Thesis (Ph.D.)--University of Wyoming, 2007. / Title from PDF title page (viewed on June 17, 2009). Includes bibliographical references (p. 167-178).

No description available.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains ix, 92 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 72-75).

Geothermal heat exchangers are a growing energy technology that improve the energy efficiency of heating and cooling systems in buildings. Vertical borehole heat exchangers (BHE) coupled with ground source heat pumps have been widely developed and researched in the past century. The major disadvantage of BHEs is the initial capital cost required to drill the boreholes. Geothermal energy piles (GEP) were developed to help offset the high initial cost of these systems. A GEP combines ground source heat pump technology with deep earth structural foundations of buildings. GEPs are relatively new technology and robust standards and guidelines have not yet been developed for the design of these systems. The main operational difference between GEPs and conventional BHEs is the length and diameter of the below ground heat exchangers. The diameter of a GEP is much larger and the length is typically shorter than BHEs. Computational fluid dynamics (CFD) analysis is used in this study to investigate and better understand how structural piles perform as geothermal heat exchangers. The CFD analysis is used to simulate an existing experimental energy pile test. The experimental test is modeled as built including fluid modeling to provide additional detail into the behavior of the circulation fluid within the pile. Two comparisons of large diameter GEPs are made using CFD analysis to gain knowledge of the effects of varying pile diameter and loop configuration. The thermal response test was successfully modeled using the CFD model. The CFD results closely match the results of the field test. The large diameter comparisons show that the performance of an energy pile will increase as the diameter increases with a constant loop density. Multiple numbers of loops were tested in a constant diameter pile and the results show that with symmetrically placed loops the performance will increase with a greater number of loops in the pile. / Master of Science

No description available.

Climate change stabilization requires an unprecedented effort to change our current approach to energy production and consumption. While rising energy prices are drawing increased attention to reducing energy demand, heightened concern about the environmental consequences of fuel choice requires that this demand be met at lower emission levels. In Canada, the realization of commitments to our GHG emission goals entails reducing residential energy use - a sector responsible for close to 20 percent of end-use energy consumption. This study focuses on the energy demand and emission levels of space and water heating, since these two components comprise 76 percent of residential energy demand. Ground source heat pumps (GSHPs) are a technology that provides heating at 25 to 30 percent of the energy consumed by even the most efficient conventional alternatives. GSHPs have been identified as the most energy-efficient, environmentally clean, and cost-effective space conditioning systems available. However, their drawbacks have been high capital costs, and uncertainty about whether the electric power used by heat pumps has higher system-wide emissions. This thesis delineates how adoption of GSHPs in the residential sector can help align Canada’s technology choices with commitments made to the Kyoto Protocol. The manuscripts delineate conditions under which GSHP systems achieve the largest net emission reductions relative natural gas, heating oil, and electric heat counterparts. Electricity generation methods and emissions embodied in inter-provincial and international electricity trade are shown to significantly affect the emission savings achievable through GSHP. The thesis quantifies how relative fuel prices influence annual operating savings that determine how rapidly the technology can achieve payback. This analysis reveals GSHPs to hold significant potential for substantial GHG reductions at a cost savings relative to conventional alternatives; the time horizons for payback are as short as nine years for average-sized homes, and significantly shorter for larger homes.

This thesis presents an experiment and an analysis that evaluates some of the long-standing assumptions in deep vertical borehole ground heat exchanger (GHX) theory. These assumptions neglect ground heterogeneity and depth variations in GHX output and the ground temperature response (GTR). This thesis describes an apparatus and an experiment that measured the GTR at several depths, times, and at two different horizontal distances from a GHX both during and immediately after its operation. This thesis also reports the temperature response data, which may not be available from other sources in such detail. The experiment showed that the GTR can be highly depth dependant. The analysis involved a parametric study to characterize the GTR by developing an effective computer simulation of the experiment. The analysis showed that ground heterogeneity significantly affected the GTR and the GHX output in this study. Furthermore, this GHX output showed depth and time, dependence.

