• The KSFM Journal of Fluid Machinery
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• v.19 no.6
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• pp.34-42
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• 2016

The organic Rankine cycle (ORC) has been used to convert thermal energy to mechanical energy or electricity. The available thermal energy could be waste heat, solar energy, geothermal energy, and so on. However, these kinds of thermal energies cannot be provided continuously. Hence, the ORC can be operated at the off-design point. In this case, the performance of the ORC could be worse because the components of the ORC system designed based on a design point can be mismatched with the output power obtained at the off-design point. In order to improve the performance at the off-design point, a few components were replaced including generator, bearing, load bank, shaft, pump and so on. Experiments were performed on the same facility without including other losses in the experiment. The experimental results were compared with the results obtained with the previous model, and they showed that the system efficiency of the ORC was greatly affected by the losses occurred on the components.

• KIEAE Journal
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• v.13 no.2
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• pp.77-84
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• 2013

Schools are one of favorable public buildings for Renewable Energy(RE) systems due to site conditions and their energy demand profiles(e.g. daytime-based use of hot water and heating/cooling). Although the government encourages schools to be equipped with RE systems, the adoption of RE systems in existing energy supply systems faces technical and financial barriers. For example, when installing a RE-based combination system(RECS) to meet the energy demand at various school scales, identifying cost effective combination of capacities of the RECS is not trivial since it usually requires technically intensive work including detailed simulation and demand/supply analysis with extensive data. This kind of simulation-based approaches is hardly implementable in practice. To address this, a simpler and applicable decision-supporting method is suggested in this study. This paper presents a simplified model in support of decision-making for optimal capacities of RECS within given budget scales and schools sizes. The proposed model was derived from detailed simulation results and statistical data. Using this model, the optimal capacities of RECS can be induced from the number of classes in a school.

• Journal of the Korean Institute of Educational Facilities
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• v.2 no.2
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• pp.17-25
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• 1995

Because of energy crisis and environment pollution, we have become more conscious of the need to conserve heat in buildings. In response to this need. new requirements have been developed for insulation and other matters relating to energy consumption. Among others, more promising is to use the energy that is all around us in the dynamic forces of nature:the wind, tides, waves, rivers, geothermal hot spots, and the sun. The problem is that we have not been forced to find the technological means to convert these natural energies into usable forms because it has been too easy simply to dig or pump our energy out of the ground. Now, the problem is not a shortage of energy itself, but a shortage of technology for converting the energy that lies aoo around us into usable forms. Energy-conversion technology is the real issue, and solar energy is one of the brightest and most promising frontiers in energy conversion. All buildings are wrapped in a skin. Generally skins protect the person in stay from rain, wind, dust, noise, cold, hot etc.. However, there are some skins that provide energy from given environment into the building. Out of aoo, transparent insulation material is one of these materials that most effectively satisfies this kind of envelope function. Since, there are no research on transparent insulation in Korea, it has been studied very actively in Europe and in America. Thus, in this thesis, we will theoratically study and analyze how the heat flows through a trans arrent insulated opaque wall of a school building in Korea. It will be an important information for the effective using guidelines of transparent insulation materials in Korea.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.6
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• pp.427-446
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• 2008

A review on the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2006 has been accomplished. Focus has been put on current status of research in the aspect of heating, cooling, ventilation, sanitation and building environments. The conclusions are as follows. (1) The research trends of fluid engineering have been surveyed as groups of general fluid flow, fluid machinery and piping, etc. New research topics include micro heat exchanger and siphon cooling device using nano-fluid. Traditional CFD and flow visualization methods were still popular and widely used in research and development. Studies about diffusers and compressors were performed in fluid machinery. Characteristics of flow and heat transfer and piping optimization were studied in piping systems. (2) The papers on heat transfer have been categorized into heat transfer characteristics, heat exchangers, heat pipes, and two-phase heat transfer. The topics on heat transfer characteristics in general include thermal transport in a cryo-chamber, a LCD panel, a dryer, and heat generating electronics. Heat exchangers investigated include pin-tube type, plate type, ventilation air-to-air type, and heat transfer enhancing tubes. The research on a reversible loop heat pipe, the influence of NCG charging mass on heat transport capacity, and the chilling start-up characteristics in a heat pipe were reported. In two-phase heat transfer area, the studies on frost growth, ice slurry formation and liquid spray cooling were presented. The studies on the boiling of R-290 and the application of carbon nanotubes to enhance boiling were noticeable in this research area. (3) Many studies on refrigeration and air conditioning systems were presented on the practical issues of the performance and reliability enhancement. The air conditioning system with multi indoor units caught attention in several research works. The issues on the refrigerant charge and the control algorithm were treated. The systems with alternative refrigerants were also studied. Carbon dioxide, hydrocarbons and their mixtures were considered and the heat transfer correlations were proposed. (4) Due to high oil prices, energy consumption have been attentioned in mechanical building systems. Research works have been reviewed in this field by grouping into the research on heat and cold sources, air conditioning and cleaning research, ventilation and fire research including tunnel ventilation, and piping system research. The papers involve the promotion of efficient or effective use of energy, which helps to save energy and results in reduced environmental pollution and operating cost. (5) Studies on indoor air quality took a great portion in the field of building environments. Various other subjects such as indoor thermal comfort were also investigated through computer simulation, case study, and field experiment. Studies on energy include not only optimization study and economic analysis of building equipments but also usability of renewable energy in geothermal and solar systems.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.154-154
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• 2011

