Ford Motor Company’s research has identified propane-based full-secondary loop heat pumps as a more efficient solution for battery electric vehicles (BEVs) than traditional direct expansion (DX) systems. This system will enhance HVAC performance and vehicle charging efficiency.

The full-secondary loop uses a closed refrigerant circuit to transfer heat to a secondary fluid, reducing refrigerant charge by 25% and system size by 20%. Ford addressed the thermal resistance challenge by introducing vapor injection technology, improving overall efficiency.

Tests by Ford and DENSO showed that an R1234yf-based full-secondary loop heat pump with vapor injection is 20% more efficient than a DX system using the same refrigerant. Switching from R1234yf to R290 further improved efficiency—by 5% in heating mode and 29% in cooling mode—while reducing compressor speed. R290 also improves battery temperature control for fast charging and has an ultra-low global warming potential (GWP).

However, R290’s flammability presents safety challenges. Ford is exploring solutions such as leak detection, limiting refrigerant charge to 150–200g, and using ventilation to disperse leaked refrigerant. The company plans to propose R290 use to the U.S. Environmental Protection Agency (EPA) and begin further testing in 2025.

The ATMO MAC Summit 2024 × TU Berlin, where these findings were presented, focused on mobile air-conditioning and heat pump systems. Ford’s representative emphasized the need for industry collaboration to develop safety standards and operational guidelines for R290-based HVAC systems in BEVs.