R-1234yf to be used in MAC systems, despite safety concerns

The most significant limitation is the complete ban of MACs designed to use fluorinated greenhouse gases with a global warming potential (GWP) higher than 150. This limit has been set for any MACs fitted to vehicles type-approved on 1 January 2011 or later [1]. Although car manufacturers have prepared themselves to the new ban by introducing a number of their new platforms prior to the deadline, this ban has definitely forced development of new MACs using low GWP refrigerants to comply with legislation. Carbon dioxide, propane, butane, R152a and HFO1234yf has seen as potential candidates to substitute R134a. Finally, HFO1234yf has been chosen due to its properties, which allow substituting R134a with minimal conversion of existing MACs.

Due to insufficient supply of R1234yf the initial deadline for banning high GWP refrigerant systems has been postponed twice. The problem with supply is reported as solved [2] and starting from 1 January 2013 the ban is finally in place.

Less harmful for the environment, potentially dangerous for humans

Although R1234yf is nothing new and the substance is already known for more than 50 years, it has been just few years back when its properties have started to be carefully investigated. Since 2007, when Honeywell and DuPont introduced R1234yf to the automotive industry, the substance has undergone a lot of testing for its properties, effectiveness and safety. In comparison with R134a – refrigerant mostly used in MACs today - R1234yf has very similar properties and characteristics, but much lower GWP of 4 (compare to 1430 of R134a).

Although R1234yf is less harmful to the environment than the currently used refrigerant, it is potentially dangerous as it is flammable and ignites at 405 ^º C [3]. When flammable – it is also emits hydrogen fluoride - dangerous substance for the human health. Information about the possibility of spontaneous combustion and possible formation hydrofluoric acid is alarming and made a number of parties to make tests on its safety.

SAE International - International Society of Automotive Engineers association of about 133,000 engineers and technicians - tested the substance in a special research program, which lasted five years. The conclusion was that the refrigerant R1234yf can be used safely in vehicles that are designed for the new refrigerant. This conclusion triggered active implementation of R1234yf in wide variety of MACs, including those installed in new Cadillac XTS, Toyota Prius+, Mercedes B-class and others.

Daimler AG - the concern behind Mercedes, Maybach, Smart, and many others brands - has recently raised new safety concerns with the usage of R1234yf by following “real-life test scenario” which corresponds to a serious head-on collision in which the refrigerant line is severed [4]. The reproducible results demonstrated that refrigerant, which is otherwise difficult to ignite under laboratory conditions, can indeed prove to be flammable in a hot engine compartment (see Figure 1). In contrast, similar test showed no risks associated with the use of R134a (which is, however, legally no longer an option to be used in new models of vehicles). Daimler reacted to its own finding by discontinuing using R1234yf in its vehicles [4] and by recalling 432 potentially affected Mercedes-Benz SL-Class vehicles to replace R-1234yf with R-134a [5].

R1234yf flammability is nothing new

DuPont – a company behind the R1234yf manufacturing denies the risks associated with R1234yf flammability claiming that Daimler test “does not represent new information”. The company refers to a number of organizations, who earlier expressed confidence in R-1234yf as substance to be safely used as refrigerant in MACs [6]. In face of new findings by Daimler, SAE International has decided to perform an updated engineering analysis based on the most recent information [7].

Full details of the Daimler simulation have not been made public yet, bringing suspicions on how the tests were conducted and what conditions were represented. Hence, some parties expressed doubts on reasons Daimler has behind publishing the tests close to MAC Directive ban’s introduction date, when the safety concerns of R1234yf has been known for years [8]. Back in 2010 German Environment Agency has already warned carmakers against R1234yf which was named as an “unsafe temporary solution” risking the life of drivers and rescue personnel. It was shown that low volumes of hydrocarbons (which can be easily present in the vehicle engine compartment) decrease required autoignition concentration of R1234yf from 6.2 (pure refrigerant) to as low as 0.5-1.3% [9].

CO₂ as an alternative

Given that Daimler denied usage of R1234yf by now – the most viable alternative for them to use is CO₂. It has a number of advantages: the substance is also climate-friendly, non-flammable, widely available and otherwise relatively harmless. The main disadvantage is an increased cost of components of the CO₂ MAC system and performance issues in warm climates. There is also safety concern associated with CO₂ in the event of its leak into the passenger area.  

VW and BMW has been expressed interest in CO₂ as a feasible, safe long-term refrigerant option. However, Daimler itself has not announced any decision on this matter, thus considering any options. Recognizing interest to CO₂, SAE International has announced plans to fully evaluate CO₂ option in MAC [10].

Given that MAC Directive requirements are already in action, the European Commission will make efforts to ensure the Member States comply on it, as it was confirmed in recent EC declaration [11]. In this renewed “refrigerant war”, CO₂ and R1234yf both have own advantages and disadvantages. Anyway, CO₂ has been given its second chance to become low GWP refrigerant choice for MACs of the future. However, by now R1234yf remains the only viable option as already available to be installed in new vehicles, bringing optimism to environmentalists and some fear to the drivers.

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