artificial control of water, light, temperature, moisture, and carbon dioxide concentration, so it requires high initial construction and operation costs. The operation costs are mainly due to the electricity consumption of lighting and air-conditioning. Past research have done much work on reducing plant factory’s electricity consumption, however, little have considered replacing traditional air-conditioning system with renewable energy or constructing an power system for plant factory.　This research innovated a new method to build up net-zero plant factory (NZPF) - by combining mat foundation heat exchanger (MFHE) system and stand-alone hybrid solar-wind (SASW) power system. 　　Performance prediction was conducted by ANSYS Icepak - a novel computational fluid dynamic (CFD) simulation software, including: two cooling models (basement model and plant factory model), three cooling designs, of four seasons. Both parts’ performance tests were anticipated to be accomplished yearend. First part’s prediction results demonstrated that cooling capacities were identical in both traditional air-conditioning system and mat foundation heat exchanger system. Namely, the latter’s energy conservation benefits analysis displayed that: (1) power consumption of air-conditioning system can be reduced by low-power water cooling apparatus, (2) basement model (indoor environment global cooling model) can achieve its energy conservation efficiency up to 93.5% (3) plant factory model (local cooling model) can achieve its energy conservation efficiency to 23.4% (with jointed fan coil) and up to 79.7% (with forced convection with cooling fan). 　　Temperature simulation data in this study is predictive to a NZPF’s environment temperature, laying foundation to future experiments. Finally, solar-wind power system’s performance test and its experimental data is shown in the end of chapter 4. The net-zero energy plant factory’s cost-benefit analysis presented its payback period as 16.6 years.

碩士
國立臺灣大學
機械工程學研究所
105
Most traditional air-conditioning systems use cooling towers to dissipate heat from cooling water to ambient air, which not only consumes lots of energy but also increases urban heat island effect. This thesis aims to investigate the application of raft foundation water shallow geothermal energy. By theoretically establishing a mathematical model and comparing it with experimental results, the possibility of replacing cooling towers with raft foundation system was evaluated. First, a model for predicting the temperature variation of raft foundation water was created and analyzed. The result showed good agreement between the predicted value and the experimental data, with an average error of 3%. However, during the time when fresh water was poured into raft foundation, due to the increasing non-uniformity of water temperature, the error went up to 10%, but still within acceptable range. Second, considering stratified phenomenon, a model based on analysis of multiple control volumes was created to predict the temperature variation within a huge water storage tank. The simulation results indicated the tank could receive cooling load of approximately 960 kW with little variation of water temperature when the flow rate of incoming tap water was 10 times as large as that of the circulation water. Through heat transfer analysis, this research showed the heat dissipation rate from raft foundation water to surrounding soil was affected by the relatively high thermal resistance in soil, hence the cooling rate was not that fast compared with the former research. In addition, the thermal resistance calculated by empirical correlations was validated through CFD simulation, with only 2% relative error. Also, it was found that the heat transfer rate through the air enclosure on top of the raft foundation water was increased due to natural convection mechanism. As a result, more attention should be paid to determine whether or not this amount of heat dissipation would have significant impact on the residential quality. Finally, through energy saving assessment, it was shown that the usage of raft foundation water thermal energy could save up to 21% electricity and reduce carbon dioxide emissions by 29,066 kg per year ; and the usage of water storage tank system could save up to 24.6% electricity and reduce carbon dioxide emissions by 183,874 kg per year.

