A study on carbon dioxide cycle architectures for light-commercial refrigeration systems

• The flash gas chamber design increased the system coefficient of performance by 15%.
• The thermostatic expansion valve design was unable to properly adjust the discharge pressure.
• The dual-stage expansion design precisely controlled the discharge pressure and the superheating.
• The coefficient of performance increased by 28% when an internal heat exchanger was added to the system.

In this study four refrigeration cycles were experimentally investigated in an attempt to enhance the thermodynamic performance of CO2-based transcritical refrigeration systems under high ambient temperatures. The cycle architectures studied were: i) capillary tube, ii) expansion valve, iii) dual-stage expansion and iv) flash gas chamber. It was found that the coefficient of performance values of the first three cycle designs were almost the same in the temperature range studied. Additionally, performance improvements of around 20% and 28% in the cooling capacity and coefficient of performance were found when an internal heat exchanger was added to the baseline cycle. Performance gains of 10% and 15% in the cooling capacity and coefficient of performance were also found with the flash gas chamber cycle design, without compromising the discharge line temperature.