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Closed-loop ground source heat pump system: (a) horizontal circulation loops and (b) vertical circulation loops

Closed-loop ground source heat pump system: (a) horizontal circulation loops and (b) vertical circulation loops

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Thesis
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The use of geothermal piles as foundation elements of residential and office buildings is an innovative and sustainable method of energy conservation. Heat exchange through piles may have significant impact on their geotechnical performance due to thermally induced mechanical stresses and additional settlements caused by constrained thermal strains...

Citations

... (a) Calcareous silty sand (after Beemer et al., 2018) (b) Silica sand (after Kramer, 2013) (c) Gulf of Mexico clay (Deirieh et al., 2018) Figure 1. SEM images of soils with varying particle size Figure 2. Mechanical response in undrained simple shear for two calcareous silts of varying particle size (Mao & Fahey, 2003) For developing oil and gas fields and harnessing renewable energies, it is necessary to found or moor facilities at calcareous seabed. ...
Conference Paper
Calcareous soils have been identified as problematic due to the special characteristics such as higher compressibility and softening, higher strain rate dependency as well as contractancy and dilatancy depending on the particle size (along with other factors). With the aim to propose an improved soil constitutive model for capturing the behaviour of calcareous silt, an experimental program on a range of reconstituted calcareous soils is undertaken for developing and calibrating the model. This paper investigates the undrained shearing response (as measured under triaxial compression conditions) of two calcareous soils of varying silt contents. The effect of particle size on the undrained shear strength and dilative or contractive response of calcareous soils is discussed.
... Therefore, it needed more energy to be rejected from the geothermal pile to observe an identical change in temperature in the saturated sand. These results are in consensus with previous work carried out by Mohamed et al. (2015), Kramer (2013) and Bao et al. (2019). The horizontal soil temperature profile at mid-height of the pile (450 mm below the soil surface) measured on both inlet and outlet sides are shown in Fig. 11. ...
... The maximum increase in the soil temperature from its initial state (20 ± 1 • C) was recorded at ̴ ̴ 15 • C in tests carried out on dry sand. This could be attributed to its lower heat capacity and thermal conductivity (Kramer, 2013, Faroki, 1986and Alrtimi et al., 2014. Whereas, when the energy pile was installed in a partly saturated sand, the maximum soil temperature difference was found to be 10 • C resulting in a reduction of 33%. ...
Article
This study aims to evaluate the impacts of using thermally enhanced concrete on the thermal performance of geo-energy structures and interaction between the thermo-active-structures and adjacent dry and partly saturated soils. Experiments using a fully instrumented testing rig were carried out on prototypes of energy pile and diaphragm wall made from normal concrete and thermally enhanced concrete by the addition of graphTHERM powder. Results illustrated that adding 36% of graphTHERM powder to the concrete by weight of cement was found to double the thermal conductivity of concrete and improve the stiffness by 15% without detrimental effects on the compressive strength. The heat transfer efficiency of energy pile and energy diaphragm wall made from thermally enhanced concrete was significantly improved by 50% and 66% respectively, in comparison with the efficiency of the same type of energy structure that was made from a typical normal concrete.
... Recently, Kramer et al. and Ghasemi-Fare and Basu designed and conducted a big scaled laboratory energy pile embedded in dry and saturated sandy soil with variable boundary conditions, and thermo-mechanical loading at the Pennsylvania State University. Their results demonstrated an increase in shaft and base bearing capacity of the pile at elevated temperatures, and higher temperature changes close to the energy pile in dry soil compared to the saturated condition [145][146][147]. Physical tests performed in literature with various geometries embedded in different soil types concluded that: (1) the influence zone in which temperature rises more than 1 to 2 ∘ C is almost identical to one diameter of the energy pile; (2) pile tip resistance increases by heating and reduces during cooling loads; ...
... The mobilized skin friction along the pile was noticeably changed by thermal cycles. Kramer and Basu 2014 [145,161] Reinforced concrete ...
