Experimental assessment of dedicated and integrated mechanical subcooling systems vs parallel compression in transcritical CO2 refrigeration plants

Mechanical subcooling systems, both dedicated and integrated, have attracted lot of attention in the recent years due to their great potential to improve transcritical CO2 refrigeration systems. Numerous studies have theoretically determined the COP increments that these systems can offer compared to classic systems and experimental works have evaluated the optimum working conditions for each individual system. However, they have not been contrasted experimentally. In this work, the dedicated and integrated mechanical subcooling systems are experimentally contrasted to the parallel compression one, which is considered as base system. The optimum energy performance of the three systems is contrasted for three heat rejection levels: 25.0 ◦C, 30.4 ◦C and 35.1 ◦C. The experimental tests show increments in COP of 4.1% at 25.0 ◦C, 7.2% at 30.4 ◦C and 9.5% at 35.1 ◦C thanks to the use of the integrated mechanical subcooling and of 7.8%, 13.7% and 17.5% respectively when using the dedicated. It is concluded that the dedicated mechanical subcooling system is the best system, however the integrated mechanical subcooling also performed better than the reference system.Funding for open access charge: CRUE-Universitat Jaume

Thermodynamic Analysis of Transcritical CO2 Ejector Expansion Refrigeration Cycle with Dedicated Mechanical Subcooling

The new configuration of a transcritical CO2 ejector expansion refrigeration cycle combined with a dedicated mechanical subcooling cycle (EMS) is proposed. Three mass ratios of R32/R1234ze(Z) (0.4/0.6, 0.6/0.4, and 0.8/0.2) were selected as the refrigerants of the mechanical subcooling cycle (MS) to further explore the possibility of improving the EMS cycle’s performance. The thermodynamic performances of the new cycle were evaluated using energetic and exergetic methods and compared with those of the transcritical CO2 ejector expansion cycle integrated with a thermoelectric subcooling system (ETS). The results showed that the proposed cycle presents significant advantages over the ETS cycle in terms of the ejector performance and the system energetic and exergetic performances. Taking the EMS cycle using R32/R1234ze(Z) (0.6/0.4) as the MS refrigerant as an example, the improvements in the coefficient of performance and system exergy efficiency were able to reach up to 10.27% and 15.56%, respectively, at an environmental temperature of 35 °C and evaporation temperature of −5 °C. Additionally, the advantages of the EMS cycle were more pronounced at higher environmental temperatures