• Proceedings of the SAREK Conference
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.288-293
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• 2008

The cooling load in winter is significant in many commercial buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a multi-heat pump with 3-piping system was investigated as a function of refrigerant charge and its performance was analyzed in cooling mode, heating mode, and heat recovery mode. COP in the heating or cooling mode showed little dependence on refrigerant charge at overcharge conditions, while those were strongly dependent on refrigerant charge at undercharge conditions and outdoor inlet temperature. In the heat recovery mode, the performance of the system was very sensitive to charge amount at all conditions. Optimum charge amount in the heat recovery mode was 14% lower than that in the cooling mode at the standard condition because the refrigerant only passed the indoor units. It is required to store the excessive refrigerant charge in a storage tank to optimize the system performance at operating modes.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제20권7호
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• pp.492-499
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• 2008

The cooling load in winter is significant in many commercial buildings and hotels because of the usage of office equipments and the high efficiency of wall insulation. The development of a multi-heat pump that can cover heating and cooling simultaneously for each indoor unit is required. In this study, the performance of a multi-heat pump with 3-piping system was investigated as a function of refrigerant charge and its performance was analyzed in cooling mode, heating mode, and heat recovery mode. COP in the heating or cooling mode showed little dependence on refrigerant charge at overcharge conditions, while those were strongly dependent on refrigerant charge at undercharge conditions and outdoor inlet temperature. In the heat recovery mode, the performance of the system was very sensitive to charge amount at all conditions. Optimum charge amount in the heat recovery mode was 14% lower than that in the cooling mode at the standard condition because the refrigerant only passed the indoor units. It is required to store the excessive refrigerant charge in a storage tank to optimize the system performance at operating modes.

• Proceedings of the SAREK Conference
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.427-432
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• 2005

This study developed a program for detecting charged refrigerant amount in system air-conditioner. System air-conditioner is an air-conditioning system with multiple indoor units. Due to the complexity of the system, it is more difficult to detect the refrigerant amount charged in system air-conditioner than in a general single air-conditioner. Experiments were performed for 6 HP outdoor units with 3 indoor units in a psychrometric calorimeter. The experimental amount of charged refrigerant were ranged from 60% to 140% with 10% increasement. Fuzzy algorithm were emploeed for detecting the charged refrigerant amount in a system air-conditioner. The experimental data were used for curve fitting for general ranges for indoor and outdoor temperature conditions. membership function were determined for whole ranges of experimentally measured data and rulebase were defined for each amount of refrigerant charge. Developed program successfully predicted the measured data within 10% resolution range.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제15권8호
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• pp.661-666
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• 2003

Constant area expansion devices such as capillary tubes, short tube orifices are being gradually replaced with electronic expansion valves (EEVs) because of increasing focus on comfort and energy conservation. In this study, the performance of a water-to-water heat pump as a function of refrigerant charge is investigated in steady state, cooling mode operation with expansion devices of a capillary tube and an EEV. The performance of the capillary tube system varies drastically according to the change of refrigerant charge amount and inlet temperature of the secondary fluid in the condenser. Cooling capacity and COP of the EEV system show little dependence on the refrigerant charge, while those are strongly dependent on the secondary fluid temperature at the condenser inlet. In general, for a wide range of operating conditions the EEV system shows much higher performance as compared with the capillary tube system. The performance of the EEV system can be optimized by adjusting EEV opening to maintain a constant superheat at all test conditions.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제31권10호
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• pp.868-875
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• 2007

In this paper, performance characteristics of a domestic kim-chi refrigerator are predicted by using the theoretical calculation and experimental method. The objective of this study is to find out the best design points of the refrigeration system and to calculate an adiabatic characteristic with variation to outdoor temperatures. The best design points such as refrigerant charge amount and capillary length were experimentally investigated. And the theoretical calculation is conducted as a function of calculation parameters and outdoor temperatures. According to this study results, the best design points of a refrigeration system with 2 rooms are 95 g of a refrigerant charge amount and 3500 / 3500 mm of capillary lengths and the best design points of a refrigeration system with 3 rooms are 100 g of a refrigerant charge amount and 3000/3000/6000mm of capillary lengths. And the power consumptions of both systems are 13.57 and 18.2 kWh/month. The worst part of heat loss is a front side of a domestic kim-chi refrigerator body.

