We developed control algorithms based on one of three artificial-intelligence-based retraining techniques (sliding window, vector adaptation, and vector augmentation) to provide the optimal indoor temperature and save on the energy expenditure for cooling in data centers. The artificial neural network prediction model predicts the computer room air handler supply air temperature of a central chilled water system and is added to the control algorithm. The proposed algorithm can determine the optimal chilled water flow rate required to cool the server to the set temperature by using the predicted computer room air handler supply air temperature. We developed a control algorithm embedded in an artificial neural network predictive model that includes three retraining techniques. Afterward, we compared the control performance and verified its adaptability by using computer simulation. When using the algorithm with sliding window control, the root mean-squared error between the set temperature and the control temperature was 0.08 °C, the maximum error was 0.81 °C, and the cooling load was 21,026.27 kWh. The accuracy, stability, and energy-saving ability of the sliding window control algorithm were higher those of the other two algorithms, and its superior adaptability and scalability under changing environmental conditions were demonstrated. 

Adaptive control algorithm with a retraining technique to predict the optimal amount of chilled water in a data center cooling system

This study performed experimental research to visualize the moisture content absorbed in R-22, refrigerant of refrigerator. Sulfuric acids were mixed with bromothylmol blue solution to make indicating solutions, and humidity papers were prepared by impregnation of the indicating solutions into solid supporters. Prior to the impregnation, small amount of lithium chloride was added into indicating solution. Moisture measuring cell was composed to test sensitivity of the humidity papers. Color changing characteristics of the humidity papers were also examined at various moisture contents in R-22. Color of the humidity paper varied linearly with the moisture content in R-22 in the range from 150 ppm to 300 ppm. The humidity papers showed complete color change to yellow at the moisture content of 300 ppm within 8 hours.

냉매 r-22에 함유된 수분 감습지 연구

Solar thermal energy can be used as a heat source for regeneration of liquid desiccant in solar desiccant cooling system. In traditional study, the effect of heated air and temperature increment of liquid desiccant for enhancing regeneration was identified. In this study, heated air and hot water made from hybrid solar air-water heater was used for regeneration of liquid desiccant and regeneration performance was investigated on the operaing methods of hybrid solar air-water heater. As a result, regeneration performance when the heated air and hot water using simultaneously shown highest value among three operating methods(using heated air, using hot water, using heated air and hot water). From this result, the possibility of application of hybrid solar air-water heater for regeneration of liquid desiccant and the necessity of profound study about regeneration performance when the heated air and hot water using simultaneously was confirmed.

복합형 태양열 가열기 운전 방식에 따른 액체 흡수제 재생 성능 비교 연구

Purpose: As cooling energy accounts for 50.5% of the data center total energy use, it is necessary to reduce cooling energy with optimal control method. Thus, this study aimed at developing an adaptive control algorithm for data center thermal environment based on Artificial Neural Network (ANN). Method: A data center thermal environment model was built to obtain variable data which is used to train and evaluate performance of the prediction model and algorithm. The thermal environment prediction model was developed using ANN and optimization process was conducted by the Bayesian Optimization Algorithm. The adaptive control algorithm, which embedded the prediction model, adopted the Sliding Windows method and was optimized to maximize the control performance. Result: The performance evaluation of the developed algorithm was conducted compared with non-adaptive algorithm. As a result, the adaptive algorithm presented better performance than the non-adaptive with 0.45 of RMSE. Therefore, the developed algorithm secured the stability and accuracy and will be applied to supervisory control platforms.

Development of a Prediction Model and an Adaptive Control Algorithm for the Data Center Thermal Environment

The objectives of this paper are to obtain an empirical equations regarding the correlations between heat transfer and pressure drop of oval fin-tube heat exchanger having large diameter using wilson plot method. It was difficult to find any recommendable heat transfer and friction factor correlation available for our large diameter experimental cases. Overall heat transfer coefficients are composed of the heat transfer coefficients both inside and outside tubes. The resulting empirical correlations for the Nui and f-factor are given as Nu i =0.0146Re 0.809 Pr 0.3 and f=4.366Re -0.64 , respectively. The empirical correlations of the Nui and f-factors were developed for the large diameter oval finned-tube heat exchanger as a function of the Reynolds number. As the EG(Ethylene glycol) and air flow rate increases, the heat transfer rate and pressure drop is increased largely.

