2,3,3,3-Tetrafluoropropene, or HFO-1234yf, is a hydrofluoroolefin with the formula CH2=CFCF3. It has been proposed as a replacement for R-134a as a refrigerant in automobile air conditioners.

HFO-1234yf is the first in a new class of refrigerants acquiring a global warming potential (GWP) rating 335 times less than that of R-134a and an atmospheric lifetime of about 400 times shorter.

HFO-1234yf, which has a 100 year GWP of 4, can be used as a "near drop-in replacement" for R-134a. HFO-1234yf has the lowest switching cost for automakers among the currently proposed alternatives, although the initial cost of the product is much higher than that of R-134a. The product could be handled in repair shops in the same way as R-134a, although it would require different, specialized equipment to perform the service. One of the reasons for that is the mild flammability of HFO-1234yf. Another issue affecting the compatibility between HFO-1234yf and R-134a-based systems is the choice of lubricating oil. The current lubrication oil is showing signs of damage to plastic, aluminium and issues with health, mouth dryness, rash, sore throat among others affects.       

Facts about HFO-1234yf, courtesy of its creators at Honeywell, comparing it to the only other popular green alternative, CO2.

1.    HFO-1234yf has the lowest Life-Cycle Climate Performance compared to CO2 and HFC-134a, regardless of region. Calculations were made based on model tests for climates in Phoenix, Arizona; Frankfurt, Germany; Tokyo, Japan; and Athens, Greece. Results were presented by the JAMA-JAPIA consortium at the 2008 SAE Alternative Refrigerant Systems Symposium in Phoenix, Arizona in June 2008.

2.    CO2 air conditioning systems have higher indirect greenhouse gas emissions than HFO-1234yf systems because they are less efficient. This lower efficiency results in higher fuel consumption for the vehicle which creates more GHG tail pipe emissions.

3.    Unlike HFCs and CFCs which take generations to decompose, HFO-1234yf does not accumulate in the atmosphere creating long-term problems. A short atmospheric lifetime means less impact on the environment. HFO-1234yf is highly stable in the compressor system, and if it escapes, will not persist in the environment.

4.    Current car designs use low-pressure air conditioning systems. HFO-1234yf is compatible with these low-pressure systems and can be used as a replacement for HFC-134a with minimal reengineering of automotive systems. Because HFO-1234yf is a near drop-in, car manufacturers can more quickly and cost-effectively comply with the new EU regulations.

5.    CO2 requires a re-designed high-pressure AC system. As with many new designs, there are questions about reliability in the field due to the unproven technology.

6.    HFO-1234yf is as effective as HFC-134a, and offers comparable cooling performance in warm and hot climates.

7.    Energy efficiency of CO2 declines as temperatures increase which means greater fuel consumption to generate the power to operate the compressor, increasing tailpipe emissions and environmental impact. Therefore, CO2 is not a global solution.

8.    CO2 requires a new high-pressure air conditioning system and cannot be used as a direct replacement for HFC-134a. In order to adopt CO2 as a refrigerant, automakers would need to completely redesign their air conditioning systems.

9.    Thorough independent tests, including documented tests performed by the Society of Automotive Engineers and automakers using real-world conditions, have demonstrated that 1234yf is safe to use in mobile air conditioning.

10.Due to the extremely high pressure and harmful health effects of CO2, the air conditioning system must be carefully designed to minimize the risk to passengers and service people.

HFO-1234yf—Environmental Benefits

DuPont believes HFO-1234yf will make an important contribution to a reduced environmental footprint for automobiles. If adopted in all new cars sold in the EU, North America, and Japan, every year those cars would have reduced emissions equivalent to using 2.3 to 4.9 billion fewer liters of fuel or driving 24 to 52 billion fewer kilometers. When comparing HFO-1234yf and CO2 as an automotive refrigerant, HFO-1234yf has very distinct benefits with regard to fuel efficiency and overall sustainability. CO2 would require a much larger, heavier air conditioning system than what is used in most cars today, which is contrary to the trend toward smaller, more fuel-efficient, sustainable cars. Lifecycle climate performance evaluations have also concluded that CO2 is not as efficient as HFO-1234yf in warmer climates, and would therefore contribute considerably more overall to total greenhouse gas emissions, and even more so as the projected vehicle sales volume in warmer, developing countries such as India and China continues to increase.

