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New study shows efficiency of CO2-CO2 cascade systems

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A new study demonstrates the potential for CO2-CO2 cascade systems to replace existing HFC systems for commercial retailers.

Showcasing ongoing research and development of CO<sub>2</sub>-based refrigeration systems, a new study has found that CO<sub>2</sub>-CO<sub>2</sub> cascade systems beat traditional R404A systems in energy efficiency by 15%.

The study, co-authored by Yukio Yamaguchi of Sanden Environmental Products Corporation and Kenji Amagai of Gunma University in Japan, was published in the MedCrave online scientific journal on 10 October.

One of the main challenges the researchers faced was the use of CO<sub>2</sub> in the high temperature cycle of the cascade system.

Typical cascade refrigeration systems use HFCs on the high temperature side as CO<sub>2</sub>’s low critical temperature makes it more suited to low-temperature applications.

To overcome this, the researchers optimised the operating pressures of the system to achieve better efficiency.

“Controlling the discharge pressure of the CO<sub>2</sub> refrigeration system can significantly improve the coefficient of performance,” the study states.

Additionally, the configuration and use of internal heat exchangers in the system was optimised to suit ambient temperature conditions and improve energy efficiency.

In the study, an experimental CO<sub>2</sub>-CO<sub>2</sub> cascade system was connected to actual showcase units in a simulated convenience store environment.

The researchers found that the CO<sub>2</sub>-CO<sub>2</sub> cascade system achieved 15% better energy efficiency than a traditional R404A system.

<strong>CO<sub>2</sub> applied to high temperature cycles</strong>

CO<sub>2</sub> has not traditionally been used in the high temperature cycle of cascade systems because of its low critical temperature.

However, the report states that there is very little research done on CO<sub>2</sub> use in the high temperature side of cascade systems.

"CO<sub>2</sub>-CO<sub>2</sub> cascade systems, which use CO<sub>2</sub> for both high-temperature cycles and low-temperature cycles have not been studied in the past, because of the general acceptance of CO<sub>2</sub>'s lower efficiency in high ambient temperature conditions due to lower critical temperature,” the study stated.

The use of CO<sub>2</sub> in both the high- and low-temperature cycles of a cascade system not only eliminates the need for HFCs, but also achieves significant energy improvements over a standard R404A system, offering more options for end users interested in saving on energy costs.

The option of CO<sub>2</sub>-CO<sub>2</sub> cascade systems adds to other CO<sub>2</sub>-based options available for commercial users such as booster systems and outdoor condensing units.

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