건조기용 타원관 대구경 핀-관 열교환기의 성능특성

In this paper, three refrigeration systems bypassing hot-gas to compressor outlet, compressor and condenser outlet and evaporator inlet are theoretically compared to offer basic design data for performance depending on cooling load using a HYSYS program. The main results are summarized as follows : First, the COP of third system is the highest. Next, the COP of second system is higher than first one. And, the temperature of compressor inlet of third system is constant for all cooling load. Compared to first and second system, the compressor inlet temperature of the first system is higher than second one for all cooling loads. From the above results, third system, which is bypassing hot-gas to evaporator inlet, is more advantageous when considering the precise temperature control and excellent performance of oil and water cooler of industrial machine.

부하변화에 따른 hot-gas 바이패스 방식별 성능 비교

Recently, Free cooling system usage has increased at many buildings in intermediate and winter season. Free cooling system is used to reduce the energy consumption of refrigeration in that season. Free cooling system is refrigeration system using cooled water. In general, this system is applied with the building having refrigeration load at all time such as a data center. In this study, energy consumption of a data center taking free cooling system in Ulsan was evaluated by the software HYSYS. the main result is as in the following : free cooling system is effective from January to April and from November to December. In case of Ulsna in 2013, using free coolng system is able to spend refrigeration energy of about 15% less than existing system. According to this result, it is appropriated that free cooling system is used in building having refrigeration load at all time such as data center.

/pdf/deiteo-senteoyi-oeginaengsunaengbang-siseuteme-daehan-eneoji-rynx73ldw5.pdf

데이터 센터의 외기냉수냉방 시스템에 대한 에너지 절감효과 분석

Using low outdoor temperature, free cooling system is used in a data center or industrial air-conditioning for energy saving. Because use of IT equipment has increased in some office building recently, there is a growing trend towards using free cooing system. Free cooling system performance is influenced by outdoor temperature. Therefore the performance is different with regions. In this study, performance characteristic of free cooling system is analysed and energy reduction is compared with some regions. Selected regions are 4 cities; including Ulsan analyzed in preceding research, Seoul, ChunCheon and Daejeon. The Aspentech software HYSYS 8.0v was used to conduct the analysis of free cooling system based on temperature per hour of 4 cities in 2013, respectively. The main result is following as. Free cooing system in this study has energy saving effect when outdoor temperature below 7℃. Becuase temperature of Chuncheon is relatively low, using free cooling system can conserve most air-conditioning energy. Energy reduction amount of Seoul is 11%, Chuncheon is 17.5%, Deajeon is 15%, Ulsan is 14%. In case of large scale of air-conditioning, it is reasonable to use free cooling system although the system is used in Seoul

지역별 프리쿨링 시스템의 에너지 절감 분석

본 논문에서는 hot-gas를 이용한 다양한 바이패스 제어 방식 중에서 증발기 흡입부 방식에 대해 각각의 성능에 영향을 미치는 외기온도, 출수온도, 과열 및 과냉도 등에 대해서 알아보았다. 그 주요 결과를 요약하면 다음과 같다. 우선, 증발기 흡입부로 hot-gas를 바이패스 하였을 경우에 냉동장치의 성능은 외기온도, 출수온도, 과열 및 과냉도 등에 영향을 받는 것을 알 수 있었다. 따라서 이러한 변수에 대한 최적화를 통해 본 냉동장치의 기초 설계 자료를 제공할 수 있다. 그리고 증발기 흡입부 hot-gas 바이패스 방식의 운전특성을 고찰하여 본 논문에서 제안하는 냉동장치에 대한 적용 가능성을 확인할 수 있었다.

운전조건 변화에 따른 hot-gas 바이패스 냉동장치의 성능 특성

In this paper, the performance analysis for evaporation capacity, total work and efficiency of the ocean thermal energy conversion(OTEC) power system using mixed refrigerant(R32,R152a) is conducted to find the effect of hot wasted water on OTEC power system. The system in this study is applied with two stage turbine, regenerator, cooler and separator on Organic Rankine Cycle. The commercial program HYSYS is used for the performance analysis. The main results were summarized as follows : The efficiency of the OTEC power cycle has a largely effect on the evaporation capacity and total work. As increasing temperature of heat source water, evaporator"s capacity is decreased but total work increase. Otherwise, using hot wasted water bring effects not only increasing system efficiency but also declining evaporator"s capacity. Thus With a thorough grasp of these effect, it is necessary to find way to use hot wasted water emitted by power plant and so on.

온배수를 이용한 혼합냉매용 해양온도차 발전 사이클의 성능 특성

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