Effects of seasonal variations on the thermal response of energy piles in an unsaturated Brazilian tropical soil

Ground-coupled heat exchanger systems have been used as acclimatization systems for residential and commercial buildings in many countries. Brazil is the ninth largest consumer of electrical energy in the world, for this reason, local researchers are investigating the use of the energy piles in order to reduce the consumption of electricity. Thermal response tests have been carried out on a heat exchanger pile at the geotechnical experimental site of the University of São Paulo in São Carlos city, a region of subtropical climate. Simultaneously, using the thermal properties obtained in these tests, numerical analysis has been performed to investigate the heat exchange performance of energy piles installed in this site. For this numerical analysis, the effect of soil and concrete properties, pile geometry and the flow rate on the pile thermal response were evaluated. The current paper presents the results obtained by the analysis of 67 models tested to found an optimal configuration of an energy pile through the software COMSOL, using Heat Transfer and Non-Isothermal Pipe Flow modules. From this work, it was observed that the optimal configuration was obtained for a turbulent flow condition in piles in the heat exchanger pipes.

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Estimating the thermal properties of soil and concrete piles from thermal response tests (TRTs) for energy piles with spiral tubes

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/861/7/072132 ◽

2021 ◽

Vol 861 (7) ◽

pp. 072132

Author(s):

Yufang Du ◽

Siyuan Li ◽

Shuowei Wang ◽

Min Li

Keyword(s):

Thermal Properties ◽

Thermal Response ◽

Concrete Piles ◽

Energy Piles ◽

Properties Of Soil

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Impact of the Seasonal Variations in Ground Temperature on Thermal Response Test Results

Geo-Chicago 2016 ◽

10.1061/9780784480137.006 ◽

2016 ◽

Author(s):

Linden Jensen-Page ◽

Guillermo A. Narsilio ◽

Asal Bidarmaghz ◽

Ian W. Johnston

Keyword(s):

Seasonal Variations ◽

Thermal Response ◽

Ground Temperature ◽

Thermal Response Test ◽

Test Results ◽

Response Test

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Field test on thermal response characteristics of an energy pile in underground row piles

E3S Web of Conferences ◽

10.1051/e3sconf/202020505011 ◽

2020 ◽

Vol 205 ◽

pp. 05011

Author(s):

Gangqiang Kong ◽

Yang Zhou ◽

Di Wu ◽

Gaoxiang Yin ◽

Hefu Pu

Keyword(s):

Thermal Response ◽

Field Tests ◽

Mechanical Analysis ◽

Input Power ◽

Underground Structures ◽

Energy Pile ◽

Response Characteristics ◽

Energy Piles ◽

Shallow Geothermal Energy ◽

Temperature Strain

Underground row piles are usually used in excavation of underground structures and abandoned after structural construction. The heat exchanger tubes embedded in the underground row piles can be severed as energy piles, which can exchange shallow geothermal energy. The construction process of the energy pile in the underground row piles was introduced. Compared with the traditional single energy pile, there is a special characteristic of the energy pile in underground row piles: piles are linked as a whole by the top beam at the top of the row pile. Field tests on the thermal response and thermo-mechanical characteristics of the energy pile in underground row piles were performed. The stable input power of 2.07 kW. The distribution of temperature, strain, and stress of pile body along depth were measured and discussed. It shows that the measured comprehensive thermal conductivity coefficient of soil is 3.72W/(m×K). In the thermo-mechanical analysis after heating, due to the end restrains by the top beam and toe in stiff rock, the rate of thermal stress to temperature change at the top and toe are -0.101 MPa/℃ (34% of fully restrain) and -0.061 MPa/℃ (20% of fully restrain).

