Thesis

Study on the Performance Improvement of a Transcritical CO2 Heat Pump
Year of publication 2005
Title of paper Study on the Performance Improvement of a Transcritical CO2 Heat Pump
Author 조홍현
Publication in journal
Publication date
Volume & other data
Abstract The objectives of this study are to investigate the main parameters that affect CO2 heat pump performance and to evaluate possible performance improvements of the CO2 cycle by applying advanced technologies. The performance characteristics of the CO2 systems were evaluated analytically and experimentally. The performance of a CO2 heat pump was predicted and analyzed by utilizing a cycle simulation model developed in this study. The developed simulation model was verified experimentally and showed a good quantitative agreement of the measured data. Cycle simulations were conducted by varying design parameters and operating conditions with the applications of advanced techniques to improve system performance. The applied advanced methods in the simulation were an IHX, an expander, a two-stage compression with an intercooler, and a two-stage compression with a flash tank. As a result, the applications of the advanced techniques improved the cooling performance of the transcritical CO2 cycle by 6-30%, respectively, over the basic cycle. To provide the basic performance data of the CO2 heat pump cycle and to compare performance sensitivity with conventional systems at various charging conditions, the performance of the CO2 heat pump system was tested. The performance of the CO2 system was compared with that of the R22, R410A, and 407C systems with charge amount. In addition, the influences of control parameters on the performance were measured and discussed as a function of compressor frequency, EEV opening, length of IHX, and outdoor temperature. As a result, the performance of the CO2 heat pump system at undercharged conditions was the most sensitive to refrigerant charge and was greatly affected by the compressor frequency and EEV opening. The modified CO2 heat pump system was tested and the performance improvement with cycle options was discussed. Two-stage compression cycle was tested by applying the following options; a basic, an intercooler, an IHX, an intercooler-IHX and a flash cycle. The performance of each cycle was measured and discussed by varying operating conditions; operating temperature, EEV opening, and 1st-2nd compressor frequency. In this study, the cycle with the intercooler, the cycle with the IHX, the cycle with the intercooler and IHX, and the cycle with the flash tank improved the cooling COPs by 5.2~11%, 6.8~16%, 13~22%, 51%, respectively, over the basic CO2 cycle.
Keywords
issn Number
Status of publication
박사학위논문