A cooling load of 12,000 Btu/hr is needed for cryogenic application. To efficiently achieve the low temperature cooling for this application, two refrigeration processes are connected in cascade configuration, where the heat rejection of the low temperature cycle is the heat input to the high temperature cycle.

If the low temperature cycle has a COP of 3.0. What is the heat rejection of the low temperature cycle?

What is the compressor work for the high temperature cycle, if the high temperature cycles also has a COP of 3.0?

What is the overall COP of the cascade refrigeration system?