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Design Guidlines of Geothermal Heat Pump System Using Standing Column Well
Abstract
For the reasonable use of low grade-shallow geothermal energy by Standing Column Well(SCW) system, the basic requirements are depth-wise increase of earth temperature like per every 100m depth, sufficient amount of groundwater production being about 10 to 30% of the design flow rate of GSHP with good water quality and moderate temperature, and non-collapsing of borehole wall during reinjection of circulating water into the SCW. A closed loop type-vertical ground heat exchanger(GHEX) with deep can supply geothermal energy of 2 to 3 RT but a SCW with deep can provide being equivalent to 10 to 15 numbers of GHEX as well requires smaller space. Being considered as an alternative of vertical GHEX, many numbers of SCW have been widely constructed in whole country without any account for site specific hydrogeologic and geothermal characteristics. When those are designed and constructed under the base of insufficient knowledges of hydrgeothermal properties of the relevant specific site as our current situations, a bad reputation will be created and it will hamper a rational utilization of geothermal energy using SCW in the near future. This paper is prepared for providing a guideline of SCW design comportable to our hydrogeothermal system.
... (Hahn et al., 2006). 이러한 수주지열정의 국내 활용을 위하여 지하수 조 건, 설치 심도 및 간격 등의 기본적인 설계 변수 설정을 위 한 몇몇의 연구들이 수행된 바 있다 (Hahn et al., 2006(Hahn et al., , 2007(Hahn et al., , 2008 (Deng, 2004;Park et al., 2010aPark et al., , 2010b 가 부피와 접촉 면적 및 간격으로 환산한 후 각각을 1차원 수직 격자의 집합으로 구성하였다 (Fig. 2). ...
... . 이러한 수주지열정의 국내 활용을 위하여 지하수 조 건, 설치 심도 및 간격 등의 기본적인 설계 변수 설정을 위 한 몇몇의 연구들이 수행된 바 있다 (Hahn et al., 2006(Hahn et al., , 2007(Hahn et al., , 2008 (Deng, 2004;Park et al., 2010aPark et al., , 2010b 가 부피와 접촉 면적 및 간격으로 환산한 후 각각을 1차원 수직 격자의 집합으로 구성하였다 (Fig. 2). 이들 파이프의 열적 물성은 Table 2에 정리되어 있다 (Titow, 1984;Lindeburg, 2013). ...
Numerical modules based on a conventional thermo-hydrological numerical model, TOUGH2, are developed to provide a numerical modeling technique for a standing column well (SCW). Cooling and heating operations for two different types of SCW are then simulated using these modules. Modeling showed these operations to be significantly influenced by heat exchange and fluid mixing between the SCW and the adjacent geologic formation and groundwater. The results also reveal that heat exchange between the oppositely flowing outflow and inflow in the PVC or PE pipe and the SCW borehole is an important factor. Overall, the numerical modeling technique developed here can reasonably simulate fluid flow and heat transport phenomena in the complex internal structures of a SCW. The proposed technique can be used practically for the quantitative analysis of heat exchange in a SCW at the design, construction, and operation stages.
... The benefits of geothermal energy provided by these systems support market demands, including providing low operating costs, eco-friendliness, and compatibility with building designs. Additionally, geothermal systems, such as those based on the use of groundwater, reportedly ensure high efficiency as the most stable, eco-friendly, and low-cost options among currently available cooling and heating systems, and have promoted increased related academic research [4,21]. ...
Groundwater samples were collected from the tubular wells of a groundwater heat pump (GWHP), and the psychrophilic, mesophilic, and thermophilic bacteria inhabiting the collected groundwater were cultured and isolated. Using the isolated bacteria, we analyzed temperature-dependent changes in autochthonous bacteria based on the operation of the GWHP. Microbial culture identified eight species of bacteria: five species of thermophilic bacteria (Anoxybacillus tepidamans, Bacillus oceanisediminis, Deinococcus geothermalis, Effusibacillus pohliae, and Vulcaniibacterium thermophilum), one species of mesophilic bacteria (Lysobacter mobilis), and two species of psychrophilic bacteria (Paenibacillus elgii and Paenibacillus lautus). The results indicated A. tepidamans as the most dominant thermophilic bacterium in the study area. Notably, the Anoxybacillus genus was previous reported as a microorganism capable of creating deposits that clog above-ground wells and filters at geothermal power plants. Additionally, we found that on-site operation of the GWHP had a greater influence on the activity of thermophilic bacteria than on psychrophilic bacteria among autochthonous bacteria. These findings suggested that study of cultures of thermophilic bacteria might contribute to understanding the bio-clogging phenomena mediated by A. tepidamans in regard to GWHP-related thermal efficiency.
