Recent investigations in HFCs substitution with lower GWP synthetic alternatives: focus on energetic performance and environmental impact  More studies about lower GWP refrigerants are needed to facilitate the phase-out HFCs.  HFO studies are mostly found in MAC and domestic refrigerators.  Stationary refrigeration equipment presents the major variety of studies.  Multipack centralized refrigeration systems studies are being dominated by CO 2 (R744).  R32 is limited by the discharge temperature and injection cycles are needed.  Mixtures could help to overcome pure fluids handicaps.

Because air conditioning and heat pump systems contribute greatly to greenhouse gas emissions, equipment with both lower global warming potential (GWP) working fluids and a higher level of performance should be used. R32 (difluoromethane) has been proposed to substitute R410A, particularly in residential air conditioning (RAC) systems. This study collected the most relevant and recent researches into R32 as a refrigerant so as to assess its viability in RAC systems in both Europe and the USA, as compared to R410A and other lower GWP RAC alternatives.The R32 value of GWP is 677, which is below the F-gas regulation limit in RAC equipment (750). According to ASHRAE standard 34, R32 is less flammable than hydrocarbons, and the amount of charge permitted for R32 is above the necessary level in RAC equipment. It can be concluded that R32 has significantly good heat transfer characteristics and a level of performance that make it acceptable at low condensing temperatures, thereby avoiding overly high compressor discharge temperatures. Its performance is very similar to that of R410A across the entire operating range, and it is therefore believed that R32 will be utilized in RAC systems in the remaining countries that prioritize lower GWP fluids but are less strict in their security regulations.To replace R410A under extreme conditions, some system modifications can be conducted, or R32 mixtures with hydrofluoroolefins (HFOs) can be used. Such mixtures achieve a lower performance than R32, but are acceptable replacements when considering their lower GWP compared to that of R32, and similar level of flammability. Finally, other (R32-based) alternative mixtures have also been developed and their behaviours studied under a wide range of operating conditions.

 R449A is retrofitted into a R404A real supermarket refrigeration system.  Cooling capacity is lower for R449A.  COP of both refrigerants is comparable.  R449A discharge temperature is higher but still admissible.  TEWI analysis indicates that CO 2-eq. emissions of R449A are lower than R404A Abstract R404A is going to be phased out from most of the commercial refrigeration systems due to its high GWP value of 3943. R449A (GWP of 1282) has been proposed to replace R404A with only minor system modifications in supermarkets. This paper presents the measurements of a light retrofit replacement of R404A using R449A in a medium temperature indirect refrigeration system (secondary fluid temperature at the evaporator outlet between-9 and-4 °C). It has been demonstrated that with a slight expansion device adjustment and 4% increase of refrigerant charge, R449A can be used in this refrigeration system designed for R404A because of its suitable thermodynamic properties and acceptable maximum discharge temperature. At a secondary fluid temperature at condenser inlet of 30 °C, the COP of R449A nearly matches that of R404A (both were between 1.9 and 2.2), despite having approximately 13% lower cooling capacity. As a conclusion, attending to the GWP reduction and similar energy performance, it was demonstrated using the TEWI methodology that the use of the recently developed refrigerant R449A in these applications can reduce the total CO 2 equivalent emissions of an indirect supermarket refrigeration system designed for R404A refrigerant.

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 R513A is experimentally compared with R134a in a refrigeration test bench.  Evaporation temperatures are varied between-15 and 12.5ºC.  R513A presents higher mass flow rate and cooling capacity than R134a.  R513A COP is always above than that of R134a due to lower cooling capacity.  R513A can substitute R134a with lower system modifications.

In recognition of the impact of the refrigeration sector on climate change, global commitments are achieved to replace hydrofluorocarbon substances with more planet-friendly alternatives. In this regard, countries with high ambient temperatures (HAT) face additional problems in identifying suitable alternatives due to the impact of such temperatures on energy performance in vapor compression systems. This paper presents an experimental analysis using R134a and two lower global warming potential (GWP) mixtures in a small capacity vapor compression refrigeration system for HAT environments. The range of evaporating and condensing conditions was selected to simulate a refrigeration system working at HAT conditions. The experimental operating results show that although R450A values are acceptable, R513A shows better adaptation to refrigeration system in terms of pressure ratio, discharge temperature and mass flow rate. Then, attending to experimental energetic results, R450A energy performance (quantified by COP) and cooling capacity is lower than R513A and R134a. TEWI analysis of a small refrigeration unit shows CO 2 equivalent emission saving when using R450A in the different condensation conditions. However, taking into account the variation of cooling capacity, R513A system results in the lowest TEWI when normalizing per unit of delivered cooling capacity.

HIGHLIGHTS R450A is tested in an R134a small capacity refrigeration unit.  Evaporating temperature is varied between -15ºC and 12.5ºC.  Average mass flow rate and cooling capacity are 9.1% and 9.9% lower for R450A.  Average compressor power consumption and COP values are 7.2 and 2.9% lower for R450A.  R450A can be considered as R134a drop-in replacement if decrease in cooling capacity is acceptable.

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