This thesis presents an experiment and an analysis that evaluates some of the long-standing assumptions in deep vertical borehole ground heat exchanger (GHX) theory. These assumptions neglect ground heterogeneity and depth variations in GHX output and the ground temperature response (GTR). This thesis describes an apparatus and an experiment that measured the GTR at several depths, times, and at two different horizontal distances from a GHX both during and immediately after its operation. This thesis also reports the temperature response data, which may not be available from other sources in such detail. The experiment showed that the GTR can be highly depth dependant. The analysis involved a parametric study to characterize the GTR by developing an effective computer simulation of the experiment. The analysis showed that ground heterogeneity significantly affected the GTR and the GHX output in this study. Furthermore, this GHX output showed depth and time, dependence.

Climate change stabilization requires an unprecedented effort to change our current approach to energy production and consumption. While rising energy prices are drawing increased attention to reducing energy demand, heightened concern about the environmental consequences of fuel choice requires that this demand be met at lower emission levels. In Canada, the realization of commitments to our GHG emission goals entails reducing residential energy use - a sector responsible for close to 20 percent of end-use energy consumption. This study focuses on the energy demand and emission levels of space and water heating, since these two components comprise 76 percent of residential energy demand. Ground source heat pumps (GSHPs) are a technology that provides heating at 25 to 30 percent of the energy consumed by even the most efficient conventional alternatives. GSHPs have been identified as the most energy-efficient, environmentally clean, and cost-effective space conditioning systems available. However, their drawbacks have been high capital costs, and uncertainty about whether the electric power used by heat pumps has higher system-wide emissions. This thesis delineates how adoption of GSHPs in the residential sector can help align Canada’s technology choices with commitments made to the Kyoto Protocol. The manuscripts delineate conditions under which GSHP systems achieve the largest net emission reductions relative natural gas, heating oil, and electric heat counterparts. Electricity generation methods and emissions embodied in inter-provincial and international electricity trade are shown to significantly affect the emission savings achievable through GSHP. The thesis quantifies how relative fuel prices influence annual operating savings that determine how rapidly the technology can achieve payback. This analysis reveals GSHPs to hold significant potential for substantial GHG reductions at a cost savings relative to conventional alternatives; the time horizons for payback are as short as nine years for average-sized homes, and significantly shorter for larger homes.