博士
國立臺灣大學
機械工程學研究所
105
The earth air heat exchanger (EAHE) is a low-energy ventilation technique using the stable temperature of the earth. In the past decade, many experimental studies deal with the performance evaluation of EAHE system worldwide; however, in Taiwan these kinds of in-situ applications are still not available. This thesis presents a systemic approach to the analysis of two EAHE systems with different heat transfer media: water and soil. The soil-based systems were studied by means of long-term monitoring in Nantou, Taiwan, and analytical simulation. The experimental setup for the soil-based EAHE consists of seven parallel PVC pipes with 50m length and 0.25m diameter, buried at 3m depth beneath the ground surface, and a centrifugal fan with airflow rate of 6800m3/h. The operating strategy is to turn on the fan at 11:00 and turn off at 13:00. The results demonstrate that the annual acceptable cooling potential of soil-based earth-air heat exchanger may lower than the heating potential, but the midday intermittent operating can reach the maximum use of the cooling potential. The maximum total heat transfer rate ranged from -15 kW for heating, humidify, to about 40 kW for cooling, or dehumidify, during the period from May 2015 to January 2016. This thesis also develops an analytical model counting into the time delay effect and air humidity ratio. Through the analytical investigation, it was concluding that the effect of operating duration and latent heat exchange on performance is significant because they influence not only the temperature changes with time but also the exchange coefficient of soil. Intending to calculate the effect, dimensionless correlations were developed. Furthermore, to develop alternative efficient heat transfer media of earth air heat exchanger, an investigation for water-based system was also conducted in this thesis by an in-situ experiment in Yilan, Taiwan. The objective for the water-based EAHE consists of four air pipes with 40m length, 0.2m diameter, immersed in the water-filled raft foundation of a three stories building. A centrifugal fan with airflow rate of 1460 m3/h circulating the air into the system. The investigation shows that the cooling potential of the water beneath a building of 1.3m during spring season was close to that of ground soil at 2 m depth or deeper. The effect of changing the media around the air pipe of EAHE is significant. In addition, a suitable treatment of the ground surface is also important to avoid extra heat added into the water in the foundation. The in-situ experiment in three selected dates showed the air temperature could be dampened close to the average water temperature in the foundation. The ability of dehumidification was around 1.5 kg/hour and 2.8 kg/hour during hot season, and the averages of total heat transfer rate in hot weather was 3.36kW and 3.66kW, which was approximately equal to 1RT. In order to carry out the dimensioning of water-based EAHE, an analytical model was developed. Finally, the thermal and economic comparison between water and soil EAHE was presented, indicating that the water-based EAHE costs less than the soil-based one. The evaluated ROI periods are 4 years for water-based EAHE and 5 years for soil-based EAHE. The initial costs have huge effect on the ROI period, therefore an appropriate dimensioning was recommended in real application.

碩士
國立高雄師範大學
工業科技教育學系
107
In response to the continued warming of the global climate, Taiwan should be for highly dependent on energy imports.It is an urgent and imperative task for us to implement the policy of green building which is friendly to the earth and protects the environment in high-energy-consuming metropolitan buildings.The underground middle layer basically has the characteristics of constant temperature. Shallow geothermal energy or Earth-Air Heat Exchanger Systems can be used to import into buildings to improve the hot summer and cold winter, but also reduce the carbon footprint of buildings.In this study, numerical evaluation and simulation of raft foundation secondary utilization are carried out based on foreign cases and literature collection, and computational simulation is carried out by using CFD (Computational Fluid Dynamics) software.The results of simulation show that, in the summer, the external air of 35℃ is fed into the pipeline of the raft foundation space at the speed of 2 meters per second by a fan for heat exchange, and the temperature is reduced by 5.5℃ ~ 7.5℃. On the other hand, in winter, the external air of 15℃ is fed into the pipeline in the same way, to obtain 1.6℃ ~ 3.3℃ warming.It is concluded that the raft foundation space, which is located in the thermostatic layer and takes into account the structure, can be utilized to make full use of the stable shallow geothermal energy all the year round so as to make the indoor of the whole building cool in summer and warm in winter.It is suggested that architects should make good use of this geothermal resource to create low energy consumption design plans for buildings and generate efficient energy-saving houses.

碩士
國立臺灣大學
機械工程學研究所
105
Temperature of Nutrient Film Technique(NFT) is one of the types of Hydroponics. As compared to other Hydroponics, it can be controlled by temperature. The purpose of this study is to derive the mathematical model by heat transfer analysis, and the model can be used to predict the changes of the temperature with different operating and environmental conditions. This study used MATLAB to simulate the changes of the temperature of NFT during the summer time based on Steady State, Incompressible Flow, Navier-Stokes equations, and Thermal Resistance Analysis. According to the results of numerical analysis, with 35 °C ambient temperature and 40 °C the top of the planting tube, if we only change the input water temperature and its flow rate, the temperature of the water in the planting tube can reach the target temperature (15 ~ 24 °C), but the temperature of the air in the planting tube cannot reach the target temperature. Therefore, we need to change the parameters of hardware to optimize the design. This study used Taguchi Method and Gray Relation Analysis to approach the optimum parametric combination, with the considering of the temperature of NFT and the power consumption. The parameters include cooling method of heat pump, volume flow rate of water, wide of planting tube, temperature of inlet water of planting tube, and slope of planting tube. The result show, cooling method of heat pump with Shallow Geothermal Energy, volume flow rate of water of 2 (L/min), wide of planting tube of 0.06 (m), temperature of inlet water of planting tube of 16 (°C), and slope of planting tube of 4 % is the best in all level for system. According to the results of optimization, the highest temperature of water of inside planting tube of 21.66 (°C) can be reduced to 17.87 (°C), the highest temperature of air of inside planting tube of 30.65 (°C) can be reduced to 25.14 (°C), and power consumption of planting tube can save 53%. Shallow Geothermal Energy accounts for 43% of the contribution in the saving energy. According to the results of simulating operation, it''s payback period is 5 months, and it can reduce carbon emission by 1,000 (kg) monthly.

