Dear Lazywebz... (Automotive Edition)

[bjarvis]

Last night, as I was driving home from a night shift at the data center, I was thanking $deity every, oh, 10 seconds or so that the passenger cabin of my Civic was warm & toasty despite a nasty windchill factor in our region. Most conventional gasoline & diesel engine vehicles use heat from the engine's operating combustion to warm the passengers and defrost the windshield.

How do the Prius, Leaf & Volt warm their human passengers?

I suppose those with an internal combustion engine could run the engine to generate heat but that would have a huge impact on gas mileage. They could use their battery power to run electrical heating elements; I have no idea how much of an impact that drain would have on their range.

Can anyone with first-hand knowledge enlighten me?

Comments

[jss]

As a Ford Fusion Hybrid owner: The combustion engine runs to generate the heat, and yes gas mileage plummets. With the same driving behavior (assuming the same clean dry roads with the same traffic) I got about 8-12 MPG less in winter than in summer, on average.

[snousle.livejournal.com]

A somewhat nerdy point - the drop in MPG you experience is not as consequential as it appears to be. Suppose your car goes from 40 mpg to 30 when you turn the heat on. You'll be using an additional 0.0083 gal/mile for heat.

If you have a less-efficient car to start with, and you go (say) from 20 mpg to 17 mpg when you turn on the heater, that's using 0.0088 gal/mile for heat. So the cost of heat is higher in the less efficient car, even though the difference in MPG appears to be lower. MPG is a very counter-intuitive measure of fuel efficiency!

[apparentparadox]

When it's cold outside, I know that our Prius ICE runs more than at other times. I'm not sure, however, how much of that is to generate heat for the passenger cabin or because it takes longer for the engine to warm up (and it has to be warm to do the nifty turn-off-and-on-in-an-instant trick).

[urbear]

GM has been less than forthcoming about the Volt's HVAC system, but they have let slip a few details. The Volt uses electricity to heat the cabin, which consumes a lot of juice and impacts the range on battery power. They try to mitigate the problem by using heated seats (apparently people with warm tushies are less likely to turn the cabin heat up full blast) and by allowing you to program the car (using an Android or iPhone app) to preheat or precool the interior while it's still plugged in. The batteries themselves need warmth for maximum efficiency, so if it's very cold when you get into the car the gas engine will start up to warm up the little puppies. The gas engine can also supplement the cabin heating system, but apparently that won't happen unless the outside temperature is really, really cold (less than -40).

As for the Leaf... no verifiable information, but I imagine that it will have to use electrical resistance heaters. Together with the problems faced by cold batteries, that'll cut into the mileage very badly in cold climates.