In the food cold chain, R-404A and R-22 are very widely used. But the ban of R-22 is now completed or ongoing according to the regions. Due to its very high GWP, R-404A will also be subject to bans or restrictions in the future. To replace R-22 and R-404A, over twenty synthetic refrigerants, mostly blends, are proposed by various producers and referenced with ASHRAE classification. This multiplicity of products is confusing. Some are proposed as alternatives to R-22, or to R-404A, or both. Some are flammable; others are not. GWP’s can vary in a wide range. This paper provides the basic concepts to understand why and when blends are needed, and the link between their formulation and their key physical and environmental properties: operating pressures, temperature glide, volumetric capacity, GWP, and flammability. The most commonly proposed alternatives are analyzed to provide some understanding of the trade-offs between GWP, flammability, and key physical parameters.

Among the possible refrigerants, low pressure fluids offer the best theoretical cycle efficiency. But because of high volumetric flow, current chiller designs must be completely revisited with such fluids; otherwise, the footprint of units can be huge, or (and) the potential fluid benefits can be wasted in penalties like high internal pressure losses etc. Low pressure fluids like R-11 and R-123 were used in the past, but new technologies were introduced since then like the extensive use of direct drive variable speed motors and falling film evaporators. It is not enough to just “recycle” platforms formerly used for low pressure fluids, or to change fluid in state of the art products using higher pressure fluids. This paper presents challenges, opportunities and trade-offs in the choice between various categories of fluids for chillers.

The comparison between fluids for a given application usually requires complex calculations; this makes it confusing for non experts to make relevant choices. In this paper, it is shown that in spite of the complexity of the issues, knowing only the critical temperature of a fluid is sufficient to make amazingly precise comparisons between fluids, regarding major parameters of practical interest. Cycle comparisons are made for a variety of natural and synthetic fluids. The conditions studied cover typical Air Conditioning applications, including warm climates, in various cycle configurations. The outputs are key parameters of practical importance: energy efficiency, operating pressures, and required volumetric flow. For most fluids, these parameters correlate amazingly well, making them predictable from the critical temperature only. This applies to the synthetic fluids and to hydrocarbons. But fluids with a very different molecular structure, like ammonia or water vapor may deviate significantly from this common behavior.