... Geothermal systems that use geothermal energy-using groundwater for heating and cooling buildings-have been attracting increasing attention [2][3][4]. This system is the most environmentally friendly approach available and numerous studies have evaluated its performance [5], design guidelines for a standing column well [6], and characteristics [7]. Nonetheless, studies have pointed to limitations of the groundwater heat pump (GWHP) system related to its physicochemical [8] and microbiological thermal efficiency [9][10][11][12][13]. ...
The geothermal energy of groundwater has aroused increasing interest as a solution to climate change. The groundwater heat pumps (GWHP) system using groundwater is the most environmentally friendly system to date and has been examined in several studies. However, biological clogging by microorganisms negatively affects the thermal efficiency of the GWHP system. In this study, we employed air surging, the most popular among well management methods, and pyrosequencing to analyze the genetic diversity in bacteria before and after air surging in a geothermal well. Furthermore, the diversity of dominant bacterial genera and those related to clogging were evaluated. The bacterial diversity of the groundwater well increased after air surging. Nevertheless, the proportion of bacterial genera thought to be related to microbiological clogging decreased. In cooling and heating systems based on the geothermal energy of groundwater, the wells should be maintained regularly by air surging to reduce efficiency problems caused by microbiological clogging and to prevent secondary damage to human health, e.g., pneumonia due to human pathogenic bacteria including Pseudomonas aeruginosa and Acinetobacter.
... 이러한 경제성 분 석은 지열이 시설농업에 적용되면서 농업분야로도 확대 되어 시설원예, 축사시설 등에도 시도되었다 (Jang et al., 2009;Choi et al., 2011;Kim and Yoon, 2012 (Kim et al, 2013). 이 중 국내에서는 수직밀폐형 지열 냉난방시스템(이하 수직밀 폐형)이 가장 많고 개방형인 SCW형 지열 냉난방시스템 (이하 SCW형)이 다음 순으로 보급되었으며 (Shim and Lee, 2010), 지하수가 풍부한 지역에서는 수직개방형의 효율이 더 높다고 보고된 바가 있다 (Hahn et al., 2006;Kim et al., 2006a;Park et al., 2006;Kim and Kong, 2011;Kim et al., 2014 (Sohn et al., 2007;Cho and Sohn, 2009;Sohn and Kang, 2009;Lee et al., 2011 (1) 초기투자비용(initial investment cost, I) (Kong, 2006 (Fig. 3. (a)). 또한, 지열 냉난방시스템의 투자비 회수기간을 살펴보면, 경유보일러 대비 SCW형 은 5년차, 수직밀폐형은 7년차에 초기투자비용이 회수 되며, 도시가스보일러와 대비해서도 같은 연차에 초기투 자비가 회수되는 것으로 나타났다 (Fig. 3. (b)). ...
The development of renewable energy technologies that can replace fossil fuels is environmentally important; however, such technologies must be economically feasible. Economic analyses are important for assessing new projects such as geothermal heating-cooling systems, given their large initial costs. This study analyzed the economics and carbon dioxide emissions of: a SCW (standing column well), a vertical closed loop boiler, a gas boiler, and an oil boiler. Life cycle cost analysis showed that the SCW geothermal heating-cooling system had the highest economic feasibility, as it had the highest cost saving and also the lowest carbon dioxide emissions. Overall, it appears that geothermal systems can save money when applied to large-scale controlled agriculture complexes and reclaimed land.
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.
Studies of the thermal properties of various rock types obtained from several locations in Korea have revealed significant differences in thermal conductivities in the thermal response test (TRT), which has been applied to the design of a ground-source heat pump system. In the present study, we aimed to compare the thermal conductivities of the samples with those obtained by TRT. The thermal conductivities of soil and rock samples were 1.32W/m-K and 2.88 W/m-K, respectively. In comparison, the measured TRT value for thermal conductivity was 3.13W/m-K, which is 10% higher than that of the rock samples. We consider that this difference may be due to groundwater flow because abundant groundwater is present in the study area and has a hydraulic conductivity of 0.01. It is natural to consider that the object of TRT is to calculate the original thermal conductivity of the ground, following the line source theory. Therefore, we conclude that the TRT applied to a domestic standing column type well is not suitable for a line source theory. To solve these problems, values of thermal conductivity measured directly from samples should be used in the design of ground-source heat pump systems.
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