• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.62-68
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• 2001

It is a serous subject for energy conservation to prevent the energy loss caused by the mixture of heated and cooled air jets in perimeter and interior zone of a building operated with tow kinds of air-conditioning system simultaneously. The purpose of this paper is to clarify the quantitative and qualitative mechanisms of mixing loss and to propose a evaluation method for it. By using the dynamic heat load calculation, heat extraction load of a typical office building in Busan are calculated. According to the results, numerical simulations based on CFD(Computational Fluid Dynamics) were performed in order to evaluate mixing loss in the physical size of HVAC system. Then, the distributions of air temperature and airflow patterns according to the differences of set-point temperature are analyzed to grasp relations how to influence mixing loss.

• 한국의상디자인학회지
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• 제7권3호
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• pp.75-81
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• 2005

The experiment aimed at knowing the effect of physiology and psychology according to season on color preference. Two tests, one of the spring and the other of the autumn was conducted. Seventy subjects with normal color vision served as subjects. The subjects entered a bioclimatic chamber controlled at a temperature of $25\pm1^{\circ}C$, a relative humidity of $50\pm5\%$ and a light of 1000 1x. The subjects wearing white shirts and trousers sat quietly on a sofa for one our. Sensation from warm to cool colors might be possibly different individually Therefore, a subject asked to array 41 randomly placed cloth colors from very warm to very cool colors during rest quietly for one our. All subjects arrayed these cloth colors in the order from red through yellow and green to blue, which had the reproducibility. After rest, they were instructed to choose a single one out of 41 cloth colors, preferred by themselves, every 10min during one our 0-ring test were measured to red, yellow, white, blue, black, favorite color, and dislike color. Most subjects preferred warmer color in April than in December. Tympanic temperature was significantly lower in December than in April. Finger presser was significantly higher in like color than in dislike color but it was no significant differences between spring and autumn. The preferring the warm color in April toward summer when basal metabolic rate is decreased than in December toward winter when it is increased can explain that physiology reaction by load error between actual core temperature and set-point induces psychological reaction to pursue visual alliesthesia. Our present experiment revealed that the preferred color could be determined by the relationship between the internal temperature and its set point according to season. It should be emphasized that the alliesthesia was observed also in the realm of visual system.

• 설비공학논문집
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• 제27권5호
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• pp.247-253
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• 2015

The presented work demonstrates the effects of flow rate on the secondary side of DHS (District Heating System). Increasing flow rate at the secondary side of DHS decreases energy consumption and time to reach the set-point of the heated room while increasing heat flux on the floor in the heating space. When flow rate increases, the overall heat transfer rate of radiant floor also increases. However, the results also show overall heat transfer rateto not increased linearly and thus the existence of an optimal flow rate for the secondary side of DHS. Control of the radiant floor with hot water may be more effectively accomplished with a combined control strategy that includes heat flux and a temperature set-point. This experimental analysis has been performed using a lab-scaled DHS pilot plant located at Jeonju University in Korea.

• 설비공학논문집
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• 제18권4호
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• pp.287-296
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• 2006

In this paper, optimal control strategy of the air-conditioning system with slab thermal storage was investigated based on the optimal control theory. An optimal heat output to the plenum chamber and the air-conditioned room was determined based on two kinds of criterion functions. The first one requires small deviation in room air temperature from a set-point value and low energy consumption. It is shown that the optimized control is to store heat through the whole storage time and to increase storage rate gradually with time. As the second case, a criterion that both a deviation of operative temperature from a set-point temperature and the energy consumption should be minimized was adopted. The room air temperature was a little high and the cooling load during storage time was reduced, compared with the results when a criterion function considering only the room air temperature is used.

• 한국환경과학회지
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• 제23권3호
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• pp.399-407
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• 2014

In this study, before and after sunset carbon dioxide concentration and air temperature were observed in two points of atmosphere (lower observation point of the GL + 0.1 m, the upper observation point of GL + 1.0 m) on the foreshore at located in Suncheon Bay and their variations were analyzed. Observation was performed on the foreshore on 2~4 August 2010. Instrument (VAISALA, GMP343) was set two hours before sunset and then observation was made continuously for six hours. In three days, observed carbon dioxide concentration was 375~419 ppm, and the air temperature was in the range of $28.7{\sim}32.5^{\circ}C$. The average concentration of carbon dioxide was 388~399 ppm in the upper observation point and 386~396 ppm in the lower observation point. It was higher in the upper observation point and its fluctuations were similar in two observation points. Correlation coefficients between carbon dioxide concentration and air temperature in the upper observation point were in the range of -0.64~-0.88, and were calculated -0.65 to -0.90 in the lower observation point. For the carbon dioxide concentration, correlation coefficients between the upper part and the lower part were very high as 0.98 in three times. For the air temperature, correlation coefficients between the upper part and the lower part were very high as 0.97 and 0.99. In the same observation time, the slope of the linear regression function as carbon dioxide concentration in the lower observation point for the upper observation point was in the range of 0.97~1.01. Carbon dioxide concentration was slightly higher in the upper observation point. Because carbon dioxide in the lower observation point was closer on the surface of the foreshore and absorbed from atmosphere to the foreshore. In this study, it was showed that the vertical variation of carbon dioxide concentration was insignificant in the several meter scale of atmosphere on the surface of the foreshore.

