Everything you need to know about CO₂ as a refrigerant. HERMETIC – operating in the CO_₂ sector for over 50 years.

Carbon dioxide (CO₂) is a long-established refrigerant that was first patented in the United Kingdom in 1850 by Alexander Twinning and was subsequently used there in air-conditioning systems and in shipping. With the development of synthetic refrigerants – CFCs, HCFCs and HFCs – which began around 1930, CO₂ fell out of favour and had almost completely disappeared by 1960.

Over the following two decades or so, experiments showed that CFC and HCFC refrigerants were depleting the ozone layer in the upper atmosphere at a rate that was likely to lead to its disappearance. In response to these findings, many countries agreed to phase out the production of these CFC and HCFC refrigerants within a reasonable timeframe to allow the ozone layer to recover. This agreement is described as the Montreal Protocol, with its second and fourth amendments relating to CFCs and HCFCs.

At the same time, Lorentzen proposed CO₂ as an alternative refrigerant to CFCs and HCFCs. Following the reintroduction of CO₂, the first applications appeared in mobile air-conditioning systems and heat pump water heaters. Further applications soon followed, including the use of CO₂ as a heat transfer fluid, as a low-temperature refrigerant in cascade cooling systems, or as the sole refrigerant.

In North America, more than 150 transcritical CO₂ systems are in operation in supermarkets, along with other CO₂ systems, and there are over 70 subcritical NH_₃–CO_₂ cascade systems for industrial applications, with many more planned.