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In recent years a growing interest in Borehole Heat Exchangers (BHEs) has been shown in Europe thanks to the increase of installations in systems connected to Ground Source Heat Pumps (GSHPs) used for heating and cooling needs. Different geometries and technical solutions have been de- veloped in order to improve heat exchange with the ground, accompanied by several descriptive models. Recently, innovative technologies as optical fiber for a new Distributed Thermal Response Test (DTRT) have been proposed. This method allows the quantification of the BHE local perfor- mances, so that a more accurate punctual analysis of thermal phenomena is allowed. The aim of this thesis is to locate an analytical model thanks to the most recent data, to achieve the definition of overall efficiency of a single BHE in terms of thermal resistance and of a BHE-GSHP system in terms of evaluation of the Coefficient of Performance. This model accuracy will be verified with new measures in a real installation. A particular attention will be given to the thermal-fluid-dynamics aspects, defining semi-empirical correlation for free and forced convection within the BHE groundwater filling.

Ground source cooling is commonly used for cooling of electronics in protected sites. Sometimes the boreholes are combined with free cooling from the air using a dry cooler to reduce the amount and length of the boreholes, which is the biggest part of the costs. The dry cooler can have two different running modes. In unloading mode the dry cooler is started at a certain temperature and the fans are slowed down at low temperatures so that the cooling power never exceeds the cooling demand. The extracted cooling is used to unload the boreholes. In recharging mode the dry cooler is started at a certain temperature and is operating at full capacity below this temperature. The excess cooling that is extracted in this mode is used to recharge the boreholes. The numerical simulation tool COMSOL Multiphysics was used to evaluate the borehole performance. The software can simulate tilted boreholes with good accuracy and makes it possible to adjust the geometry in any desired way. In this thesis, the performance of a 100 kW ground source cooling system is evaluated for a number of cases both with and without dry coolers in different running modes and sizes. The best solution in respect to life cycle cost, technical feasibility and environmental impact is chosen to be an unloading case with a dry cooler with 100 kW capacity at 8 °C. Using only boreholes gives less carbon dioxide emissions but much higher costs.

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京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20922号 / 理博第4374号 / 新制||理||1628(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 James Mori, 教授 中西 一郎, 准教授 久家 慶子 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

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No description available.

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.

Existing models of the hydrogeology in the Blue Ridge Province in the eastern United States generally assume a simplified two-layered system consisting of shallow unconsolidated and relatively homogeneous and porous regolith with a water-table aquifer that slowly supplies water downward to the underlying variably fractured crystalline bedrock. In these models, interconnected fractures in the crystalline bedrock act as conduits for predominantly downward vertical and limited horizontal flow. Fracture density is depthà limited and correlated with proximity to topographic lineaments. Current models consider the porous regolith as the primary water storage reservoir for the entire aquifer system. In this research, detailed hydrogeologic studies in the Blue Ridge Province in Floyd County, Virginia reveal a substantially different framework for groundwater flow. Recent acquisition of two-dimensional surface resistivity profiles collected using a variety of array techniques combined with borehole geophysical logs revealed new insights into this geologically complex province. Dipole-dipole arrays were particularly important in gathering high resolution resistivity profiles that document horizontal and vertical resistivity variation reflecting changes in subsurface geology and anomalous low resistivity areas in crystalline bedrock associated with fault zones. The shallow regolith contains unsaturated areas and also localized sand and clay prone facies with water table and confined aquifer conditions residing locally. Hydraulic heads between the shallow aquifer and the deeper fractured bedrock aquifer can vary by 20 m vertically. Within the crystalline bedrock are anomalous lower resistivity intervals associated with ancient fault shear zones. Brecciated rock adjacent to the shear zones, and the shear zones themselves, can be hydraulically conductive and serve as pathways for groundwater movement. Aquifer testing of the regolith-bedrock fracture system occurred over a 6-day period and produced rapid and relatively uniform drawdowns in surrounding wells completed in the fractured bedrock aquifers. The shallow aquifers experienced minimal drawdowns from the aquifer test indicating low vertical hydraulic conductivity and limited communication between the shallow and deeper bedrock aquifers. Water chemistry and chlorofluorocarbon (CFC) age dating analyses indicated significant differences between water samples from the shallow and deep aquifers. A new conceptual model for Blue Ridge aquifers is proposed based on these research findings. / Ph. D.

The Coles Hill uranium deposit in Pittsylvania County, VA, is the largest un-mined uranium deposit in the United States. The deposit is located in the Virginia Piedmont in a geologic unit located immediately west of the Chatham Fault, which separates the granitic rocks of the Virginia Piedmont to the west from the metasediments of the Danville Triassic basin to the east. Groundwater at the site flows through a complex interconnected network of fractures controlled by the geology and structural history of the site. In this study groundwater is characterized in a small study area just south of the main deposit. Methods used in this investigation include electrical resistivity profiling, bore hole logging, a pumping test, and age dating and water chemistry. In this thesis groundwater flow is confirmed to occur from the Piedmont crystalline rocks across the Chatham Fault and into the Triassic basin at the study area as evidenced by pumping test data and static water-level data from observation wells. Well logs have identified fractures capable of transmitting water in the granitic rocks of the Piedmont, the Triassic basin metasediments and the Chatham Fault but the largest quantities of flow appear to occur in the Triassic basin. A definable recharge area for the groundwater present at Coles Hill can not yet be determined due to the complexity of the fracture system, but age dating confirms that groundwater is composed of both young and old (>60 years) components, indicating that at least a portion of groundwater at Coles Hill originates from a more distant area. / Master of Science