kubel wrote:Lance, that was something I was curious about. Assuming I'm using the heater, what is the break even speed at which it's more efficient to drive faster (so as to minimize time spent using the heater)?
I think there are way too many variables at play! Outside temp, what inside temp is set to, whether you pre-heated or not.
Here are my findings limited to the specific scenario I have had experience with:
- outside temps in the mid-40's (sorry, that's pretty much as cold as it gets here, and if it's warmer I don't bother with heating the cabin anyway. Earlier this winter when the temps were in the 30's I wasn't looking this closely at things)
- cabin and heating system thermal mass are already warm (i.e. through pre-heating)
- inside temp set to 72F and on AUTO (unlike others I have come to really like the AUTO setting--I was skeptical, but it actually does properly direct hot air to the feet when warming, AND as a bonus it doesn't even run the fan at all (or at least at low speed) until there is actually hot air to blow)
- driving in ECO mode (you would probably eventually reach this steady state in D mode, but I never drive in D)
It generally takes about 1-1.5kW of power draw to maintain cabin heat
So from that you can calculate how much power you are going to consume per time period. For example if you have a half hour drive, or if the difference in drive time between your comparison points is 30 minutes, you'll consume between 0.5 and 0.75 kWh to heat.
It's easy enough to repeat the observations using whatever scenario you want once you have the car in hand. You just need to monitor the energy info screen to see what the power draw is.
It's even harder to quantify your energy use instantaneously at different speeds/driving styles. But the car does give you the tools to measure it. You would just need to reset the efficiency meter, drive one way and note the mi/kWh, and reset and repeat for the other way. Of course this takes into account your use of accessories including the heat, so to really do a valid experiment you'd have to run without heat.