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Seoul, South Korea

Park S.,Korea University | Lee D.,Korea University | Choi H.-J.,Korea University | Jung K.,S Technology Consulting Group | Choi H.,Korea University

Energy piles encase heat exchange pipes in a pile foundation to use geothermal energy. This paper evaluates the constructability and thermal performance of energy piles equipped in a large-diameter drilled shaft. Two energy piles were constructed by fabricating coil-type heat exchange pipes in cast-in-place concrete piles. The coil pitch was designed to be 200 mm and 500 mm, respectively. The constructability of each energy pile was evaluated in terms of time and ease for installing. In-situ TRTs were performed to compare the thermal performance of energy piles. The relative heat exchange efficiency for the coil pitch 200 mm is only 1.2 times greater than that of the coil pitch 500 mm energy pile, even though the coil pitch 200 mm energy pile encases the heat exchange pipe 2.4 times as longer as the coil pitch 500 mm. In addition, the result of TRTs was compared with two well-known analytical to estimate thermal properties of ground formation. A thermal performance test was carried out by applying artificial cooling operation to the energy piles, and indicates the heat exchange rate is not directly proportional to the pipe length because the tighter coil pitch configuration may cause thermal interference between the coil loops. © 2014 Elsevier Ltd. All rights reserved. Source

Na K.,Korea University | Lee D.,Korea University | Lee H.,Korea University | Jung K.,S Technology Consulting Group | Choi H.,Korea University
Advances in Intelligent Systems and Computing

Helical piles are a manufactured steel foundation composed of one or multiple helix plates affixed to a central shaft. A helical pile is installed by rotating the central shaft with hydraulic torque motors. There are three representative theoretical predictions for the bearing capacity of helical piles: individual bearing method, cylindrical shear method, and torque correlation method. The bearing capacity of helical piles is governed by the helical pile’s configuration, geologic conditions and penetration depth. The high variability of influence factors makes an optimum design for helical pile configuration difficult in practice. In this paper, the harmony search algorithm is adopted to minimize the material cost of helical piles by optimizing the components composing a helical pile based on the proposed bearing capacity prediction. The optimization process based on the combined prediction method with the aid of the harmony search algorithm leads to an economical design by saving about 27percent of the helical pile material cost. © Springer-Verlag Berlin Heidelberg 2016. Source

Park S.,Korea University | Sung C.,Korea University | Jung K.,S Technology Consulting Group | Sohn B.,Korea Institute of Construction Technology | And 2 more authors.
Applied Thermal Engineering

A new ground heat exchanger (GHEX) assembled in a ground source heat pump (GSHP) system has been devised, which is equipped in a structural pile, and thus called an "energy pile". In this study, six large-diameter cast-in-place energy piles that encased various types of heat exchange pipes (i.e., three parallel U-types with 5 pairs, 8 pairs and 10 pairs; two coil-types with 200mm coil pitch and 500mm coil pitch; and S-type) were constructed in a test bed, and the constructability of each type of the energy pile was compared. Additionally, a 30m-deep closed-loop vertical GHEX was separately constructed to compare the thermal performance and economic feasibility with the energy piles. A series of in-situ thermal response tests (TRTs) was performed to evaluate the relative heat exchange efficiency of each energy pile according to the various heat exchange pipe configurations. The relative heat exchange efficiency obtained in the cast-in-place energy piles and the down-sized 30m-deep closed-loop vertical GHEX was normalized by the pile length (or borehole length) and the total heat exchange pipe length. The result from the in-situ tests indicates that the longer the heat exchange pipe installed, the higher heat exchange efficiency per pile length. However, in the case of tight layouts of the heat exchange pipe, thermal interference occurs between adjacent pipe loops, which decreases heat exchange efficiency. Economic feasibility of the energy piles was evaluated, considering the material and installation costs for assembling the heat exchange pipe with consideration of the heat exchange efficiency. It is concluded that the coil-type cast-in-place energy pile can achieve sufficient capacity for heat exchange, compared with the closed-loop vertical GHEX. © 2015 Elsevier Ltd. Source

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