碩士
淡江大學
航空太空工程學系碩士班
106
In the generation of ever-changing technology, the use of energy is increasing. Green buildings, smart grids, etc. are all required to use electricity. This study will focus on the analysis of the thermal performance of drilling U-tube soil heat exchangers and try to change the shapes and material of the pipes, then find out ways to increase the efficiency of the soil heat exchanger. The project will use the commercial software ANSYS Fluent to create geometric shapes and meshes, and use the Fluent solver to perform simulation calculations. Finally, the results will be imported into Tecplot for analysis and discussion. We maintain the cross-sectional area of the U-tube for fractal structures and change the material of the tube wall for better heat dissipation. According to the analysis of the simulation results, fractal star pipes have the lowest outlet temperatures in both the PVC material and the carbon steel material. And the star tube increasing the most heat transfer efficiency from the carbon steel material. The round pipe which use the carbon steel pipe, which the outlet temperature has been lower than the star tube using PVC material. So we can change the tube’s material to reduce the temperature in the tube except to the reference mentioned in the use of different backfill material.

碩士
國立臺北科技大學
能源與冷凍空調工程系碩士班
97
Due to the limited indigenous resources in Taiwan, most energy resource are relied and imported from other countries. In addition, people are aware of carbon dioxide reducing and also the importance of clean renewable energy. With the inefficiency of the traditional fossil fuel systems and the pollutant emission, we need to look for any clean energetic system. Traditional refrigeration and air-conditioning are vapor compression refrigeration cycle that not only causes an enormous amount of electrical energy but leads to ozone-depleting and the global warming by releasing synthetic refrigerant substances. The reason why we need to seek the alternative refrigerant or even other energy lies in driven refrigeration and air-conditioning system. Because of the abundance of natural geothermal resources in Taiwan, the thesis presents mainly on（1）Using low temperature geothermal energy to drive LiBr/H2O absorption system and analyze the performances of it. Furthermore, this thesis compares primary energy ratio (PER) and carbon dioxide emission of the various energy-driven absorption systems.（2）Using high temperature geothermal energy to drive district cogeneration system that provides thermal energy, electricity and cooling energy to the residence of the region. Analyze the geothermal energy cogeneration system with thermodynamic first and second laws, showing the analysis of the energy losses and efficiency of each subsystem and entire cogeneration system. Therefore, the results of this research can be used to improve the further systematical performance and achieve optimum of district geothermal energy cogeneration system.

In the context of energy transition, geothermics play an important role for the heating and cooling supply of both residential and commercial buildings. Thereby, the increasingly and intensive utilisation of shallow geothermal resources bears the risk of over-exploitation and thus poses a future challenge to ensure the sustainability and safety of such systems. Particularly, the well-established technology of borehole heat exchanger-coupled ground source heat pumps is applied for the thermal exploitation of the shallow subsurface. Due to the complexity of the involved physical processes, numerical modelling proves to be a powerful tool to enhance process understanding as well as to aid the planning and design processes. Simulations can also support the management of thermal subsurface resources, planning and decision-making on city and regional scales. In this work, the so-called dual-continuum approach was adopted and enhanced to develop a coupled numerical model considering flow and heat transport processes in both the subsurface and borehole heat exchangers as well as the heat pumps’ performance characteristics, and including the relevant phenomena influencing the underlying processes. Beside the temperature fields, the efficiency and thus the consumption of electrical energy by the heat pump is computed, allowing for the quantification of operational costs and equivalent carbon-dioxide emissions. The model is validated and applied to a number of numerical studies. First, a comprehensive sensitivity analysis on the efficiency and sustainability of such systems is performed. Second, a method for the quantification of technically extractable shallow geothermal energy is proposed. This procedure is demonstrated by means of a case study for the city of Cologne, Germany and its implications are discussed.
