CO₂ (R744), propane (R290) and ammonia (R717) have low or zero GWP but different hazards.

In short: CO₂ uses high pressure, propane is highly flammable, and ammonia is toxic and mildly flammable.

Select equipment, charge, ventilation, detection and service capability for the specific application.

CO₂ (R-744)

CO₂ is a century-old refrigerant that returned to favour as HFC restrictions bit, especially in European and Asian commercial refrigeration.

• GWP of 1 and no flame propagation. Its very low GWP does not remove the need for ventilation, detection and pressure-safe design.
• Excellent efficiency in cool ambient conditions. A transcritical CO₂ system stays subcritical more of the year in cold climates, where it is highly efficient.
• Very high operating pressures — often above 100 bar in transcritical operation — demanding purpose-built compressors, pipe, and valves, which raises cost and requires specialist design and commissioning.
• Hot-climate penalty. When ambient is high, the system spends more time transcritical and efficiency drops. Modern mitigations — parallel compression and ejectors — substantially close this gap and have made transcritical CO₂ viable even in warm regions.

Hydrocarbons — propane (R-290) and isobutane (R-600a)

• Very low GWP and zero ozone-depletion potential. Current EU regulatory tables should be used for the applicable value; older publications may show different figures because their calculation basis differs. “Very low” should not be confused with “zero”.
• Highly flammable (A3). The permitted charge, ventilation, ignition-source control and equipment construction follow the applicable standards and risk assessment. Do not transfer a charge limit from one equipment category or installation arrangement to another.

Low-charge ammonia (R-717)

• Zero GWP and outstanding thermodynamic efficiency — long the workhorse of heavy industrial refrigeration.
• Toxic and mildly flammable (B2L). Modern low-charge packages reduce the inventory, but they do not remove the need for controlled siting, detection, ventilation and emergency procedures.

Emerging technologies (context, not yet mainstream)

Magnetocaloric refrigeration and absorption chillers remain niche for cold storage. Absorption makes sense only where abundant waste heat or solar thermal energy is available; magnetocaloric cooling is still largely pre-commercial. Neither is a standard option for CAM-LOCK installations today, but both are worth tracking.

Related articles

• Cold room refrigeration systems: an overview
• Direct expansion (DX) cold room systems
• Secondary-loop (indirect) cold room systems
• F-gas rules and refrigerant selection
• Choosing the right system for your cold room

Want a future-proof refrigerant spec? Contact [email protected].