• Journal of Institute of Convergence Technology
• /
• v.7 no.1
• /
• pp.1-6
• /
• 2017

The Heat exchanger for deep geothermal system is very important to enhance the efficiency of the system. The co-axial heat exchanger is used due to the limitation of digging space. The heat transfer on the external surface of outer pipe should be high to receive a large amount of heat from the ground. However, the inner pipe should be insulated to reduce the heat loss and increase the temperature of discharge water. This study made experiment apparatus to describe the co-axial heat exchanger and measure the heat transfer coefficients on the internal and external surface. And the pin-fin was designed and fixed on the internal surface to increase the efficiency of heat exchanger. Finally, we calculated the temperature of discharge water using the heat transfer circuit of co-axial heat exchanger and heat transfer coefficient which from experimental results. The water temperature was reached the ground temperature at -500 m and following the ground temperature. When the water return to the ground surface, the water temperature was decreased due to heat loss. As the pin-fin case, the heat transfer coefficient on the internal surface was decreased by 30% and it mean that the pin-fin help to insulate the inner pipe. However, the discharge water temperature did not change although pin-fin fixed on the inner pipe.

• 한국태양에너지학회:학술대회논문집
• /
• 2012.03a
• /
• pp.206-210
• /
• 2012

Ground source heat pump is a central heating and cooling system that pumps heat to or from the ground. Building Integrated Geothermal system used in this experiment is one of the Ground Source Heat Pump Systems which utilize energy pile. The purpose of this study is to evaluate heating performance of the system. The building is a low-energy experiment apartment in Yonsei University Songdo Campus and the subject is one of the energy reduced houses in this apartment. In the experiment, indoor temperature, outdoor temperature and the inlet and outlet temperature of ground heat exchanger and subject model, were measured. Then the heat pump's Coefficient of performance(COP) of the heat pump was calculated. As a result, the COP of heat pump is 4-5. Although the depth of the ground heat exchanger in this experiment is shallower than usual heat exchanger, the result of heating performance of this system was good as well.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
• /
• v.3 no.1
• /
• pp.11-16
• /
• 2007

The purpose of this study is to use the CFD(Computational Fluid Dynamics) method for the ground source heat pump(GSHP) system with vertical U-tube ground heat exchangers. In order to predict LWT(leaving water temperature) in the length of time, This simulation is used by utilizing FLUENT which is commercial CFD code. It was performed by based on four boreholes in the field. Comparing with the results of CFD and field measurement for LWT, the results of CFD was presented very good agreement with 1.0% average difference.

• Journal of the Architectural Institute of Korea Structure & Construction
• /
• v.34 no.5
• /
• pp.43-50
• /
• 2018

The temperature of underground water generally remains constant regardless of the season. therefore, it is possible to get plenty of energy if we use characteristics of underground water for both cooling and heating. This study evaluates efficiency of real size coaxial and U-tube type complex geothermal system which is combined with underground water well. This study also evaluates relative efficiency/adaptability through comparison with existing geothermal systems(vertical closed loop system, open loop system(SCW)). The heat exchange capacity of complex geothermal system according to temperature difference between circulating water and underground water shows very high significance by increasing proportionally. The temperature change of underground water according to injection energy, shows very high linear growth aspect as injection thermal volume heightens. As a result of evaluation of heat exchange volume between complex geothermal system and comparative geothermal system, coaxial type has 26.1 times greater efficiency than comparative vertical closed type and 2.8 times greater efficiency than SCW type. U-tube type has 26.5 tims greater efficiency than comparative vertical closed type and 2.8 times greater than SCW type as well. This means complex geothermal system has extremely outstanding performance.

