R422A as substitute for R22 and R502
Amongst other aims, R422A (ISCEON® MO79 – Chemours) was developed in order to obtain a chlorine-free refrigerant (ODP = 0) for the simple conversion of existing medium and low temperature refrigeration systems using R22 and R502.
For this, it was necessary to formulate a refrigerant with comparable performance and energy efficiency to that of R404A, R507A, and R22, which also permits the use of conventional lubricants.
R422A is a zeotropic blend of the basic components R125 and R134a with a small addition of R600a. Due to its relatively high R134a percentage, the temperature glide (Refrigerant data) lies higher than for R404A, but lower than other refrigerants with the same component blends – such as R417A and R422D (R417A/417B/422D/438A as substitutes for R22).
The adiabatic exponent, and therefore also the discharge gas and oil temperatures of the compressor, are lower than for R404A and R507A. At extremely low temperatures, this can be advantageous. However, in cases of low pressure ratio and suction gas superheat, this can be a disadvantage due to increased refrigerant solution if ester oil is used.
The material compatibility is comparable to the blends mentioned previously, the same applies to the lubricants. On account of the good solubility of R600a, conventional lubricants can also be used under favourable circumstances.
In particular, advantages result during the conversion of existing R22 and R502 systems as mentioned above. However, for plants with high oil circulation rates and/or large liquid charge in the receiver, oil migration might occur – for example if no oil separator is installed.
If insufficient oil return to the compressor is observed, the refrigerant manufacturer recommends replacing part of the original oil charge with ester oil. But from the compressor manufacturer's view, such a measure requires a very careful examination of the lubrication conditions. For example, if increased foam formation in the compressor crankcase is observed, a complete change to ester oil* will be necessary. Under the influence of the highly polarized blend of ester oil and HFC, the admixture of or conversion to ester oil leads to increased dissolving of decomposition products and dirt in the pipework. Therefore, generously dimensioned suction clean-up filters must be provided. For further details, see the refrigerant manufacturer's guidelines.
From a thermodynamic point of view, a heat exchanger between suction and liquid line is recommended, improving the refrigerating capacity and coefficient of performance. Besides this the resulting increase in operating temperatures leads to more favourable lubricating conditions (lower solubility).
Due to the high global warming potential (GWP ≥ 2500), R422A is no longer allowed for new installations in the EU from 2020 onwards. The requirements and restrictions are specified in the F-Gas Regulation 517/2014.
* General recommendation for screw compressors and liquid chillers when used with DX evaporators with internally structured heat exchanger tubes. Furthermore, an individual check regarding possible additional measures will be necessary.