Automotive air conditioning: which refrigerant for electric cars?

Different alternatives exist today to replace R134a in automotive air conditioning systems. Update on possible solutions for electric cars. 

Optimizing the thermal comfort of the passengers of an electric car requires meeting certain challenges: indeed, with regard to heating, electric cars cannot use the heat emitted by the engine, as opposed to internal combustion vehicles. 
As for air conditioning, two systems are currently marketed: 

  • A system using conventional refrigeration cycles. The refrigerants used are now mainly CO2 and R1234yf;
  • A heat pump system. These systems can use CO2, R1234yf. 

The advantage of the second system is that a reversible heat pump can meet both heating and air conditioning needs. 
The most common refrigerant is R1234yf, but studies have shown that the capacity of a heat pump running on this refrigerant is reduced by around 40% when the ambient temperature drops from 0 to -10°C, which is a major major in cold climates. 
ASHRAE has just approved a new refrigerant, composed of R1234yf and HFO R1132(E), the latter also recently approved. 
This new refrigerant, R474A, has been classified in the A2L (lower flammability) category. It is announced to perform better in cold climates than R1234yf alone. Daikin holds the patents allowing the production of R1132(E) and therefore R474A. Its GWP is less than 1. The first tests show that it could be effective down to temperatures of -30°C. 
CO2 is also an interesting alternative. It is more efficient than R134a, especially in cold climates, as demonstrated by a study published in 2019 and summarized in this news
An article by the IJR published in 2021 even showed the strong potential of CO2 to replace the HFC traditionally used in mobile air conditioning systems, R134a.