As an alternative and renewable energy source, the shallow geothermal energy evolving as one of the most popular energy source due to its easy accessibility and availability worldwide, and the ground source heat pump (GSHP) systems are the most frequent applications for extracting the energy from the shallow subsurface. As the heat extraction capacity of the GSHP system applications arises, the design of the borehole heat exchangers (BHE), which is the connected part of the system in the ground, become more important. The backfilling materials of BHEs, particularly, the grout material must provide a suitable thermal contact between the ground and the heat carrier fluid in the high density polyethylene (HDPE) pipes and ensure durability to the induced thermal stresses due to the heat loading. In addition, for the heating purposes of buildings, BHEs immerged in groundwater may be operated below the freezing point of water with anti-freeze mixture in the pipe, leading to freezing-induced ice pressure which may damage the grout.In order to propose a proper grouting for BHEs, the thermo-hydro-mechanical behavior of the grout and its interferences with the adjacent ground conditions must be evaluated in the near field, and the thermal interactions of each BHE in a multi-BHEs field in the long-term operations must also be considered at a further field.Primarily, we have evaluated the performance of various grouting materials, through thermal, hydraulic and mechanical laboratory characterizations. In particular, we have proposed a homemade grout material, with the addition of graphite powder to improve the thermal properties of grout material. In parallel, the characteristics of two different widely used commercial grouting materials (i.e. calcite-based and silica-sand based materials) have been also investigated. In the subsequent study, the heat flow rate per meter of a BHE and the borehole resistance of borehole heat exchangers are assessed experimentally in a 1×1×1 m3 sandbox under, successively, dry sand and fully water-saturated sand conditions. During the operations, the monitored temperatures in the sandbox are in good agreement with analytical predictions. This study demonstrated that the homemade admixture prepared with 5 % natural flake graphite can be considered as an appropriate grout for BHEs regarding to its rheological and thermo-physical properties. Thermally-enhanced grouting can be of significant interest in a high thermal conductivity ground (such as saturated sand) because it minimizes the thermal resistance of the BHE.After characterizing and testing the efficiency of various grout materials, the thermal stresses occurred in BHEs due to heat injection or extraction has been investigated with the analytical solution of hollow cylinder model that is adapted for time-dependent heat loading, the geometry of a BHE, and the thermo-mechanical properties of surrounding ground conditions. Firstly, the hollow cylinder model has been solved for the considered boundary conditions in 2D plane stress. Secondly, the temperature differences at the inner and outer circles of the cylinder is evaluated with the heat line source models for continuous and discontinuous loadings to observe the impact of the heat loading schedule. The developed analytical solution for thermal stress investigation is validated with numerical models. It is demonstrated that the analytical solutions agree well with numerical results for two types of BHE configurations (co-axial and single U-shaped pipes). Furthermore, the calculated maximum stresses are compared with the tensile strength of grout materials obtained from Brazilian tests. It is predicted that thermal contraction of the grout, partially constrained by the surrounding rock, generates tensile stresses that may lead to cracking in the BHE. According to the results, the stiffness of rock has primary role on the developed tensile stresses, and the relationship between the thermal conductivity of the ground and of the grout induces a proportional impact on the magnitude of thermal stresses.Another major concern is the freeze-resistance of the grout materials, when the system is operated for heating purposes. Firstly, we conducted an experimental setup in a small-scale sandbox to understand the behavior of the grout material by evaluating the permeability change during freeze-thaw cycles of a BHE. According to the results, the permeability of grout materials did not change after 10 freeze-thaw cycles due to the thermal transfer with the adjacent soil partially reducing the impact of freezing in the grout material. Therefore, in order to test the freeze-resistance of a BHE, we have investigated the freezing impact of pore water pressure and thermal stress with analytical models and experimental setups on BHEs. For the theoretical approach, an analytical solution has been developed by using the hollow cylinder model that accounts for both the HDPE pipe and the grout material. Firstly, the freezing pore water pressure is adapted to the generalized Hooke’s law equations in 2D plane stress, and secondly the model is solved for the considered boundary conditions. In order to validate the developed model, the experimental setup is conducted in agreement with the geometry of the considered analytical model and the BHE probes are prepared with three different grout materials having large difference in the thermal and hydraulic characteristics (i.e. silica-sand based, calcite based and the homemade enhanced thermally with natural flake graphite powder). According to the experiments for 50 h of freezing operation, the calcite based grout and the homemade grout, having lower permeability and relatively higher porosity, are fractured. In contrast, the silica-sand based grout having higher permeability did not exhibit any damage. Compared with the theoretically obtained results, the observations from the experiments are consistent with the calculated stress results. The effective tangential stress induced by the freezing pore water pressure causes the crack development and agrees with the crack patterns. As a conclusion, the porosity and the permeability play a significant role on the grout failure.In a multi-BHEs field, the thermal interaction between each BHE may have a significant influence on the near-field investigation results in long-term operations. Therefore, in order to complete the near-field investigation, a far-field long-term operation study is required. However, existing analytical solutions for thermal analysis of ground source heat pump (GSHP) systems evaluate temperature change in the carrier-fluid and the surrounding ground in the production period of a single BHE only if a continuous heat load is assigned. In this study, we modified the Green’s function, which is the solution of heat conduction/advection/dispersion equation in porous media, for discontinuous heat extraction by analytically convoluting rectangular function or pulses in time domain both for single and multi-BHEs field. The adapted analytical models for discontinuous heat extraction are verified with numerical finite element code. The comparison results agree well with numerical results both for conduction and advection dominated heat transfer systems, and analytical solutions provide significantly shorter runtime compared to numerical simulations (approx. 1500 times shorter). Furthermore, we investigated the sustainability and recovery aspects of GSHP systems by using proposed analytical models under different hydro-geological conditions. According to the engineering guideline VDI 4640, a linear relationship between thermal conductivity of the ground and the sustainable heat extraction rate is demonstrated for multi-BHEs. In addition, we developed an MATLAB interface for users in which the analytical model can be used easily and more efficiently.In addition, in order to extend the case studies for a ground including several layers, we proposed a finite line source model for BHEs that takes into account conduction/advection/dispersion mechanism in multilayer porous media. Firstly, the anisotropy is added to the moving finite line source model, and we used an existing composite model approach for conductive multilayer ground. The comparison with the numerical model results demonstrates the suitability of the approach. The proposed model can provide a faster solution than classical numerical approaches and help to optimize the heat extraction rate in multilayer media. However, further investigations are required to validate the model with the field measurements. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished