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Substitutes for R22 in refrigeration systems Whether these favourable conditions are confirmed in real applications is subject to the system design. An important factor is the significant temperature glide, which can have a negative influence upon the capac- ity/temperature difference of the evaporator and condenser. With regard to the material compatibility, R32 blends can be assessed similarly to R404A and R507A; the same applies to the lubricants. Despite the relatively high proportion of R125 and R134a in the R32 blends, the dis- charge gas temperature is higher than with the R143a based alternatives (especially for R407F and even to a higher degree with R407H). This results in certain limitations in the application range as well as the require- ment for additional cooling of compressors when operating at high pressure ratios. 2-stage compressors can be applied very efficiently where especially large lift condi- tions are found. An important advantage in this case is the use of a liquid subcooler. Resulting design criteria The experience with R404A/R507A and R22 can be used for plant technology in many respects, although the temperature glide as well as the difference in the ther- modynamic properties have to be consid- ered. This especially concerns the design and construction of heat exchangers and expansion valves. Converting existing R22 plants to R407A/407B/407F/407H Practical experiences show that qualified conversions are possible. Compared to R22 the volumetric refrigeration capacity is near- ly similar while the refrigerant mass flow is only slightly higher. These are relatively favourable conditions for the conversion of medium and low temperature R22 systems. The main components can remain in the system provided that they are compatible with HFC refrigerants and ester oils. However, special requirements placed on the heat exchanger with regard to the signif- icant temperature glide must be considered. A conversion to ester oil is also necessary, which leads to increased dissolving of de- composition products and dirt in the pipework. Therefore, generously dimen- sioned suction clean-up filters must be pro- vided. Conversion of existing R404A/R507A systems to R407A/407B/407F/407H Larger differences in thermodynamic prop- erties (e.g. mass flow, discharge gas tem- perature) and the temperature glide of R407A/F/H may require the replacement of control components and if necessary retrofitting of additional compressor cooling when existing systems are converted. For newly built systems, a specific design of components and system is necessary. BITZER offers a comprehensive program of reciprocating and screw compressors for R407A and R407F. An individual selection of compressors for R407H is possible upon demand. 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 me- dium 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 (see chapter Refrigerant Properties, page 42) lies higher than for R404A, but lower than other refrigerants with the same com- ponent blends – such as R417A and R422D (see page 22). 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 super- heat, this can be a disadvantage due to in- creased 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 lubri- cants 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 migra- tion 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 com- pressor manufacturer's view, such a meas- ure requires a very careful examination of the lubrication conditions. For example, if in- creased 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 con- version to ester oil leads to increased dis- solving 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. Be- sides this the resulting increase in operat- ing temperatures leads to more favourable lubricating conditions (lower solubility). Due to the high global warming potential (GWP ≥ 2500), R422A will no longer be allowed for new installations in the EU from 2020 onwards. The requirements and re- strictions are specified in the F-Gas Regula- tion 517/2014. * General proposal for screw compressors and liquid chillers when used with DX evaporators with internal- ly structured heat exchanger tubes. Furthermore, an individual check regarding possible additional meas- ures will be necessary. BITZER compressors are suitable for R422A. An individual selection is pos- sible upon demand. 19PDF Image | REFRIGERANT REPORT 21
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