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
Open Access Monthly
  • ISSN : 1229-6422 (Print)
  • ISSN : 2465-7611 (Online)

Korean Journal of Air-Conditioning
and Refrigeration Engineering

A journal devoted to investigations of HVAC and building technologies in various climatic conditions

• Editors-in-Chief: Doosam Song

홍고추 건조 시 건조기의 건조 에너지에 관한 연구 A Study on the Drying Energy for a Dryer with Red Pepper

https://doi.org/10.6110/KJACR.2021.33.10.485

Bu Chul Kim ; Jeachul Jang ; Imkyeong Lee ; Youn Cheol Park

In the Korean food culture, chili peppers (Capsicum annuum L.) are often used to make spicy seasonings. These peppers are mainly used in the powdered form, obtained as a result of a drying process and chili peppers powders generally have a moisture content of 14-20%. Chili peppers are dried naturally using solar radiation (sunlight) or using dryers. Dryers are used to reduce the drying time as compared to the natural drying method. In this paper, a membrane-heat pump hybrid dryer was developed in order to find efficient drying methods by controlling the membrane and heat pump. Furthermore, the drying energy calculation method was proposed in the drying process. The results showed that the cross over control method used 20.5% more drying energy as compared to the time control method.

고밀도 데이터센터의 독립모듈 컨테인먼트 및 구역단위 냉각시스템 성능평가에 관한 실증연구 An Empirical Study on Cooling Performance Evaluation of Independent Modular Air Containment and Row-based Cooling System for High-Density Data Centers

https://doi.org/10.6110/KJACR.2021.33.10.494

Jinkyun Cho ; Beungyong Park ; Yongdae Jeong ; Min-Geon Go

Owing to the rapid growth of information technology (IT) services over the past decades, data centers have become the core infrastructures of Industry 4.0. Meanwhile, the energy use of data centers has rapidly increased. In this study, a prototype of an independent module containment system that applied the row-level cooling system of a high-density data center was developed to overcome the limitations of the existing room-based cooling system and satisfy the demand for energy efficiency. The main purpose was to evaluate the cooling performance of multi-fluid (refrigerant-water cooled type) in-row CRAH unit package in independent row-based air containment. Based on in-situ measurements, the applicability and cooling efficiency of the row-level cooling system were evaluated. While complying with the international test method standard for CRAC/H unit, the cooling performance and efficiency of the row-based cooling system were derived through real-time field measurement in connection with the actual operation situation of the data center and the partial energy contribution was analyzed. The row-based cooling system with the multi-fluid heat exchange in-row CRAH unit package was found to be the most efficient in removing heat output of IT equipment based on the observations and experimental results.

칼만 상태 관측기와 피드포워드 제어기를 갖는 슬라이딩 모드 제어 기반의 가변속 냉동시스템의 강인한 온도 제어 Robust Temperature Control for a Variable Speed Refrigeration System Based on Sliding Mode Control Using a Kalman State Observer and Feedforward Controller

https://doi.org/10.6110/KJACR.2021.33.10.506

Ji Eun Lee ; Seok Kwon Jeong

This paper describes sliding mode control using a state observer with Kalman filter and feedforward controller for a variable speed refrigeration system (VSRS) to ensure robust control performance against model uncertainty and disturbance. The sliding mode control was designed using a state space model obtained from a practical transfer function model, which was obtained by conducting experiments near operation point. The control input of SMC was achieved from estimation of state variables by a state observer with Kalman filter. Additionally, the feedforward controller was designed to minimize the steady state error due to saturation function. Simulations and experiments were conducted to verify the control performance of the suggested SMC with the feedforward controller and the state observer with Kalman filter. The results of simulations and experiments showed that the proposed controller was capable of robust temperature control for VSRS despite stepwise changes of reference and external heat load.

외란과 모델 불확실성이 존재하는 가변속 냉동시스템의 강인제어를 위한 H-infinity 제어기 설계 H-infinity Controller Design for Robust Control of Variable Speed Refrigeration System with Disturbance and Model Uncertainty

https://doi.org/10.6110/KJACR.2021.33.10.520

Dong Geun Kim ; Seok Kwon Jeong

This paper describes the design of H-infinity controller for robust control of a variable speed refrigeration system. The suggested controller can ensure robustness against disturbance and model uncertainty by minimizing H-infinity norm of the transfer function from exogenous input to performance output and applying the small gain theorem. In particular, the controller was designed to simultaneously reduce the effects of disturbance and model uncertainty by formalizing these problems as a mixed sensitivity problem. In addition, an integrator was included to the controller to prevent the occurrence of steady state error. The validity of the proposed controller was demonstrated by computer simulations and real experiments. Moreover, the effectiveness of the proposed controller was confirmed by comparing its performance to the PI controller, which was tested under the same experimental conditions as the H-infinity controller.

코로나19 사회적 거리두기 기준 설정을 위한 공기 중 기침 입자의 확산에 대한 연구 Analysis on Dispersion of Airborne Cough Droplets for COVID-19 Social Distancing Policy

https://doi.org/10.6110/KJACR.2021.33.10.533

Minji Jung ; Jin Kwan Hong

Many epidemiological studies have found that SARS-CoV-2 laden droplets from an infected human could be transmitted through the air and cause infection. CFD simulation was used to simulate the evaporation and dispersion of droplets under the Korean weather conditions. Numerical results showed that about 59% of the cough droplets evaporated to their droplet nuclei sizes (5 μm) within seconds. In quiescent air, cough droplets could travel more than 1 m and droplets less than 50 μm remained suspended for long periods, with a high concentration in the vapor plume. When the wind speed was 2.3 m/s and 2.4 m/s, which is the average wind speed of summer and winter, respectively, in Korea in 2020, droplets less than 100 μm followed the airflow streamlines and deposited on receiver 2 m away from the emitter. Therefore, based on environmental conditions, such as, wind, relative humidity, and temperature, 2 m social distancing policy may not be sufficient.

데이터센터의 성능기반설계를 위한 냉방 시스템 설계지원 및 에너지 성능분석 툴 개발 The Cooling System Design Support and Energy Analysis Tool for Performance-based Design of a Data Center

https://doi.org/10.6110/KJACR.2021.33.10.543

Ji Hye Kim ; Hee Gang Kim

Recently, the annual PUE level of data centers in Korea was around 1.3, which corresponds to a significantly improved energy performance as compared to conventional data centers. In order to achieve an annual PUE of 1.3, a cooling system equipped with an economizer is essential. Since the cooling energy saved by the application of the economizer depends on outdoor air conditions, annual energy simulation is required to evaluate the energy performance of the system. Meanwhile, most data centers operate under partial load conditions and only have cooling loads throughout the year. Therefore, evaluating system energy consumption requires considering the dynamic performance of the equipment under off-design conditions. The purpose of this study is to develop data center cooling system designs and energy analysis tools for mechanical equipment engineers. For verification of the developed tool, simulation results were compared to DesignBuilder model.