• Journal of the Korean Solar Energy Society
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• v.31 no.5
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• pp.140-145
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• 2011

In this study, the performance and behavior of solar heating system according to the system control scheme, variable flow control (proportional control) and constant flow control (on-off control) was carried out by experiment. The on-off control is used generally for solar thermal system by now. But the proportional control is used for the solar district heating system which is supplied the higher temperature of water than that of desired. The proportional control logic that pump speed is varied in an attempt to maintain a specified outlet temperature of solar heating system was developed and tested for the use widely for the small and medium solar thermal system. The results are as following. First, the proportional controller which is made here could be adopted the characteristics for setting temperature control. Second, the proportional control is better than the on-off control in the side of the performance of thermal stratification in storage tank. Third, the operating energy(electricity consumption by pump) of solar thermal system can be saved more than 60% using the proportional control comparing to the on-off control.

• Journal of the Korean Solar Energy Society
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• v.25 no.2
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• pp.1-8
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• 2005

On-off differential controller is one of the very important components which affect the system performance of the active solar thermal system. In this study, analyses were made regarding the influence of "on-off" setting temperature on the system efficiency and on the electrical consumption by circulation pump. This study was performed by experiment as well as the computer simulation using TRNSYS program. The simulation system was developed in this study was verified the its reliability by the experimental results. As a results, the turn off temperature(${\Delta}T_{off}$) is much more influence than the turn on temperature(${\Delta}T_{on}$) on the system efficiency. It is more clear and sensitivity in winter season. Finally the optimum on-off setting value and the system on-off pattern according to the several different kind of system was also represented.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05a
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• pp.221-226
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• 1998

과잉온도 차온(Overtemperature $\Delta$T) 및 과잉출력 차온(Overpower $\Delta$T)트립에 쓰이는 온도 측정계통 총 지연시간은 6초로 구성되며 RTD 우회배관 제거시 4.5초의 RTD 응답시간(일차지연 상수로 가정)과 1.5초의 순수지연시간(전자회로 지연시간 + 그립퍼 풀림시간등)으로 구성된다. 그러나 RTD우회배관 제거전 사고분석을 일차지연상수를 3.5초, 순수지연을 2.5초로 모델링하였으므로 Simulink를 통한 영향분석과 Rack 응답시험 계단파 입력신호의 타당성을 평가하였다. RTD 응답시간은 전형적인 1차 지연요소로 나타내며 계전기나 제어봉 Gripper Release 시간 등은 순수 지연으로 가정하고 분석을 수행하고 기타 지연/지상 필터를 발전소와 동일하게 모델링하여 분석하므로써 발전소에서 일어나는 과도현상을 묘사할 수 있다는 점을 고려할 때 RTD우회배관 제거후 응답시간 지연상수가 바뀌더라도 안전하다는 결론에 도달했다.

• Journal of the Korean Solar Energy Society
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• v.27 no.4
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• pp.167-173
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• 2007

This study analyzed by simulation using TRNSYS as well as by experiment on the solar district heating system installed for the first time for the district heating system in Bundang. Simulation analysis using TRNSYS focused on the thermal behavior and long-term thermal efficiency of solar system. Experiment carried out for the reliability of simulation system. This solar system where the circuits of two different collectors, flat plate and vacuum tube collector, are connected in series by a collector heat exchanger, and the collection characteristics of each circuit varies. Therefore, these differences must be considered for the system's control. This system uses variable flow rate control in order to obtain always setting temperature of hot water by solar system. Specifically, this is a system that heats returning district heating water (DHW) at approximately $60^{\circ}C$ using a solar collector without a storage tank, up to the setting temperature of approximately $85{\sim}95^{\circ}C$ To realize this, a flat plate collector and a vacuum tube collector are used as separate collector loops. The first heating is performed by a flat plate collector loop and the second by a vacuum tube collector loop. In a gross collector area basis, the mean system efficiency, for 4 years, of a flat plate collector is 33.4% and a vacuum tube collector is 41.2%. The yearly total collection energy is 2,342GJ and really collection energy per unit area ($m^2$) is 1.92GJ and 2.37GJ respectively for the flat plate vacuum tube collector. This result is very important on the share of each collector area in this type of solar district heating system.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.245-251
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• 2006

The main idea of this study is to turn attention on the question of good cooling ability of customer substations in large district heating networks. The main reason for that is based on our experience that the optimization of district heating very often is directed toward production, whereas questions of optimal distribution are neglected if only the necessary load can be supplied and the customer's request for comfort is met. Our view is that low return temperature(operational temperature differences, ${\Delta}T$) in district heating systems is an Important feature for efficient net operation and gives both economic and operational benefits to the district heating supplier Furthermore, it is as well a prerequisite for meeting the customers demand for reliable supply of the heat load. However, in many practical cases we have seen that district heating return temperatures are higher than necessary. Hence, the aim of the study is to propose and verify a method for detection of the most critical consumers of the net and to identify the reasons for resulting high return temperature. From the results, temperature control system is presented as one of the most important reason of high return temperature in DH networks.

• Journal of the Korea Convergence Society
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• v.13 no.3
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• pp.191-196
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• 2022

Unlike an international combustion engine car, a battery-powered electric vehicle requires an additional heat source for its heating system. A high-voltage coolant heater has the advantages of high efficiency and a wide operating temperature range. In its development, the geometry design of the coolant flow path is essential. This paper presents the thermal flow simulations of a 7kW high-voltage heater with symmetric serpentine flow channels arranged parallelly. The heater performance was evaluated from the simulation results in terms of the pressure and temperature differences and the flow uniformity. The proposed design showed a greater flow resistance and similar heat exchanging capability than the existing parallel serpentine design. It has the advantage of a relatively wide low-temperature surface area, where the control circuit board susceptible to high temperatures can be located.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.1
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• pp.28-34
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• 2019

Solar energy is one of the most abundant renewable energy sources on Earth but there are restrictions on the use of solar thermal energy due to the time-discrepancy between the solar-rich season and heating demand. In Europe and Canada, a seasonal solar thermal energy storage (SSTES), which stores the abundant solar heat in the summer and uses the heat for the winter heating load, is used. Recently, SSTES has been introduced in Korea and empirical studies are actively underway. In this study, a $2,000m^2$ flat plate type solar collector and $20,000m^2$ of borehole thermal energy storage (BTES) were studied for a greenhouse in Hwaseong City, which has a heating load of 2,164 GJ/year. To predict the dynamic performance of the system over time, it was simulated using the TRNSYS 18 program, and the solar fraction of the system with the control conditions was investigated. As a result, the solar BTES system proposed in this study showed an average solar fraction of approximately 60% for 5 years when differential temperature control was applied to both collecting solar thermal energy and discharging BTES. The proposed system simplified the configuration and control method of the solar BTES system and secured its performance.