CO2 as a Refrigerant – Selecting the Best System

May 03, 16 | Efficiency & Refrigerant Regulations, Refrigerants

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This is post number 13 of a series.

Selecting the Best System – Booster Versus Cascade Versus Secondary


Table 1 lists the advantages and disadvantages of cascade, transcritical, and secondary retail systems


The advantages and disadvantages of booster versus cascade versus secondary
Life Cycle Climate Performance Analysis
Figure 16: Variables used in system comparison calculations



Transcritical operation is generally less efficient than subcritical operation, so system type selection is usually driven by the ambient temperature profile:

    • Transcritical systems are normally used in areas where the ambient temperature is generally low (i.e., predominantly below 68 °F to 77 °F (20 °C to 25 °C), such as northern Europe and Canada.
    • Cascade and secondary systems (subcritical R744) are usually used in high ambient areas such as southern Europe, the U.S., much of central and South America, southeast Asia, Africa and Australia. The use of transcritical systems in high ambients generally results in lower efficiency, hence cascade or secondary systems are preferred in these areas.
    • Efficiency improvement for booster transcritical system for high ambient conditions is being aggressively developed to allow wider use of these systems.


The next articles in this series will provide more detailed information about the design and components of R744 cascade, transcritical booster and secondary systems.