The paper identifies and describes the possibilities for heat and mechanical energy recovery within refrigeration systems using CO₂ as a working fluid, employed in commercial and industrial applications. The heat and mechanical energy recovery methods that can be utilized for beneficial purposes are taken into consideration. These methods could increase the energy efficiency of the refrigeration system or the building in which it operates. This paper summarizes various configurations and recovery methods and critically compares and evaluates them (COP improvements, exergy performance, and system integration complexity) based on the data available in the literature. As a result, the internal heat exchangers can be used as a superheater, in which case the COP can increase to 35%. If the internal heat exchanger is used as a subcooler, it could lead to a COP increase of 17% compared to a CO₂ refrigeration system without subcooling for an evaporating temperature of −10 °C and the temperature of the gas cooler outlet of 30 °C. The heat and mechanical energy recovery possibilities are presented using the available scientific literature.

The present work proposes a phase change material-based defrosting system (PCM-DS) for vapor compression refrigeration systems (VCRSs). The primary objective is to determine the optimal PCM mass and refrigerant mass flow rate required to melt 1 kg of accumulated evaporator ice. A steady-state macroscopic thermodynamic model, governed by global energy balances and driven by experimental boundary conditions, evaluates the VCRS in both cooling and defrosting operating modes. The PCM-DS is not installed on the experimental setup. The latter is used to obtain experimental data to be used as inputs in the steady-state model. Among the three candidates investigated (OM42, OM46, OM48), OM42 was selected for minimizing system mass and volume constraints. Results demonstrate that integrating the PCM-DS induces only a 3% reduction in the theoretical coefficient of performance (COP) compared with a 5.6% reduction in the case of using the electric heater defrosting (EHD). The core innovation of this work involves proposing and evaluating three distinct energy storage management strategies: unique superheating, unique bypass, and intermittent bypass. The results show that the highest COP is obtained for unique superheating (2.93), followed by unique bypass (2.82) and intermittent bypass (2.81). The work conducted proves the theoretical feasibility of such PCM-DS.