화석연료의 가격 및 공급의 불안정과 온실가스감축 국제 규제 강화 등에 대한 대안으로 여기는 신 재생에너지는 높은 초기 투자 부담으로 인하여 관련기술의 연구개발과 보급정책 등 전과정에 걸친 정책 지원체계가 필요하다. 본 연구에서는 지열에너지를 이용하는 지열냉난방기술에 중점을 두고 이에 대한 중장기 정책 포트폴리오 작성을 위한 기술 및 정책적 접근방안을 제시하고자한다. 지열에너지의 가장 큰 특징은 기후 등에 영향을 크게 부하가 변하는 태양광, 풍력 등과 달리 일정한 부하를 유지함으로써 안정적인 에너지공급이 가능하다는 것이다. 또, 품질 측면에서도 화석연료를 이용한 기존의 연료보다 쾌적한 환경을 조성하여 고급에너지로 평가받고 있다. 반면, 설비를 갖추기 위한 천공, 히트펌프 설치 등에 큰 비용이 든다는 단점을 가지고 있다. 현재 히트펌프 제작기술은 국산화를 완료한 상태로 사실상 기술개발에 의한 큰 폭의 원가절감은 기대하기 힘든 상황이다. 하지만, 유사분야인 시스템 에어컨이 표준화 및 대량생산을 통한 시장 보급 확대로 보급단가가 하락한 것을 고려해 볼 때 이를 통한 가격하락은 어느 정도 기대해 볼 수 있을 것으로 생각된다. 에너지 외적인 측면에서 볼 때도 지열에너지의 공급은 상당한 의미를 갖는다. 건물 냉 난방용 이외에 다양한 용도의 개발을 통해 비닐하우스나 온실 등에 지열에너지를 이용할 경우 정부차원에서 농어촌에 대한 지원이 가능하다. 또, 기존의 에너지원을 조달하는데 어려움이 있는 산간, 도서지방에서는 도시지역보다 투자대비 큰 효과를 볼 수 있어 지역간 에너지 불균형 해도에도 도움이 될 수 있다. 이와같은 지열에너지의 특성에 따라 향후 발전방향을 정리해 보았다. 핵심기술인 지열 히트펌프의 산업구조와 시장 보급 확대를 통한 가격하락을 기대한다. 지역개발 및 고립지역에서 타 신 재생에너지와 함께 독립적인 전력, 냉난방 등의 완전 에너지 공급시스템을 갖출 수 있다. 또한 특수 작물 등의 고급 농수산물 생산등의 용도개발을 통해 지열에너지 공급역량을 성장시킬 수 있을 것이다. 이와 함께 중장기 비젼을 제시하기 위해 추진되어야 할 연구과제로는 시장 보급 확대에 따른 가격경쟁력 도달 가능성에 대한 연구를 통해 산업육성 방안 마련, 타 신 재생에너지기술과 복합 설치에 의한 시너지 효과 및 이에따른 초기 투자비 증가에 대한 대책, 보급 잠재량 조사, 지열시스템의 자금 조달 및 관련 정책 검토 등이 있을 수 있다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.6
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• pp.521-537
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• 2012