Im Rahmen der Energiewende nimmt die Geothermie eine besondere Rolle in der thermische Gebäudeversorgung ein. Die zunehmende, intensive Nutzung oberflächennaher geothermischer Ressourcen erhöht die Gefahr der übermäßigen thermischen Ausbeutung des Untergrundes und stellt damit eine wachsende Herausforderung für die Nachhaltigkeit und Sicherheit solcher Systeme dar. Zur Erschließung oberflächennaher geothermischer Energie wird insbesondere die etablierte Technologie Erdwärmesonden-gekoppelter Wärmepumpen eingesetzt. Aufgrund der daran beteiligten komplexen physikalischen Prozesse erweisen sich numerische Modelle als leistungsfähiges Werkzeug zur Erweiterung des Prozessverständnisses und Unterstützung des Planungs- und Auslegungsprozesses. Zudem können Simulationen zum Management thermischer Ressourcen im Untergrund sowie zur Planung und politischen Entscheidungsfindung auf städtischen und regionalen Maßstäben beitragen. Im Rahmen dieser Arbeit wurde, basierend auf dem sogenannten ”dual-continuum approach” und unter Berücksichtigung des Einflusses der Wärmepumpe, ein erweitertes gekoppeltes numerisches Modell zur Abbildung der in Erdwärmesonden und dem Untergrund stattfindenden Strömungs- und Wärmetransportprozesse entwickelt. Das Modell ist in der Lage, alle relevanten Einflussfaktoren zu berücksichtigen. Neben den Temperaturfeldern im Untergrund und der Erdwärmesonde werden die Effizienz und damit der Stromverbrauch der Wärmepumpe simuliert. Damit können sowohl die Betriebskosten als auch der äquivalente CO 2 -Ausstoß abgeschätzt werden. Das Modell wurde validiert und in einer Reihe numerischer Studien eingesetzt. Zuerst wurde eine umfassende Sensitivitätsanalyse zur Effizienz und Nachhaltigkeit entsprechender Anlagen durchgeführt. Weiterhin wird ein Verfahren zur Quantifizierung des technisch nutzbaren, oberflächennahen geothermischen Potentials vorgestellt und anhand einer Fallstudie für die Stadt Köln demonstriert, gefolgt von einer Diskussion der Ergebnisse.

Geothermal energy is the energy naturally present inside the earth crust. When a large volume of hot water and steam is trapped in subsurface porous and permeable rock structure and a convective circulating current is set up, it forms a geothermal reservoir. A geothermal system can be defined as - convective water in the upper crust of earth, which transfers heat from a heat source (in the reservoir) to a heat sink, usually the free surface. A geothermal system is made up of three main elements: a heat source, a reservoir and a fluid, which is the carrier that transfers the heat. As an alternative source of energy geothermal energy has been under attention of the researchers for quite some time. The reason behind this is the existence of several benefits like clean and renewable source of energy which has considerable environmental advantage, with no chemical pollutants or wastes are generated due to geothermal emissions, and the reliability of the power resource. Hence research has been directed in several directions like exploration of geothermal resources, modeling the characteristics of different types of geothermal reservoirs and technologies to extract energy from them. The target of these models has been the prediction of the production of the hot water and steam and thus the estimation of the electricity generating potential of a geothermal reservoir in future years. In a geothermal power plant reinjection of the heat depleted water extracted from the geothermal reservoir has been a common practice for quite some time. This started for safe wastewater disposal and later on the technology was employed to obtain higher efficiency of heat and energy extraction. In most of the cases a very small fraction of the thermal energy present in the reservoir can be recovered without the reinjection of geothermal fluid. Also maintaining the reservoir pressure is essential which gradually reduces due to continuous extraction of reservoir fluid without reinjection, especially for reservoirs with low permeabilities. Although reinjection of cold-water has several benefits, the possibility of premature breakthrough of the cold-water front, from injection well zone to production well zone, reduces the efficiency of the reservoir operation drastically. Hence for maintaining the reservoir efficiency and longer life of the reservoir, the injectionproduction well scheme is to be properly designed and injection and extraction rates are to be properly fixed. Modeling of flow and heat transport in a geothermal reservoir due to reinjection of coldwater has been attempted by several researchers analytically, numerically and experimentally. The analytical models which exist in this field deal mostly with a single injection well model injecting cold-water into a confined homogeneous porous-fractured geothermal reservoir. Often the thermal conductivity is neglected in the analytical study considering it to be negligible which is not always so, as proved in this study. Moreover heterogeneity in the reservoir is also a major factor which has not been considered in any such analytical study. In the field of numerical modeling there also exists a need of a general coupled