Experimental performance of borehole heat exchangers and grouting materials for ground source heat pumps

Desmedt, Johan; Bael, Johan Van; Hoes, Hans; Robeyn, Nico

doi:10.1002/er.1898

Cited by 39 publications

(17 citation statements)

References 12 publications

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“…Details on these conductivity values are listed in Table 3. Desmedt et al (2012) and Zhang et al (2015) declared that the application of thermally enhanced grout will improve the performance of the BHE. For the DBHE system, considering the large quantity of grout required to seal a deep borehole, the additionally initial investment needs to be justified by the long-term gain in performance.…”

Section: Simulated Scenariosmentioning

confidence: 99%

Numerical investigation on the performance, sustainability, and efficiency of the deep borehole heat exchanger system for building heating

et al. 2019

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IntroductionWith the growing demand on renewable energy all over the world, geothermal heating and cooling is increasingly utilized by applying borehole heat exchanger (BHE) coupled ground source heat pump (GSHP) systems. One of the factors preventing the further application of GSHP system in densely populated urban areas is the limiting land surface for installing the BHEs. Therefore, deeper boreholes with a depth of 2302 m have been AbstractIn densely inhabited urban areas, deep borehole heat exchangers (DBHE) have been proposed to be integrated with the heat pump in order to utilize geothermal energy for building heating purposes. In this work, a comprehensive numerical model was constructed with the OpenGeoSys (OGS) software applying the dual-continuum approach. The model was verified against analytical solution, as well as by comparing with the integrated heat flux distribution. A series of modeling scenarios were designed and simulated in this study to perform the DBHE system analysis and to investigate the influence of pipe materials, grout thermal conductivity, geothermal gradient, soil thermal conductivity, and groundwater flow. It was found that the soil thermal conductivity is the most important parameter for the DBHE system performance. Both thermally enhanced grout and the thermally insulated inner pipe will elevate the outflow temperature of the DBHE. With an elevated geothermal gradient of 0.04 °C m −1 , the short-term sustainable specific heat extraction rate imposed on the DBHE can be increased to 150-200 W m −1 . The quantification of maximum heat extraction rate was conducted based on the modeling of 30-year-long operation scenarios. With a standard geothermal gradient of 0.03 °C m −1 , the extraction rate has to be kept below 125 W m −1 in the long-term operation. To reflect the electricity consumption by circulating pump, the coefficient of system performance (CSP) was proposed in this work to better quantify the system efficiency. With the typical pipe structure and flow rate specified in this study, it is found that the lower limit of the DBHE system is at a CSP value of 3.7. The extended numerical model presented in this study can be applied to the design and optimization of DBHE-coupled ground source heat pump systems. which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Section: Simulated Scenariosmentioning

confidence: 99%

Numerical investigation on the performance, sustainability, and efficiency of the deep borehole heat exchanger system for building heating

et al. 2019

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“…These materials allow the heat exchange between ground and pipes and must comply with a series of factors explained in Section 1 [23][24][25][26][27].…”

Section: Grouting Materialsmentioning

confidence: 99%

Efficiency Analysis of the Main Components of a Vertical Closed-Loop System in a Borehole Heat Exchanger

et al. 2017

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Abstract:In vertical closed-loop systems, it is common to use single or double U-tube heat exchangers separated by longitudinal spacers. In addition, the helical-shaped pipe is another configuration that requires lower drilling lengths but it is less used. The aim of the present research is to study the influence of these components on the total efficiency of a borehole heat exchanger (BHE). Thus, the differences between using single/double U-tubes (with or without spacers) and helical pipes are analysed in terms of efficiency. Through different laboratory tests, a small vertical closed-loop system was simulated in order to analyse all these possible configurations. The grouting materials and the temperatures of the ground were modified at the same time in these tests. Regarding the heat exchange process between the ground and the heat carrier fluid, it must be highlighted that the best results were obtained for the helical-shaped pipe configuration. Some of the improvements offered by this heat exchanger typology with respect to the vertical configuration is that a lower drilling depth is required even it requires a larger diameter. This leads to significant economic savings in the performing drilling process. Finally, it is also worth noting the importance of using spacers in vertical U-tubes and that no improvements have been found regarding the use of single or double configuration of U-tubes. Thanks to the laboratory results derived from this study it is possible to establish the optimum behaviour pattern for the entire vertical closed-loop systems.

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“…geothermal gradient) and varying input boundary conditions of the circulating fluid temperature to the inlet were adopted in the FLUENT model. The increase of ground temperature with depth in the test site is applied at the outer and bottom boundary of the model using Equation (2). The upper boundary at the ground surface is assumed as the no-flux boundary except both on the inlet and outlet face of the circulating pipe.…”

Section: Numerical Modelingmentioning

confidence: 99%

Back-analyses of in-situ thermal response test (TRT) for evaluating ground thermal conductivity

Lee

Park

et al. 2012

Int. J. Energy Res.

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SUMMARY In this study, a series of computational fluid dynamics (CFD) numerical analyses was performed in order to evaluate the performance of six full‐scale closed‐loop vertical ground heat exchangers constructed in a test bed located in Wonju, South Korea. The high‐density polyethylene pipe, borehole grouting and surrounding ground formation were modeled using FLUENT, a finite‐volume method program, for analyzing the heat transfer process of the system. Two user‐defined functions accounting for the difference in the temperatures of the circulating inflow and outflow fluid and the variation of the surrounding ground temperature with depth were adopted in the FLUENT model. The relevant thermal properties of materials measured in laboratory were used in the numerical analyses to compare the thermal efficiency of various types of the heat exchangers installed in the test bed. The numerical simulations provide verification for the in‐situ thermal response test (TRT) results. The numerical analysis with the ground thermal conductivity of 4.0 W/m⋅K yielded by the back‐analysis was in better agreement with the in‐situ TRT result than with the ground thermal conductivity of 3.0 W/m⋅K. From the results of CFD back‐analyses, the effective thermal conductivities estimated from both the in‐situ TRT and numerical analysis are smaller than the ground thermal conductivity (=4.0 W/m∙K) that is input in the numerical model because of the intrinsic limitation of the line source model that simplifies a borehole assemblage as an infinitely long line source in the homogeneous material. However, the discrepancy between the ground thermal conductivity and the effective thermal conductivity from the in‐situ TRT decreases when borehole resistance decreases with a new three pipe‐type heat exchanger leads to less thermal interference between the inlet and outlet pipes than the conventional U‐loop type heat exchanger. Copyright © 2012 John Wiley & Sons, Ltd.

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Experimental performance of borehole heat exchangers and grouting materials for ground source heat pumps

Cited by 39 publications

References 12 publications

Numerical investigation on the performance, sustainability, and efficiency of the deep borehole heat exchanger system for building heating

Numerical investigation on the performance, sustainability, and efficiency of the deep borehole heat exchanger system for building heating

Efficiency Analysis of the Main Components of a Vertical Closed-Loop System in a Borehole Heat Exchanger

Back-analyses of in-situ thermal response test (TRT) for evaluating ground thermal conductivity

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