R407A/B/F/H as substitutes for R22 and R502
As an alternative to the earlier described substitutes, additional mixtures have been developed based on R32 which is chlorine free (ODP = 0) and flammable like R143a. The refrigerant R32 is also of the HFC type and initially was regarded as a main candidate for R22 alternatives. However, due to extent of blend variations comparable thermodynamic characteristics to R404A/R507A can also be obtained.
These kinds of refrigerants were marketed at first under the trade name KLEA® 60/61 (ICI) and are listed as R407A/B in the ASHRAE nomenclature. (Meanwhile, R407B is no longer available in the market. Due to the historical development of HFC blends this refrigerant will, however, still be considered in this Report.)
Honeywell has developed another blend with the trade name Performax® LT (R407F according to ASHRAE nomenclature) and introduced it into the market, similar Daikin Chemical with R407H. For both blends, the R32 proportion is higher than for R407A, while the R125 proportion is lower. With R407H, this results in certain restrictions for low temperature applications.
However, the necessary conditions for alternatives containing R32 are not quite as favourable compared to the R143a based substitutes discussed earlier. The boiling point of R32 is very low at -52°C, in addition the isentropic compression exponent is even higher than with R22. Rather high proportions of R125 and R134a are necessary to match the characteristics at the level of R404A and R507A. The flammability of R32 is thus effectively suppressed, but the large differences in boiling points with a high proportion of R134a lead to a larger temperature glide.
The main advantage of R32 is the relatively low global warming potential (GWP = 675), so that even in combination with R125 and R134a it is significantly lower than with the R143a based alternatives mentioned above (R407A: GWP = 2107, R407F: GWP = 1825, R407H: GWP = 1490).
Thus, they also comply with the requirement of the new EU F-Gas Regulation which only allows refrigerants of GWP < 2500 since 2020.
Measurements made with R32 containing blends do show certain capacity reductions compared to R404A and R507A, with low evaporating temperatures. The COP however shows less deviation and is even higher in medium temperature applications (Comparison of performance data of a semi-hermetic compressor).
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 capacity/ 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 discharge 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 requirement for additional cooling of compressors when operating at high pressure ratios.
2-stage compressors can be applied very efficiently where especially large lift conditions are found. An important advantage in this case is the use of a liquid subcooler.
