History of a New Technology - Part 1
The Rediscovery of CO2 in refrigeration
1. Introduction: The Era of Natural Fluids and the Advent of Synthetics
Mechanical refrigeration took its first steps around 1850. Until 1930, systems exclusively used natural fluids, including ammonia, sulfur dioxide, and—starting in 1890—carbon dioxide.
A major turning point occurred around 1930 with the synthesis of the first artificial refrigerants, such as R12 and R11. These “miracle” molecules quickly replaced most of the natural fluids in use, with the exception of ammonia, which remained the standard in large industrial plants. It was only fifty years later that the truth emerged: those synthetic substances that made refrigeration systems so simple and efficient were damaging the environment.
2. The Montreal Protocol: An Industrial Earthquake
The modern cooling industry grew up relying on synthetic refrigerants: CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons). Both contained chlorine, one harmful substance for atmospheric ozone.
In the decade between 1990 and 2000, I lived through this change on the front lines as a technical manager of a large commercial refrigeration company. It was a time when established certainties were overturned by scientific evidence. Studies by Rowland, Molina, and Crutzen (Nobel Prize winners in 1995) proved that chlorine, and bromine, were responsible for the “hole” in the ozone layer. The Montreal Protocol (1987) mandated the phase-out of the fluids containing these elements; now, in 2026 and after several years from ban of harmful substances and with ozone hole recovering, we can say that Montreal Protocol was an environmental success, but at that time for the industry it was a kind of earthquake.
3. The Ozone Crisis and the Role of R22
The sector’s first response was pragmatic: falling back on R22 (an HCFC), which had a significantly lower Ozone Depletion Potential (ODP) than CFCs (0.05 versus 1.0). However, R22 was not suitable for all applications. Consequently, the chemical industry began proposing HFCs (hydrofluorocarbons), fluids with zero ODP because they did not contain chlorine.
The market was searching for the “ultimate refrigerant,” but a new obstacle soon appeared: HFCs, much like CFCs and HCFCs, contributed heavily to the greenhouse effect.
4. From the Ozone Problem to Global Warming (GWP)
While efforts were being made to save the ozone, the issue of the greenhouse effect and global warming emerged with force. To measure the impact of these fluids, GWP (Global Warming Potential) was defined. New refrigerants like R404A or R134a, despite being “Ozone Friendly,” turned out to be extremely powerful greenhouse gases.
To put it in perspective: just one kilogram of R404A released into the atmosphere has an impact equivalent to nearly 4 tons of CO2.
During those years, we witnessed a chaotic proliferation of new refrigerants and blends. Complexity increased drastically:
- For manufacturers: Every new fluid required long and time consuming compatibility and reliability tests.
- For technicians: Managing several different cylinders and oils became an unsustainable burden.
Above all, there was no clear direction—a total lack of ideas on how to solve this situation at its root. Various methods were proposed, some of them difficult to believe today, e.g. acetone with CO2 as a brine or Flo-ice.
5. The Limitations of Indirect Systems
To reduce the charge of synthetic gases, some companies tried the path of indirect systems: a reduced primary circuit cooled a secondary fluid (glycol water) to be pumped to the end users. However, field analysis revealed insurmountable physical limits:
- Low energy efficiency: Intermediate heat exchangers and pumps for viscous liquids increased electricity consumption, making not sustainable, at least for low-temperature applications, an indirect system.
- Low reliability: The use of aggressive secondary fluids (such as acetate or formiate of potassium) caused frequent corrosion.
- Costs: Mechanical complexity made the systems more expensive and prone to failure.
Conclusion: Toward the CO2 Revolution
By the late 1990s, it was clear that adding layers of complexity or seeking new synthetic molecules was not the final solution. While Southern Europe remained anchored to old patterns, news filtered in from Northern Europe regarding the use of carbon dioxide (CO2 or R744) as a phase-changing secondary fluid.
Using CO2 not merely as a secondary fluid, but directly as the primary fluid—an idea that seemed obvious by that point—would not just be an evolution, but a revolution. In 1995, however, this meant embarking on a massive industrial effort: components had to be designed from scratch because they simply did not yet exist on the market.