Colloquia

Summary

Thermal energy is essential in industrial processes, accounting for a substantial portion of global energy consumption. Heat pumps are set to play a crucial role in the transition from fossil fuels to sustainable energy production. Their environmental impact can be further reduced by utilizing low-GWP (Global Warming Potential) natural refrigerants and increasing their Coefficient of Performance (COP). The present study investigates the effect of ejectors, zeotropic fluids, and cascade systems on the COP when utilizing natural refrigerants. Four systems are examined, namely the conventional vapor-compression heat pump (HP), the ejector heat pump (EHP), the cascade heat pump (CHP), and the ejector cascade heat pump (ECHP) for 5 zeotropic fluids and 7 azeotropic refrigerants. The systems are investigated and compared in terms of their COP increase with respect to their unmodified counterparts. The constant-pressure ejector model, developed by Kornhauser, is used and validated against the same model for a zeotropic mix of R134a/R143a within 7%. Ejectors show an average COP increase of 20%. Zeotropic fluids show an increase of 50% on average, due to a large decrease in the required compressor work compared to dry fluids, the higher latent heat of vaporization compared to wet fluids, and effectively lower heat sink temperature. Combinations of these methods do not yield a consistent increase in performance. Their individual inclusion in a cascade cycle does not consistently increase performance, while the combination of ejectors and zeotropic fluids shows up to a 77% decrease in performance.