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2011. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends of thermal and fluid engineering have been surveyed as groups of fluid machinery and fluid flow, thermodynamic cycle, and new and renewable energy. Various topics were presented in the field of fluid machinery and fluid flow. Research issues mainly focused on the rankine cycle in the field of thermodynamic cycle. In the new and renewable energy area, researches were presented on geothermal energy, fuel cell, biogas, reformer, solar water heating system, and metane hydration. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer, nanofluids and industrial heat exchangers. Researches on heat transfer characteristics included heat transfer above liquid helium surface in a cryostat, methane hydrate formation, heat and mass transfer in a liquid desiccant dehumidifier, thermoelectric air-cooling system, heat transfer in multiple slot impinging jet, and heat transfer enhancement by protrusion-in-dimples. In the area of pool boiling and condensing heat transfer, researches on pool boiling of water in low-fin and turbo-B surfaces, pool boiling of R245a, convective boiling two-phase flow in trapezoidal microchannels, condensing of FC-72 on pin-finned surfaces, and natural circulation vertical evaporator were actively performed. In the area of nanofluids, thermal characteristics of heat pipes using water-based MWCNT nanofluids and the thermal conductivity and viscosity were measured. In the area of industrial heat exchangers, researches on fin-tube heat exchangers for waste gas heat recovery and Chevron type plate heat exchanger were implemented. (3) Refrigeration systems with alternative refrigerants such as $CO_2$, hydrocarbons, and mixed refrigerants were studied. Heating performance improvement of heat pump systems were tried applying supplementary components such as a refrigerant heater or a solar collector. The effects of frost growth were studied on the operation characteristic of refrigeration systems and the energy performance of various defrost methods were evaluated. The current situation of the domestic cold storage facilities was analyzed and the future demand was predicted. (4) In building mechanical system fields, a variety of studies were conducted to achieve effective consumption of heat and maximize efficiency of heat in buildings. Various researches were performed to maximize performance of mechanical devices and optimize the operation of HVAC systems. (5) In the fields of architectural environment and energy, diverse purposes of studies were conducted such as indoor environment, building energy, and renewable energy. In particular, renewable energy and building energy-related researches have mainly been studied as reflecting the global interests. In addition, various researches have been performed for reducing cooling load in a building using spot exhaust air, natural ventilation and energy efficiency systems.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.7
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• pp.492-507
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• 2010

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2009. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends of thermal and fluid engineering have been surveyed as groups of general thermal and fluid flow, fluid machinery and piping, and new and renewable energy. Various topics were covered in the field of general thermal and fluid flow such as an expander, a capillary tube, the flow of micro-channel water blocks, the friction and anti-wear characteristics of nano oils with mixtures of refrigerant oils, etc. Research issues mainly focused on the design of micro-pumps and fans, the heat resistance reliability of axial smoke exhaust fans, and hood systems in the field of fluid machinery and piping. Studies on ground water sources were executed concerning two well type geothermal heat pumps and multi-heat pumps in the field of new and renewable energy. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics and industrial heat exchangers. Researches on heat transfer characteristics included the heat transfer in thermoelectric cooling systems, refrigerants, evaporators, dryers, desiccant rotors. In the area of industrial heat exchangers, researches on high temperature ceramic heat exchangers, plate heat exchangers, frosting on fins of heat exchangers were performed. (3) In the field of refrigeration, papers were presented on alternative refrigerants, system improvements, and the utilization of various energy sources. Refrigeration systems with alternative refrigerants such as hydrocarbons, mixed refrigerants, and $CO_2$ were studied. Efforts to improve the performance of refrigeration systems were made applying various ideas of suction line heat exchangers, subcooling bypass lines and gas injection systems. Studies on heat pump systems using unutilized energy sources such as river water, underground water, and waste heat were also reported. (4) Research trend in the field of mechanical building facilities has been found to be mainly focused on field applications rather than performance improvements. In the area of cogeneration systems, papers on energy and economic analysis, LCC analysis and cost estimating were reported. Studies on ventilation and heat recovery systems introduced the effect on fire and smoke control, and energy reduction. Papers on district cooling and heating systems dealt with design capacity evaluation, application plan and field application. Also, the maintenance and management of building service equipments were presented for HVAC systems. (5) In the field of architectural environment, various studies were carried to improve indoor air quality and to analyze the heat load characteristics of buildings by energy simulation. These studies helped to understand the physics related to building load characteristics and to improve the quality of architectural environment where human beings reside in.

