• 설비공학논문집
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• 제22권10호
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• pp.687-696
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• 2010

In this study, FDD algorithm was developed using the normalized distance method and general pattern classifier method that can be applied to constant air volume air handling unit(CAV AHU) system. The simulation model using TRNSYS and EES was developed in order to obtain characteristic data of CAV AHU system under the normal and the faulty operation. Sensitivity analysis of fault detection was carried out with respect to fault progress. When differential pressure of mixed air filter increased by more than about 105 pascal, FDD algorithm was able to detect the fault. The return air temperature is very important measurement parameter controlling cooling capacity. Therefore, it is important to detect measurement error of the return air temperature. Measurement error of the return air temperature sensor can be detected at below $1.2^{\circ}C$ by FDD algorithm. FDD algorithm developed in this study was found to indicate each failure modes accurately.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.912-918
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• 2008

In this study, the exergy which could be reflected on energetic and economic value was used to assess on heat tariff of district heating system instead of enthalpy. Exergy is difficult to apply directly to present heat charge system because of complex calculation. Therefore, the difference between supply and return temperature was converted to the exergy temperature difference for easily calculating the amount of heat. As a result of exergy analysis for a DH substation, the exergy temperature difference were not affected on surrounding temperature and pressure loss. Supply temperature, maximum difference between supply temperature and return temperature had a main effect on the exergy temperature difference. The new heat charge of a DH user was slightly reduced in winter compared with previous heat charge. Heat charges in other seasons were almost same. It is thought that heat tariff using exergy will be appropriate in terms of both DH supplier and consumer.

• 설비공학논문집
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• 제29권4호
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• pp.202-211
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• 2017

In this study, the exergy that can be reflected in the energetic and economic values was used to assess the heat tariff of a district heating (DH) system instead of the enthalpy. It is difficult to directly apply the exergy to the current heat-charge system because of the complicated calculation; therefore, the difference between the supply and return temperatures was converted to the exergy-temperature difference for the ease of the heat-amount calculation. As a result of the exergy analysis for a DH substation, the exergy-temperature difference did not affect the surrounding temperature and pressure loss. The supply temperature and the maximum difference between the supply temperature and the return temperature exerted the main effect on the exergy-temperature difference. The new heat charge of a DH user was slightly reduced in winter compared with the previous charge, but the heat charges in the other seasons are almost the same. It is concluded from the assessment of the heat tariff for which the exergy is used that this tariff is more feasible for both DH suppliers and consumers compared with enthalpy.

• 설비공학논문집
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• 제26권12호
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• pp.572-578
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• 2014

Heating energy was measured in an apartment housing unit with a district heating system, varying the kind of hot water distributors. Ondol coils passing through a living room raised the temperature of the room where the heating was turned off. Including this characteristic of Ondol heating into the modeling, we performed simulations and showed a verification by comparison with the results of measurements. As a result, a main flow control method, which changes hot water flow rate supplied to a housing unit according to the thermal load, can reduce the supplied flow rate and lower the return temperature, compared with a constant flow method. That can result in decreased heat loss in utility-pipe conduits even though the heating energy supplied is almost the same. An outdoor reset control that raises the temperature of the supplied hot water if the outdoor temperature falls has the effect of a quicker response in heating than the reduced flow rate and return temperature.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2006년도 영호남 합동 학술대회 및 춘계학술대회 논문집 센서 박막 기술교육
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• pp.77-81
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• 2006

We report the performance of a four-element, 11.67 GHz, high-Tc superconducting (HTS) microstrip antenna array with corporate feed network and circular polarization for direct broadcasting satellite (DBS) system. Our array antennas were designed and built on a 0.5 mm thick MgO substrate. To compare the superconducting antennas with normal conducting counterpart, One antenna pattern was fabricated from gold thin film, and a second pattern was fabricated from $YBa_2Cu_3O_{7-x}$ (YBCO) superconducting thin film. To improve the axial ratio of circularly polarized arrays, sequential rotation technique were used. Efficiency, radiation pattern, return loss and bandwidth were measured for both antennas at room temperature and at cryogenic temperature. The array produced good circular polarization, and the gain of the array at 77 K, relative to a copper array at room temperature was approximately 1.54 dB. The measured return loss of our HTS antenna array was 35.79 dB at the resonant frequency of 11.67 GHz and The total effective bandwidth was about 3.4 %. The results showed that high-temperature superconductors, when used in microstrip arrays, improved the efficiency of the HTS antenna array for circularly polarization.

