• International Journal of Air-Conditioning and Refrigeration
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• 제13권3호
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• pp.119-127
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• 2005

Liquid pressure amplifiers have been proposed as an energy saving technology for vapor compression refrigeration systems configured with direct-expansion evaporators. The technology utilizes a refrigerant pump in the high pressure liquid line as a means of maintaining a suitable pressure differential across the expansion valve while lowering condensing pressure to achieve the reduction of compressor energy consumption. Applications have been proposed on systems ranging from small unitary air-conditioning to large supermarket and commercial refrigeration systems. This paper clarifies the role of such a device in a vapor compression refrigeration system. Limitations are presented and discussed. Finally, results of detailed analyses are presented to quantify the energy consumption both with and without a liquid pressure amplifier in a unitary air conditioning system. The estimated energy savings associated with the installation of a liquid pressure amplifier are minimal.

• 한국산학기술학회논문지
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• 제10권1호
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• pp.32-38
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• 2009

R744용 초임계 증기압축식 냉동시스템의 작동변수에 대한 기초설계자료를 제공하고자 냉동능력, 압축일량, 성적계수에 대한 사이클 성능분석을 실시하였다. 본 연구에서 고려된 작동변수는 R744 증기압축식 사이클의 과열도, 가스냉각기 출구온도, 증발온도이다. R744의 냉동능력은 과열도가 증가할수록 증가하는 반면, 증발온도와 가스냉각기 출구온도가 증가할수록 감소한다. 압축일량은 R744의 과열도와 냉각압력과 함께 증가하나 증발온도는 증가할수록 감소한다. 그리고 성적계수는 가스냉각기의 출구온도와 증발온도가 증가할수록 증가하는 반면, 과열도는 감소한다. 그러므로, R744용 초임계 증기압축식 냉동시스템의 냉동능력, 압축일량, 성적계수는 과열도, 가스냉각기 출구온도, 증발온도에 영향을 받는 것을 알 수 있었다. 따라서, R744용 초임계 증기압축식 냉동시스템을 설계할 경우에는 이러한 영향을 면밀하게 파악하여야 한다.

• Journal of Advanced Marine Engineering and Technology
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• 제38권7호
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• pp.828-833
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• 2014

본 연구는 이젝터 팽창기를 적용한 냉동기에서 팽창한 냉매가 액기분리기에 포집된 후, 이 중 포화기체의 일부는 이젝터로 재흡입되고, 포화액체는 증발기에 유입되어 증발된 후 액기분리기의 잔여 기체와 혼합되어 압축되는 공정을 고안하여 특성을 해석하였다. 본 공정의 특성은 이젝터에서 등엔트로피 팽창 후 액체량의 증가로 냉동능력이 증가하고, 압축기에 유입되는 기체의 압력이 상승하게 되어 압축일이 감소함으로써 효율이 증가하게 된다. 냉매 R134a를 적용하는 냉장고 시스템과 본 고안 시스템을 비교한 결과, 이젝터에서 압력이 65% 저하될 때 COP는 27.8%가 증가된 최대값이 되었다. 다른 냉매의 경우 R401A가 75% 압력강하에서 40.1%의 COP 증가를 보였다. 이젝터의 디퓨져에서의 압력 상승율이 20%~60%까지 변화될 때, COP 증가율은 2.6%~3%로 영향이 매우 적었다.

• 동력기계공학회지
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• 제13권6호
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• pp.70-75
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• 2009

In this paper, cycle performance analysis of R744($CO_2$) two-stage compression and one-stage expansion refrigeration system is presented to offer the basic design data for the operating parameters of the system. The operating parameters considered in this study include superheating degree, compressor efficiency, gas cooling pressure, mass flowrate ratio, outlet temperature of gas cooler and evaporating temperature in the carbon dioxide two-stage refrigeration cycle. The main results were summarized as follows : The cooling capacity of two-stage compression and one-stage expansion refrigeration system increases with the increasing superheating degree, compressor efficiency and gas cooling pressure, but decreases with the increasing mass flowrate ratio and evaporating temperature. The compression work of two-stage compression and one-stage expansion refrigeration system increases with the increasing superheating degree, outlet temperature of gas cooler, gas cooling pressure and evaporating temperature, but decreases with the increasing compressor efficiency and mass flowrate ratio. The COP of two-stage compression and one-stage expansion refrigeration system increases with the increasing compressor efficiency, but decreases with the increasing superheating degree, gas cooling pressure, mass flowrate ratio and evaporating temperature. Therefore, superheating degree, compressor efficiency, gas cooling pressure, mass flowrate ratio, outlet temperature of gas cooler and evaporating temperature of R744($CO_2$) two-stage compression and one-stage expansion refrigeration system have an effect on the cooling capacity, compressor work and COP of this system.

