• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.4
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• pp.354-362
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• 2000

Optimal supervisory control strategy for the set points of controlled variables in the central cooling system has been studied by computer simulation. A quadratic linear regression equation for predicting the total cooling system power in terms of the controlled and uncontrolled variables was developed using simulated data collected under different values of controlled and uncontrolled variables. The optimal set temperatures such as supply air temperature, chilled water temperature, and condenser water temperature, are determined such that energy consumption is minimized as uncontrolled variables, load, ambient wet bulb temperature, and sensible heat ratio, are changed. The chilled water loop pump and cooling tower fan speeds are controlled by the PID controller such that the supply air and condenser water set temperatures reach the set points designated by the optimal supervisory controller. The influences of the controlled variables on the total system and component power consumption was determined. It is possible to minimize total energy consumption by selecting the optimal set temperatures through the trade-off among the component powers. The total system power is minimized at lower supply, higher chilled water, and lower condenser water set temperature conditions.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.3
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• pp.53-59
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• 2011

In this study, a two-phase closed loop cooling system is desinged and tested for a laptop computer using a FC-72. The cooling system is characterized by a parametric study which determines the effects of existence of a boiling enhancement microstructure, initial system pressure, volume fill ratio of coolant and inclination angle of condenser on the thermal performance of the closed loop. Experimental data show the optium condition when the volume ratio of working fluid is 70%, the pump flowing is 6ml/min, and the inclination angle of condenser is $0^{\circ}$. This research shows the maximum values which can dissipate 33W of chip power with a chip temperature maintained at $95^{\circ}C$.

• Journal of Power System Engineering
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• v.21 no.6
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• pp.79-85
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• 2017

A heat pump system is a highly efficient, eco-friendly device which consumes a small amount of energy and supply a lot of energy for heat formation. In addition, it is a single device system that has low generation effect about carbon dioxide. There are many researches related to the electronic expansion valve and the heat pump, but the detailed data analysis of each influence is insufficient. In this study, the cooling capacity and COP of the heat pump system were investigated by varying frequency of the inverter connected to compressor, inlet temperature of chilled water into evaporator and inlet temperature of cooling water into condenser. The results are as follows : (1) The cooling capacity increased as the inverter frequency, inlet temperature of chilled water into evaporator increased, and inlet temperature of cooling water into condenser decreased. (2) The COP increased as the frequency of inverter, inlet temperature of cooling water into condenser decreased and the inlet temperature of chilled water into evaporator increased.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.1111-1116
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• 2008

The purpose of this study is to maintain high efficiency and reasonable use of cold-heat storage systems operated the showcase. An experimental study is carried out to manufacture the showcase system in a laboratory. Comparing the result at general operation condition with that at the new condition using ice storage system, this study showed the effects of the refrigerant sub-cooling, and with using inverter. At the condition using ice storage system, the ice making process was operated during midnight being not needed the cooling of the showcase through the continuous running of the condenser unit. And then, the refrigerant was sub-cooled using stored cold-heat after being discharged from the air cooling condenser during the day time. The cooling performance was increased owing to the sub-cooling of refrigerant during day time, hence the running time of the compressor was effectively decreased. In other words, this study showed that power consumption during daytime can be transferred to the midnight for making use of the refrigerant sub-cooling.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.43-48
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• 2011

Cooling system's operation ratio shall be controlled automatically by the internal external temperature sensors in rolling stock. The Cooling System shall be the automatic operation ratio control system which automatically controlling the rotation speed of condenser, evaporator etc. using temperature detection from outside and inside of cabin. This paper will examine the cooling system that can be provide comfortable cooling service for passenger in summer.

• KIEAE Journal
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• v.17 no.5
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• pp.69-76
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• 2017

Purpose: This study aimed at developing an Artificial Neural Network (ANN) model for predicting the amount of cooling energy consumption of the variable refrigerant flow (VRF) cooling system by the different set-points of the control variables, such as supply air temperature of air handling unit (AHU), condenser fluid temperature, condenser fluid pressure, and refrigerant evaporation temperature. Applying the predicted results for the different set-points, the control algorithm, which embedded the ANN model, will determine the most energy efficient control strategy. Method: The ANN model was developed and tested its prediction accuracy by using matrix laboratory (MATLAB) and its neural network toolbox. The field data sets were collected for the model training and performance evaluation. For completing the prediction model, three major steps were conducted - i) initial model development including input variable selection, ii) model optimization, and iii) performance evaluation. Result: Eight meaningful input variables were selected in the initial model development such as outdoor temperature, outdoor humidity, indoor temperature, cooling load of the previous cycle, supply air temperature of AHU, condenser fluid temperature, condenser fluid pressure, and refrigerant evaporation temperature. The initial model was optimized to have 2 hidden layers with 15 hidden neurons each, 0.3 learning rate, and 0.3 momentum. The optimized model proved its prediction accuracy with stable prediction results.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.3
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• pp.488-500
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• 1995

