<VV> Cooling

[Frank DuVal]

This comes up a lot, so it is humorous to me.

Horsepower the fan uses is determined by the design of the fan. Part of 
the design is the air needed to flow through the device needing cooling. 
As long as the cooling need does not get smaller (and no one accused GM 
of over cooling the Corvair engine), then the horsepower needs will stay 
the same. Making the fan drive electric just moves the horsepower from 
mechanical directly off the crankshaft to now having to convert the 
mechanical crankshaft energy to electricity by way of the alternator and 
then converting it back to mechanical horsepower at the fan shaft. So in 
actuality, more horsepower is needed for the same work, as energy is 
turned into heat in both the electric motor and alternator. 746 watts 
per horsepower at 100% efficiency.

Now, if one can control the electric fan speed, then horsepower needs 
will be less when cooling needs are less. Of course the mechanical fan 
does vary horsepower already, as the shaft speed increases at higher 
road speeds and that is also when cooling needs are greater.

Or one can redesign the fan, but you cannot change the CFM needs of 
cooling the engine or static pressure that the system develops at that CFM.

I have to explain this to engineers at work when they try to replace a 
1/2 horsepower fan with a muffin fan (15 watts)  and wonder why it will 
not cool as well. They get CFM ratings close, but don't get static 
pressure ratings any where it needs to be.

Frank DuVal

Jon, How's the El Vair, has it arrived yet?


On 3/11/2013 7:24 PM, Jon Woolf wrote:
> Has anyone tried an electric fan instead of mechanical drive?  That
> thing must suck up a lot of HP.  And does it need to run all the time?
> A thermostat controlled electric might give a boost in power.