• 설비공학논문집
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• 제18권3호
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• pp.218-224
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• 2006

The performance of an air to water vapor compression heat pump has been investigated experimentally. The main purpose of this study was to study the possibilities of using hydrocarbon refrigerants as a working fluid to replace R-22 for vapor compression heat pumps. Pure R-22 and R-290, R-600a, R-1270 were considered as working fluids. The performance of the system was characterized by compression shaft work, refrigeration capacity, pressure ratio, discharge temperature and COP. The experimental apparatus has basic parts of cycle that uses the air as a heat source. The experimental results show that refrigeration capacity of HC refrigerants is same or higher than that of R-22. On the other hand, compression shaft work of HC refrigerants is lower than that of R-22. Compression shaft work is lower than that of R-22. Come to the conclusion that, it is possible that hydrocarbon refrigerants could be drop-in alternatives for R-22.

• Advances in Energy Research
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• 제7권1호
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• pp.1-19
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• 2020

Energy consumption of air-conditioning and refrigeration systems is responsible for about 25 to 30% of the energy demand especially in hot seasons. This equipment is mostly electricity dependent and their use in principle affects negatively the environment. Enhancing the energy efficiency of the existing equipment is important as one of the measures to reduce environment impacts. This paper reports the results of an experimental study to evaluate the impacts of the use electronic expansion valve and variable velocity compressor on the performance of vapor compression refrigeration system. The experimental rig is composed of two independent circuits one for the vapor compression system and the other is the secondary fluid system. The vapor compression system is composed of a forced air condenser unit, evaporator, hermetic compressor and expansion elements, while the secondary system has a pump for circulating the secondary fluid, and an air conditioning heat exchanger. The manufacturer's data was used to determine the optimal points of operation of the system and consequently tests were done to evaluate the influence of variation of the compressor velocity and the opening of the expansion device on the performance of the refrigeration system. A fuzzy logic model was developed to control the rotational velocity of the compressor and the thermal load. Fuzzy control model was made in LabVIEW software with the objective of improving the system performance, stability and energy saving. The results showed that the use of fuzzy logic as a form of control strategy resulted in a better energy efficiency.

• 동력기계공학회지
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• 제20권2호
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• pp.85-90
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• 2016

Coefficient of performance (COP) for two-stage compression system is investigated in this paper to develop seawater ice machine. The system performance is analyzed with respect to degrees of superheating and subcooling, condensing and evaporating temperatures, compression and mechanical efficiencies and mass flow ratio in an inter-cooler. The main results are summarized as follows : The COP of the system grows when the mass flow ratio, subcooling degree and evaporating temperature edge up. Contrariwise, the system performance descends in case that superheating degree and condensing temperature increase. The most effective factor for the COP is the mass flow rate ratio. Each refrigerant has different limitation for a value of the mass flow ratio in the inter-cooler because of difference in material property.

• 설비공학논문집
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• 제17권1호
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• pp.47-55
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• 2005

An experimental study has been peformed to develop a scheme for fault detection and diagnosis(FDD) in a vapor compression refrigeration system. This study is to analyze fault effect on the system performance and to find efficient diagnosis rules for easy determination of abnormal system operation. The refrigeration system was operated with a variable speed compressor to modulate cooling capacity. The FDD system was designed to consider transient load conditions. Four major faults were considered, and each fault was detected over wide operating load range by separating the system response to the load change. Rule-based method was used to diagnose and classify the system faults. From the experimental results, COP degradation due to the faults in a variable speed system is severer than that in a constant speed system. The method developed in this study can be used in the fault detection of refrigeration systems with a variable speed compressor.

• 설비공학논문집
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• 제12권5호
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• pp.486-493
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• 2000

A theoretical model for the transient performance of vapor-compression air-conditioning system has been developed to evaluate the influence of the refrigerant charge on the system performance. A set of mass and energy equations for the simulation of the heat exchangers and the capillary tube and a polytropic compression model for the compressor are used. The present model successfully predicts the transient behavior of the vapor-compression air-conditioner from the startup. As the refrigerant charge is increased, both the evaporating and condensing pressures increase gradually, and the cooling rate and the COP show a maximum in the range of 0.75-0.8 kg of refrigerant charge. This amount of refrigerant mass is determined to be the optimum charge of the model system. Also, the effect of outdoor air temperature on the optimum refrigerant charge is discussed.

• 설비공학논문집
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• 제15권12호
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• pp.979-986
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• 2003

The performance characteristics of heating and cooling operation for a heat pump system using seawater heat source and exhaust energy are presented. The heat pump system is made of a waste heat recovery system and a vapor compression refrigeration system. The working fluid is R-22. The heat pump system COPs are measured during heating and cooling operation modes, and the resultant COPs were 9.7 and 7.9, respectively, which are three times higher than those of the heat pump itself. Therefore, the performance of the heat pump system using exhaust energy is excellent compared to that of a general heat pump. The experimental data can be effectively used for the design of the high efficient heat pump using a seawater heat source.