Revival of carbon dioxide as a refrigerant

In the present situation it seems appropriate to avoid as far as possible the use in large quantities of substances that are foreign to nature and will unavoidably be lost into the biosphere. A much safer philosophy must be to revert to ‘natural’ refrigerants: substances that are already present in our environment and which are known to be harmless. One such possibility is carbon dioxide (CO2), which comes very close to being the ideal working medium, provided that a process to give competitive energy performance can be designed. The paper presents some examples of how this can be done.