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4.6.4. R1270 The considerations on propylene are very similar to the ones made for propane, as it is evident when comparing Figure 4.21 to the previous Figure 4.20. The reduction in COP is comparable. Though, the heating capacity reduction from R410A is lower, as the volumetric heating capacity is higher. Between the two options therefore, R1270 can be seen as a better choice in terms of producible heat, or, if constant heating capacity, in terms of smaller charge needed. The discharge temperatures reached are generally slightly higher than with R290, but still well below the limit and R410A values. This refrigerant is also highly flammable, and concerns can be raised on its chemical stability at high temperatures. It could then be seen as a better solution for restricted low temperature applications. TEWI SCOP Discharge temperature 0% -10% -20% -30% -40% -50% -60% COP VHC Figure 4.21. Summary of evaluated parameters for R1270 4.6.5. R1234yf As can be observed in Figure 4.22, the use of R1234yf entails a reduction of all the parameters involved. The reduction in TEWI is remarkable, though as its SCOP is the lowest between the evaluated alternatives, its indirect effect is the highest one. The discharge temperature is also decreased when compared to R410A, bringing benefits to the compressor’s lifetime. The volumetric heating capacity is very low, so the same charge considerations seen previously can be applied in this case as well. In addition, R1234yf belongs to the flammability category A2L, that in many countries’ regulations is still considered equal to A2, thus requiring restrictions more severe than necessary. Being a relatively new substance, moreover, its cost is still quite high. -49-PDF Image | Next generation of refrigerants for residential heat pump systems
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