CO2 Transcritical Refrigeration Cycle with Dedicated Subcooling: Mechanical Compression vs. Absorption Chiller

The objective of this paper is the comparison of two dedicated subcooling methods, after the gas cooler, in a CO2 transcritical refrigeration system. The use of vapor compression refrigeration with R134a for subcooling is the first method, and the second is the use of an absorption chiller that operates with a LiBr-H2O working pair. The examined systems are compared energetically and exegetically with the reference transcritical CO2 refrigeration cycle without subcooling. The analysis is conducted for different operating scenarios and in every case, the system is optimized by selecting the proper temperature and pressure levels. The analysis is performed with a developed and validated model in Engineering Equation Solver. According to the final results, the use of the absorption chiller is able to decrease the system electricity consumption by about 54% compared to the simple transcritical cycle, while the decrease with the mechanical subcooling is 41%. Both systems with dedicated subcooling are found to have an important increase in the system exergy performance compared to the simple transcritical cycle. However, the system with the mechanical subcooling is found to be the best choice exegetically, with a small difference from the system with the absorption chiller.