An air-cooled ammonia/water GAX(Generator-Absorber heat eXchange) absorption cooling cycle is proposed and its performance is numerically evaluated. It is shown that the performance of the system is greatly dependent on the quality of the refrigerant leaving the evaporator. For any refrigerant concentration in the investigated range(99.1~99.9% ammonia), the cycle COP(coefficient of performance) reaches the highest value, when some amount(about 7%) of refrigerant evaporates in the refrigerant heat exchanger. Among temperature differences in various heat exchangers, the temperature difference between GAX-absorber and the GAX-generator shows the greatest effect on the system performance, whereas pressure losses cause no significant decrease in COP. The system COP increases almost linearly with increasing evaporator temperature, decreasing absorber temperature or decreasing condenser temperature. If both absorber and condenser temperature increase simultaneously, the decrease in the COP becomes larger.

• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.55-68
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• 1999

In this study, computer simulation programs were developed for single-stage, two-stage, and three-stage condensation heat pumps and their performance with CFC11, HCFC123, HCFC141b was examined under the same external conditions. The results showed that the coefficient of performance(COP) of an optimized 'non-split type' three-stage condensation heat pump is 25-42% higher than that of a conventional single-stage heat pump. The increase in COP, however, differed among the fluids tested. The improvement in COP is largely due to the decrease in average LMTDs in condensers, which results in the decrease in thermodynamic irreversibility in heat exchange process. For the three-stage heat pump, the highest COP is achieved when the total condenser area is evenly distributed among the three condensers. For the two-stage heat pump, however, the optimum distribution of the total condenser area varies with an individual working fluid. For the three-stage system, 'splitting the condenser cooling water'for the use of intermediate and high pressure subcoolers helps increase the COP further. When the individual cooling water entering the intermediate and high pressure subcoolers is roughly 10% of the total condenser cooling water, the maximum COP is achieved showing roughly an 11% increase in COP as compared to that of the 'non-split type' heat pump.

• Journal of Energy Engineering
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• v.18 no.1
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• pp.17-21
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• 2009

By using the heat recovery of water-cooled chillers, it is possible to reduce the energy operating costs positively and at the same time it could fulfill the heating re-heat air conditioning system as well as the hot water requirements. Basically templifiers are designed to economically to turn the waste heat into useful heat. Waste heat is extracted from a fluid stream by cooling it in the evaporator, the compressor amplifies the temperature of the heat and the condenser delivers the heat to heating loads such as space heating, kitchens and domestic hot water. Design of higher water temperature requirements and split condenser heat recovery chiller system (using of templifiers) produced hotter condenser water approximately up to $60^{\circ}C$ and control the entire heat recovery system.

• Journal of the Korean Solar Energy Society
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• v.32 no.5
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• pp.52-58
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• 2012

Experimental study was performed to understand the real operation conditions of a showcase working usually in a convenient store and discount store. The purpose of this study was to show the possibility for practical use of cold-heat storage systems being operated for the showcase. To do that, evaporator and condenser temperatures were measured and the compressor electric power consumption were measured simultaneously. To use the ice storage system, the ice making process was typically operated during midnight being not needed the cooling of the showcase through the continuous running of the condenser unit. And then, the refrigerant was subcooled using the stored cold-heat after being discharged from the condenser during daytime. So, the cooling performance was increased with the sub-cooling of refrigerant during daytime,hence the actual running time of the compressor could be effectively decreased. Through the experiments, this study showed that the compressor electric power consumption during daytime could be transferred to nighttime for applying the refrigerant sub-cooling. So, for the convenient store, the maximum load transfer rates for each working cooler and showcase were estimated about 31.1% and 19.9% respectively. And for the discount store, the maximum load transfer rates for each refrigeration and freezing showcase were estimated about 34.1% and 49.0% respectively.