• Research Article

    Simulation Analysis of Waste Heat Recovery Effects from Fuel Cells for District Heating Networks

    지역난방 시스템과 연계한 연료전지 폐열 회수 효과 분석

    Jeong, Jin-A, Kim, In-Su, Cho, Kyu-Chan, Kim, Eui-Jong

    정진아, 김인수, 조규찬, 김의종

    This study proposes a district heating network that uses the existing 3rd generation district heating but modifies the configuration of heat exchangers … + READ MORE
    This study proposes a district heating network that uses the existing 3rd generation district heating but modifies the configuration of heat exchangers to enable a low temperature network in the second loop. By lowering the supply temperature, the system can increase the use of renewable energy such as fuel cells. The study aims to quantitatively calculate the effectiveness of the proposed method through simulation. Results show that the proposed district heating system decreases the source-side total flow rates compared to the existing 3rd generation district heating. In addition, installation of fuel cells in the proposed model can reduce energy consumption by 23% with 10% of the capacity of the whole district heating system. The proposed model has the potential to induce efficiency improvement of the entire district heating system, reduce energy loss of the long-distance heat pipe network, and increase the efficiency of the heat supply facility. - COLLAPSE
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    30 August 2023

  • Research Article

    Predicting Internal Environment of Underground Utility Tunnel Using Machine Learning Model

    기계학습을 활용한 지하 공동구 내부 환경 예측

    Kim, Da-In, Lee, In-Bok, Jung, Woo-Sug, Lee, Byung-Jin

    김다인, 이인복, 정우석, 이병진

    Underground utility tunnel is located underground, which makes the ventilation system operation and internal environment monitoring important. By designing a machine learning … + READ MORE
    Underground utility tunnel is located underground, which makes the ventilation system operation and internal environment monitoring important. By designing a machine learning regression model for predicting the internal environment, the effects of the input variables were verified. Temperature, relative humidity and fan operation hour data was collected hourly by sensors installed near the exhaust fan. The external weather data was obtained from the nearest meteorological station in the same experimental period. The results of machine learning regression analysis model showed accuracy of random forest (R2: 0.891), support vector regression (0.800), k-nearest neighbor (0.774), and multi linear regression (0.744). In order to design the accurate model, the n estimator was set to 157, in which the accuracy of temperature prediction was 0.837 by R2, and the accuracy of humidity prediction was 0.950. Using the RF model, the correlating factors correlating were verified and the internal environment of underground utility pipe according to fan operation time was verified. - COLLAPSE
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    30 August 2023

  • Research Article

    A Feasibility Study on an Application of the Building Envelope Design Modification for the Reduction of Ground Heat Exchangers

    건물 외피 설계 요소 조정을 통한 지중 열교환기 용량 감축 방안 연구

    Lee, Ye-Jin, Lee, Young-Ae, Baek, Seung-Hyo

    이예진, 이영애, 백승효

    Although ground-source heat pump (GSHP) system is promising for implementing a zero-energy building, the high initial cost of the system limits its … + READ MORE
    Although ground-source heat pump (GSHP) system is promising for implementing a zero-energy building, the high initial cost of the system limits its applications. Most of all, reducing the drilling cost, which accounts for more than 50% of the total installation cost of the GSHP, is necessary. In other words, reducing the length of borehole can most effectively make GSHP affordable. In the design of the ground heat exchanger, a modification of building heating and cooling loads, which has not been considered carefully in previous studies, can be promising. Accordingly, this study aims at proposing load modification approaches and investigating their feasibility. First, heating and cooling loads were calculated for the medium office building using EnergyPlus 7.2.0, and based on them, the borehole length was determined using GLHEpro 5.0.4. Second, peak and total of heating and cooling loads were modified by changing values of design variables related to building envelope, such as thickness of insulation material, U-value, and SHGC of window and infiltration rate. Finally, the results of peak and total of heating and cooling loads were classified and effects of each load pattern on the borehole length were analyzed. The results showed two major insights for the application of load modification strategy on reducing the borehole length. Even lower SHGC did not reduce the heating peak load but contributed to an alleviation of thermal accumulation of the ground. Consequently, the borehole length was reduced by 16.0%. Lowering of the infiltration rate was intended to reduce peak heating load; however, it increased the borehole length 1.6%. Therefore, besides a reduction of peak load, a balance between total heating and cooling loads was concluded to be essential for reducing borehole length. Additionally, proper load modification strategy needs to be carefully investigated owing to the difference in the loads pattern caused by the climate of a region, building type, and envelope configuration. - COLLAPSE
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    30 August 2023

  • Research Article

    Analysis of Insulation Performance According to Argon Gas Filling Rate Variation in the Insulating Glass Space Iayer

    단열 유리 공간층 내 아르곤 가스 충진율에 따른 단열 성능 분석

    Cho, Kyung-Joo, Koo, Bo-Kyoung, Cho, Dong-Woo

    조경주, 구보경, 조동우

    As of June 2013, 15,174 window sets obtained high-efficiency energy equipment certifications, among which 5,519 window sets obtained first-class certification. Among the … + READ MORE
    As of June 2013, 15,174 window sets obtained high-efficiency energy equipment certifications, among which 5,519 window sets obtained first-class certification. Among the window sets that obtained the first grade, about 63% of the window sets have a thermal transmittance of 0.8~0.9 W/m2 K, and most of them are multi-layered insulating glass filled with argon gas. However, leakage defects of the gas filled in the windows occur frequently, and it is difficult to say that the windows with gas leakage have the above insulation performance. Therefore, this study attempted to present basic data on the degradation of insulation performance through investigating the current thermal performances of high-performance windows filled with argon gas, carrying out KS experiments, and simulations. As a result, it was analyzed that the insulation performance of high-performance windows can be reduced by up to about 30% depending on the filling rate of argon gas in this tests and simulations, which shows that grade fluctuations of the windows can occur depending on the filling rates of argon gas. Therefore, in order to maintain the insulation performances of the insulating glass windows for a long period of time, it is necessary to prevent leakage of the filled gas by increasing the adhesive strength between the gap bar and the sealing material. In addition, it is necessary to develop gas filling technologies in various ways to minimize changes in the filling rates of argon gas due to secular changes. - COLLAPSE
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    30 August 2023
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