Why does Tesla use a Resistance Heater instead of Heat Pump

[AWDtsla]

Only my 2 cents here, but I have some experience from a BMW i3 which had a heat pump.

Cold weather around zero Celsius they don't work good at all, heating consumption of i3 was crazy even with heat pump
They consume a certain amount of energy to just heat their own circuit, means it all takes time and energy, not good on a short trip
They also need a resistive system to back them up, means you need both anyway

To be honest when I changed over to Tesla, I was happy to learn they don't bother with the heat pump approach.

Maybe on exactly the right day, with exactly the right temperature and a long trip the heat pump would be worth it. Otherwise, with a big battery and supercharging its a waste of time.

Get a nice coat

Lot of Celsius between 0 and room temperature. Although as discussed above 0C is not meaningful for a heat pump, it's still 273K

 

[mongo]

Lot of Celsius between 0 and room temperature.

Even more Fahrenheit!

 

[wdolson]

I was thinking about this yesterday when we were out and I noticed energy usage was up even though the HVAC was off. We've had a fairly mild fall so far, but it was a bit colder yesterday and the car had been sitting a few days when we left. I think the battery was more cold soaked than it has been and the battery heater had to kick in to warm the battery as we headed out.

Tesla is more obsessed with good battery management than any other EV maker and I think they need the resistance heater to warm the battery on cold days faster. This is especially needed if the battery is still cold when you try to supercharge. I did go to a supercharger once when the battery was cold and I got glacial charge speeds, it would probably be even worse if the car also had a heat pump instead of resistance heater for the battery pack.

The Nissan Leaf has a heat pump, but it also is known for it's poor battery management. Better now than when the Leaf was first introduced, but I don't think the new systems are as good as Tesla's. (Though I could be wrong.)

 

[AWDtsla]

I was thinking about this yesterday when we were out and I noticed energy usage was up even though the HVAC was off. We've had a fairly mild fall so far, but it was a bit colder yesterday and the car had been sitting a few days when we left. I think the battery was more cold soaked than it has been and the battery heater had to kick in to warm the battery as we headed out.

Tesla is more obsessed with good battery management than any other EV maker and I think they need the resistance heater to warm the battery on cold days faster. This is especially needed if the battery is still cold when you try to supercharge. I did go to a supercharger once when the battery was cold and I got glacial charge speeds, it would probably be even worse if the car also had a heat pump instead of resistance heater for the battery pack.

The Nissan Leaf has a heat pump, but it also is known for it's poor battery management. Better now than when the Leaf was first introduced, but I don't think the new systems are as good as Tesla's. (Though I could be wrong.)

Given model 3 heats the battery with resistance heat with a 0 part count, heat pump is not an exclusive option. If anything, you would be able to heat the pack FASTER.

 

[DParker]

It is true that heat pumps simultaneously heat and cool, but some clever air mixing & bypass arrangements would be needed to deliver air in varied proportions both from the evaporator and condenser sides, swapping places to the interior to exterior. Could it be done? Yes, of course, but it would also be more complex. However, the promise of a true HP for heating is at least a 40% savings over current PTC designs-- even at low temperatures.

https://bit.ly/2Q5Pczo

There are also VRF heat pump designs that do allow separate heating and cooling within a single compressor heat pump configuration. In any case these designs are more complex, but for sure heat pumps (regardless of the arrangement) for heating would be superior to PTC heaters and a useful feature in the Tesla family.

 

[JohnnyG]

I was thinking about this yesterday when we were out and I noticed energy usage was up even though the HVAC was off. We've had a fairly mild fall so far, but it was a bit colder yesterday and the car had been sitting a few days when we left. I think the battery was more cold soaked than it has been and the battery heater had to kick in to warm the battery as we headed out.

Tesla is more obsessed with good battery management than any other EV maker and I think they need the resistance heater to warm the battery on cold days faster. This is especially needed if the battery is still cold when you try to supercharge. I did go to a supercharger once when the battery was cold and I got glacial charge speeds, it would probably be even worse if the car also had a heat pump instead of resistance heater for the battery pack.

The Nissan Leaf has a heat pump, but it also is known for it's poor battery management. Better now than when the Leaf was first introduced, but I don't think the new systems are as good as Tesla's. (Though I could be wrong.)