• Korean Chemical Engineering Research
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• 제59권1호
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• pp.77-84
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• 2021

Plug flow reactor (PFR) 내의 과열점(hot spot) 온도를 조절하는 것은 생성물의 수득률 및 순도, 안전성 측면에서 중요하다. 본 연구에서는 더 현실에 가깝게 모델링 하기 위하여 PFR 내부의 냉각액 온도를 상태변수로 설정하고 방사 방향의 열 및 물질전달을 고려하였다. 모델은 반응물의 농도 및 온도와 냉각액의 온도 총 3개의 상태변수로 이루어져 있으며, 등온 냉각액의 유량을 조작변수로 가진다. 본 연구에서는 방사 방향의 열 및 물질전달을 고려한 제어식이 그렇지 않은 제어식보다 과열점의 온도를 set point 부근으로 더 효과적으로 유지한다는 것을 보였다. 본 연구에서 제안한 제어식은 냉각액의 온도가 반응물 온도의 약 0.7배 부근일 때 St가 1.3 이상이고 Ac/A가 2.0 이하인 조건에서 강건성을 유지하였다. 이 조건에서 반응기로 유입되는 반응물의 온도가 5% 범위에서 바뀔 때 본 연구에서 제안된 제안식을 이용하면 과열점의 온도를 set point의 1% 이내로 유지할 수 있다.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.532-545
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• 2022

In-depth convergence analyses for neutronics/thermal-hydraulics (T/H) coupled calculations are performed to investigate the performance of nonlinear methods based on the Fixed-Point Iteration (FPI). A simplified neutronics-T/H coupled system consisting of a single fuel pin is derived to provide a testbed. The xenon equilibrium model is considered to investigate its impact during the nonlinear iteration. A problem set is organized to have a thousand different fuel temperature coefficients (FTC) and moderator temperature coefficients (MTC). The problem set is solved by the Jacobi and Gauss-Seidel (G-S) type FPI. The relaxation scheme and the Anderson acceleration are applied to improve the convergence rate of FPI. The performances of solution schemes are evaluated by comparing the number of iterations and the error reduction behavior. From those numerical investigations, it is demonstrated that the number of FPIs is increased as the feedback is stronger regardless of its sign. In addition, the Jacobi type FPIs generally shows a slower convergence rate than the G-S type FPI. It also turns out that the xenon equilibrium model can cause numerical instability for certain conditions. Lastly, it is figured out that the Anderson acceleration can effectively improve the convergence behaviors of FPI, compared to the conventional relaxation scheme.

• 한국지열·수열에너지학회논문집
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• 제3권2호
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• pp.31-37
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• 2007

The fuzzy control algorithm for HVAC system has been developed for minimizing energy consumption while maintaining the comfort of indoor thermal environment in terms of the environmental variables such as time varying indoor cooling load and outdoor temperatures. The optimal set-points of control parameters with fuzzy control are supply air temperature, chilled water temperature and condenser temperature. This study has been done by using TRNSYS program in order to analyze the HVAC system response. As a result, the fuzzy control algorithm with PID algorithm shows good energy performance in comparison with conventional one.

• 설비공학논문집
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• 제18권11호
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• pp.896-905
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• 2006

An optimal control of an air-conditioning system with slab thermal storage is investigated by making use of the Maximum Principle. An optimal heat input to a plenum chamber and an air-conditioned room is determined by minimizing a criterion function which is given as integral sum of two terms. The first term is the square of the deviation in the room air temperature from the set-point value, and the second is the absolute value of the heat input. The result indicates that it tries to keep a room air temperature in set-point value by heating as much as possible at the time of a setup of a room air temperature or just before that, in order to avoid a heat loss arising at the time of the non-air conditioning. The result is compared with that of the case when the square of the heat input is used as a criterion.

• 한국항공우주학회지
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• 제46권2호
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• pp.167-174
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• 2018

달 착륙선에는 14일에 이르는 밤 구간동안 극한의 열환경에서 생존하기 위한 열원공급을 목적으로 히터가 적용되며, 이 때 전력생성이 제한되는 착륙선의 소요전력을 최소화하는 히터 작동 온도 설정치가 결정되어야 한다. 또한 상기 온도 설정치에 따른 착륙선의 온도 변화는 탑재 전장품에 적용된 전자소자의 솔더 접합부에 대한 열기계적 신뢰성과 연관되는 중요한 설계인자이다. 본 논문에서는 임무수명이 1년인 달 착륙선의 열해석 결과를 토대로 상용 신뢰성 수명예측도구인 Sherlock을 활용하여 상기의 온도 설정치에 따른 솔더 접합부의 열 기계적 신뢰성을 검토하였다.