History of a New Technology - Part 2
The Return to basics – Why Physics Beat Chemistry
In the 1990s, while the chemical industry was hunting for a new “magic molecule,” thermodynamics suggested the opposite direction: instead of searching for a fluid suited to the standard refrigeration cycle, it was necessary to modify the system design to allow the use of a natural, non-toxic, and non-flammable fluid, namely CO2.
Choosing carbon dioxide (R744) meant clashing with a physical limit that had been considered insurmountable for decades: its low critical temperature (31.1°C).
1. The End of Synthetic Alternatives
Around 1995, research by NIST (conducted by McLinden and Domanski) reached a definitive conclusion: the atomic combinations for creating new refrigerants that were simultaneously safe, efficient, and stable had been exhausted.
There were no more new synthetic molecules capable of replacing old gases without reintroducing environmental (GWP) or safety issues. The “chemical solution” was stalling; in its place, the thermodynamic solution began to take shape.
2. The Transcritical Cycle: Lorentzen’s Revolution
The work of Professor Gustav Lorentzen in Trondheim between the late 1980s and 1995 was the turning point. Lorentzen theorized that CO2 should not be used like traditional fluids.
Above 31.1°C, the fluid no longer condenses like a normal refrigeration fluid in use, but it enters a “transcritical” state (or “dense gas”). Although practical experiences dated back to the 1920s—primarily in the maritime sector—it was necessary to carefully evaluate the advantages and resolve the drawbacks:
- The Advantage: High energy density and optimal heat exchange properties.
- The Challenge: Very high operating pressures—up to 120 bar, compared to the 15-20 bar of traditional systems.
3. 1995: From Theory to Reality – The First Compressor
At the time, using CO2 in refrigeration was a beautiful theory without real machines. Quite simply, there were no components capable of withstanding those pressures, let alone compressors and valves suited for the purpose.
The practical breakthrough came from a collaboration launched in 1995 between Costan (the company I worked for at the time) and Officine Mario Dorin. In 1996, the world’s first prototype of a semi-hermetic compressor for transcritical CO2 was born.
The testing phase had an almost heroic, artisanal feel:
- Tests were conducted outdoors, as equipped test rooms for managing such pressures did not yet exist.
- The gas cooler and evaporator were built by hand.
- Valves were “borrowed” from the hydraulic sector.
- Lubrication problems were solved directly in the field through continuous adjustments.
But the results were unmistakable: the compressor performed excellently, and the machine “produced cold.” Above all, we proved that managing high pressures was not an impossible task.
The Technical Lesson
Even though in 1996 the only existing component was the compressor, we had proven that using CO2 was not a problem of principle, but a technological problem of pressure containment and regulation. Once the high pressure was managed, the road toward natural cooling was finally open.