three-dimensional thermo-hydrogeological model including all the modes of heat transport (advection and conduction), the heat loss to the confining rocks, the regional groundwater flow and the geothermal gradient. No study existing so far reported such a numerical model including those mentioned above. The present study is concerned about modeling the non-isothermal flow and heat transport in a geothermal reservoir due to reinjection of heat depleted water into a geothermal reservoir. Analytical and numerical models are developed here for the transient temperature distributions and advancement of the thermal front in a geothermal reservoir which is generated due to the cold-water injection. First homogeneous geothermal aquifers are considered and later heterogeneities of different kinds are brought into picture. Threedimensional numerical models are developed using a software code DuMux which solves flow and heat transport problems in porous media and can handle both single and multiphase flows. The results derived by the numerical models have been validated using the results from the analytical models derived in this study. Chapter 1 of the thesis gives a brief introduction about different types of geothermal reservoirs, followed by discussion on the governing differential equations, the conceptual model of a geothermal reservoir system, the efficiency of geothermal reservoirs, the modeling and simulation concepts (models construction, boundary conditions, model calibration etc.). Some problems related with geothermal reservoirs and geothermal power is also discussed. The scenario of India in the context having a huge geothermal power potential is described and different potential geothermal sites have been pointed out. In Chapter 2, the concept of reinjection of the heat depleted (cold) water into the geothermal reservoir is introduced. Starting with a brief history of the geothermal reinjection, the chapter describes the purpose and the need of reinjection of geothermal fluid giving examples of different geothermal fields over the world where reinjection has been in practice and benefitted by that. The chapter further discusses on the problems and obstacles faced by the geothermal projects resulting from the geothermal reinjection, most important of which is the thermal-breakthrough and cooling of production wells. Lastly the problem of this thesis is discussed which is to model the transient temperature distribution and the movement of the cold-water thermal front generated due to the reinjection. The need of this modeling is elaborated which represents the motivation of taking up the problem of the thesis. Chapter 3 describes an analytical model developed for the transient temperature in a porous geothermal reservoir due to injection of cold-water. The reservoir is composed of a confined aquifer, sandwiched between rocks of different thermo-geological properties. The heat transport processes considered are advection, longitudinal conduction in the geothermal aquifer, and the conductive heat transfer to the underlying and overlying rocks of different geological properties. The one-dimensional heat transfer equation has been solved using the Laplace transform with the assumption of constant density and thermal properties of both rock and fluid. Two simple solutions are derived afterwards, first neglecting the longitudinal conductive heat transport and then heat transport to confining rocks. The analytical solutions represent the transient temperature distribution in the geothermal aquifer and the confining rocks and model the movement of the cold-water thermal front in them. The results show that the heat transport to the confining rocks plays an influential role in the transient heat transport here. The influence of some parameters, e.g. the volumetric injection rate, the longitudinal thermal conductivity and the porosity of the porous media, on the transient heat transport phenomenon is judged by observing the variation of the transient temperature distribution with different values of the parameters. The effects of injection rate and thermal conductivity have been found to be high on the results. Chapter 4 represents another analytical model for transient temperature distribution in a heterogeneous geothermal reservoir underlain and overlain by impermeable rocks due to injection of cold-water. The heterogeneity of the porous medium is expressed by the spatial variation of the flow velocity and the longitudinal effective thermal conductivity of the medium. Simpler solutions are also derived afterwards first neglecting the longitudinal conduction, then the heat loss to the confining rocks depending on the situation where the contribution of them to the transient heat transport phenomenon in the porous media is negligible. Solution for a homogeneous aquifer with constant values of the rock and fluid parameters is also derived with an aim to compare the results with that of the heterogeneous one. The effect of heat loss to the confining rocks in this case is also determined and the influence of some of the parameters involved, on the transient heat transport phenomenon is assessed by observing the variation