• The Journal of Engineering Geology
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• v.24 no.4
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• pp.487-499
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• 2014

While the vertical open type of heat exchanger is more effective in areas of abundant groundwater, and is becoming more widely used, the heat exchanger most commonly used in geothermal heating and cooling systems in Korea is the vertical closed loop type. In this study, we performed numerical simulations of the optimal utilization of geothermal energy based on the hydrogeological and thermal properties to evaluate the efficiency of the vertical open type in areas of abundant groundwater supply. The first simulation indicated that the vertical open type using groundwater directly is more efficient than the vertical closed loop type in areas of abundant groundwater. Furthermore, a doublet system with separated injection and extraction wells was more efficient because the temperature difference (${\Delta}$) between the injection and extraction water generated by heat exchange with the ground is large. In the second simulation, we performed additional numerical simulations of the optimal utilization of geothermal energy that incorporated heat transfer, distance, flow rate, and groundwater hydraulic gradient targeting a single well, SCW (standing column well), and doublet. We present a flow diagram that can be used to select the optimal type of heat exchanger based on these simulation results. The results of this study indicate that it is necessary to examine the adequacy of the geothermal energy utilization system based on the hydrogeological and thermal properties of the area concerned, and also on a review of the COP (coefficient of performance) of the geothermal heating and cooling system.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.19 no.3
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• pp.1-13
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• 2023

Hydronic heated road pavement (HHP) systems have been well established and documented to provide road safety in winter season over the past two decades. However, most of the systems run on asphalt, only a few are tested with concrete, and there rarely is a comparison between those two common road materials in their performance. The aim of this study is to investigate the thermal performance of the concrete HHP systems, including surface temperature variations of experimental pavements in winter season. For preliminary study a small-scale experimental system was installed to evaluate the heat transfer characteristics of the concrete HHP in the test field. The system consists of 3 concrete slabs made of 1 m in width, 1 m in length, and 0.25 m in height. In these slabs, circulating water piping was embedded with different pipe depths of 0.08 m (Case A), 0.12 m (Case B), and 0.20 m (Case C) and same horizontal space of 0.16 m. Heating performance in winter season was tested with different inlet temperatures of 25℃, 30℃, 35℃ and 40℃ during the entire measurement period. Overall, the surface temperature of the concrete HHPs remained above 3℃ in all experimental conditions applied in this study. The results of the surface temperature measurement with respect to the pipe depth showed that Case B was the highest among the three cases. However, the closer the circulating water pipe was to the pavement surface, the greater the heat exchange rate. This results is considered that the heat is continuously accumulated inside the pavements and then the temperature inside the pavements increases, while the amount of heat dissipation decreases as the temperature difference between the inlet and outlet of circulating water decreases. In this preliminary test the applicability of the concrete HHP on road deicing was confirmed. Finally, the results can be used as a basis for studying the effects of various variables on road pavements through numerical analysis and for conducting large-scale empirical experiments.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.4
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• pp.1-7
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• 2016

This paper presents a design method for the horizontal straight ground heat exchanger (GHE) based on the Kavanaugh design method. In order to examine suitability of the suggested design method, a horizontal line type GHE was installed in a steel box of which the size was $5m{\times}1m{\times}1m$ filled with dried Joomunjin standard, and a thermal response test (TRT) was conducted for 21 hours. A numerical analysis was performed for a simulation of a peak month operation and for its verification by finite element method (FEM). According to the simulation results, it was concluded that the suggested design method for a horizontal straight GHE is reliable for the estimation of a design length.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.195.1-195.1
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• 2011

This paper presents an experimental study on a new potential geothermal energy source obtained from tunnel structures. An "energy textile", which is a textile-type ground heat exchanger, was fabricated between a shotcrete layer and a guided drainage geotextile in the tunnel lining system. To examine the long-term thermal behavior of the energy textile, the difference in temperatures of the inlet and outlet fluid circulating through the heat exchange pipe within the energy textile was monitored using a constant-temperature water bath. Daily heat exchange rate of the energy textile during cooling operation was estimated from the measured temperatures of the inlet and outlet fluid through the energy textile. The air and ground temperature was also continuously monitored. The operation of the energy textile as a ground heat exchanger was simulated using a 3D numerical CFD model (Fluent). The thermal conductivity of shotcrete and concrete lining components and temperature variation of air in the tunnel were incorporated in the model. The numerical analysis shows a good agreement with the long-term monitoring result.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.8
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• pp.427-431
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• 2013

Ground heat pump systems utilize the annually stable underground temperature to supply heat for space heating and cooling. The underground temperature affects not only the underground ecosystem, but also the performance of these systems. However, in spite of the widespread use of these systems, there have been few researches on the effect of the systems on underground temperature. In this research, case studies with numerical simulation have been conducted, in order to estimate the effect of ground heat pump systems on underground temperature. The simulation was coupled with the ground water-ground heat transfer model and the ground surface heat transfer model. In the result, it was found that the underground change depends on the heat transfer from the ground surface, the heat exchange rate, and the heat conductivity of soil.

