A detailed study of candidate chemicals able to replace R-410A in small air conditioning equipment has identified, after screening a comprehensive database of potential candidates, 27 fluids that had the desired characteristics for refrigerant use : a low GWP, no ODP, thermodynamic properties matching the application, chemical stability, no or limited flammability, lack of toxicity, being the most important.
However, all the 27 identified fluids are flammable, some of them only mildly, and many of them highly, which makes them typically not appropriate for some larger systems. Other limitations caused the authors to conclude a number of the remaining fluids should not be retained for some air conditioning applications : CO2 refrigerant is a high pressure fluid that has some performance disadvantages for small systems or would requires new designs; ammonia is toxic and corrosive; and novel molecules present unknown safety risks.
The study major conclusion is that “there is a very limited number of viable candidates for single component low-GWP alternatives for small air conditioning systems, especially for refrigerants with volumetric capacities similar to R-410A”.
The authors state that didn’t find a perfect refrigerant fluid to replace R-410A in the future. As they argue that it is unlikely that other new fluids might be found, they insist policymakers to understand the limits and trade-offs of the HFC substitution when considering phase-down schedules.
While the study focused on pure fluids, some blends were considered, involving a compromise: low GWP blends present an increased flammability, and conversely, less flammable blends present a higher GWP.
A huge number of unitary air conditioning equipment is installed worldwide, and their penetration is going to increase, especially in developing countries. R-410A is presently the dominant refrigerant in this application, with HCFC-22 still allowed in developing countries. However, due to its GWP of 2,088, R-410a will eventually have to be phased down, in line with the EU F-Gas Regulation and the Kigali amendment to the Montreal Protocol, so that substitutes must be implemented.