Cascade, Secondary, and Indirect refrigeration systems

[NMLS]

It seem to me that a cascade refrigeration system is the same as a secondary refrigeration system and also the same as an indirect refrigeration system.

I see no difference between the secondary and idirect methods.

Are they the same type of refrigeration system?

The only thing possibly different in the cascade refrigeration system is the cascade heat exchanger.

If so, what make the cascade heat exchanger different from the heat exchanger used in a secondary or indirect refrigeration system?

Thank you for your help and the time you took to answer my questions.

 

[waross]

I did the controls for a cascade system years ago. This was used to develop temperatures close to minus 100F. The refrigerant used for the low temperature system had such a high condensation pressure at normal ambient temperatures that the condensor was cooled by another refrigeration system. As I remember, the low temperature side was about 75HP and the high temperature system was about 150 HP. On shutdown, the low temperature system had to pump its refrigerant into a receiver. The system piping could not withstand the pressures developed when the refrigerant was allowed to rise to ambient temperature. In the event of loss of primary cooling the secondary system could open the safety valves and vent some very expensive refrigerant.
respectfully