• Journal of the Korean Geotechnical Society
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• v.30 no.7
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• pp.55-61
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• 2014

The need of geothermal energy is constantly increasing for economical and environmental utilization. Horizontal ground heat exchangers (GHEs) can reduce installation cost and increase efficiency. There are many kinds of GHEs, and it is known that slinky and spiral coil type GHEs show high thermal performance. Therefore, this paper presents experimental results of heat exchange rates in horizontal slinky and spiral coil type GHEs installed in a steel box whose size is $5m{\times}1m{\times}1m$. Dried Joomunjin standard sand was filled in a steel box, and thermal response tests (TRTs) were conducted for 30 hours to evaluate heat exchange rates by changing different pitch spaces of horizontal slinky and spiral coil type GHEs. As a result, spiral coil type GHE showed 30~40% higher heat exchange rates per pipe length than horizontal slinky type GHEs. Furthermore, long pitch interval (Pitch/Diameter=1) showed 200~250% higher heat exchange rates per pipe length than short pitch interval (Pitch/Diameter=0.2) in both spiral coil and horizontal slinky type GHEs, respectively.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.18 no.3
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• pp.1-6
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• 2022

Ground source heat pump (GSHP) system is highly efficient and environment-friendly and supplies heating, cooling and hot water to buildings. For an optimal design of the GSHP system, the ground thermal properties should be determined to estimate the heat exchange rate between ground and borehole heat exchangers (BHE) and the system performance during long-term operating periods. However, the process increases the initial cost and construction period, which causes the system to be hindered in distribution. On the other hand, much research has been applied to the artificial neural network (ANN) to solve problems based on data efficiently and stably. This research proposes the predictive performance model utilizing ANN considering local characteristics and weather data for the predictive performance model. The ANN model predicts the entering water temperature (EWT) from the GHEs to the heat pump for the modular GHEs, which were developed to reduce the cost and spatial disadvantages of the vertical-type GHEs. As a result, the temperature error between the data and predicted results was 3.52%. The proposed approach was validated to predict the system performance and EWT of the GSHP system.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.2C
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• pp.69-77
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• 2012

In general, geothermal energy pile and horizontal ground heat exchangers are installed in shallower depths than conventional vertical ground coupled heat pumps. Consequently their heat exchange performance is strongly governed by thermal conductivity of soil layer. Previous studies have shown that the thermal conductivity of soil above ground water table significantly affects the heat exchange rate because of partially saturated condition in soil and consequent variation of soil thermal conductivity. This paper presents a study result on the prediction of thermal conductivity of weathered granite soils. For weathered granite soils sampled from 5 locations, thermal conductivity tests were conducted with varying porosity and degree of saturation. The existing thermal conductivity models in literatures appeared inappropriate to the weathered granite soils. Hence, an empirical equation was proposed in this paper and its validity was examined by applying it to thermal conductivity test results obtained for weathered granite soils in this study and from literatures.

• The Journal of Engineering Geology
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• v.25 no.1
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• pp.131-148
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• 2015

The purpose of this study is to analyze and compare the heat transfer efficiency of using copper pipe, stainless pipe and traditional PE pipe commonly used for geothermal heat exchanger, with aims at seeking improved methods. In addition, the varying efficiency of heat transfer from ground heat and groundwater heat was assessed and its applicability was discussed. Design parameters for empirical field study were derived by controlling flow rate, velocity and caliber of pipes of the heat exchanger after the thermal efficiency of the heat exchanger material was evaluated. The heat exchange efficiency and effective thermal conductivity were measured with changing pattern through field thermal efficiency and thermal response test. Experimental results show that the metal material showed higher heat transfer efficiency than the PE pipe. Although the heat transfer efficiency was not high with the increase of the pipe diameter in the flow rate, it was high with the increase of the pipe diameter in the velocity.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.5C
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• pp.177-183
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• 2012

The use of energy pile foundation has been increased for economic utilization of geothermal energy. In particular, a coil-shaped ground heat exchanger (GHE) is preferred than conventional U-shaped heat exchanger to ensure better efficiency of heat exchange rate. This paper presents experimental results by changing different pitch spaces of spiral coils. Joomunjin sand was filled in a steel box of which the size was $5m{\times}1m{\times}1m$. Thermal response tests (TRTs) were conducted to measure the ground thermal conductivity with temperatures of circulating water using line source model and ring coil model. Experimental results and analytical solutions were compared to validate the applicability of these models. Ring coil model showed more accurate similar results with experimental data rather than line source model and cylindrical source model.