There could be more? Seems like a lot of energy wasted on heat with a Volt. Kind of explains the 40 mile range.
Without trying to promote or defend the Volt...
Multiple heat exchangers can be the source of energy efficiency as it may be using these as heat/energy recovery devices.
Most of the inefficiency in a traditional style internal combustion engine and automobile can be associated with energy lost as heat.
In refineries, petrochemical plants, etc, we often use multiple heat exchangers as a way to boost overall system efficiencies by recovering energy otherwise lost as heat.