• Land and Housing Review
• /
• v.9 no.4
• /
• pp.25-32
• /
• 2018

Application of geothermal energy in buildings has been gaining popularity as it provides the benefits of both heating and cooling a building. Among the various types of geothermal energy systems, ground-coupled heat pump system is the most commonly applied one in South Korea. A ground heat exchanger plays an important role as a heat source in winter and a heat sink in summer. For the stable operation of a ground-coupled heat pump system, a ground heat exchanger should be sized so that it provides sufficient heating and cooling energy. Heating and cooling energies generated in ground heat exchangers mainly depend on the temperature difference between the heating medium in ground heat exchangers and the surrounding ground. In addition, the performance of ground heat exchangers influences the change in ground temperature. Therefore, it is necessary to consider this interrelation between the change in the ground temperature and the performance of ground heat exchanger for an accurate estimation of its performance. However, previous thermal analysis models for ground heat exchangers are not competent enough to allow a complete understanding of this interrelation. Therefore, this study proposes a three-dimensional equivalent, transient ground heat exchanger analysis model. First, a previous thermal analysis model for ground heat exchangers, including an analytical model, a g-function, and a numerical model are analyzed. Next, to overcome the limitations of the previous models, a three-dimensional equivalent, transient ground heat exchanger model is proposed. Finally, this study validated the proposed model with the measurement data of the thermal response test, sandbox test, and TRNSYS DST model. All validation results showed a good agreement. These findings helped us to investigate the thermal performance of ground heat exchangers more accurately than the analytical models, and faster than the numerical models. Furthermore, the proposed model contributes to the design of ground heat exchangers by considering the different operation conditions of buildings.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.17 no.4
• /
• pp.364-369
• /
• 2005

An experimental study was conducted on the thermal conductivity of various grouting materials for geothermal heat exchanger which is used as a heat sink or source in the heat pump system. The grouting of the vertical heat exchanger is important for environmental and heat transfer reasons and is generally accomplished by the placement of a low permeability material into the annular space between the borehole wall and the pipes suspended in the borehole. In this study, a lab scale test apparatus was made and measured the thermal conductivity of four grouting materials. As a result, the temperature rising tendency was similar among them, but the increasing rate was different. Thus the thermal conductivity showed a maximum difference of $27\%$ among grouting materials.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
• /
• v.3 no.2
• /
• pp.9-15
• /
• 2007

Thermal conductivity of rocks is one of the most important parameters in designing a geothermal heat pump system, because heat exchange rate depends primarily on thermal conductivity of rocks. In this paper, the measurement methods of thermal conductivity, thermal conductivity of rocks, and heat exchange rate are discussed.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.16 no.4
• /
• pp.2966-2970
• /
• 2015

Recently, solar light power generation is widely extended by support policy to regeneration energy. However generation efficiency is decreased when solar module maintain higher than certain point temperature. Therefore, it is need to maintenance under certain point temperature. An method of solving this problem, this paper is developed geothermal exchanger for efficiency improvement of solar cell module. Geothermal exchanger consisted of heat absorber of solar cell module and heat conductor and radiator. Heat of solar cell module is radiated in the earth by geothermal exchanger. An a result, geothermal exchanger is increased generation amount of solar cell module and experiment result showed costs to about 36% increment of generation power.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
• /
• v.16 no.3
• /
• pp.8-16
• /
• 2020

This paper presents the heating performance analysis results of a ground-source heat pump (GSHP) system using hybrid ground heat exchanger (HGHE). In this paper, the HGHE refers to the ground heat exchanger (GHE) using both a surface water heat exchanger (SWHE) and a vertical GHE. In order to evaluate the system performance, we installed monitoring sensors for measuring temperatures and power consumption, and then measured operation data with 4 different load burdened ratios of the HGHE. During the entire measurement period, the average heating capacity of the heat pump was 37.3 kW. In addition, the compressor of the heat pump consumed 9.4 kW of power, while the circulating pump of the HGHE used 6.7 kW of power. Therefore, the average heating coefficient of performance (COP) for the heat pump unit was 4.0, while the system including the circulating pump was 2.7. Finally, the parallel use of SWHE and VGHE was beneficial to the system performance; however, further researches are needed to optimize the design data for various load ratios of the HGHE.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.11a
• /
• pp.511-514
• /
• 2007

This study was performed to construct a geothermal data base about thermal conductivity of ground heat exchanger and thermal properties of grouting material which used to refill the borehole. We have acquired geothermal data sets from 39 sites over wide area of South Korea except to Jeju island. From data analysis, the range of thermal conductivity is $1.5{\sim}4.0$ W/mK. It means that thermal conductivity varies with grouting material as well as regional geology and ground water system.