Not that I'm an advocate for HP, but just as a point of clarification... The battery has it's own dedicated PTC; separate from the one for the cabin. You could still have a PTC for the battery, and a HP for the cabin.

 

[arnis]

A year ago I already made estimation of cost effectiveness of heat pump. Depending on climate, heat pump plumbing will pay itself back within some years. Definitely within a decade.
Literally megawatts of electricity wasted on heating. That electricity has a price.
Saying that HP doesn't really make a difference on EV is as stupid as saying HP doesn't really make a difference for house heating.
It's literally the same thing.

Having up to 100% efficiency for EV heating is.. well... outdated tech. Technically, even ICE vehicles are better at that.

 

[mongo]

A year ago I already made estimation of cost effectiveness of heat pump. Depending on climate, heat pump plumbing will pay itself back within some years. Definitely within a decade.
Literally megawatts of electricity wasted on heating. That electricity has a price.
Saying that HP doesn't really make a difference on EV is as stupid as saying HP doesn't really make a difference for house heating.
It's literally the same thing.

Having up to 100% efficiency for EV heating is.. well... outdated tech. Technically, even ICE vehicles are better at that.

Yes, HP can use downwards of 25% of the energy of a pure resistive heater.
However, cars are not houses. The heat load of a house spread over 20-30 years is a different animal that a car which someone may have for 5.
You are saying your ROI numbers show a HP may pay back in the years to decade time frame. We both know that in some climates it will never pay back the additional cost. Bumping up the price of all cars based on the potential to recoup the cost on some of them eventually is not a clear cut win.

 

[AWDtsla]

Yes, HP can use downwards of 25% of the energy of a pure resistive heater.
However, cars are not houses. The heat load of a house spread over 20-30 years is a different animal that a car which someone may have for 5.

Irrelevant. You'll be driving a car just as long as you're living in a house. Plus there is the massive efficiency loss of pulling up to 11kW to heat both the pack and the interior. Assuming you live in a modern house, the heating energy for your Tesla(s) may be greater than that for your house. It's not that hard to do with good insulation and a state of the art heat pump that's 30 SEER.

 

[roblab]

Just adding my experience with the RAV4EV. It had a heat pump. It was terribly slow. By the time I got home from a game at the nearby college, my windows were beginning to defrost. Not only was I cold and unable to see, the friend I'd offered to drive home was unimpressed with EVs and my demonstration.

Thankfully, Tesla chose to give us heat and safety. The battery is large enough that it can heat and move us. They made the right choice.

Yes, heat pumps are more efficient, but the battery makes that a moot point in nearly all cases. When I see people living in 2000 sq ft houses (sorry, I live in 400 sq ft.) it makes me wonder how much importance they put on efficiency when heating them.

 

[arnis]

The heat load of a house spread over 20-30 years is a different animal that a car which someone may have for 5.

I bought a heat pump for my home and it payed back on third winter. Third...

Bumping up the price of all cars based on the potential to recoup the cost on some of them eventually is not a clear cut win.

The most basic thing is custom order. Literally, in California, it is reasonable to have AC and no rear seat heaters. In Norway, huge market for Tesla, Heat pump and seat heating is a must. With insulation all around the cabin.

Also I said plumbing and not the whole system.
Practically all EV's have AC compressor. Adding some valves and pipes costs less than 10% of the whole system. Of course compressor is the most expensive part.

Heat pump is especially useful on EV's that REQUIRE pack heating. Like Tesla. In my climate, pack heating would be activated for 3-4 months per year. That is a lot of electricity heating a block of stuff under the vehicle

 

[arnis]

Just adding my experience with the RAV4EV. It had a heat pump. It was terribly slow.

Irrelevant. HP is addition to PTC heater not replacement.
My Leaf heats up faster than Tesla. When I switch on Leaf, it can draw 2kW with heat pump and 3-4kW with PTC heater. Easily giving 7-10kW of heating during 1-2 minutes. Tesla can't do that.

 

[croman]

LEAF heats up faster, better defog and in everyway better than Tesla HVAC.

 

[AWDtsla]

LEAF heats up faster

Flaw in Tesla code. Unless they hire software devs outside of Palo Alto, never will be fixed.. Pretty much any controls having to do with heating are always full of FAIL.

