Carbon dioxide refrigeration systems (CO₂)

Carbon dioxide (R744) is a natural refrigerant with a global warming potential (GWP) of 1 and zero ozone depletion potential (ODP).

Its favourable thermodynamic properties and low direct environmental impact have contributed to its wider use in industrial and commercial refrigeration.

CO₂ systems involve specific design challenges, including high operating pressures and a relatively low critical temperature of approximately 31°C. These characteristics require specialised components and precise control systems.

CO₂ can be used in subcritical systems, including cascade refrigeration, as well as transcritical systems in which heat rejection occurs above the refrigerant’s critical point.

Marco & Alex experience

In 2009, Marco & Alex specialists completed Romania’s first transcritical CO₂ installation at Sindan.

The installation was a heat pump operating at a maximum pressure of approximately 100 bar and capable of producing hot water at 75–85°C.

This milestone marked an early application of a technology that would expand considerably in subsequent years.

Marco & Alex has since designed and installed numerous CO₂ refrigeration systems in different configurations:

• Centralised transcritical CO₂ systems for chilling and freezing applications.
• Subcritical CO₂ systems for freezing applications.
• NH₃/CO₂ cascade refrigeration, including arrangements with an intermediate glycol circuit.
• Heat recovery and hot-gas defrost, depending on the system configuration.

Recent experience includes CO₂ refrigeration packs ranging from approximately 10 kW to several hundred kW for cold storage, food processing and other industrial and commercial uses.

System selection depends on temperature requirements, operating conditions, energy efficiency and each project’s specific needs.