(546d) Direct and Indirect Emissions From Mobil Air Conditioner Units in Transportation By Truck and Rail

The U.S. EPA has announced repeatedly that hydrofluorocarbons (HFCs) will become regulated, not for their direct impacts on the environment, but because of their contributions to global climate change.  HFCs are used in many industrial processes as solvents and refrigerants because they are relatively inert, inexpensive and have physical properties that allow them to function well.  The use of HFCs is largest in the refrigeration sector.  R-134a (1,1,1,2-tetrafluoroethane is the dominant refrigerant used currently in mobile air conditioner systems and has emissions of about 38.6 x 10⁶ kg/year per year from all sources, with approximately 47% of that being due to vehicle emissions. The European Union took steps in January 2011 to eliminate fluorinated greenhouse gases in certain classes of vehicles with 100 year GWP’s greater than 150 as defined by the third assessment report adopted by the IPCC, including R-134a. Currently passed legislation in Europe also calls for a complete phase-out by January 2017.

 Mobile air conditioning units (MAC) are in use in several applications, with their use in passenger cars having been evaluated for greenhouse gas emissions in the prior literature.  If HFCs are banned as a class of compounds, alternatives will need to be developed or exploited.  While MAC and environmental impacts have been investigated for passenger cars, there are other MAC units where the temperature constraints and demands may lead to a more restricted range of possible refrigerants.  Mobile air conditioning units used in the shipping of temperature sensitive products, like foods and medication, is common on both tractor trailers and on refrigeration, reefer, units installed on rail cars.  With the large number of US and worldwide refrigerated shipping units, evaluations of the emissions for this application of refrigeration need to be obtained before deciding if banning hydrofluorocarbons is indeed better for the environment.

 This work uses chemical engineering heuristics and design parameters, combined with actual operating conditions and design specifications of manufactures to estimate the direct and indirect greenhouse gas emissions for MAC using diesel powered reefer units in transport.  We find that many refrigerants that can be used in dedicated non-mobile units where water cooling is possible fail for this application.  The remaining refrigerants are small in number and it appears that banning HFCs would be unattractive due to the indirect emissions.