Mobile QR Code QR CODE : Korean Journal of Air-Conditioning and Refrigeration Engineering
Korean Journal of Air-Conditioning and Refrigeration Engineering

Korean Journal of Air-Conditioning and Refrigeration Engineering

ISO Journal TitleKorean J. Air-Cond. Refrig. Eng.
Open Access Monthly
  • ISSN : 1229-6422 (Print)
  • ISSN : 2465-7611 (Online)

2차 유체에 따른 증기압축식 액체냉각시스템의 성능특성에 관한 해석적 연구 Numerical Study on the Performance Characteristics of Vapor Compression Liquid Cooling System with Secondary Fluids

https://doi.org/10.6110/KJACR.2019.31.1.001

Jeong Hoon Lee ; Hoon Kang ; Yongchan Kim ; Kwang Jin Lee ; Sung Woo Park ; Sung Wook Kang ; Kwang Hee Kang ; Wan Soon Shin

In this study, a numerical model is developed to predict the performance of a vapor compression liquid cooling system for electronic devices using EGW (ethylene glycol water) as a secondary fluid. A compressor model was developed by calculating the efficiency based on the compression ratio, while the heat exchangers were analyzed using finite volume method. The performance characteristics of the liquid cooling system were analytically investigated by varying the air temperature at the condenser inlet, heat load, condenser air flow rate, and secondary fluid flow rate. As the heat load increases, the COP of the liquid cooling system increases. However, the heat load decreases as the inlet and outlet temperatures of EGW decrease, resulting in a higher pressure drop. Various secondary fluids, such as Dowtherm J, Dowtherm Q, Syltherm HF, Syltherm XLT, Marlotherm XC, and Marlotherm XD, were analyzed to solve this problem. The heat transfer and pressure drop characteristics of the liquid cooling system were numerically analyzed using these fluids. As a result, Marlotherm XC showed the higher heat transfer and lower pressure drop characteristics among the secondary fluids.

저등급 열원 활용을 위한 수정 유기플래시 사이클(OFC)의 성능 특성에 관한 연구 Study on Performance Characteristics of a Modified Organic Flash Cycle (OFC) for Recovery of Low-Grade Heat Source

https://doi.org/10.6110/KJACR.2019.31.1.013

Kyoung Hoon Kim ; Chul Ho Han ; Hyung Jong Ko

This paper proposes a modified organic flash cycle (OFC) employing a two-phase expander and regeneration for recovery of low-grade heat source. The following working fluids were considered; R134a, R152a, propane, isobutane, butane, R245fa, R123, isopentane, and o-xylene. The effects of the selection of working fluid and flash temperature on the systems' performance including heat input rate, net power production, and system thermal efficiency were investigated. The results showed that while the net power production peaked with respect to flash temperature, the system thermal efficiency increased with flash temperature. Both of them were maximum when the working fluid was o-xylene. The modified OFC system shows a potential for performance improvement as compared to the basic OFC.

딥러닝을 이용한 재실정보 기반 건물의 전기 수요 예측 모델 Short-Term Electricity Consumption Prediction based on Occupancy Information Using Deep-Learning Network Models

http://dx.doi.org/10.6110/KJACR.2019.31.1.022

Byung-Ki Jeon ; Eui-Jong Kim ; Kyung-Ho Lee ; Min-Suk Kong ; Young-Gy Shin

Recently, numerous studies on the prediction of electricity consumption using deep-learning models have been conducted. The prediction models were mostly developed for a district scale since the influence of occupants' behaviors in such cases is small. On the other hands, the occupants generate huge uncertainty in predicting the future electricity demand. In this study, the unpredictable occupancy information was fed to a deep-learning model as a true value by assuming that in the future, the occupants may actively interact with the control systems using various smart device. The proposed model uses simple input values such as time of the day, base electricity load and occupancy information, while learning is achieved using measured data. Deep-leaning models with single and deeper layers were tested in this study. Both models showed excellent performance for data matching during the learning periods. The models also showed acceptable prediction performance for use in predictive control, with errors less than 30% in RMSE (cv).

데이터센터 공조·냉각시스템 효율개선을 위한 실험적 연구 Experimental Study on Data Center Cooling System for Improving Thermal Performance : Comparing with Room-based Cooling and Row-based Cooling

http://dx.doi.org/10.6110/KJACR.2019.31.1.032

Jinkyun Cho ; Beungyong Park ; Yongdae Jeong ; Youngpal Kim ; Jesang Woo

As server and IT equipment densities become more, the need for proper installation facilities is also becoming high. In addition to higher power supply density, cooling has become a major issue in data centers. This study evaluates two thermal performance strategies in data center cooling. The advantage of row-based cooling is that it is close to the hot spots, as opposed to room-based cooling systems where are losses in the air delivery path in the room. This paper examines IT environment (temperature and humidity distribution) and air distribution efficiency by field measurement of 6 performance indices. Row based cooling strategy was suggested, as it was found to be the more efficient in server cooling based on the observations and index evaluation results as compared to a room-based cooling system. Air management helps to reduce operating costs by enhancing economizer utilization and improving efficiency of the cooling system. Metrics play a significant role in providing performance indices of air management systems.

공동주택 기계설비 공사 하자 유형분석과 실무적 관점에서의 예방 및 개선 가이드라인 제안 An Analysis of Construction Defects of Residential Mechanical and Plumbing Systems : A Preventive Guideline for Practitioners

https://doi.org/10.6110/KJACR.2019.31.1.045

Jung Hee Choi ; Sean Hay Kim

While MEP/FP construction scope and cost for apartments are getting increased, defect disputes between owners and constructors are also getting increased. More than often, owners' dissatisfaction over construction defects and constructor's reaction tends to increase filing lawsuits. This study aims to provide an analysis of residential building construction defects, in particular for mechanical and plumbing works, which are classified into nine groups and typed according to defect severity to investigate the causality. Based on the analysis, this study suggests a preventive and continuous construction quality improvement guideline for practitioners. The defect data has been collected for about 20,050 apartments units built by A construction firm from 2010 to 2017. 84.6 percent of the collected defects are found in sanitary plumbing, drain and sewage piping, hot water piping, and unit ventilator and fan installation works; the detailed defects for each work are classified and the causes are carefully investigated. Eventually the database containing case studies, causes and effects, preventive measures, and warranty measures has been developed. This database can be used as an education material for agents in charge of the quality warranty on after project delivery as well as the quality assurance right before project delivery. It is authors' strong recommendation that the construction defect database should be built and managed at the enterprise level, the experience and knowledge of which needs to be shared by all stakeholders.