• 한국전기전자재료학회논문지
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• 제17권7호
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• pp.776-781
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• 2004

We report the performance of a four-element, 11.67 GHz, $high-{T}_c$ superconducting (HTS) microstrip antenna array with corporate feed network. The HTS antenna array used in this work had a circular polarization for direct broadcasting satellite (DBS) system. Our array antennas were designed and built on a 0.5 mm thick MgO substrate. To compare the superconducting antennas with normal conducting counterpart, One antenna pattern was fabricated from gold thin film, and a second pattern was fabricated from ${YBa}_2{Cu}_3{O}_7-x(YBCO)$ superconducting thin film. To improve the axial ratio of circularly polarized arrays, sequential rotation technique were used. Efficiency, radiation pattern, return loss and bandwidth were measured for both antennas at cryogenic temperature and room temperature. The array produced good circular polarization, and the gain of the array at 77 K, relative to a copper array at room temperature was approximately 1.54 dB. The measured return loss of our HTS antenna array was 35.79 dB at the resonant frequency of 11.67 GHz and The total effective bandwidth was about 3.4 %. The results showed that high-temperature superconductors, when used in microstrip arrays, improved the efficiency of the HTS antenna array for circularly polarization.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.866-871
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• 2006

Recently according to the fashion of well-being, the case study of under floor heating system type for residential space is increasing. Specially double slab floor system can make several roles as reducing the acoustic noises and also supplying fresh air through the gap. So in present study floor heating performance was examined with various location of the space in the case of floor supply air and ceiling supply air. In both cases return air went out through ceiling opening. As one of the result is that when using the heat pipe type floor heating system the temperature difference between supply and return water was $15.2^{\circ}C$, but in case of commercial type floor heating system the temperature difference was $5.3^{\circ}C$ when the supply water temperature was $50^{\circ}C$.

• 한국농림기상학회지
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• 제14권4호
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• pp.155-160
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• 2012

이 연구는 1월 일 최저기온의 평균을 이용하여 재현기간별 일 최저기온의 극값을 예측하는 방법을 개발하기 위해서 수행되었다. 전국 61개 기상관서의 1961~2010년의 50년 간의 일 최저기온자료를 이용하여 전체 연구를 수행하였다. 1월의 일 최저기온의 분포는 대부분 정규분포를 나타내고 있어, 이는 평균과 표준편차로부터 일 최저기온을 확률적인 기댓값으로 예측될 수 있었다. 이를 위하여 일 최저기온평균으로부터 일 최저기온의 표준편차의 변이를 추정하는 2차식을 개발하였다. 과거 10, 20, 30, 40, 50년의 재현 기간별로 관측된 일 최저기온의 평균, 표준편차, 극값을 분석하여 재현기간별 극값을 예측할 수 있는 계수를 도입하였고, 이 계수를 재현기간별로 추정할 수 있는 로그함수식도 개발하였다. 이 방법을 이용하여 과거 두 기간의 30년 자료를 이용하여 61개 지점에 대해 검증하였는데 평균 $1.1^{\circ}C$, 최대 $5.3^{\circ}C$의 오차를 가지고 과거 30년 재현기간의 일 최저기온의 극값을 예측할 수 있었다.

• 한국농공학회논문집
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• 제49권1호
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• pp.17-22
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• 2007

The heat flow characteristics of the Gudle (traditional Ondol) used a lot at farm houses have been performed with variations of Bunengki (Fireridge) by numerical analysis and field experiment. The Doedon-Gorae (Return-Firetunnel) Gudle is analyzed among the structure of Gudle. The distribution of heat flow in Gorse (Firetunnel) and the temperature distribution in floor of 3 Buneomgi (Fire ridge) was more uniform than that of 1 Buneomgi. The heat efficiency of 3 Buneomgi was higher than that of 1 Bunengki. That is, the 3 Bunengk is more efficient and more uniform temperature.

• 대기
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• 제33권1호
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• pp.1-20
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• 2023

Holding the longest observation data from April 1904, Busan is one of the essential points to understand the climate variability of the Korean Peninsula without missing data since implementing the modern weather observation of the South Korea. Busan is featured by coastal areas and affected by various climate factors and fluctuations. This study aims to investigate climate variability and changes in climatic variables, extremes, and several weather indexes. The statistically significant change points in daily mean rainfall intensity and temperature were found in 1964 and 1965. Based on the change point detection, 117 years were divided into two periods for daily mean rainfall intensity and temperature, respectively. In the long-term temperature analysis of Busan, the increasing trend of the daily maximum temperature during the period of 1965~2021 was larger than the daily mean temperature and the daily minimum temperature. Applying Ensemble Empirical Mode Decomposition, daily maximum temperature is largely affected by the decadal variability compared to the daily mean and minimum temperature. In addition, the trend of daily precipitation intensity from 1964~2021 shows a value of about 0.50 mm day^-1, suggesting that the rainfall intensity has increased compared to the preceding period. The results in extremes analysis demonstrate that return values of both extreme temperatures and precipitation show higher values in the latter than in the former period, indicating that the intensity of the current extreme phenomenon increases. For Wet-Bulb Globe Temperature (effective humidity), increasing (decreasing) trend is significant in Busan with the second (third)-largest change among four stations.