this post was submitted on 03 Sep 2024
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I realize the energy still has to come from the traction battery, but don't most EVs use heat pumps now? The energy use would be the same as using the A/C in the summer (though the battery does have less "oomph" in the winter due to ambient temperature).
My hybrid just uses the engine block as a heat source and storage (coolant pump is electric and circulates coolant through the warm engine block when it's in EV mode and occasionally kicks the engine on to warm it back up when needed). I think the coolant also loops through the motor controller and DC-DC converter which adds a little heat, but not really enough to heat the cabin with alone.
I wonder if it would make sense on EVs to have some kind of "chargeable" thermal mass you could pre-heat while it's charging and extract as you drive (and/or acts as a reservoir the heat pump can draw from)
Yes, heat pumps are really common in new EVs, but I'm not sure if it's most worldwide or not.
Your idea about thermal storage is interesting; I'm very much unclear on whether it would make sense to do that or simply have a bigger battery or some amount of insulation on the passenger compartment.
Adding thermal storage would require mass to be added, unless some existing component could be converted to dual-purpose. More mass in an EV means lower range and an increase in the already high vehicle weight.
And I can't imagine the thermal accumulator + insulation would have a higher energy intensidensity than just the battery alone.
After thinking about it a bit more, a bigger battery would probably be the most practical.
Using my hybrid as a reference point (it uses the whole engine as a thermal mass for heat storage), the stored heat only lasts about 5-10 minutes at most before the engine kicks back on to warm it up again (the controller lets it cool to the lowest "operating" temperature for efficiency). If it could use the full stored heat in the engine, it would probably only be good for another 5 minutes at most. Granted, it's using that heat directly with a traditional heater core rather than feeding a heat pump.
Given that it would be used seasonally and be "dead" weight the rest of the year, I'm not sure adding a thermal mass would be all that practical unless it's something that can be heavily insulated and super-heated beyond the temperatures engines run at or has an additional year-round use.
The only downside to a larger battery is purely a human perception/marketing issue. The extra battery capacity would most likely be advertised in the range, and people would still probably be upset about the reduced range in the winter. It would have to be, ideally, not factored into the range and act as a "reserve" capacity.
Regardless, yeah, better cabin insulation would also help, to a point.
I just work around the problem by not running the heat most of the time (barring the need to defrost/defog). Most of my trips are short, so I just wear my coat/gloves and deal with the cold lol.
How about using the thermal mass for both heating and cooling? Too bad EVs don't have throwaway power like hybrids, could use the excess to heat/cool the mass as necessary. Probably still not as efficient as raw power storage.