Electric Vehicles (EVs) have rapidly grown as a means for clean mobility, as they zero down tail pipe emission of greenhouse gases. Additionally, greenhouse gases such as Hydro-Fluoro-Carbon (HFCs) based refrigerants used in Mobile Air-Conditioning (MAC) are under global scrutiny for their high Global Warming Potential (GWP). To prevent earth environment to pass the climate tipping point that will be irreversible within human capacity, actions such as rapid phase down of high GWP rated HFCs under Kigali Amendment to Montreal Protocol are enacted. India being amongst signatory nations is now working to fast track phase-down use of high GWP refrigerant and transit to low GWP refrigerant options. Nearly half of national HFCs use and emissions are for manufacture and service MAC. Vehicle OEMs supplying to markets in developing countries (e.g. European nation and non-Article 5 Parties) have already phased out HFC-134a (GWP=1400) through alternate refrigerant solutions.
The work presented here discusses a novel methodology to use sustainable low GWP refrigerant-based MACs in EVs. The existing MAC system operates through dual DX (Direct expansion) system cooling loop, one for cabin cooling requirement and another to ensure optimum cell temperature of high voltage battery. The refrigerant HFC-134a is not sustainable. To meet global commitments, alternative low GWP options such as R152a (GWP=124) can be considered. The superior thermal properties and low direct cost of R152a, makes it a suitable alternative to HFC-134a. The work also discusses development of intelligently controlled Secondary Loop-Mobile Air Conditioning (SL-MAC) system to address operational constraint with mildly flammable nature of R152a. In the proposed architecture, R152a is use as primary medium to produce refrigeration effect to cool the coolant by deploying chiller unit. The cooled coolant is then circulated in secondary loop comprising of two parallel cooling loops, to extract heat from cabin and HV battery systems. Suitable decision matrices have been consider to design the SLMAC configuration and components involved with it. Cooling performance have been compared basis the transition from DX system with HFC-134a to SLMAC system with R152a refrigerant, together with gap analysis and proposed solutions for bridging performance gaps.