• 한국산학기술학회논문지
• /
• 제14권7호
• /
• pp.3164-3169
• /
• 2013

본 연구에서는 수직형 지중 열교환기의 3차원 CFD 해석 기법을 제안하여 2개소의 현장 열응답 시험과 비교하였다. CFD 해석 비교를 위해 GAMBIT을 이용하여 지중과 지중 열교환기 형상을 모델링하였으며, 상용코드인 FLUENT를 사용하여 3차원 열전달 유동 해석을 수행하였다. 2개소의 현장 열응답 시험에서 도출된 지중 유효 열전도도와 지중 초기온도를 경계조건으로 사용하였으며, 시간에 따른 지중 열교환기의 입구온도 변화는 profile을 사용하여 실제 조건을 모사하였다. CFD 해석 결과 2개소의 지중 열교환기 출구온도는 $0.5^{\circ}C$ 범위 내에서 예측하였고, 기울기는 1.6% 이내에서 적절히 예측하였다. 향후 CFD 해석 기법을 활용하여 지중 열교환기 깊이, 형상 및 배열 변화 등에 따른 성능예측에 활용하고자 한다.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2007년도 추계학술대회 논문집
• /
• pp.550-554
• /
• 2007

A one-dimensional heat transfer model coupled with parameter estimation is developed in this study to predict the effective thermal conductivities of soil formation and borehole resistances from in situ field test data. In this application a new method of using initial ignoring time(IIT) obtained from error estimation is tried and turned out to be successful in determining soil thermal conductivities. The validity of this model is accomplished through comparison of the predicted temperature profiles of the model with the data from laboratory scale experimental setting. Eleven test boreholes were constructed in Ochang, Chungcheong Buk Do, and thermal response test was carried out with each borehole. The results of the in situ tests were analyzed with our 1-D numerical model and compared with the results of line source method. The comparison shows that the thermal properties from line source method is a little lower (${\sim}95%$)than those from numerical method. The reason of such result seems to be the lower thermal conductivity of grout material, which is not counted in line source method.

• 한국지반공학회논문집
• /
• 제32권7호
• /
• pp.5-14
• /
• 2016

최근 들어 경제적이고 친환경적인 에너지 활용을 위하여 지열에너지의 필요성이 점차 증대되고 있다. 특히 지열히트펌프 시스템(geothermal heat pump system)으로 불리는 지열 냉난방 시스템의 적용성이 계속 확대되고 있다. 이러한 지열히트펌프 시스템에서 지반의 열전도도와 열확산계수와 같은 지중 열물성은 설계 과정에서 매우 중요한 변수이기에 현장 열응답 시험(thermal response test)을 통해 지반의 열전도도를 산출해야 한다. 본 논문에서는 U와 2U 타입의 지중 열교환기를 매립지 지반에 설치한 후 48시간 동안 현장 열응답 시험을 수행하였으며 지반의 열전도도 뿐만 아니라 지반의 열확산계수를 비선형 회귀분석을 통해 산정할 수 있는 방안을 제시하였다. 또한 지중 열교환기가 설치된 지반의 시료를 채취하여 실내 열물성 실험을 수행하였으며 이를 현장 열응답 시험을 통해 도출된 지반의 열전도도 및 열확산계수 값과 비교하였다.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2010년도 추계학술대회 초록집
• /
• pp.122.1-122.1
• /
• 2010

수평형 지중열교환기의 지중온도 및 지중열전도도를 분석하기 위해서 경기테크노파크 화단에 수평형 지중열교환기를 설치하였다. 수평형 지중열교환기는 수평 길이 50m, 폭 2.7m, 깊이 2m에 파이프 규격 30mm, 파이프 길이 400m 1본을 매설하였다. 2009년 7월부터 2010년 5월까지 총 7회에 걸쳐 현장열응답방식을 이용하여 지중열전도도를 측정하였다. 측정결과를 분석해보면 수평형 지중열교환기의 지중온도는 계절적인 영향을 많이 받았으며, 지중열전도도는 계절적인 요인과는 무관하게 $1.51{\pm}0.1W/mk$ 범위에서 잘 일치함을 보였다. 이러한 결과로서 수평형 지중열교환기의 현장열응답시험은 현장설치 조건을 모두 반영한 결과를 도출할 수 있을 것으로 판단된다.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
• /
• pp.195.2-195.2
• /
• 2011

The borehole heat exchanger of Geothermal Heat Pump (GHP) system should be sustainable and cost effective for long term operation. To guaranty the performance of the system thermal Response Tests (TRTs) with simple recommended procedures have been applied in many countries. Korea government developed a standard TRT procedure in order to control the quality on GHP projects. In the TRT procedure interpretation method has a rule that data set has to be interpreted by the line source model(LSM). The LSM employes some assumptions that surrounding medium is homogeneous and the line source is infinite and constant heat flux, however real ground condition is unisotropic and heterogeneous, and showing regional or local ground water flows in many cases. We need to develope improved evaluation models to estimate accurate ground thermal conductivity with respect to geological and influence of ground water because current TRT standard test procedure has limitations to be applied for every locations and system. This study surveyed the uncertainty of the thermal parameters from the interpretation method considering different evaluation period. The interpretation of 208 TRT data sets represents limitations of LSM application that some obtained ground thermal conductivities are statistically unstable and convergence time of ground thermal conductivity over test period shows trends responding the length of test period. This evaluation study will be helpful to provide some effective procedure for the thermal parameter estimation and to complement current TRT standard procedure.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2008년도 하계학술발표대회 논문집
• /
• pp.776-781
• /
• 2008

