www. refrigerationandaircon. co. za RACA Journal I November 2025 37
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• Examine the documentation to ensure all necessary documents, markings and manuals are there
• Inspect the volume of the receiver
• Check the surface temperature of the piping in public areas
• Compare the specifications and electrical drawings with the actual refrigeration system
• Ensure sufficient power supply
• Inspect the system, whether any vibrations exist
• Inspect the joins, valves and brackets( material, piping run)
• Inspect protection elements against mechanical damage
• Inspect protection of moving parts
• Check insulation( specification, quality and damages)
• Inspect cleanliness of the heat exchanger surfaces
• Provide easy access for maintenance and visual inspection
• Record pressures, temperatures amps in accordance with the commissioning report
OPERATION In normal operation the CO2 system has no special features. One or two regular inspections per year are necessary. The gas cooler and evaporator have to be cleaned periodically. The energy consumption of the motors should be tested regularly.
DECOMMISSIONING The CO2 system can be vented to atmosphere or into suitable recovery cylinders. Caution: possible dry ice formation. Venting into recovery cylinders is only possible with subcritical gas phase or if the pressure in the cylinder is higher than 5 600kPa. Note: With regards to possible recovery, CO2 systems have the handicap that the supply companies generally do not permit the refilling of the CO2 refrigerant cylinders.
Commonly used R744 refrigerant cylinders are equipped with a non-return valve. This is to ensure that the cylinders cannot be refilled which would be otherwise be possible depending on the system pressure. Non-return valves negate the risk of overfilling and contamination of the cylinder with oil. It should be stressed that the recycling of R744 is best carried out by the supplier of the material who will have the necessary product handling and container filling expertise.
For these reasons, as already mentioned, the most logical and viable option is to release it directly into the atmosphere. Keeping in mind that its main risk is asphyxiation due to concentration, we must take the following precautions:
• Always vent it to the outside, directly or through an extraction system. Never release it inside a confined space.
“ With regards to possible recovery,
CO2 systems have the handicap that the supply companies generally do not permit the refilling of the CO2 refrigerant cylinders.”
• Even if it is vented to the outside, since CO2 is heavier than air, make sure that it cannot accumulate in low, unventilated areas( pits, basements, etc).
Explosion prevention: The increase of pressure in CO2 systems can especially be a problem if the system is in standstill, for example during a break-down of the system, general switch-off due to maintenance or even when the system pauses during normal operation when enough cooling capacity has been provided. There are two options of handling this, either by supplying an additional cooling system specifically for standstill operation or by limiting the charge size to ensure that the maximum allowable pressure will not be exceeded.
Cooling in standstill: Increase in pressure during standstill can be prevented by installing a small additional( auxiliary) refrigeration system. This usually activates automatically, usually based on pressure readings in the system that indicate standstill during normal operation or breakdowns( emergency cooling) in the system due to different reasons, such as power outages. The system should be filled with a different refrigerant, such as propane, have a cooling load of about 1kW, and have an evaporation temperature below the triple point of CO2. It should always run on a different power supply. Sub-critical cascadesystems are often equipped with additional cooling units or safety operation functions. The upper stage is activated in case the pressure in the CO2 system exceeds the limit. The charge of the receiver is limited to 80 % of the receiver volume.
Limit charge: Smaller, simple single-stage systems can be designed without additional cooling if the design limits the charge size and pressure in the system below a dangerous level. These systems also do not have safety relief valves. During the design stage, the total volume, or piping and components, refrigerant charge and maximum pressure for expected ambient temperatures is determined. The receiver of such a system must be in the middle or low-pressure stage.
www. refrigerationandaircon. co. za RACA Journal I November 2025 37