of the results with different magnitudes of those parameters. Results show that the heterogeneity plays a major role in controlling the cold-water thermal front movement. The transient temperature distribution in the geothermal reservoir depends on the type of heterogeneity. The heat loss to the confining rocks of the geothermal aquifer also has influence on the heat transport phenomenon. In Chapter 5 another analytical model is derived for a heterogeneous reservoir where the heterogeneous geothermal aquifer considered is a confined aquifer consisted of homogeneous layers of finite length and overlain and underlain by impermeable rock media. All the different layers in the aquifer and the overlying and underlying rocks are of different thermo-hydrogeological properties. Results show that the advancement of the cold-water thermal front is highly influenced by the layered heterogeneity of the aquifer. As the cold-water thermal front encounters layers of different thermo-hydrogeological properties the movement of it changes accordingly. The analytical solution derived here has been compared with a numerical model developed by the multiphysics software code COMSOL which shows excellent agreement with each other. Lastly it is shown that approximation of the properties of a geothermal aquifer by taking mean of the properties of all the layers present will lead to erroneous estimation of the temperature distribution. Chapter 6 represents a coupled three-dimensional thermo-hydrogeological numerical model for transient temperature distribution in a confined porous geothermal aquifer due to cold-water injection. This 3D numerical model is developed for solving more practical problems which eliminate the assumptions taken into account in analytical models. The numerical modeling is performed using a software code DuMux as mentioned before. Besides modeling the three-dimensional transient temperature distribution in the model domain, the chapter investigates the regional groundwater flow has been found to be a very important parameter to consider. The movement of the thermal front accelerates or decelerates depending on the direction of the flow. Influence of a few parameters involved in the study on the transient heat transport phenomenon in the geothermal reservoir domain, namely the injection rate, the permeability of the confining rocks and the thermal conductivity of the geothermal aquifer is also evaluated in this chapter. The models have been validated using analytical solutions derived in this thesis. The results are in very good agreement with each other. In Chapter 7 the main conclusions drawn from the study have been enlisted and the scope of further research is also pointed out.

博士
國立臺灣大學
機械工程學研究所
100
The purpose of this dissertation is to investigate the optimal design of geothermal heat pump. This dissertation experimentally and mathematically investigates the performance of the geothermal heat pump system which consists of a heat pump and a borehole heat exchanger. Furthermore, optimal method for analyzing the cost influences of the life cycle of the system were developed based on different operation strategies and the capacity of the equipment (combination of heat pumps and borehole heat exchangers). For the performance of the heat pump system, the comparison between the mathematical modeling and the experimental approaches are identical. The relation of correlation R2 is about 0.9867. On the contrary, the capability of the borehole heat exchangers was investigated. The variation of the water temperature inside the cylindrical tube and the outlet water temperature in the spiral pipe were solved by using the thermal resistance method. The result shows that the error of the temperature for spiral pipe outlet and water temperature inside the cylindrical tube with compare to the mathematical model is 0.31% and 3.12%. While in the optimum design, it compares the performances of four updating rules of the particle swarm optimization (PSO) through applying five mathematic problems. The linear-decayed inertia weight method is favorable for this study because stability of solutions can be obtained. This dissertation also developed a solution for the discrete problem of the on-off system in the water pump and heat pump by using PSO with Roulette Wheel Method. Finally a case study was conducted. The geothermal heat pump system was developed in a factory in order to obtain the optimization. The primary parameters include the turn-off states of heat pump and water pump, the heat pump capacity, the UA of heat exchanger, the initial cold and heat water temperature and the capacity of cold and heat tank. The results indicated that the cost of life cycle of the geothermal heat pump system can be reduced by NT 1,446,552, the ratio of energy saving is 56.23%. The energy consumption decrement is 965,756 kJ/day, the ratio of energy saving is 46.50% and the reduction of CO2 emissions is 167 kg/day for a period of 10 years which compare to the conventional boiler combined with chiller.

Dissertação de Mestrado Integrado em Engenharia do Ambiente apresentada à Faculdade de Ciências e Tecnologia da Universidade de Coimbra.