A ground heat exchanger in a GSHP system is an important unit that determines the thermal performance of a system and its initial cost. The Size and performance of this heat exchanger is highly dependent on the thermal properties. A proper design requires certain site-specific parameters, most importantly the ground effective thermal conductivity, the borehole thermal resistance and the undisturbed ground temperature. This paper is part of a research project aiming at constructing a database of these site-specific properties, especially ground effective thermal conductivity. The objective was to develop and evaluation method, and to provide this knowledge to design engineers. To achieve these goals, thermal response tests were conducted using a testing device at nearly 150 locations in Korea. The in-situ thermal response is the temperature development over time when a known heating load imposed, e.g. by circulating a heat carrier fluid through the test exchangers. The line-source model was then applied to the response test data because of its simplicity. From the data analysis, the range of ground effective thermal conductivity at various sites is $1.5{\sim}4.0\;W$/mK. The results also show that the ground effective thermal conductivity varies with grouting materials as well as regional geological conditions and groundwater flow.

• 대한토목학회논문집
• /
• 제35권2호
• /
• pp.361-375
• /
• 2015

에너지파일은 기존의 수직밀폐형 지중열교환기를 경제적으로 대체할 수 있는 새로운 형태의 지중열교환기이다. 즉, 에너지파일은 건물의 기초 구조물과 지중열교환기의 역할을 동시에 수행하는 에너지 구조체로서, 말뚝 기초 내부에 열교환 파이프를 삽입하고 파이프를 통해 유체를 순환시켜 지반과의 열교환을 유도한다. 본 연구에서는 병렬 U형(5쌍, 8쌍, 10쌍)의 열교환 파이프를 대구경 현장타설 에너지파일에 삽입하여, 3본의 에너지파일을 실규모로 시공하였다. 또한 현장 열응답 시험(In-situ thermal response tests, TRTs)을 수행하고 시공된 현장타설 에너지파일과의 열교환 효율을 비교하기 위하여 30m 깊이의 수직밀폐형 지중열교환기를 별도로 시공하였다. 병렬 U형 현장타설 에너지파일에 대해서는 냉난방 부하를 인공적으로 주입하는 열교환 성능 평가시험을 수행하여 열교환 성능(heat exchange rate)을 평가하였다. 마지막으로 현장타설 에너지파일의 적용성 평가를 위해 산정된 상대 열교환 효율(relative heat exchange efficiency) 및 열교환 성능을 선행 연구 결과와 비교하였으며, 본 연구에서 시공된 현장타설 에너지파일은 안정적이고 효율적인 열성능을 보이는 것으로 나타났다.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2010년도 추계 학술발표회
• /
• pp.800-807
• /
• 2010

In this study, a series of numerical analyses has been performed in order to evaluate the performance of a full-scale closed-loop vertical ground heat exchanger constructed in Wonju. The circulation pipe HDPE, borehole and surrounding ground were modeled using FLUENT, a finite-volume method (FVM) program, for analyzing the heat transfer process of the system. Two user-defined functions (UDFs) accounting for the difference in the temperatures of the circulating inflow and outflow water and the change of the surrounding ground temperature with depth were adopted in the FLUENT model. The thermal properties of materials estimated in laboratory were used in the numerical analyses to compare the thermal efficiency of the cement grout with that of the bentonite grout used in the construction. The results of the simulation provide a verification of the in situ thermal response test data. The numerical model with the ground thermal conductivity of 4W/mK yielded the simulation result closer to the in-situ thermal response test than with the ground thermal conductivity of 3W/mK. From the results of the numerical analyses, the effective thermal conductivities of the cement and bentonite grouts were obtained to be 3.32W/mK and 2.99 W/mK, respectively.

• 한국신재생에너지학회:학술대회논문집
• /
• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
• /
• pp.168.2-168.2
• /
• 2010

The growing market for geothermal heat pump system requires great consideration of quality control and assurance in design and construction. The borehole heat exchanger of GHP system should be sustainable, economical and ecological. Thermal Response Test (TRT) is a useful method for site investigation to obtain reliable data for a optimal system design from the technical and economical aspect. Intensive researches combined with exchange of experiences on an international level within the IEA ECES Annex 21 improved the technology. Major subjects on the interpretation of TRT are development of improved evaluation models, evaluation of the TRT with respect to geological layers and investigation of the influence of ground water. Current status of TRT in South Korea, as well as a new version of the Korean TRT standard test procedure was presented. TRT is mostly used for governmental supported projects with corresponds to more than 100 GCHP systems per year. More than 200 tests are applied, mostly on single U-tube heat exchangers (about 95%). Bentonite is the most common grouting to be used. KIGAM (Korea Institute of Geoscience & Mineral Resources) is also keeping a GIS geological and geothermal database. In the institute also laboratory measurements of rock properties are carried out. About 90% of the laboratory measurements of the rock heat conductivity shows higher values than the in-situ TRT.

• 설비공학논문집
• /
• 제24권4호
• /
• pp.306-314
• /
• 2012

Several numerical or analytical models have been proposed to analyze the thermal response of vertical ground heat exchangers (GHEX). However, most models are valid only after several hours of operation since they neglect the heat capacity of the borehole. Recently, the short time response of the GHEX became important in system simulation to improve efficiency. In this paper, a simple new method to evaluate the short time response of the GHEX by using an analogy model of electric circuit transient analysis was presented. The new transient heat exchanger model adopting the concept of thermal capacitance of the borehole as well as the steady-state thermal resistance showed the transient thermal resistance of the borehole. The model was validated by in-situ thermal response test and then compared with the DST model of the TRNSYS program.