Design and Operational Considerations of Geothermal Energy Piles

Abdelaziz, Sherif L.; Olgun, C. Güney; Martin, James R.

doi:10.1061/41165(397)47

Cited by 37 publications

(18 citation statements)

References 3 publications

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“…More sophisticated numerical models used to study the interaction between heat exchanger piles and the surrounding soil mass focus on material properties and fluid flow in the tubes. For instance, Abdelaziz et al (2011) studied the influence of ground thermal conductivity, grout characteristics, flow pipe diameter, flow rate and heating power on the temperature distribution around a heat exchanger pile. Water content of the soil around the pile can also impact heat exchanger pile operation as the thermal conductivity is strongly influenced by the degree of saturation.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Friction Induced Thermo-Mechanical Stresses on a Heat Exchanger Pile in Isothermal Soil

2014

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In most analytical and numerical models of heat exchanger piles, strain incompatibilities between the soil and the pile are neglected, and axial stresses imposed by temperature changes within the pile are attributed to the thermal elongation and shortening of the pile. These models incorporate thermo-hydro-mechanical couplings in the soil and within the pile foundation, but usually neglect thermomechanical couplings between the two media. Previous studies assume that the stress changes imposed by temperature variations in a heat exchanger pile are mainly due to the constrained thermal elongation and shortening of the pile. Also, several recent approaches utilize spring models that focus only on the soil-pile interface in modeling temperature-induced stresses in a heat exchanger pile and implicitly ignore the effect of the full displacement field on soil-pile interaction. By contrast, in this paper, interface elements are introduced in a numerical model of a heat exchanger pile, analyzed in axisymmetric and stationary conditions. The pile is subjected to a uniform temperature increase, with free top and fixed top conditions in elastic and elasto-plastic soil profiles. Simulation results show that the constrained vertical elongation is the most detrimental factor for pile foundation performance. However it is worth noticing that while mechanical constraints (e.g., fixed top and/or fixed bottom) impose maximum stress increases at the ends of the pile, interface effects result in maximum stresses around the mid-length of the pile. This preliminary study indicates that soil-pile friction does not increase pile internal stresses to the point where it would be necessary to over-dimension the foundation pile for heat exchanger use. Furthermore, one cannot expect a significant gain in foundation performance due to the improvement of soil-pile frictional resistance as a result of increased lateral stresses at soil-pile contact. Additional numerical analyses are ongoing, in order to investigate the role of the degree of fixity induced by the building on the heat exchanger pile, and to extend these preliminary analyses to transient operational modes and cyclic thermo-mechanical loading of the heat exchanger pile.

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Section: Introductionmentioning

confidence: 99%

Analysis of Friction Induced Thermo-Mechanical Stresses on a Heat Exchanger Pile in Isothermal Soil

2014

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“…Typical examples are bored or pre-fabricated piles, retaining walls, diaphragm walls, tunnel walls, basement slabs, basement walls and soil anchors (Brandl, 2006, Adam and Markiewicz, 2009, Franzius and Pralle, 2011. Although energy foundations are considered to be new relative to other forms of renewable energy technologies such as wind, solar or biomass (Abdelaziz et al, 2011, Peron et al, 2011 they have now been installed in a number of engineering structures throughout the world (Boennec, 2008, Gao et al, 2008, Laloui, 2011. This is in contrast to the Republic of Ireland where it is believed that no such systems exist (Hemmingway and Long, 2011a).…”

Section: Introductionmentioning

confidence: 84%

Energy piles: site investigation and analysis

Hemmingway

Long

2013

Proceedings of the Institution of Civil Engineers - Geotechnica

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Despite an increasing use world-wide of geothermal energy foundations there is a lack of published guidelines and results from thermal response testing of such installations. In this paper the results from thermal response, thermal recovery and laboratory thermal testing performed at two sites in Ireland are presented. Some practical issues concerned with use of thermal response testing rigs, designed for use with deep boreholes, on relatively short piles are discussed and addressed. Given the relatively short geothermally active depth of the energy foundations tested and due to the fact that the UCD thermal response testing rig has been designed primarily for testing on medium and deep geothermal boreholes, shorter thermal response test durations than are normally

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“…To take into account the effect of the working fluid flowing at a defined velocity, V, within the heat exchanger pipes located in the foundation piles, the convection-diffusion equation is considered [9].…”

Section: Model Descriptionmentioning

confidence: 99%

“…While, there are several analysis studies reported for conventional GSHP systems [4][5][6][7][8], few models of thermo-active foundations are available in the literature [9][10][11]. However, these models are based on simplified assumptions and do not account for the thermal interactions between thermal piles and building thermo-active foundations.…”

Section: Introductionmentioning

confidence: 98%