HCFCs (hydrochlorofluorocarbons): compared with CFCs they contain hydrogen and therefore less chlorine; they are thus less dangerous for the ozone layer, but these gases are no longer used either; these compounds, containing at least one hydrogen atom, are more toxic than their CFC counterparts
To make the composition of refrigerant fluids less persistent over time, it is sufficient to replace the chlorine in the molecule with hydrogen.
This makes the fluid molecules less stable once released into the atmosphere, where they tend to decompose more rapidly, while it does not affect the chemical and physical stability of the refrigerant (i.e. it does not lead to the formation of new substances or compounds) when it is inside a refrigeration circuit.
Since they contain chlorine, HCFCs have a non-zero impact on the depletion of the atmospheric ozone layer (ODP).
For this reason their progressive elimination was scheduled: after an initial phase-down (progressive restriction of use), from 2015 HCFCs can no longer be used for maintenance, even if reclaimed/recycled.
In new systems HCFCs have been banned since 2010.
This means a complete ban on these gases and therefore also on R22.
However, R22 systems that have no recharging or top-up problems can continue to operate undisturbed. To ensure their continued operation, it is therefore very important to avoid any refrigerant leakage from the circuit at all costs.
Since 1 January 2015 the use of R22 has been completely prohibited, even if recycled and recovered. This is laid down by European Regulation 1005/09, which therefore poses major problems for the owners of all appliances that use this gas, either pure or in a blend. Although there is no obligation to decommission working machines, from that date it is no longer possible to carry out top-ups in the event of repairs, not even with recycled gas.
So how should one deal with such a situation? There are several options, depending on the type of system, its size and its use.
The first option is, of course, replacement with a new system. Technically this is certainly the best solution, because it makes it possible to ensure high efficiency by installing more modern machines, designed according to recent regulations on energy saving and GWP. However, it is an expensive solution, and that is precisely why it is sometimes worth choosing other routes.
The alternative is retrofit, i.e. the complete replacement of the gas inside the machine with an HFC. This is, however, an option that must be assessed carefully according to the size, condition and operation of the system. Although the immediate cost is generally lower than that required for the complete replacement of the system, expenditure could in fact increase in the long term, as a result of malfunctions due to the age of the machine and lower efficiency. Retrofitted appliances rarely manage to maintain their original performance.
Moreover, not all gases are interchangeable. For example, R410A, currently the most widely used refrigerant in air-conditioning systems, would require, due to its higher operating pressures, the redesign of the refrigeration circuits and the replacement of components with others specifically designed for it. It is therefore suitable for new equipment, but not for retrofitting R22.
There are also other critical issues that must be considered before proceeding, first and foremost the lubrication of the system. Systems charged with CFC (R12, R502) and HCFC (R22) refrigerants worked well with compressors that used mineral oils (hydrocarbon-based) for compressor lubrication. HFC refrigerants, on the other hand, have shown reduced miscibility with those products and therefore use different lubricants, known as POE. The conversion procedure to HFC therefore requires flushing of the circuit to ensure the removal of the mineral oil present in the system. A residual mineral oil content in the POE of no more than 5% is considered acceptable. This is perhaps the most complex part of the whole process and, precisely for this reason, refrigerant gas manufacturers have introduced blends with a high residue tolerance (10-15% residual mineral oil) that are suitable for replacing CFCs and HCFCs without having to change the oil (at least in most cases).
So which gases can be used to retrofit R22?
Especially in the past, R407C was considered the most suitable candidate for this type of application, as it allowed the same circuits to be used without significant changes to the components. However, due to certain handling issues with this gas, other types of refrigerants have become established over time. R417A and R419A, for example, are zeotropic blends that allow the use of mineral oil. They do, however, have some limitations: the use of the former, for example, is not recommended in systems with flooded evaporators, liquid separators or centrifugal compressors.
R422D and R422A are blends designed to replace R22. The former can be used in large air-conditioning systems, in chillers and in refrigeration other than low-temperature refrigeration, while the latter is used in low-temperature commercial refrigeration. In the retrofit operation the expansion device must be replaced, but there is no need to replace the oil. This gas has some advantages, as it has a refrigerating capacity up to 15% higher than R22 and significantly lower discharge temperatures, which can lead to longer compressor life. However, it is not advisable to use it in systems with flooded evaporators, liquid separators or centrifugal compressors.
Other gases that can be used without any particular work on the circuit are R427A (air conditioning and refrigeration), R428A (refrigeration) and R438A (in chillers where the expansion valve has been sized strictly sufficient for the required capacity), while R434A (air conditioning and refrigeration) may require replacement of the expansion device and the capillary tube.
Taking all these critical issues into account, in practice the retrofit operation is not overly complex. First of all, it is necessary to check the operation of the system and record the reference performance with the existing refrigerant. As we have said, the new replacement gases are generally compatible with the old lubricant, so in most cases it is not necessary to remove it from the circuit. Where this is necessary, the operation must be carried out at this stage, taking care not to leave excessive residues. The R22 is then recovered and weighed to determine the quantity of new fluid to be charged, and the filter drier, the moisture indicator and, where required, the expansion valve are replaced. It is not strictly necessary to change the seals, but it is recommended, especially in very old systems. After checking the tightness of the system with nitrogen, the system is recharged with the new refrigerant and its operation is checked.
This is what must be considered, in practice, when faced with an R22 system that needs a gas top-up. Clearly, beyond technical musings, the fundamental aspect is the economic one, and the best choice, at least in this case, is the one that allows the greatest savings.