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Effect of nearby piles and soil properties on the thermal behaviour of a field-scale energy pile

Canadian Geotechnical Journal ◽

10.1139/cgj-2020-0353 ◽

2020 ◽

Author(s):

Aria Moradshahi ◽

Mohammed Faizal ◽

Abdelmalek Bouazza ◽

John S. McCartney

Keyword(s):

Thermal Conductivity ◽

Thermal Expansion ◽

Elastic Modulus ◽

Soil Properties ◽

Thermal Expansion Coefficient ◽

Thermal Stresses ◽

Thermal Response ◽

Soil Thermal Conductivity ◽

Energy Pile ◽

Energy Piles

The thermal response of an energy pile that is part of a pair of energy piles spaced at 3.5 m, was examined experimentally and numerically. The field tests included: (1) heating of the energy pile alone; (2) heating of both energy piles simultaneously, and (3) heating of the other energy pile while the considered energy pile was not heated. Parametric studies of the validated numerical model was performed to understand the effects of varying soil thermal conductivity, thermal expansion coefficient, and elastic modulus on the thermal response of the considered energy pile. The numerical results confirmed the field results that radial thermal stresses were insignificant compared to axial thermal stresses. The impact of the soil elastic modulus was more significant on the thermal stresses of the energy pile compared to the effects of soil thermal conductivity and thermal expansion coefficient. The thermal stresses of the considered energy pile were not significantly affected when both energy piles were heated simultaneously, even though ground temperature changes between the energy piles were more significant due to thermal interaction. Only minor thermal effects on the non-thermal pile were observed during heating of one of the energy piles for different soil properties.

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Behaviour of a group of energy piles

Canadian Geotechnical Journal ◽

10.1139/cgj-2014-0403 ◽

2015 ◽

Vol 52 (12) ◽

pp. 1913-1929 ◽

Cited By ~ 67

Author(s):

Thomas Mimouni ◽

Lyesse Laloui

Keyword(s):

Pore Water Pressure ◽

Water Pressure ◽

Thermal Response ◽

Structural Constraints ◽

Soil Layers ◽

Federal Institute ◽

Energy Piles ◽

Institute Of Technology ◽

The Individual ◽

Stiff Soil

A full-scale experimental site with four energy test piles was built on the campus of the Swiss Federal Institute of Technology in Lausanne, Switzerland. This site was used to investigate interaction effects within a group of energy piles. First, the ground constraints were evaluated by testing the piles without any structure on top. Next, each pile was individually tested once the overlying structure was built, which provided information on the structural constraints and allowed the quantification of the pile–structure–pile interactions. Finally, the four test piles were simultaneously heated to quantify the group effects. A thermal response test was performed on one pile and the thermohydraulic response of the soil between the piles was monitored with piezometers and thermistors. Load redistributions may occur in mixed foundations, i.e., with conventional and energy piles, because of differential displacements. Conversely, heating an entire foundation increases the individual pile displacements, but reduces the differential displacements and consequently the pile thermal efforts. Radial strains may also have a significant impact on the axial thermomechanical response of the piles in stiff soil layers. Heat barely propagated farther than a couple of metres with no significant pore-water pressure variation observed.

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Thermal Response Testing of Large Diameter Energy Piles

Energies ◽

10.3390/en12142700 ◽

2019 ◽

Vol 12 (14) ◽

pp. 2700 ◽

Cited By ~ 2

Author(s):

Linden Jensen-Page ◽

Fleur Loveridge ◽

Guillermo A. Narsilio

Keyword(s):

Steady State ◽

Large Diameter ◽

Thermal Response ◽

Analytical Models ◽

Real Field ◽

Routine Practice ◽

Energy Piles ◽

Response Testing ◽

Analytical Approaches

Energy piles are a novel form of ground heat exchanger (GHE) used in ground source heat pump systems. However, characterizing the pile and ground thermal properties is more challenging than for traditional GHEs. Routine in-situ thermal response testing (TRT) methods assume that steady state conditions in the GHE are achieved within a few hours, whereas larger diameter energy piles may take days or even weeks, thereby incurring significant costs. Previous work on pile TRTs has focused on small diameters up to 450 mm. This paper makes the first rigorous assessment of TRT methods for larger diameter piles using field and laboratory datasets, the application of numerical and analytical modelling, and detailed consideration of costs and program. Three-dimensional numerical simulation is shown to be effective for assessing the data gathered but is too computationally expensive for routine practice. Simpler fast run time steady state analytical models are shown to be a theoretically viable tool where sufficient duration test data is available. However, a new assessment of signal to noise ratio (SNR) in real field data shows how power fluctuations cause increased uncertainty in long duration tests. It is therefore recommended to apply transient models or instead to carry out faster and more cost-effective borehole in-situ tests for ground characterization with analytical approaches for pile characterization.

