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

Transportations Role in Reducing U.S. Greenhouse Gas Emissions: Volume 2
Refrigerant release also takes place at vehicle EOL. When a vehicle is scrapped, all
refrigerant will eventually be released into the atmosphere unless an attempt is made to
recover it. While recovery is required in the U.S., compliance is not 100 percent and
recovery methods do not remove all of the remaining refrigerant. EOL refrigerant
recovery is less than 50 percent of the factory charge according to many estimates.
Recovery challenges at vehicle EOL are similar to those encountered during servicing,
except that conditions after scrappage make recovery more difficult and less effective.
Vehicles are almost always outside where cooler ambient conditions limit drawdown
efficiency, and in many cases the engine cannot be run to facilitate refrigerant recovery.
Additionally, salvage and recycling operations are time-sensitive and extended efforts to
recover refrigerant could have a negative effect on scrap operation profitability (U.S. EPA,
2007d).
Both professional servicing and EOL recovery can utilize similar improvements to
minimize refrigerant leakage. Changes such as heating the accumulator and increasing
vacuum pressures can raise recovery levels substantially. These efforts, along with
performing a second drawdown to the system, will increase refrigerant recovery but also
will require additional time and equipment. In addition to more robust recovery
processes, accurate charging can help reduce refrigerant losses and waste. Charging
based on the mass of refrigerant added is the proper method, but is limited in accuracy by
the quality of the preceding recovery.
Alternative refrigerants exist that have a lower GWP than HFC-134a. Of the refrigerants
that could be substituted for HFC-134a within the next five years, HFC-1234yf is one of
the leading candidates. HFC-1234yf has a GWP of 4 and can operate in systems similar to
current designs, with the potential for direct replacement of HFC-134a in existing systems
(Yau, 2008). A second refrigerant under evaluation is HFC-152a, with a GWP of 124. This
refrigerant is more toxic than either HFC-134a or HFC-1234yf, and is unlikely to be used in
existing MAC systems, as protection from leakage into the passenger compartment would
be required. The third refrigerant commonly considered is R-744, which consists of CO2.
This refrigerant is primarily being considered in Europe where R-134a will by phased out
starting in 2011. However, CO2 is less efficient than other refrigerants and its use would
require a significant redesign of MAC components (Andersen, 2008). It also is unlikely
that CO2 would be able to provide acceptable levels of cooling in hot or humid
environments, and the lower efficiency of these systems means their associated fuel use
would be much greater than systems using the other alternatives.
MAC systems are sized to have the capacity to keep the vehicle comfortable on a hot and
sunny day. Reducing vehicle cabin temperatures will in turn reduce MAC system
capacity requirements and energy demand. Solar reflective window glazing can reflect
most infrared (IR) light, and still allow acceptable light transmission for visibility.
Similarly, solar reflective paint can be used on the vehicle’s body in order to minimize the
amount of heat absorbed from light, especially in the IR spectrum. Technologies to make
darker colors (especially black) significantly more reflective do not yet exist, however
(CARB, 2009).
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