Steady state testing and modeling of a CO2 two-stage refrigeration system with mechanical subcooler.

Transcritical refrigeration systems typically suffer from a drop in the system efficiency especially in warm climates. However, using a mechanical subcooler in such systems may help to reduce or eliminate this penalty in efficiency. In this research, a CO2 two-stage refrigeration system with mechanical subcooler is experimentally tested and simulated under steady state conditions. The system consists of supercritical medium temperature (MT) and subcritical low temperature (LT) compressor racks with the LT compressor rack boosting the refrigerant to the medium pressure level. The heat rejection from both stages occurs in the same gas cooler. The MT compressor rack also has a mechanical subcooler (SC), which uses R134a refrigerant. A new vapor compression system steady state solver is developed and presented in this paper. This solver is used to simulate the refrigeration system and study the effect of the different ambient conditions on its performance. The results of this study show the possibility of eliminating one of the challenges for transcritical refrigeration systems by improving their performance in warm climates. Also, the new solver can be used to optimize the design and further improve the performance of the system.