Global warming is commonly issue in worldwide. From point of global warming point of view, alternate HFC refrigerant to natural refrigerant is one of the means to reduce global warming gas which is used to refrigeration system in food store such as supermarket and convenience store. Carbon dioxide (hereinafter CO_(2)) is one of the dominant candidates as low Global Warming Potential (hereinafter GWP) refrigerant. However CO_(2) refrigerant has lower efficiency for refrigeration because of low critical temperature. Also CO_(2) refrigerant has higher system pressure than HFC refrigerant. Therefore typical cascade refrigeration system is equipped HFC refrigerant in higher temperature cycle. This report indicate the potential of CO_(2)-CO_(2) cascade system even CO_(2) refrigerant itself has lower efficiency than HFC refrigerant. And this report shows optimization of discharge pressure, suction pressure and internal heat exchanger are important to get better performance.
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