Article
Ground Source Heat Pumps (GSHPs) have been installed all around the world to harvest shallow geothermal energy for heating and cooling building envelopes. However, the high initial cost of these systems (e.g., drilling and installation costs) limits the popularity and total usage of GSHPs around the world. To reduce the initial cost of these systems, geothermal heat exchangers are combined with structural components of the building, such as deep foundations, or energy walls. Energy piles or thermo-active foundations that serve dual purposes have been widely utilized in the last two decades in many developed countries. However, in most of the developing countries like Iran, there are several critical impediments to install these systems to harvest shallow geothermal energy. This study aims to propose practical suggestions to increase the rate of energy piles installation as an alternative environmentally friendly energy system to heat and cool residential and commercial buildings in Iran by I) summarizing the lessons learned from energy piles projects in different countries, II) providing crucial information regarding design, construction, and implementation of energy piles to prepare a design code based on Iran's economic and environmental condition, III) reporting disadvantages of energy piles to determine challenges for engineers to find a solution for minimizing these issues, and IV) proposing key impediments in the way of implementation of energy piles in Iran and providing some practical suggestions to tackle these impediments.
... Blue arrows mark the depth of the water table below the surface for our experiments in the Capillary (CR) and Unsaturated (UR) regimes. this sand is 0.025 to 0.038 cm/s (Kramer, 2013). Based on bulk density, porosity was ϕ ¼ 0:358 ± 0:003 (ϕ ¼ 1 − ρ bulk =ρ particle , where ρ bulk is the mass of sand added to the chamber divided by its volume, and ρ particle is 2.65 g/cm 3 ). ...
Article
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Strong earthquakes can cause different kinds of hydrological responses, and several mechanisms have been suggested to explain them. Verification of these mechanisms, however, is often lacking. Here we test some hypotheses with a laboratory experiment, in particular the hypothesis that dynamic strain mobilizes trapped water in the unsaturated zone. We construct a sand chamber, partially saturated with water, and subject it to “seismic” shaking of controlled energy. Pore pressure in the saturated and unsaturated zones is monitored before and after shaking. We identify three distinct mechanisms: consolidation of sediments in the saturated zone, release of capillary water from the capillary fringe, and mobilization of isolated pore water in the unsaturated zone. Each mechanism may cause pore pressure in the saturated zone to suddenly increase with shaking, and each may offer new insights to understand the source of the extra water and other shallow hydrological responses that appear after earthquakes.
... Early attempts to perform small-scale tests were done by Wang et al. [14] and later by Kalantidou et al. [15] and Yavari et al. to better understand the performance of energy piles [16]. Kramer et al, and Ghasemi-Fare and Basu analyzed the TM behavior of energy piles using a fully controlled physical model test [17] [18]. ...
Article
Full-text available
Energy piles have been used around the world to harvest geothermal energy to heat and cool residential and commercial buildings. In order to design energy geo-structures, thermo-mechanical response of the geothermal pile must be carefully understood. In this paper, a small scale physical model is designed and a series of heating thermal cycles with various vertical mechanical loads are performed. The instrumented pile is installed inside a dry sand bed. Changes in pile head displacement, shaft strains and pile and sand temperatures are monitored using an LVDT, strain gauges and thermocouples, respectively. Prolonged heating cycles, which would continue until boundary temperature changes, would allow the investigation of excessive heat injection when service loads are active on the pile. The thermal response is discussed including confirmation of a temperature influence zone around the pile, the increase in soil temperature, and minimum vertical heat dispersion in the soil. The mechanical response includes plastic settlements when the vertical load passes 20% of ultimate capacity. Plastic settlements have been observed at the half of the capacity reported for the shorter thermal cycles in similar models. The decrease in the capacity indicates a reduction in elastic response of the soil during longer thermal cycles.
... 11. SEM image of F50 silica sand at 65x magnification(Kramer 2013) ...
