Refrigerant blends

Refrigerant blends have been developed for existing as well as for new plants with properties making them comparable alternatives to the previously used substances. It is necessary to distinguish between three categories:

  1. Transitional or service blends,
    which mostly contain HCFC R22 as the main constituent. They are primarily intended as service refrigerants for older plants with view on the use ban of R12, R502 and other CFCs. Corresponding products are offered by various manufacturers, there is practical experience covering the necessary steps of conversion procedure.
  2. However, the same legal requirements as for R22 apply to the use and phase-out of these blends (R22 as transitional refrigerant).
  3. HFC blends
    These are substitutes for the refrigerants R502, R22, R13B1 and R503. Above all, R404A, R507A, R407C and R410A are being used to a great extent.
    One group of these HFC blends also contains hydrocarbon additives. The latter exhibit an improved solubility with lubricants, and under certain conditions they allow the use of conventional oils. In many cases, this permits the conversion of existing (H)CFC plants to chlorine-free refrigerants (ODP = 0) without the need for an oil change.
  4. HFO/HFC blends
    as successor generation of HFC refrigerants. It concerns blends of new "low GWP" refrigerants (e.g. R1234yf) with HFCs. The fundamental target is an additional decrease of the global warming potential (GWP) as compared to established halogenated substances ("Low GWP" HFOs and HFO/HFC blends as alternatives to HFCs).

Blends of several components already have a long history in the refrigeration trade. A difference is made between the so called "azeotropes" (e.g. R502, R507A) with thermodynamic properties similar to single substance refrigerants, and "zeotropes" with "gliding" phase changes (General characteristics of zeotropic blends). The original development of "zeotropes" mainly concentrated on special applications in low temperature and heat pump systems. Actual system construction, however, remained the exception. A somewhat more common earlier practice was the mixing of R12 to R22 in order to improve the oil return and to reduce the discharge gas temperature with higher pressure ratios. It was also usual to add R22 to R12 systems for improved performance, or to add hydrocarbons in the extra low temperature range for a better oil transport.

This possibility of specific "formulation" of certain characteristics was indeed the basis for the development of a new generation of blends.

At the beginning of this Report (Refrigerant developments and legal situation), it was already explained that no direct single-substance alternatives (on the basis of fluorinated hydrocarbons) exist for the previously used and current refrigerants of higher volumetric refrigeration capacity than R134a. This is why they can only be "formulated" as blends. However, taking into account thermodynamic properties, flammability, toxicity and global warming potential, the list of potential candidates is strongly limited.

For the previously developed CFC and HCFC substitutes, the range of substances was still comparably large, due to the fact that substances of high GWP could also be used. However, for formulating blends with significantly reduced GWP, in addition to R134a, R1234yf and R1234ze(E), primarily refrigerants R32, R125 and R152a can be used. Most of them are flammable. They also exhibit considerable differences with respect to their boiling points, which is why all "Low GWP" blends of high volumetric refrigerating capacity have a substantial temperature glide (General characteristics of zeotropic blends).