Posted by W. Mahuson on Monday, June 18, 2001 at 11:12AM :
Let me take a shot at this...
I agree that belt driving the fan and water pump directly from the engine uses power that could otherwise be used to propel the vehicle.
I also agree that driving the fan and water pump at belt-drive speeds using motors driven by electricity from the engine-driven alternator takes as much (or more due to inefficiency) engine power as driving them directly via belt.
But there may be a practical advantage to using electric driven accessories in that they can be designed to use only the power they need to do the job. Take the fan for example; short of fancy mechanical stuff, the designer must select a drive ratio, blade pitch and size to give the needed airflow under worst case conditions. I wouldn't be surprised if this choice sucked a lot more power (and delivered more air) than is required under "high speed" cruising conditions. An electric fan can have sophisticated controls to run at the speed necessary for conditions - thus saving engine power - sometimes. Maybe this sophistication is enough to make up for the engine-alternator-motor inefficiencies and thus is a net power saver.
Bill
(who gets frustrated when people open the fridge door to cool off the room)
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