• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.29 no.9
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• pp.75-78
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• 2000

환경친화적 자동차에 대한 관심이 커질수록 여러 분야에서 시스템 설계의 영향을 더욱 더 잘 이해하려는 노력이 진행되고 있다. 자동차용 냉방기의 경우 냉방시스템의 세밀한 분석과 환경에 미치는 영향을 최소화하기 위한 설계가 이루어지고 있다. 그 중에서도 냉매의 선택과 그 냉매의 환경적 영향에 대한 자세한 연구가 필요하다. 몬트리올 조약 이후 자동차 산업계는 대부분 R-134a를 채택하고 있는데 이는 R-134a가 오존층을 파괴하지 않을 뿐 아니라 적절한 사이클 효율을 가지면서 안전하고 비독성이며 불연성이기 때문이었다. 최근 지구온난화와 이산화탄소($CO_2$)의 발생원에 대한 관심은 산업계가 사용냉매를 재검토하게 하는 계기가 되었으며, R-134a도 교토 조약의 규제냉매에 속해 있어 자동차용 냉방기의 대체냉매에 대한 연구가 시급하다고 여겨지고 있다. R-134a와 관련된 주된 논점은 냉매 누설시의 영향이다. R-134a의 지구온난화지수(GWP)는 1,300인데, 이는 누출되었을 때 1,300배의 이산화탄소가 누출된 것과 동일하다는 것을 의미하다. 최근 자연냉매의 선호와 맞물려 냉매로서 이산화탄소의 평가에 많은 관심이 모아지고 있다. 본 글에서 자동차용 냉방기의 대체냉매로서 이산화탄소의 상대적인 장점과 R-134a와의 비교에 대해 수행된 연구결과를 나타내었다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.12
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• pp.5457-5463
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• 2011

The objective of this study is to investigate cooling performance characteristics of mobile air conditioning system using R744 as an alternative of R-134a. In order to analyze the cooling performance characteristics of the air conditioning system using R744 for a passenger vehicle, the developed air conditioning system using R744 was applied in a real passenger vehicle and tested under various operating conditions with the variation of gas-cooler inlet air conditions, evaporator inlet air temperatures and compressor speeds. As a result, cooling capacity and coefficient of performance (COP) of the tested air conditioning system decreased with the rise of the inlet air temperature of the gas cooler but increased with the rise of the inlet air temperature of the evaporator. In addition, cooling capacity and coefficient of performance (COP) increased by 42.2 % with the rise of the compressor speed from 900 rev/min to 1800 rev/min, but it decreased by 55.4%.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.681-686
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• 2006

In order to protect the environment from the refrigerant pollution, the $CO_2$ may be regarded as one of the most attractive alternative refrigerants for an automotive air-conditioning system. Control methods for a $CO_2$ system should be different because of $CO_2's$ unique propel-ties as a refrigerant. Especially, the high-side pressure of a $CO_2$ system should be controlled for the effective operation of the system. In this study, dynamic models of a $CO_2$ air-conditioning system were developed by using experimental data. Control algorithms for a high-side pressure control and an indoor air temperature control were developed and analysed by using the dynamic simulation program of a $CO_2$ system.

• Transactions of the Korean Society of Automotive Engineers
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• v.14 no.4
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• pp.49-58
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• 2006

In the respect of the environmental protection viewpoint, $CO_2$ may be one of the most attractive alternative refrigerants for an automotive air-conditioning system. For the development of control algorithm of a $CO_2$ automotive air-conditioning system, characteristics of a $CO_2$ refrigerant should be considered. The high-side pressure of a $CO_2$ system should be controlled in order to improve the system efficiency. In this study, dynamic physical models of a $CO_2$ system were developed and dynamic behaviors of the system were predicted by using these models. Control algorithms of a $CO_2$ system were also developed and the effectiveness of these algorithm was verified by using dynamic models.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.29-33
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• 2007

In order to protect the environment from the refrigerant pollution, the $CO_2$ may be regarded as one of the most attractive alternative refrigerants for an automotive air-conditioning system. Control methods for a $CO_2$ system should be different because of $CO_2$'s unique properties as a refrigerant. Especially, the high-side pressure of a $CO_2$ system should be controlled for the effective operation of the system. In this study, the high-side pressure setpoint algorithm was developed by using a neural network and a Lagrange interpolation method. These methods were compared. Simulation results showed that a Lagrange interpolation method was more effective than a neural network in the respect of its easiness of programming and shorter execution time.

