BMW i3 User Investigates Where The Heat Is Going
When you are in the habit of driving an EV for long distances it is surprising what strange things can come into your head. I haven't been an EV owner for long, just four months, but I've put a lot of miles on my BMW i3 Rex. Running on a battery, my thoughts tend to run toward better efficiency and getting the last mile possible out of a charge.
Driving in our recent hot weather I started thinking about the heating and cooling used on modern electric vehicles. Specifically I was thinking about what heat is generated by the operation of the EV at highway speeds, and where that heat goes. Most EV models use a combination of classic resistive heating or the more efficient heat pump technology. Seat and steering wheel heat is always from resistive elements, but the cabin air is usually heated using a heat-pump.
ICE vehicles have always relied on engine heat to warm the cabin, which is why we all grew up waiting for the engine to warm before the vents would melt ice on the windows or earlobes. ICE vehicles use air conditioners (essentially heat pumps in reverse) to cool the cabins with frigid air, but the hot air coming from the exhaust manifold was always considered free.
With EV, you have to budget for all cooling and heating. The good news is bigger, higher density batteries make the impact of cabin conditioning a smaller and smaller part of the energy budget - since the cabin size is staying put while the kWh ratings keep going up. But what about the heat from the batteries and the electric motor? Couldn't we use that to warm the cabin, and get a benefit from the wasted heat?
I decided to do some investigating on a few cars to see where the heat was going. I'll be running some tests and taking measurements on a few popular models to see what's going on in the cabin and around the car when it has been working hard to move you around. I'll use a FLIR camera to show what area of the car get hot, and how hot, compared to a base-line ICE.