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내부열교환기 및 전자팽창장치를 적용한 가변속 이산화탄소 사이클의 냉방성능에 관한 실험적 연구
조홍현,류창기,김용찬 대한설비공학회 2005 설비공학 논문집 Vol.17 No.3
Since a transcritical CO2 cycle shows lower performance than conventional air conditioners in the cooling mode operation, it is required to enhance the performance of the CO2 cycle by applying advanced technologies and optimizing components. In this study, the cooling performance of a CO2 system measured by varying refrigerant charge amount, compressor frequency, EEV opening and length of internal heat exchanger. As a result, the cooling COP of the basic system without internal heat exchanger was 2.1. The cooling performance of the modified cycle applying internal heat exchanger improved by 4-9% over the basic cycle.
이산화탄소를 적용한 주거용 냉난방 겸용 열펌프 시스템의 시뮬레이션
조홍현,이무연,김용찬 대한설비공학회 2003 설비공학 논문집 Vol.15 No.12
The performance of a residential heating and cooling system with CO2 is predicted by using a cycle simulation model. The simulations are conducted by varying design parameters and operating conditions. The efficiency of the transcritical cycle can be improved by utilizing the advantages in heat transfer characteristics of CO2 and developing microchannel indoor and outdoor heat exchangers. For the designed system of this study, the predicted COP of the heat pump system is approximately 3.5 in the heating mode and 3.0 in the cooling mode. The predicted optimal discharge pressure for the heat pump system is approximately 11 MPa in the heating mode and 9 MPa in the cooling mode.
팽창기를 적용한 이산화탄소 냉방시스템의 성능특성에 관한 해석적 연구
조홍현,백창현,류창기,김용찬 대한설비공학회 2007 설비공학 논문집 Vol.19 No.9
A CO2 cycle shows large throttling loss during the expansion process. The application of an expander into the CO2 cycle can reduce the throttling loss and then improve system performance. In this study, the performance of a transcritical CO2 cycle with an expander was analytically investigated in order to improve the cooling performance of the system. The expander was applied to the single-stage and two-stage compression cycles. The performance was analyzed with the variations of compressor frequency, outdoor temperature, and expander efficiency. The single-stage and two-stage compression cycles with the expander showed COP improvement of 25% and 32%, respectively, over the single-stage cycle with an EEV.
2단압축 이산화탄소 사이클의 냉방성능 향상 특성에 대한 실험적 연구
조홍현,이호성,김용찬 대한설비공학회 2006 설비공학 논문집 Vol.18 No.10
A CO2 system using the two-stage compression cycle was tested by varying 1st-2nd compressor frequencies in the cooling mode. To improve the cooling performance of the two-stage compression CO2 cycle, the following cycle options were applied: a basic cycle, a cycle with an intercooler, a cycle with an IHX(internal heat exchanger), and a cycle with an intercooler and IHX. The cycle with the intercooler-IHX showed the highest cooling capacity improvement among the cycle options at all compressor frequencies. The cycle with the intercooler, the cycle with the IHX, and the cycle with the intercooler-IHX improved the cooling COP by 7, 12, and 15%, respectively, over the basic CO2 cycle when the compressor frequencies for the first and second compressors were 50Hz and 30Hz, respectively. In addition, the applications of the selected cycle options enhanced system reliability.