Ford and Denso explore hydrocarbon refrigerant for EV thermal management

Ford announced at the recent ATMOsphere MAC Summit in Berlin that it aims to tackle the challenge of electric vehicle thermal management with the use of R290-based full secondary loop heat pumps. 

Developed with Denso, the technology uses propane as a refrigerant and is said to surpass traditional direct expansion systems by demonstrating significant efficiency improvements, resulting in a greater battery range.

Direct expansion systems circulate refrigerant directly through the HVAC system to heat or cool the cabin, but they often rely on a high-voltage heater in cold weather, impacting efficiency and complicating refrigerant management. Additionally, these systems require an extra loop for the vehicle’s battery and drive system.

Full secondary loop systems, on the other hand, use refrigerant purely for transferring heat with a secondary fluid, which then regulates both cabin and battery temperatures.

This design reduces the refrigerant charge by 25 per cent and the system’s footprint by 20 per cent, though it faces challenges with thermal resistance of the secondary loop.

Ford product development engineer Angelo Patti shared the ATMOsphere MAC stage with Denso senior technical manager of advanced systems R&D Werner Hünemörder, a key collaborator in developing propane-based full-secondary loop heat pumps for Ford’s upcoming electric vehicles.

Their testing demonstrated that their R1234yf-based full secondary loop heat pump with a vapour injector achieved 20 per cent greater efficiency than traditional direct expansion systems in both heating and cooling modes.

This significant improvement can be attributed in part to the elimination of the high-voltage heater.

Further development revealed an even greater potential when R1234yf was switched to propane refrigerant (R290) in full secondary loop systems, resulting in a five per cent increase in heating efficiency and a remarkable 29 per cent improvement in cooling efficiency owing to the hydrocarbon refrigerant’s thermodynamic properties.

“R290 is the best global option for BEVs if safety is addressed,” said Patti.

“Refrigerants currently in use are not ideal from a thermal perspective,” he said, adding that “typically, their boiling points are too high to suit the heat pump temperature range”.

“In contrast, R290 has characteristics that are much closer to the ideal target.”

The shift towards R290 is being driven by a combination of factors, including the European Union’s revised F-gas Regulation, along with proposed restrictions on harmful substances such as per- and polyfluoroalkyl substances (PFAS), in a broader effort to encourage the adoption of refrigerants with lower global warming potential (GWP).

Ford and Denso engineers saw R290’s potential in this respect due to its ultra-low GWP and the notable absence of harmful substances, including PFAS, making it a compelling choice in the ongoing initiative to reduce greenhouse gas emissions.

However, R290’s flammability presents significant safety challenges, which Ford is addressing through a comprehensive research program focused on mitigating leak risks by limiting refrigerant charge to below 150-200 grams, deploying leak detection systems, and segmenting refrigerant modules to contain potential leaks.  

Despite the U.S. Environmental Protection Agency (EPA) previously advising against propane in mobile air conditioning systems, Ford and Denso are collaborating with regulatory bodies to establish safety standards for R290 in automotive applications.

They aim to gain approval for R290 in automotive cooling systems, initiating bench testing and vehicle development by 2025. Their goal is to establish industry-wide standards for the safe use of propane in mobile systems, advocating it as the “best global option” for EV thermal management.