R-1234yf may be the choice of most car manufacturers worldwide as the new low-global-warming (LGW) A/C refrigerant to replace R-134a, but as many in the industry have learned, there are several German automakers who have had second thoughts. They have reactivated a project to use R-744 (carbon dioxide as a refrigerant) instead, and development assignments to members were distributed by VDA (German association of the automotive industry). The leadership assignments went to vehicle manufacturers; Tier 1 suppliers also are participating.
VDA President Matthias Wissmann said his organization's policy is that the European Commission (EC), the regulatory body, should leave openings for both R-1234yf, a mildly flammable chemical, and R-744, which is nonflammable (in fact, a fire-extinguishing agent), and give German manufacturers who opposed R-1234yf extra time to develop R-744 systems. Projected introduction date for R-744 is 2017, although earlier installations (by 2016) seem possible.
VDA now will be working with SAE International's Interior Climate Control Standards Committee (ICCSC) to harmonize applicable documents so R-744 also will satisfy U.S. regulations. ICCSC had workgroups developing R-744 standards until 2010, when VDA announced it was mothballing the R-744 effort and would use R-1234yf. There was no great enthusiasm among several members for this move, but VDA recognized that going it alone with R-744 would be costly and affect worldwide service of a system. Daimler, Volkswagen/Audi (and Porsche), and BMW since have changed their minds.
R-744 operates at up to 10-15 times the pressures of R-1234yf or R-134a, and poses cooling efficiency challenges at higher ambient temperatures. DuPont and Honeywell, joint-venture producers of R-1234yf, have released numerous studies to demonstrate its safety (http://articles.sae.org/11807, http://articles.sae.org/12574/).
Both R-1234yf and R-744 can be used legally in the U.S. The refrigerants are on the EPA’s SNAP (Significant New Alternatives Policy) program list as replacements for installation in mobile air-conditioning, with "use conditions" to mitigate safety issues. In both cases an issue is the integrity of the under-dash evaporator to prevent a major leak from a sudden burst into the passenger cabin, although the safety concerns are different. With R-1234yf, it's the mild flammability; for R-744, it's that carbon dioxide is an asphyxiant and EPA has set a short-term exposure limit (15 min) for the passenger cabin of 3% and a peak of 4% for the passenger breathing zone.
SAE standards in development
The SAE committee will focus on reviewing and, where necessary, completing these standards for R-744 mobile A/C systems:
J2683—refrigerant purity and container requirements
J2769—service hoses, fittings, and couplers
J2771—refrigerant removal and recharging equipment
J2772—measurement of refrigerant concentration in the cabin under leakage conditions
J2774—minimum performance for electronic leak detectors
J2775—minimum requirements for ultraviolet (trace dye) leak detection
J2842—design criteria for evaporators (covers both R-1234yf and R-744; already applied to R-1234yf)
J2845—technician training for service and containment of refrigerants (already applied to R-1234yf).
U.S. mobile A/C also must meet J639, which sets safety standards, including a flame symbol label to warn of flammability for R-1234yf. Because R-744 is not flammable, cars so equipped would not be required to have the warning symbol and notice on the underhood J639 label.
VDA has been working on R-744 standards with the German Institute for Standardization (DIN), which uses a three-year time frame vs. SAE's five-year period for review. SAE ICCSC standards for A/C generally are performance-related, whereas DIN’s—like those of the American National Standards Institute (ANSI)—are more construction-related.
The DIN specifications are expected to be ready by June, the ICCSC was told by Dr. Ulf Bunge, R&D engineer at Volkswagen. They are being translated into English, and Bunge said ICCSC members would have the opportunity to provide input during a commenting period this spring.
The R-744 project, which began at Daimler in the early 1990s and was expanded through VDA to other German automakers and their suppliers, was halted in 2010. That's when it was apparent that most other automakers preferred R-1234yf, a LGW refrigerant with similar pressure-temperature characteristics and other operating similarities to R-134a. R-1234yf's global warming potential number (GWN) is now specified at as low as one, the same as carbon dioxide. European regulations set a GWN limit of 150, and R-134a is listed at 1430, so its phase-out was mandated by the EC regulators. Additionally, EPA has awarded Corporate Average Fuel Economy (CAFE) credits for low GWN refrigerant in fuel-economy regulations, so the issue is important here, too.
Daimler flammability test
In September 2012, Daimler announced results of a controversial test that it said produced flammability results that led it to discontinue use of R-1234yf and retrofit the few cars already equipped back to R-134a. An SAE Cooperative Research Group (CRG) reviewed the data and concluded R-1234yf was safe, as did the EC regulators, among others.
However, Daimler, Volkswagen/Audi/Porsche, and BMW have indicated they prefer only R-134a until the R-744 systems are ready. The applicability of the EC regulations to a new Daimler A-body, B-body, CLA, and SL cars, which were to be enforced at the start of 2013, had been tied up in a dispute between Germany and France, which initially halted the sales. But a French high court overturned that rule and sales resumed. It appears that new interpretations of the R-134a phase-out rules will enable automakers to continue with R-134a to the start of 2017.
Both R-1234yf and R-744 involve measurably higher costs than the R-134a systems. With R-1234yf, the price premium is primarily the cost of the refrigerant, which at an estimated $40-45 lb ($100 kg) for an OE and up to $124 lb ($273 kg) for the aftermarket, is perhaps 10-15 times that of R-134a. With an upgraded evaporator and an additional heat exchanger to improve efficiency, the system is about $100 more costly per car.
Although R-744 itself is very inexpensive, the components and sealing requirements for the high-pressure refrigerant were estimated at $500 more per car in 2010. However, cost-reduction efforts and further development have been under way, with the expectation of a far smaller price premium to the cost of an R-744 system—but still perhaps $150 above the cost of an R-134a system.
Also under consideration is R-445A, a three-part blend (85% R-1234ze, 9% R-134a, and 6% R-744) with a GWN of about 130. It is being developed by Mexichem in conjunction with an SAE CRG, also with leadership from Renault and Jaguar Land Rover. ICCSC is developing a suite of standards for R-445A.