European Union and Mobile Air Conditioning (MAC)

The European Union has been a global leader in setting sustainability standards, including actions to fight climate change.  In 2006, the EU adopted the Mobile Air Conditioning (MAC) Directive that would reduce the climate impact of air conditioning in cars sold in the EU.  The MAC Directive requires an automotive refrigerant with a GWP of less than 150 for use in new model vehicle platforms.  This requirement is scheduled to go into force on January 1, 2013. In a 2007 presentation on the MAC Directive, a representative of the European Commission referred to climate change as “the greatest environmental and economic challenge facing humanity.”  Action on climate change is a priority of the EU’s Sustainable Development Strategy, and the MAC Directive is a central program in this effort.  While compliance with this regulation involves some additional cost to automakers, failure to maintain the MAC Directive would come at a much higher cost to the environment and society as a whole.

Cost Benefits

Cost benefits of HFO-1234yf reflect the fact that HFO-1234yf is a near drop-in replacement forR-134a. Adopting HFO-1234yf would require automakers to make minor system modifications compared to R-134a, but they would continue to use a similar air conditioning system design. In contrast, adopting CO2 would require a totally different system design, and this would involve significant additional costs that would likely be passed along to consumers. While auto repair shops would need to invest in new equipment to service cars with HFO-1234yf, we expect that the service industry will gradually implement these changes. The new equipment and servicing itself will be quite similar to what service shops currently use with HFC-134a.  However, service shops are not presently prepared to service CO2 systems, and infrastructure would need to be developed for handling/servicing CO2 systems.  Most importantly, CO2 operates at a much higher pressure, so safety and use standards would need to be well communicated to service shop owners.

Global Evaluations—Flammability

HFO-1234yf has properties similar to HFC-134a, but is mildly flammable. Flammability was thoroughly considered in the multiple rigorous evaluations by industry stakeholders and by independent globally recognized third-party laboratories. According to an SAE International presentation, “Flammability testing at Hughes, Ineris, and Exponent labs have demonstrated the difficulty in igniting the HFO-1234yf refrigerant under the most severe testing conditions.”  The presentation also states that “Risk assessment indicates a very low probability that an accidental release of refrigerant creates a sufficient concentration at the same time and location as a sufficient ignition source.”   The risk assessments concluded that HFO-1234yf can be safely used in mobile air-conditioning. Safety standards have been published and address safe use guidelines. Automobiles have in the engine compartment a number of materials that are significantly more flammable  than HFO-1234yf, including brake and transmission fluids, coolant, lubricants, and gasoline. Automakers developed ways to enable them to safely use these materials, just as they have established recommendations to enable the safe use of HFO-1234yf.

Performance and Safety Testing

HFO-1234yf performed extremely well in an extensive industry evaluation of the safety and performance of low GWP candidates for automotive refrigeration. A Cooperative Research Program, conducted by SAE International, was sponsored by 33 major automotive manufacturers and Tier One suppliers, based in Europe, Asia and the U.S. As part of the SAE Program, research was conducted at international laboratories, including independent third-party facilities, to investigate safety and risk, including flammability and toxicity, efficiency and performance, and material compatibility. In November 2009, the sponsors of the SAE CRP1234 concluded that “HFO-1234yf can be used as the global replacement refrigerant in future mobile air conditioning systems and it can be safely accommodated through established industry standards and practices for vehicle design, engineering, manufacturing, and service.” An SAE presentation on this program stated that “Extensive testing at third-party facilities did not identify significant risks for the use of HFO-1234yf in mobile air-conditioning systems.”