29 September 2009

Staying warm

Mini wants the air recirculation control off most of the time.  I agree generally, especially in combustion powered cars where carbon monoxide poisoning is always a danger.

But in the Mini E the story is a little different.  First, the colder September weather now  in the North East US means using the cabin heater.  And I can stay warmer while using less power when the air is recirculating.  Besides, the battery ventilation is always pulling air out of the cabin, even if only through air leaks when the air is set to recirculate.

Now I would like to use heat with the cabin air fan off, since the lowest setting is still too high for these 40 degree mornings.  The battery fan draws enough air though the cabin ventilation vents. But the heater won't come on without the cabin air fan being on.  So the next best way to reduce cold air ingress is to use the recirculation button.

Of course, Mini set it on a timer to turn off after 5 minutes or so. When I notice it getting cold again, I push it again.

There are conventional Minis where I work, so I'll have to ask if this functions the same way on the gasoline powered models which have waste heat to spare.

I would like to see a reversible air flow where battery heat could go into the cabin, but maybe that would not work.  Maybe that was too much to get into a prototype.  In any case, the heater load appears to be much smaller than I expected.  I always assumed the heater in winter would be the Achilles' heel of electric cars.  So far from my measurements (see earlier posting) the heater load looks small. 


  1. Hey Jim,

    A great way to get heat for an e-car would be to have the electric motor(s) wrapped in copper and run cooling fluid through that, then to a heat exchanger core for hot air.
    I'm sure those puppies get plenty hot and having some heat exchange out of them would help to cool the motors.

  2. Ted - A quick run of the numbers suggest you are right. If average power is 10 Kw and efficiency is 90%, there should be 1 Kw of waste heat from the motor. And maybe 50% of that could be easily captured and moved to the cabin.

    I wonder if the battery heat is a greater source? It would be a tricky control problem but maybe in cold weather the battery pack could be preheated on shore power to the warm end of optimum and than cooled by venting to the cabin rather than to the outside as the Mini E does.

    But all this might practically require a liquid cooling system, which this prototype did not get.