R-1234yf continues to demonstrate safety as a replacement refrigerant for R-134a, which must be phased out in the European Union starting Jan. 1, 2011. The refrigerant, close to a drop-in replacement, now has passed the latest of its toxicity tests, on two generations of rats, an SAE World Congress session was told by Mark W. Spatz, Global Leader of Refrigerant Technology at Honeywell.
The refrigerant also has passed new flammability risk evaluations, he said; even in a worst-case leak scenario, the passenger compartment would not have a flammable concentration of R-1234yf. The tests were performed in two passenger compartments: one a small car with 1.34 m3 (47.3 ft3) of space and one a midsize car with 2.23 m3 (78.8 ft3).
With the HVAC systems in recirculation mode (virtually no outside air to cause air dilution), a 0.5-mm (0.02-in) evaporator leak, equal to a major corrosion failure, was induced in both vehicles, which were equipped to collect air samples throughout the cabins. The samples were analyzed by high-accuracy gas chromatography to measure refrigerant concentrations. In neither case did the concentration even touch the 6% lower flammability level, hitting a peak of approximately 5.6% in the small car and only 4% in the midsize.
The leading alternative, R-744 (carbon dioxide used as a refrigerant), raises health/safety concerns, as above a 3% level can affect driver performance. Similar tests and measurements were performed on a small and midsize car with an induced 0.5-mm evaporator leak from an R-744 system in recirculation mode. In both cases, the R-744 concentration was high, above 8% even in the midsize car, not including background contamination from passengers.
Spatz addressed questions raised by some European environmentalists regarding hazardous residue from materials released in a vehicle fire. He pointed out that R-134a releases the same substances as R-1234yf: "R-134a has been in use for 15 years and there are no documented cases where combustion of automotive refrigerants has resulted in injury or death."
Formal announcements of R-1234yf installation by OEMs are still forthcoming. Despite the tight time frame to January 2011, Spatz believes it still is possible for refrigerant producers to have some capacity available for the EU deadline for "new type" vehicles specified in the regulations.
R-1234yf installations are likely to start in Europe because of the regulatory requirements, so there will be a need to produce them on the same assembly lines as R-134a systems continuing in production. Visteon HVAC technical fellow Dr. John Meyer told the SAE World Congress session that it would be feasible, with the likely procedures determined by how the R-134a systems were configured.
A characteristic of R-1234yf is that it produces more vapor than R-134a, he noted. To increase the amount of liquid refrigerant for efficient cooling, he said that an internal heat exchanger (IHX) is a logical addition (using suction-side gas to further cool and condense the high-pressure-side refrigerant). If an IHX also were used with an R-134a system, although likely to be a different unit internally, the packaging issue would already be solved, he said.
If an R-134a system did not have an IHX, the vehicle manufacturer simply could replace both liquid and suction lines with an R-1234yf module that included both lines and an IHX, Meyer said. He pointed out that each refrigerant requires specific service valve fittings, and it would simplify vehicle assembly by putting the fittings on the IHX.
R-1234yf requires a relatively large diameter suction line, said Meyer, noting that some R-134a systems already have one. If a system does not, a specific R-1234yf system could need one, and the packaging would have to be considered, he said.
The pressure-temperature curve of the two refrigerants is very close, but there are differences that could require specific software and component calibrations for control. However, he told the meeting, many new systems have electronically controlled compressors that use evaporator air temperature regulation based on passenger compartment cooling load for the control strategy, not system pressures. Therefore, they could use exactly the same software for this purpose.
Meyer said it is likely that the high-efficiency, high-strength evaporator with increased corrosion resistance, anticipated for R-1234yf, might also be used for R-134a systems to simplify manufacturing, if the cost penalty were reasonable.