• Transactions of the Korean Society of Automotive Engineers
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• v.16 no.2
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• pp.150-157
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• 2008

The main objective of this paper is to investigate the performance characteristics of a $CO_2$ air conditioning system for fuel cell electric vehicles (FCEV). The present air conditioning system for FCEV uses the electrically driven compressor and electrically controlled expansion valve for $CO_2$ as a working fluid. The experimental work has been done with various operating conditions, which are quite matching the actual vehicle's driving conditions such as different compressor speed and high pressure to identify the characteristics of the system. Experimental results show that the cooling capacity and coefficient of performance (COP) were up to 6.3kW and 2.5, respectively. This paper also deals with the development of optimum high pressure control algorithm for the transcritical $CO_2$ cycle to achieve the maximum COP.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.4
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• pp.67-75
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• 2007

This paper deals with the research for the effects of the operating parameters that could be used for a transcritical $CO_2$ mobile air-conditioning system on the cooling performance. The experimental conditions of the performance tests for a system and components such as a gas cooler and an evaporator were suggested to compare the performance of each with the standardized test conditions. And this research presents experimental results for the performance characteristics of a $CO_2$ mobile air conditioning system with various operating conditions such as different gas cooler inlet pressures and frontal air velocities/temperatures passing through an evaporator and a gas cooler. Experimental results show that the cooling capacity was more than 5kW and coefficient of performance (COP) was more than 2.1, also. Therefore, we checked that the mobile air-conditioning system using $CO_2$ has good performance compared to that using HFC-134a.

• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.16-21
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• 2008

In order to protect the environment from the refrigerant pollution, the $CO_2$ may be regarded as one of the most attractive alternative refrigerants for an automotive air-conditioning system. Control methods for a $CO_2$ system should be different because of $CO_2$'s unique properties as a refrigerant. Especially, the high-side pressure of a $CO_2$ system should be controlled for the effective operation of the system. High-side pressure algorithms, which were composed of the pressure setpoint algorithm and the pressure setpoint reset algorithm, were developed. Pressure setpoint algorithms, by using a neural network and by using a least square method, were developed and compared. Pressure setpoint reset algorithms, by using a fuzzy logic and by using a proportional logic, were also developed and compared. Simulation results showed that a least square method was more useful than a neural network for the pressure setpoint algorithm. And a proportional logic was more practical than a fuzzy logic for the pressure setpoint reset algorithm.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.1
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• pp.146-153
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• 2009

The performance characteristics of heat exchangers which consist of a gas cooler, an evaporator and an internal heat exchanger have been investigated at various operating conditions of $CO_2$ air conditioning system by experiments. The heat exchangers were designed for use in the vehicle $CO_2$ air conditioning system, when considering the characteristics of heat transfer and high pressure as $CO_2$ refrigerant. This paper studied the performance of heat exchangers at various compressor speeds and expansion valve openings, and quantified the heat transfer rates and pressure drops. Heat transfer rates at the gas cooler and the evaporator were 6.9 kW and 5.2 kW, respectively, when the compressor speed was 4000 rpm and refrigerant vapor quality at the evaporator outlet was 0.98. Therefore, this paper carried out that the heat exchangers were analyzed to achieve superior performance for the vehicle transcritical $CO_2$ cycle.

• 한국신재생에너지학회:학술대회논문집
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• 2005.06a
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• pp.378-383
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• 2005

This experimental study presents the results of the cooling performance test of a $CO_2$ heat pump system for fuel cell vehicles. The experimental facility provides the cool ing and heating environment for cabin and heat releasing component. The test loop is designed to target the cooling capacity of 5kW and its coefficient of performance (COP) of 2.2. The cooling performance of the heat pump system is strongly dependent on the refrigerant charge and the degree of superheat. We carried out basic experiments to obtain optimum refrigerant charge and the degree of superheat level at the internal heat exchanger outlet. The heat pump system for fuel cell vehicles is different from that of engine-driven vehicles, where the former has an electricity-driven compressor and the latter has the belt-driven (engine-driven) compressor. In the fuel cell vehicle, the compressor speed is an independent operating parameter and it is controlled to meet the cooling/heating loads. Experiments were carried out at cooling mode with respect to the compressor speed and the incoming outdoor air speed. The results obtained in this study can provide the fundamental cool ing performance data using the $CO_2$ heat pump system for fuel cell vehicles.