Study on Improving the Performance of the Cascade Heat Pump Cycle using Ejectors

Abstract

Background: The cascade heat pump cycle is used when a large difference between the condensing temperature and the evaporating temperature exist. Methods: This study uses ejectors to improve the performance of a cascade heat pump cycle that utilizes refrigerants R134a and R404a. Ejectors were applied to the high-stage cycle, the low-stage cycle and then to both cycles. Changes in performance according to the condensing temperature, evaporating temperature and ejector entrainment ratio were tracked. Results: Results of the numerical analysis showed that applying ejectors to both the highstage and low-stage cycles provided the greatest efficiency, yielding a 26.9% increase in the COP compared to standard cascade cycles. Conclusion: For COP enhancement, it is beneficial to apply ejectors to both-stage cycles as well as to lower the ejector entrainment ratio as much as possible.