• 한국신재생에너지학회:학술대회논문집
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• 2006.06a
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• pp.459-460
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• 2006

현재 남한의 지열류량 측정값으로는 총 363개 지점의 자료가 측정 및 수집되어 있다. 이것은 Mizutani et at. (1970), 장정진 외(1970), 그리고 서정희(1976) 등의 자료, 총 35개의 자료도 추가된 것이다. 1989년 이후부터 측정된 지열류량 자료는 217개 자료이며(임정웅 외, 1989; 임정웅 외, 1996; Lim and Kim, 1997; 염병우 외, 1997), 모두 직접 측정한 것이나, 1989년 이후 보고된 지열류량 자료에 약간의 오류가 있어 이번 연구에서 수정 보완하였다. 또한 과거의 자료 35개 자료는 이미 지열류량 측정치가 논문화 되어 있는 것으로 암석시료는 없다 1989년 이후 2004년까지 자료 217개 2005년도 추가 자료 111개의 지열류량 자료는 암석시료도 있으며, 측정기기가 서로 달라 오차가 있을 수 있어 서로 보정을 해야 할 필요가 있어 시추공 주변 암석을 새로 수집해서 신장비로 다시 측정 보정하였다. 지열류량 D/B 구축은 각 자료의 일련번호, 고유번호 (Sn.), 위경도 좌표 (longitude, lattitude), 암석의 열전도도(thermal conductivity), 지온경사 (thermal gradient), 지열류량 (heat flow)등으로 구성되어 있다. 지열류량 자료 공간 데이터베이스는 점 속성을 가지며 자료형태는 각종 소프트웨어와 호환성이 좋은 shape 파일 형태로 작성하였다. 또만 최근 천부 토양 및 암석 열물성을 이용한 냉난방시스템 즉, Heat Pump System 설계를 위하여 반드시 들어가야 하는 요소인 열확산율, 공극율, 밀도, 비열 등 열물성 특성을 추가하여 GIS 공간 D/B구축하였다. 대륙붕 자료 4개 자료를 제외하고 359개의 지열류량 자료를 이용하여 한반도 남부, 즉 남한의 지열류량 분포도를 작성 분석해 본 결과(그림 1), 우리나라의 지열류량 이상대는 아산만 주변, 보령, 유성, 진안, 울진, 포항, 부산 지역과 포천, 속초, 충주, 수안보 등 지역에서 나타난다 이러한 이상대 주변에는 대개 온천이 발달되어 있었거나 새로 개발되어 있는 곳이다. 온천에 이용하고 있는 시추공의 자료는 배제하였으나 온천이응으로 직접적으로 영향을 받지 않은 시추공의 자료는 사용하였다 이러한 온천 주변 지역이라 하더라도 실제는 온천의 pumping 으로 인한 대류현상으로 주변 일대의 온도를 올려놓았기 때문에 비교적 높은 지열류량 값을 보인다. 한편 한반도 남동부 일대는 이번 추가된 자료에 의해 새로운 지열류량 분포 변화가 나타났다 강원 북부 오색온천지역 부근에서 높은 지열류량 분포를 보이며 또한 우리나라 대단층 중의 하나인 양산단층과 같은 방향으로 발달한 밀양단층, 모량단층, 동래단층 등 주변부로 NNE-SSW 방향의 지열류량 이상대가 발달한다. 이것으로 볼 때 지열류량은 지질구조와 무관하지 않음을 파악할 수 있다. 특히 이러한 단층대 주변은 지열수의 순환이 깊은 심도까지 가능하므로 이러한 대류현상으로 지표부근까지 높은 지온 전달이 되어 나타나는 것으로 판단된다.

• Journal of the Korean Geotechnical Society
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• v.26 no.12
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• pp.19-30
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• 2010

Bentonite-based grout has been widely used to seal a borehole constructed for a closed-loop vertical ground heat exchanger in a geothermal heat pump system (GHP) because of its high swelling potential and low hydraulic conductivity. Three types of bentonites were compared one another in terms of viscosity and thermal conductivity in this paper. The viscosity and thermal conductivity of the grouts with bentonite contents of 5%, 10%, 15%, 20% and 25% by weight were examined to take into account a variable water content of bentonite grout depending on field conditions. To evaluate the effect of salinity (i.e., concentration of NaCl : 0.1M, 0.25M, and 0.5M) on swelling potential of the bentonite-based grouts, a series of volume reduction tests were performed. In addition, if the viscosity of bentonite-water mixture is relatively low, particle segregation can occur. To examine the segregation phenomenon, the degree of segregation has been evaluated for the bentonite grouts especially in case of relatively low viscosity. From the experimental results, it is found that (1) the viscosity of the bentonite mixture increased with time and/or with increasing the mixing ratio. However, the thermal conductivity of the bentonite mixture did not increase with time but increased with increasing the mixing ratio; (2) If bentonite grout has a relatively high swelling index, the volume reduction ratio in the saline condition will be low; (3) The additive, such as a silica sand, can settle down on the bottom of the borehole if the bentonite has a very low viscosity. Consequently, the thermal conductivity of the upper portion of the ground heat exchanger will be much smaller than that of the lower portion.