The US EPA has proposed to list HFO-1234yf as an acceptable refrigerant in motor vehicle air conditioning systems under use conditions that will be very costly and technically difficult to meet. The Agency is accepting comments on the elements of proposal, including on TFA deposition from HFO-1234yf that at certain levels is toxic. NEW: The EPA has extended the comment period on the proposed rule through 1 February 2010.
The US Environmental Protection Agency (EPA) has proposed to list HFO-1234yf as an acceptable alternative with use conditions for CFC-12 in motor vehicle air conditioning (MVAC) systems. Auto manufacturers that opt to adopt this refrigerant will be required to mitigate risks of fire associated with this refrigerant in the event of an accidental release during servicing or vehicle operation. The specific use conditions included in the proposal not only are very costly but also technically very difficult to meet, with HFO–1234yf MVAC system manufacturers required for example to incorporate engineering strategies and devices so that leaks into the engine compartment do not result in refrigerant concentrations above the lower flammability limit (LFL) of 6.2% v/v for any period of time.
The required features significantly increase the cost of the HFO-1234yf MVAC compared to R744 systems and come in addition to the high cost of the HFO itself, which will cost approximately 10 times more than HFC-134a. Moreover, several unanswered questions remain with regards to the safety of the refrigerant, indicating that HFC-1234yf is not a sustainable solution and from its outset poses many risks in terms of both safety and cost.
The use conditions proposed by the EPA
The proposed use conditions under which HFO-1234yf if approved will be allowed to be used in new MVAC systems in passenger cars and trucks include:
No leaks into the passenger compartment that result in HFO concentrations above 6.2% v/v for more than 15 seconds: Accordingly, HFO–1234yf MVAC systems must incorporate engineering strategies and/ or devices so that leaks into the passenger compartment do not result in HFO–1234yf concentrations at or above the lower flammability limit (LFL) of 6.2% v/v for more than 15 seconds.
No leaks into the engine compartment or vehicle electric power source storage areas that result in HFO concentrations above 6.2% v/v for any period of time: Accordingly, HFO–1234yf MVAC systems must incorporate engineering strategies and/ or devices so that leaks into the engine compartment or vehicle electric power source storage areas do not result in HFO–1234yf concentrations at or above the LFL of 6.2% v/v for any period of time.
Requirement for HFO MVAC systems to incorporate protective devices, isolation and/or ventilation techniques for hybrid/electric vehicles: In recognition of the fact that hybrid and electric vehicle sales are on the rise and that the electric power source in these type of vehicles is an additional ignition source, additional requirement are called for. More specifically, HFO–1234yf MVAC systems must incorporate protective devices, isolation and/or ventilation techniques in areas where processes, procedures or upset conditions such as leaks have the potential to generate HFO concentrations at or above 6.2% v/v in proximity to hybrid/electric vehicle electric power sources and exhaust manifold surfaces.
Requirement for a label indicating HFO flammability: HFO–1234yf MVAC systems must include a detailed label identifying the refrigerant and that the refrigerant is flammable.
Concerns and further investigations needed
TFA: According to the proposed rule, one concern about HFO-1234yf is trifluoroacetic acid (TFA) that is produced from atmospheric oxidation of HFO. Although the EPA believes that sufficient technical information on the TFA deposition from HFO-1234yf is available for the basis of its proposal, the Agency welcomes additional comments on the issue.
A related issue that would need further investigation is the case of HFO leaks at locations that experience weather inversion conditions (Los Angeles, Athens…) that result in the formation of a low ceiling that can trap smoke and other pollution for a several number of consecutive days. In such locations and given the very short atmospheric lifetime of HFO (only 11 days, as opposed to 100 years for CFC-12 and 14 years for HFC-134a), the atmospheric oxidation of HFO that produces TFA will not happen high up in the stratosphere, but at much lower levels of the atmosphere having, therefore, a much more direct impact on human health and the environment. Given the increasing number of locations experiencing weather inversion, there is an imperative need to scientifically investigate this issue.
Enabling smog creation: What is more, HFO enables the creation of smog also during inversion weather situations, as it is a Volatile Organic Compound (VOC). A chemical reaction between oxides of nitrogen (NOx) and VOCs in the presence of sunlight results in the creation of Ozone (O
3), a primary constituent of smog. Therefore, when released into the atmosphere, HFO first facilitates the creation of smog also during inversion weather situations and after 11 days decomposes in TFA with detrimental impacts on humans when weather inversion situations have actually occurred.
Formation of highly toxic HF: Another issue to be further investigated is the formation of highly toxic HF not only when 1234yf is burning but also at temperatures below the auto-ignition point of 405degC. Investigating the conditions under which HF is formed is crucial, as its concentration in a passenger compartment poses a serious life threat to passengers.
Lower flammability limit: The proposal sets the lower flammability limit (LFL) for HFO at the level of 6.2%v/v. Given the presence of hydrocarbons in the engine compartment, further investigation is needed with regards to whether this value should be lowered to 4%.
HFO could only be a short-term solution
All the unanswered questions with regards to HFO - such as flammability, HF issue, the formation of TFA and the fact that it enables the creation of smog - cast serious doubts on whether HFO could be a long-term solution, while if selected the industry has pretty good chances will to carry the cost of doing the job twice in a short period of time.
Next steps and important dates
The EPA initially accepted comments on the proposed rule until 18 December 2009.
However, after receiving a request for an extension to the 18 December 2009 comment deadline, the EPA has reopened the comment period through 1 February 2010.
