When the heat is turned on for the HVAC system, where does it come from? Just wondering if heat comes from a heat exchanger scavenging heat from the battery/motor cooling system, or if it is electric resistance heaters. I would assume it would be more efficient (and save the battery for the drive) like in a IC engine car.
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Where Does the Heat Come From?
- Thread starter hanknum
- Start date
The heat is only from an electric resistance heater (PTC, positive thermal coefficient). I was told that Tesla considered trying to capture battery and motor heat but concluded that the plumbing was too much of a complication to try to fit it into this first car design.
Adding, running the main heat will cost you something like 10% of your range, or a bit more if you crank it up. As an alternative, or to offset the urge to turn the temperature to "toast", using the seat heaters costs almost nothing in range.
Electric Swede
Member
The reason you lose 10% of your range is because converting electricity (AC or DC) into heat is one of the most inefficient uses of electricity there is. You would be better off towing a BBQ grill and pumping the heat into the cabin. lol
I think you mean 'most wasteful' uses of electricity, or something like that...
There was an interesting discussion on this recently regarding a kickstarter project using the magical powers of 'graphite' to improve the efficiency of radiative heating elements. The thing is, converting electricity to heat is, by definition, 100% efficient. The PTC element in the car is 100% efficient. If not, where does the lost energy go? The core problem is that heating air takes a lot of energy (wherever that energy comes from).
As Gregd says - use the heat seaters to avoid having to heat up the large volume of air that is the interior of the car (aggravated by all the losses involved with unwanted heat exchange to/from the cold environment the car is in).
ICE cars do use the (usually unwanted) heat byproduct of burning fuel to heat the cabin in winter, and that is pretty neat. Of course, in summer it is counter-productive. Even in winter, other inefficiencies caused by cold fuel, and metal parts of the transmission and engine, counter this.
One missing point in this is that more "modern" heating systems - heat pumps - can be more than 100% efficient. They deliver more heat than they consume, because they're not creating the heat, just harvesting it from outside (what little there is) and dumping it inside. They're an air conditioner in reverse. The newer Teslas can also harvest heat from the drive train and battery to heat the cabin. The Roadster does not use either of these methods.
Running the air conditioning has less impact on range than running the heat, but as with the heat, it depends on local conditions. Something under 10% is my experience. Don't forget that if things are hot enough (they are here), the car will turn on the A/C for a few minutes to cool the battery. You'll feel it a little in the cabin, either the presence of a bit of cooling if you didn't have it running, or a bit less cooling if you were.
Oldschool496
Member
Never had it on by itself, but yes to the bit less cooling or quite a bit less cooling. I was certain it was related to the battery temp regulation. Its hard to explain to passengers that are getting warm. They lived and they were skeptical, I was ok with it, but still wondering if that was truly the case or did the AC take a ....? Funny thing I was not going fast for a long time, cruising in fact at night.
Yes, pretty sure it was the A/C going to the battery. You can hear a soft "click" from up front when it kicks in, and then watch the battery temp drop a notch or two on the VDS.
To the passengers, well, it only lasts a couple of minutes.
In the roadster, seemingly very little.
If you look at the Amps display on the dashboard instrument cluster, when the car is idle, you can turn on/off the aircon and see the impact. Then, push down on the accelerator pedal and see the difference. IMHO spirited (vs chilled, relaxed) driving has a far greater impact on range.
You can still beat the max range with AC at 65mph, you loose about 10km over every 100km doing the driving. That’s heat on full and coming from a heated garage. At AC on full. I can get to Lewiston across the border and back in summer, in winter on range mode (charged standard) I stop 35km from home with 50km indicated at max, not worth the risk for me. Heat certainly takes its toll.
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