US EPA determines final use conditions for R744 in new motor vehicle AC

By Alexandra Maratou, Jun 04, 2012, 13:42 3 minute reading

Under the Significant New Alternatives Policy (SNAP) programme, the US Environmental Protection Agency (EPA) has published a final rule listing R744 as an acceptable substitute for ozone-depleting substances in new motor vehicle air conditioning (MVAC) systems subject to use conditions for its safe use. The rule modifies the Agency’s previous determination that listed CO2 as an acceptable substitute with no use restrictions.

The 2012 final rule, follows an initial September 2006 Notice of Proposed Rulemaking and subsequent notice of data availability and public comment request by the US EPA.

Under scope: New motor vehicle air conditioning systems

The rule does not apply to the use of carbon dioxide (CO2, R744) as a conversion or retrofit for existing MVAC systems. Similarly, it does not apply to the use of CO2 in the air conditioning or refrigeration systems of buses, trains, rail or subway cars, or appliances such as refrigerated transport.

Use conditions require compressor cut-off switch and unique fittings

With this action, CO2 is removed from the list of acceptable substitutes for MVAC systems and is instead listed as acceptable subject to the following use conditions:

1. CO2 concentration limits: Engineering strategies and/or mitigation devices shall be incorporated such that in the event of refrigerant leaks the resulting CO2 concentrations do not exceed the short term exposure level (STEL) of 3% or 30,000 ppm averaged over 15 minutes in the passenger free space, and the ceiling limit of 4% or 40,000 ppm in the passenger breathing zone. To help ensure that use condition regarding CO2 concentration limits, the has included several recommendations in the decision, such as the use of specific industry standards, or additional training for service technicians that will service CO2 MVAC systems.

2. Record keeping: Vehicle manufacturers must keep records of the tests performed for a minimum period of three years demonstrating that CO2 refrigerant levels do not exceed the STEL of 3% averaged over 15 minutes in the passenger free space, and the ceiling limit of 4% in the breathing zone.

3. High-pressure system warning label /compressor cut-off switch /unique fittings: The use of CO2 in MVAC systems must adhere to the standard conditions identified in SAE7 Standard J639 (2011 version) including:
  • Installation of a high-pressure system warning label
  • Installation of a compressor cut-off switch; and
  • Use of unique fittings with:
                 i. Outside diameter of 16.6 +0/-0.2 mm (0.6535 +0/-0.0078 inches) for the MVAC low-side service port,
                ii. Outside diameter of 18.1 +0/-0.2 mm (0.7126 +0/-0.0078 inches) for the MVAC high-side service port,
             iii. Outside diameter of 20.955 +0/-0.127 mm (0.825 +0/-0.005 inches) and right-hand thread direction for CO2 refrigerant service containers

Rationale for swift from “acceptable” to “acceptable under use conditions”

Following the 1994 initial SNAP rulemaking listing CO2 acceptable with no use restrictions, the EPA issued rules regarding the acceptability of other refrigerants for use in new MVAC systems requiring unique fittings. Although requirements did not apply to CO2, the Agency reserved the right to determine that additional conditions or restrictions should be added or removed for any decision made under SNAP through future rulemaking.

More recently, the EPA was made aware of potential interest in using CO2 in MVAC systems and of technology being developed, but also of concerns regarding health risks to exposure of CO2 from leaks into the passenger compartment. As a result, in September 2006, EPA issued a Notice of Proposed Rulemaking proposing to find CO2 acceptable in new MVAC systems subject to the use conditions.

Background: the four possible decision categories for substitutes under SNAP

The Agency has identified four possible decision categories for substitutes:
  • acceptable
  • acceptable subject to use conditions
  • acceptable subject to narrowed use limits
  • unacceptable

Use conditions and narrowed use limits are both considered “use restrictions”. Substitutes that are deemed acceptable with no use restrictions can be used for all applications within the relevant end-uses within the sector. Substitutes that are acceptable subject to use restrictions may be used only in accordance with those restrictions.

Besides R744, other substitutes that EPA has found acceptable subject to use conditions for use in new MVAC systems include HFC152a and HFC1234yf. 


By Alexandra Maratou

Jun 04, 2012, 13:42

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