Energy and exergy performance investigation of a transcritical CO2 vapor ejector-based refrigeration system for marine provision plants

Abstract

Marine refrigeration has a high energy share in a vessel’s performance which can lead to up to 19 % of its total power consumption. Traditional cooling systems employing refrigerants of high GWP are subject of continuous imposed restrictions, leading to the need for adoption of more efficient and sustainable alternatives such as CO₂ refrigeration applications. This study investigates a novel transcritical CO₂ vapor ejector-based refrigeration system delivering the refrigeration needs of marine provision plants. The examined topology is analyzed in terms of energy efficiency, and it is compared with a conventional marine refrigeration system using R407F as the working media. Additionally, the advanced exergy analysis approach is employed to specify and quantify the irreversibilities minimization potential for improving the performance of the system examined. The thermodynamic simulation analysis is conducted using validated numerical models that are developed in MATLAB using the CoolProp library. The system is parametrically investigated for different sea water temperatures ranging from 5 to 32 °C. The results show that the proposed configuration has a maximum COP improvement of 13.2 % for the sea water temperature of 26 °C in comparison to the baseline direct expansion system using R407F. The highest exergy destruction ratios are calculated for the components of the gas cooler, the vapor ejector and the constant pressure valve, with values of 31.3 %, 22.6 % and 17.2 % respectively. Finally, for the examined sea water temperature of 32 °C, 33.6 % of the total exergy destruction is avoidable showing a significant amelioration potential. The latter figure splits further to 16.4 % endogenous-avoidable and the rest 17.2 % to exogenous-avoidable exergy destruction, verifying the potential for extra optimization of the system in the future.