Transportation's Role in Reducing U.S. Greenhouse Gas Emissions ...

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
conditioning, and, as a result, nearly all in-use LDVs are estimated to have a MAC system
(Atkinson, 2007). For these reasons the following section focuses on LDV refrigerant
control and reduction options, although some of these strategies will have applicability for
other modes.
Legislation controls the safety characteristics of refrigerants, certification of service
professionals, and service and EOL refrigerant recapture. Currently, professional service
stations must use certified personnel, attempt to recover all refrigerant for recycling, and
must initiate leak repairs. These requirements do not apply if the vehicle owner performs
the work, however. Additional control initiatives are promoted by programs such as the
Improved Mobile Air Conditioning (IMAC), which is designed to address all aspects of
lifetime MAC performance. IMAC participants include the U.S. EPA, vehicle
manufacturers and suppliers, and air conditioning component manufacturers. Their
findings are guiding EPA in future MAC-related rulemaking, and manufacturers in the
technologies they pursue (U.S. EPA, 2007d).
There are three approaches to reducing GHG emissions associated with MAC system
operation:
1. Reduce the leakage of the refrigerant to the atmosphere;
2. Reduce the GWP of the refrigerant itself; and
3. Reduce the engine load (and concomitant CO2 emissions) associated with running the
air conditioning system.
One way to reduce refrigerant leaks is to simply reduce the amount of refrigerant in the
system itself. Increases in MAC system efficiencies over time have resulted in a decrease
in average charge volumes. Currently, the average vehicle charge size for a light-duty
vehicle is 22.3 ounces (SAE, 2008). Reducing charge size limits the releases that can take
place from in-use, service, and EOL leakage. Nevertheless, new air conditioning systems
will continue to leak a small amount of refrigerant. The many connections among system
components and slow seepage through hoses mean that some leakage is inevitable,
estimated to be approximately 8–18 grams/year for current LDVs (Sciance, 2005). This
leakage rate represents between 1 and 3 percent of a typical new vehicle system charge, so
such losses are not likely to be noticed and repaired by vehicle operators.
System designs for new vehicles are continuously being improved to reduce the leakage
rates of crimps, fittings, hoses, compressors, and other MAC system components, with
many of these improvements based on IMAC findings and guidelines. As MAC systems
age, leaks become more severe, but a certain amount of refrigerant can be leaked before
degradation in performance is noticed. For this reason, it may be beneficial to implement
a method of monitoring MAC system leakage. Monitoring could include a professional
system check, for example during a vehicle’s regular Inspection and Maintenance (I/M) or
safety test. On-board diagnostic-type equipment also could be added to vehicles to
monitor system leaks in order to alert the driver to a leak in a manner similar to the check
engine light on today’s vehicles. Both of these methods may offer long-term benefits, but
are likely to require additional regulations and incurred costs.
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