• International Journal of Air-Conditioning and Refrigeration
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• 제17권3호
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• pp.100-106
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• 2009

As an effort to prevent environmental problems caused by ozone depletion and global warming, alternative refrigerants are being developed, and one of the candidates is carbon dioxide. To overcome slightly low efficiency of $CO_2$ refrigeration system, air-conditioning cycle using an ejector was suggested. Ejector compensates throttling loss in an expansion device by reducing compression work. In this study, the ejector refrigeration cycle using $CO_2$ as a refrigerant is investigated to understand the effect of the mixing section diameter and refrigerant charge amount on the performance. If mixing section diameter is too large or too small, either cases show low performance. The optimum refrigerant charge amount which gives the best performance is found for standard operating conditions. The air-conditioning cycle was analyzed for several operating conditions.

• Proceedings of the SAREK Conference
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1484-1490
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• 2009

Since the cooling performance of a $CO_2$ cooling cycle is varied significantly with a variation of refrigerant charge amount and outdoor temperature, the reliability of $CO_2$ system is down. In this study, the performance characteristics of three kinds of $CO_2$ systems were measured and analyzed by varying refrigerant charge amount and outdoor temperature so as to study the characteristics of variation with cycle option. The applied system options are the single-stage compression(1C-1E) system, two-stage compression with 1-EEV(2C-1E) system, and two-stage compression with 2-EEV(2C-2E) system. The performances of two-stage compression with 2-EEV system were less sensitive than those of other systems and the system operated safely and steadily for wide charge amount. The performance of the two-stage compression with 1-EEV(2C-1E) system was the most sensitive to the charge amount, and that of the single-stage compression(1C-1E) system varied a lot with outdoor temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• 제21권6호
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• pp.319-325
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• 2009

The purpose of this study is to investigate the performance characteristics of a bypass two-circuit refrigerator. A bench scale refrigeration system was designed and constructed to estimate possible performance improvement of the bypass two-circuit refrigerator. The experiments were conducted in the bench scale refrigeration system by varying capacity of the condenser and refrigerant charge amount with an adoption of a refrigerant storage vessel. The COPs of the bypass two-circuit refrigeration system in the refrigerator and freezer (RF)-mode and freezer(F) only-mode were increased by 10% and 17%, respectively, with increasing the capacity of the condenser. Besides, the COP of the system in the F only-mode was increased by 10% by adopting the refrigerant storage vessel.

• International Journal of Air-Conditioning and Refrigeration
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• 제16권3호
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• pp.77-82
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• 2008

For heat pumps used in a cold region, it is very important to obtain appropriate heating capacity. Several studies using a variable speed compressor and an additional heater have been performed to enhance heating capacity at low ambient temperatures. However, for outdoor temperature conditions below $-15^{\circ}C$, it is still difficult to obtain enough heating capacity above the rated value. In recent studies, the application of gas injection technique into a two-stage heat pump yielded noticeable heating performance improvement at low temperature conditions. In this study, the heating performance of a two-stage gas injection heat pump with a rated capacity of 3.5 kW was measured and analyzed by varying refrigerant charge amount and EEV opening at the standard heating condition. The heating performance of the two-stage gas injection heat pump was compared with that of a two-stage non-injection heat pump. The heating capacity and COP of the two-stage gas injection heat pump were improved by 2-10% at the optimal charging condition over those of the two-stage non-injection heat pump.

• Transactions of the Korean Society of Mechanical Engineers B
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• 제29권2호
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• pp.271-278
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• 2005

In this paper, the performance of Kim-chi refrigerator with three evaporator and one compressor was investigated in employing $55\%$ propane and $45\%$ isobutane (R290/R600a) refrigerant mixture as an alternative refrigerant of R134a. The drop-in test was performed by varying both refrigerant charge and capillary tube length in order to find both the performance and reliability of a small multi-refrigeration system. Results show that the power consumption is decreased by about $15\%$ and COP is increased by about $10\%$, respectively as compared to the baseline system using R-134a. In addition, the propane/isobutane refrigerant mixture system took advantage of the minimization of modification and redesigning of system components because thermodynamic properties such as saturation pressure, temperature, normal boiling point(NBP) characteristics are similar to those of R134a. The reduction of sales cost is caused by the decrease of refrigerant cost per unit mass and refrigerant charge amount necessary for the refrigeration system.