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개방형 지열시스템의 효율적 설계를 위한 영향인자에 대한 연구
박병학,전원탁,이보현,이강근,Park, Byeong-Hak,Joun, Won-Tak,Lee, Bo-Hyun,Lee, Kang-Kun 한국지하수토양환경학회 2015 지하수토양환경 Vol.20 No.4
Open-loop groundwater heat pump (GWHP) system generally has benefits such as a higher coefficient of performance (COP), lower initial cost, and flexible system size. The hydrogeological conditions in Korea have the potential to facilitate the use of the GWHP system because a large number of monitoring wells show stable groundwater temperatures, shallow water levels, and high well yields. However, few studies have been performed in Korea regarding the GWHP system and the most studies among them dealt with Standing Column Well (SCW). Because the properties of the aquifer have an influence on designing open-loop systems, it is necessary to perform studies on various hydrogeological settings. In this study, the hydrogeological and thermal properties were estimated through various tests in the riverside alluvial layer where a GWHP system was installed. Under different groundwater flow velocities and pumping and injection rates, a sensitivity analysis was performed to evaluate the effect of such properties on the design of open-loop systems. The results showed that hydraulic conductivity and thermal dispersivity of the aquifer are the most sensitive parameters in terms of performance and environmental aspects, and sensitivities of the properties depend on conditions.
Testifying LTE Assumption for Heat Transport in GWHP Systems
Ji-Young Baek(백지영),Byeong-Hak Park(박병학),Kang-Kun Lee(이강근) 한국신재생에너지학회 2021 한국신재생에너지학회 학술대회논문집 Vol.2021 No.7
Accurate prediction of thermal plume propagation is very important in the design stage of groundwater heat pump (GWHP) systems. Generally, a single differential transport equation has been applied to interpret the propagation of thermal plume by assuming local thermal equilibrium (LTE), immediate thermal equilibrium between the solid and neighboring fluid. With the increase of flow velocity, however, the thermal equilibrium cannot be reached immediately. Despite this possibility, there is a lack of studies that enable to verification of the LTE assumption for the hydrogeological systems. In this study, laboratory experiments were performed using both heat and solute as tracers at various background flow velocities (Reynolds number, Re 〈0.37) to testify the LTE assumption. Observed responses to the tracer injection were analyzed by mathematical models and derived velocities and dispersion coefficients of solute and heat were compared using retardation factors. Consequently, it was experimentally confirmed that the LTE assumption can be violated in Darcy range (Re 〈3). Thermal dispersion coefficients derived by the heat tracer were larger than those estimated by the solute tracer due to violation of the LTE. This result suggests that the LTE assumption needs to be verified for the design of the GWHP system.
Sensitivity Analysis of Factors Influencing Thermal Conductivity Estimation in Thermal Response Test
Hae-Rim Oh(오해림),Byeong-Hak Park(박병학),Ji-Young Baek(백지영),Kang-Kun Lee(이강근) 한국신재생에너지학회 2021 한국신재생에너지학회 학술대회논문집 Vol.2021 No.7
A thermal response test (TRT) has been commonly used as a method for estimating thermal properties of the subsurface. Determining thermal parameters is important because it is directly related to the installation costs and sustainable performance of shallow geothermal systems. In this study, to investigate how several design factors (i.e., starting time, test duration, and data acquisition interval) can affect analysis results, a field experiment was conducted at Eumseong, South Korea. Two types of reference data from previous studies were additionally employed to determine whether the effects of these factors depended on the experimental conditions and obtained temperature data were analyzed using four analytical models. The influence of these factors on thermal conductivity estimation was evaluated quantitatively by comparing a base case with various scenarios. In the results, the starting time and the test duration affected the thermal conductivity estimate by more than 10% whereas the data acquisition interval had a small impact of less than 10%. In addition, the impacts of each influence factor differed for three different TRTs conducted under different experimental conditions. Therefore, the starting time and the test duration need to be carefully set for accurate thermal conductivity estimation taking into account the experimental conditions.