Dear All,
Do friends have any experiences about ultra low temperature ?
There is cascade system that using R404A in high temp. cycle and R23/R13/R508A/R508B in low temp. cycle.
Also there is R290 in one stage cycle (ultra low temp. freezers) to reach to lower that -80.

Are there any other ways and cycles ? Do you have any other experiences to share it with me and others ?