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Concerning R513A, a mixture of R134a/R1234yf (44/56 in mass percentage), the available literature is very limited. Similarly to R450A, it is non-flammable, and has a GWP of 631. Schultz and Kujak (2013) performed drop-in tests of R513A in an R134a chiller, obtaining a comparable capacity, but an efficiency reduction of 3-4%. 2.4. Selected refrigerants for further analysis When selecting the refrigerants to elaborate a shortlist of R410A replacement options within the described above, the criteria kept into consideration can be summarised as follows: Low GWP, no ODP Non-toxic Chemical and thermal stability, inert Suitable physical and thermodynamic properties: – Critical point and boiling point temperatures appropriate for the application – Low vapour heat capacity – Low viscosity – High thermal conductivity Compatibility with materials, miscibility with lubricants Other: – High dielectric strength of vapour – Low freezing point – Easy leak detection – Low cost It is evident that a compromise must be sought, as no refrigerant currently available can satisfy all of the characteristics ideally requested. A low GWP is considered for a preliminary round of elimination, as the alternative refrigerant has to have a GWP at least inferior to R410A (2088). This eliminates R134a. As far as safety is concerned, toxic refrigerants (classified B by the ASHRAE 34) will not be considered as options, whereas flammability will not be a deterring in this phase of the research. Hence, ammonia will not be analysed further. The main thermodynamic aspects to be kept into account can be summarised in Figure 2.5, applied to the saturated vapour pressure curves, seen in Figure 2.2. The operational envelope identified in the figure by the red square is built by combining pressure and temperature boundaries to the refrigerants. -17-PDF Image | Next generation of refrigerants for residential heat pump systems
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