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Refrigerants for special applications Alternatives for R13B1 Besides R410A, ISCEON® MO89 (DuPont) can be regarded as potential R13B1 substi- tute. For R410A, a substantially higher dis- charge gas temperature than for R13B1 is to be considered, which restricts the appli- cation range even in 2-stage compression systems to a greater extent. ISCEON® MO89 has been used for many years, preferably in freeze-drying plants. Meanwhile, production has ceased. Howev- er, for historical reasons the refrigerant will continue to be included in this Report. It is a mixture of R125 and R218 with a small pro- portion of R290. Due to the properties of the two main components, density and mass flow are relatively high, and discharge gas temperature is very low. Liquid subcool- ing is of particular advantage. Both of the mentioned refrigerants have fairly high pressure levels and are therefore limited to 40..45°C condensing temperature with the usually applied 2-stage compressors. They also show less capacity than R13B1 at evaporating temperatures below -60°C. In addition to this, the steep fall of pressure limits the application at very low tempera- tures and may require a change to a cas- cade system with e.g. R23, R508A/B or R170 (ethane) in the low temperature stage. Lubrication and material compatibility are similar to other HFC blends. The EU F-Gas Regulation (Annex III) pro- vides an exemption "for applications designed to cool products below -50°C". This means that even after 2020, refriger- ants with GWP > 2500 can be used in new plants. Due to the "phase-down" however, quantities will be limited, resulting in a con- siderable increase in price and very limited availability. It is therefore imperative to develop alterna- tive solutions for which, however, no overall recommendation is possible. Two-stage compressors may be operated e.g. with R448A/449A (safety group A1) or R1270 (A3) down to an evaporation temperature of -60..- 65°C. Although R404A/ R507A alter- natives with GWP < approx. 250 (safety group A2L) are potentially possible, so far only limited experience has been gained even for typical low temperature refrigera- tion. At evaporating temperatures of down to -50..-52°C, operation with CO2 is also possible − either in a two-stage or a cas- cade system. However, each variant generally requires a specific design and laboratory tests. Δ Fig. 33 R13B1/HFC alternatives – comparison of discharge gas temperatures of a 2-stage compressor 39PDF Image | REFRIGERANT REPORT 21
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