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Thermo-Mechanical Performance of a Phase Change Energy Pile in Saturated Sand

Symmetry ◽

10.3390/sym12111781 ◽

2020 ◽

Vol 12 (11) ◽

pp. 1781

Author(s):

Ting Du ◽

Yubo Li ◽

Xiaohua Bao ◽

Waiching Tang ◽

Hongzhi Cui

Keyword(s):

Heat Transfer ◽

Numerical Model ◽

Phase Change ◽

Thermal Loading ◽

Plastic Material ◽

Thermal Response ◽

Thermal Loads ◽

Saturated Sand ◽

Energy Pile ◽

Energy Piles

To reduce the thermal response and improve the heat storage capacity of energy piles, a phase change (PC) energy pile was proposed. This innovative PC pile is made of concrete containing macro-encapsulated PCM hollow steel balls (HSB) as coarse aggregates. A numerical model was developed to simulate the thermo-mechanical behaviors of the PC pile under thermal cycles and sustained loading. The computational model is a three-dimensional model that is symmetrical for the two horizontal directions in geometry. Heat transfer process follows conservation laws of energy. The numerical model was validated by the experiments conducted on the PC pile and the results show that the model can reproduce the major thermo-mechanical effects. Then, the model was used to compare the performance between the ordinary concrete pile and the PC pile in saturated sand under the same experimental conditions, where the piles were considered to be thermo-elastic in nature and the sand was considered as a Mohr–Coulomb elastic-plastic material. The thermo-mechanical response of the PC pile under different thermal loads was analyzed. The results show that at the end of heating, the temperature, strain, and displacement of the PC pile were lower than those of the ordinary pile. As the thermal loading increased, the range of temperature change in the soil around the PC pile increased, as well as the strain and displacement of the pile. The residual strain and plastic displacement after the temperature cycles also increased with the increase of thermal loading. Therefore, when designing phase change energy piles, full consideration should be given to the matching of thermal loads and PC temperature, so as to balance the heat transfer rate of the pile and the thermal response.

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Mechanical response of a thermal micro-pile installed in stratified sedimentary soil

E3S Web of Conferences ◽

10.1051/e3sconf/202020505007 ◽

2020 ◽

Vol 205 ◽

pp. 05007

Author(s):

Brunella Casagrande ◽

Fernando Saboya ◽

Sergio Tibana ◽

John S. McCartney

Keyword(s):

Mechanical Response ◽

Mechanical Performance ◽

Thermal Response ◽

Deep Understanding ◽

Tropical Soil ◽

Temperate Climate ◽

Strain Gauges ◽

Vibrating Wire ◽

Wire Strain ◽

Surrounding Soil

Data regarding the behavior of thermal piles in tropical countries is not as readily available as those in European or other temperate climate regions, where most applications are directed toward extracting heat from the subsurface. Similarly, a deep understanding of thermal piles constructed using the micropile technique has not been obtained. In micropiles, the installation process can disturb the surrounding soil, especially at the tip. This paper presents the results from a set of thermal response tests (TRT) performed on a 12 m-long instrumented thermal micro-pile installed in a sedimentary tropical soil. Vibrating wire strain gauges were installed in order to assess the mechanical performance of the pile when subject to thermal loads. Results indicate that the temperature distribution with depth is far from being homogeneous through the entire length of the pile. The resulting induced strains are strongly dependent on the subsoil conditions.

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