The rediscovery of CO2 as a refrigerant
CO 2 ’s Role in sustainable cooling
Carbon dioxide, CO2, is a naturally occurring substance. It is not harmful to the atmospheric ozone layer and, although it is a “greenhouse gas,” it has a very low Global Warming Potential (GWP).
By definition, the GWP of CO2 is 1. CO2 is a molecule produced by combustion, and the issue with CO2 lies more in the enormous quantity continuously produced worldwide. In refrigeration applications, however, CO2 is not produced but rather reused from what has already been emitted. With this distinction, the CO2 used in refrigeration has a net-zero GWP.
Carbon dioxide was used in refrigeration up until around 1930, but was abandoned following the invention of synthetic refrigerants, which were later found to be harmful to the environment. CO2 has excellent thermophysical properties and is also well suited for use in heat pumps.
Transcritical CO₂ refrigeration systems show strong efficiency across a wide range of European climates. The Seasonal Energy Performance Ratio (SEPR) rises in colder regions, and advanced system architectures—such as parallel compression, liquid ejectors, and vapor ejectors consistently deliver higher efficiency compared to basic configurations.
At the same time, the data demonstrates that CO₂ technology performs reliably and efficiently even in warmer climates.
Intro: the Winds of Trondheim and the Italian frontier
Chapter 1: The false miracles and the Montreal Earthquake
Chapter 2: How physics beat chemistry
Chapter 3: Ice, fire, and the birth of Enex
Chapter 4: the Geometry of Cold and the Alpine Sanctuaries
Chapter 5: the Ejector – An unexpected miracle in the pipes