O aquecimento global, associado à elevada dependência nos combustíveis fósseis e ao crescente consumo energético, provocou situações dramáticas e impactes ambientais, bem como impactes socio-económicos. No sentido de inverter este cenário surgiram as energias renováveis para produção de energia eléctrica e para reduzir a dependência do petróleo, do carvão, etc., os quais são altamente poluentes e estão nos limites das suas reservas. Neste contexto surge o estudo da Energia Geotérmica. Esta energia, que se encontra no subsolo, tem-se afirmado como uma das alternativas, mas com fraco crescimento, quando comparado com outras energias renováveis. O aproveitamento da energia geotérmica, quer seja de alta entalpia, para produção de energia eléctrica, de baixa entalpia para usos directos ou de muito baixa entalpia para climatização de edifícios, tornase solução evidente, eficaz e rentável face a energias renováveis como a solar ou a eólica, uma vez que pode ser utilizada em continuidade. A energia geotérmica é já bastante usada mundialmente, mas ainda requer incentivos para um maior desenvolvimento em muitos países. No nosso país, apenas na ilha de S. Miguel nos Açores há produção de electricidade de forma significativa através da energia geotérmica, e no Continente basicamente apenas há aproveitamentos dos pólos termais para efeitos de climatização. Este estado insípido de Portugal na utilização da Energia Geotérmica, exige um grande impulso, principalmente a Energia Geotérmica de Baixa Entalpia e de Muito Baixa Entalpia, para que possam ter um papel de destaque no contributo para o mix energético nacional. Com esta dissertação pretende-se contribuir para a divulgação da Energia Geotérmica de Baixa Entalpia e de Muito Baixa Entalpia como alternativa sólida às energias primárias para produção de energia eléctrica, aquecimento e climatização de edifícios.
The Earth global warming, associated with the high dependence on fossil fuels and the ever growing energy consumption, caused dramatic situations and environmental impacts, as well as socio-economic impacts. To reverse this scenario, the use of renewable energy for production must be considered in order to reduce the dependence on oil, coal, etc, which are highly polluting and are within the limits of its reserves. In this context, the study of Geothermal Energy emerges. This energy contained in the Earth underground has established itself as one of the alternatives, but with a feeble growth up to now, when compared with other renewable energy. The use of geothermal energy, whether it be High-Enthalpy, for production of electrical energy, Low- Enthalpy, for direct uses, or Very Low Enthalpy, for buildings air conditioning, becomes an obvious, efficient and cost effective solution, compared to renewable energy such as solar or wind, since it can be used in continuity. Geothermal energy is already widely used worldwide, but it still requires incentives for greater development in many countries. In Portugal, there is electricity production only in the S. Miguel Island in the Azores, and in the Continent there is only exploitation of thermal poles. This insipid state of Portugal in concerning the use of geothermal energy requires a big boost, especially Energy Low and Very Low Enthalpy Geothermal, so that they can have a major role in contributing to the national energy mix. This dissertation aims at contributing for spreading the Geothermal Energy of Low and Very Low Enthalpy as a solid alternative to the primary energies for the production of electricity, heating and cooling of buildings.

碩士
國立臺北科技大學
建築與都市設計研究所
100
As we know, the nature resources in Taiwan is not sufficient, geothermal energy is one of important nature energy. So far 26 famous geothermal places were developed and used in Taiwan. Geothermal energy can be used to generate power, warm up the air condition system, and heat the water; as well as develop the tourism of spring water for leisure and other multiple functions. The operation of air condition unit is occupied 30% of energy consumption in the building equipment. To analyze different parts of the operation of air condition, main power station is occupied 60% sharing, water pump is 11%, air condition box and indoor fan is 13% and others is 16%. Using geothermal energy to assist air condition system will reduce the power consumption on the start of main station and decrease the energy exhaustion. Comparing with traditional air condition, geothermal energy can save the energy, prolong the time of maintenance, extend the life cycle of air condition system and reduce the cost for operation. The thesis is a study of geothermal energy application to assist air-conditioning system to save energy-a case study of Taiwan Sea Gaia Spring Hotel, using spring water with the temperature 90℃~100℃ to assist main power station of air condition, to discuss the possibility to save main power station energy consumption and reduce the energy exhaustion.