CO2 as a Refrigerant – Introduction to Retail Cascade Systems

This is post number 11 of a series.

Retail Cascade Systems

The cascade system comprises:

• The low stage, which provides cooling for the load. It uses R744 and is always subcritical
• The high stage, which absorbs heat from the condensing R744 at the cascade heat exchanger

Within the cascade heat exchanger the evaporating high-stage refrigerant absorbs heat rejected by the condensing R744. The condensing temperature is maintained below the critical point. The high stage is usually a simple, close-coupled system controlled by the pressure in the low-stage receiver.

In this case the high stage provides cooling for the MT load as well as removing heat from the condensing R744 in the low stage at the cascade heat exchanger. The high-stage refrigerant is usually an HFC,HC or Ammonia, in which case the cascade is a hybrid system. In some systems R744 is used in the high stage. It will be transcritical at ambient temperatures above 68 °F to 77 °F (20 °C to 25 °C ).

In the next article of this series we’ll take a closer look at secondary systems.