Thesis
Earthquake-induced liquefaction is a cause of substantial damage to geotechnical structures. The examples of liquefaction-induced damage include slope failures, foundation failures and flotation of buried structures. Underground structures embedded at shallow depths such as large underground parking garages, pipelines and manholes, can suffer significant uplift in liquefied soil. Understanding the seismic performance of a liquefiable ground during and after shaking is urgently needed. The main objectives of this research are to (1) investigate the seismic performance of a liquefiable sand deposit under a series of shaking events, (2) investigate the strength gain of the liquefied sand deposit using piezo-cone penetration (CPTu) testing, (3) simulate the shaking table testing using advanced constitutive model (PM4Sand) and understand the predictive performance of this model. A uniform liquefiable sand deposit was air-pluviated and fully saturated in a large laminar shear box (L×W×H: 2.29 m × 2.13 m × 1.83 m). The sand deposit was subjected to a liquefying shaking event (1st shaking) in the laminar box. Accelerometers and piezometers were embedded at different depths to capture the seismic response of liquefied sand. The measured excess pore pressures were used to verify the occurrence of liquefaction. LVDTs were attached to different frames of the laminar shear box to monitor the lateral displacements of the soil. The test recordings from piezometer, accelerometer and LVDT were presented and discussed. Another three major shaking events were designed and performed on the sand deposit after the first shaking. The shake table test results from different shaking events were compared to investigate the seismic response of the sand deposit under multiple shaking events. The time-dependent liquefaction resistance of a post-liquefaction sand deposit was studied using CPTu after 1st shaking event. A series of CPTu tests were conducted to measure the cone penetration resistance, friction resistance, and pore water pressure throughout the depth of the post-liquefaction sand deposit. To capture the sand aging effect after liquefaction, CPTu tests were done at different locations over a total elapsed time of 135 days. The results suggest that (1) the cone penetration resistance of the sand deposit decreased significantly immediately after liquefaction when compared with that before liquefaction; (2) the cone penetration resistance of the post-liquefaction sand deposit increased with time. The CPTu results were normalized with respect to effective overburden stress and the relationship between normalized CPTu results of the post-liquefaction sand deposit and time was proposed. To evaluate the predictive capabilities of the PM4Sand model, a numerical simulation of the shake table test was developed. The model was first calibrated using cyclic direct simple shear tests. The calibrated model was then used to simulate the seismic performance of the uniform soil deposit under sinusoidal seismic motions. Further insight into the strengths and limitations of the PM4Sand model gained from this research was presented.
... All the modules were connected to the NI cDAQ 9178 chassis. Temperature measurements were collected, displayed, and logged in real time at a rate of 0.1 Hz using data collection software written in LabVIEW 2011 (National Instruments 2013) (Kramer 2013, Kramer and Basu 2014a). ...
... The load cell module has an aggregate sampling rate of 250×103 S/s. The data was gathered, logged, and displayed in real time at an acquisition rate of 2 Hz using the Labview code (Kramer 2013, Kramer and Basu 2014a. ...
... However a given data was actually the average of 100 measurements made at a rate of 1000Hz. Since, very high data acquisition rates were required; a producer-consumer architecture was used to separate data acquisition from display and logging (Kramer 2013, Kramer et al. 2013. The developed GUI code has two major benefits, (1) the load versus time graph would confirm that the loading steps were consistent, (2) the load displacement curve shows the start of plunging behavior that could be used as an indicator to terminate a load test. ...
Technical Report
Full-text available
In this study, the authors investigated the feasibility of a ground-coupled system that utilizes heat energy harvested from the ground for deicing of bridge decks. Heat exchange is performed using circulation loops integrated into the deep foundations supporting the bridge or embedded within the approach embankment. The warm fluid extracted from the ground is circulated through a tubing system embedded within reinforced concrete bridge deck to keep the deck temperature above the freezing point. A circulation pump that requires a minimal amount of power is used for fluid circulation. This is different from ground-source heat pump systems used for heating and cooling of buildings. In this study, a proof-of-concept testing is developed to investigate the operational principles and key design parameters. Experiments were performed on a model-scale instrumented bridge deck and model heat-exchanger piles to investigate heat transfer within different components of the ground-coupled bridge deck system. Heat transfer within ground and concrete bridge deck is quantified through numerical simulations under a variety of design and operational conditions. Experimental and numerical studies performed both at Penn State and Virginia Tech campuses demonstrate that this technology has a significant potential in reducing the use of salts and deicing chemicals. The knowledge and experience gained from this research will guide future research on real-life implementation of the proposed alternative bridge deck deicing method and will eventually help the concept to grow as a ready-to-use technology. Consequently, it will be possible to reduce bridge deck deterioration and offset the detrimental effects and environmental hazards caused by these chemicals.
Article
A geothermal energy pile is a revolutionary piling technique that combines a pile foundation with a ground source heat pump system that not only supports the structure but also provides heating and cooling for buildings and bridges. The thermo-mechanical behavior of long energy piles in soft clay has rarely been investigated, despite their increasing utilization. A long floating energy pile with a length-to-diameter ratio of 66.7 was evaluated on its own and monitored in service of the supported structure in the city of Kunshan, China. With vertical mechanical loads, the experiment involved alternate cooling and heating cycles, allowing for careful analysis and assessment of the pile’s temperature, stress, and displacement. Temperature-induced stress, axial force, and friction resistance of the pile shaft, as well as the change in displacement of the energy pile throughout building, were all studied. The field observations revealed without any surprise that a longer energy pile outperformed a shorter one in terms of heating exchange capacity with a more homogenous temperature distribution along the pile. Following a quasi-linear relationship with the temperature variation, the thermo-induced additional axial force soared with the larger length-diameter ratio of the pile and may even reach four times that of the pile under pure mechanical loads. Important additional settlements were also observed especially in cooling conditions. The shaft frictions along the long bored energy pile were found to have a complicated distribution, which requires further investigations.
Thesis
Heat exchanger piles are innovative technologies used to harvest heat from shallow ground. Heat exchanger pile, also known as energy pile, transfers mechanical (structural) loads to the ground while acting as a heat exchanger. Heat extraction in winter and heat rejection during summer changes the pile, pile-soil interaction and the surrounding soil temperature. Therefore, pile temperature increments have been recognized as a new factor of controlling the behavior of energy piles in recent decades. Besides, thermal cyclic loadings may affect the serviceability and geotechnical performance of heat exchanger piles. Physical models provide an affordable experimental medium through which new designs and elements can be more deeply understood. A physical model of a heat exchanger pile is developed and instrumented to study the thermo-mechanical performance of an energy pile. A sand raining device was used to achieve a homogeneous relative density of dry sand throughout the model. A closed-end aluminum tube of 2 cm diameter is used as the model geothermal pile. Four strain-gauges are placed at four locations on the length of pile to monitor the changes in the mechanical and thermal strain of the pile. An LVDT is used to measure the heave or settlement of the pile cap. To monitor the soil temperature variations surrounding the model pile, 10 thermocouples were buried in the soil tank. To provide the cyclic thermal loading, a heater and a thermostat is embedded inside the pile model and it is filled with water to reach a homogenous temperature. The model pile is embedded in dry Babolsar Sand in the rigid box and it simulates non-displacement piles (drilled-shafts). The model is assembled in a temperature controlled room. The pile is tested under sustained mechanical loads and thermal cyclic loadings. The thermo-mechanical behaviour of the pile is investigated and compared with previously built models of similar type. The effects of the thermal load cycles on the geotechnical performance of the heat exchanger pile will be discussed. The initial results showed temperature increments are more dominant in the vicinity of the pile. Also for loads less than 20% of the ultimate load capacity of the pile, the pile would act in an elastic manner after undergoing thermal cycles. The initial results showed temperature increments slightly change the shaft and base capacity (up to 10%). The increase in pile capacity is more dominant under the serviceability condition. However cyclic thermal loading does not show any irreversible thermal stress and strain. Further studies are being performed. Further studies are required and being performed for a reliable framework of the behaviour of geothermal piles to be developed. The model can be easily modified and augmented to perform more advanced tests in the future.