 

[mongo]

Irrelevant. You'll be driving a car just as long as you're living in a house. Plus there is the massive efficiency loss of pulling up to 11kW to heat both the pack and the interior. Assuming you live in a modern house, the heating energy for your Tesla(s) may be greater than that for your house. It's not that hard to do with good insulation and a state of the art heat pump that's 30 SEER.

Yes, I will be driving, but not the same car. If you were buying a new heating system every 5 years, versus once or twice, the economics change.

SEER is a rating of cooling, the best unit in the US for 2017 was 26 (Lennox XC25). Heating efficiency is HPSF (season adjusted COP), Lennox was 10.2 or COP of 3.
Let's look at the energy used driving. 300wh/mile at 60 MPH is 18kW is about 60k BTU continuous (while driving). A 2 hour commute would be 120 k BTU or 5kBTU over 24 hours. Running a COP 3 HP for your house would be a 15kBTU furnace. Maybe with a modern super insulated house you can pull that off, but not typically.
Say pack and cabin heating was 11kW continuously, and you could get a COP of 3 out of a car. You could save 7.3 kW, or 14.6kWh for 2 hours. Average that over 24 hours and you're at 0.611 kW average, less than 2k BTU. Say the house has a 3 COP HP, 2k BTU in gets you 6k BTU out, enough energy to heat 15 gallons of water from 55F to 120F. You could get the same heat output for a couple hours by having a party with 20 people...

I bought a heat pump for my home and it payed back on third winter. Third...

Again, duty cycle and total energy usage. My car does not stay climate controlled 24 hours a day. If you drive 2 hous a day, that is a 12x usage difference.

The most basic thing is custom order. Literally, in California, it is reasonable to have AC and no rear seat heaters. In Norway, huge market for Tesla, Heat pump and seat heating is a must. With insulation all around the cabin.

This is a great concept, I've thought perhaps an add on HP could be added specifically for regions with appropriate climate. Still has all the HP issues though.

Also I said plumbing and not the whole system.
Practically all EV's have AC compressor. Adding some valves and pipes costs less than 10% of the whole system. Of course compressor is the most expensive part.

Heat pump is especially useful on EV's that REQUIRE pack heating. Like Tesla. In my climate, pack heating would be activated for 3-4 months per year. That is a lot of electricity heating a block of stuff under the vehicle

The pack heating is mostly needed for regen/charging (and avoiding strange effects at really low temps) same limitation as most lithium chemistries. Parking in an insulated garage might yield better energy savings if it is that cold.

 

[Reeler]

Tesla is facing some tough competition next year. Once there is another AWD EV option, I am likely to switch. The heat pump in my LEAF worked flawlessly and seriously increased the range in the winter months in Denver. I saw 20% more range when commuting in slow traffic on very cold days. The Tesla designers in CA must believe their needs are the only ones that matter.

 

[mongo]

Tesla is facing some tough competition next year. Once there is another AWD EV option, I am likely to switch. The heat pump in my LEAF worked flawlessly and seriously increased the range in the winter months in Denver. I saw 20% more range when commuting in slow traffic on very cold days. The Tesla designers in CA must believe their needs are the only ones that matter.

Not arguing, just confused. 20% more range compared to what? Did it have the ability to turn the HP on/off?

 

[dgpcolorado]

Tesla is facing some tough competition next year. Once there is another AWD EV option, I am likely to switch. The heat pump in my LEAF worked flawlessly and seriously increased the range in the winter months in Denver. I saw 20% more range when commuting in slow traffic on very cold days. The Tesla designers in CA must believe their needs are the only ones that matter.

When the range is several hundred miles, why does it matter? 20% increase in range in a short-range LEAF would work out to a much lower percentage in a long range Tesla. Unless you routinely drive 150 or more miles per day in winter, the relatively small range loss from the heater just doesn't matter IME.

 

[AWDtsla]

When the range is several hundred miles, why does it matter? 20% increase in range in a short-range LEAF would work out to a much lower percentage in a long range Tesla. Unless you routinely drive 150 or more miles per day in winter, the relatively small range loss from the heater just doesn't matter IME.

Yes it does. Electric heat is very expensive, and therefore bad for the environment. Not only heating the cabin, but the pack. City driving is dominated by climate control. Will see 1000+Wh/mile in 1-2 months.

I don't know what's up with this thread. We can put a car in solar orbit and land rockets, but we can't make a heat pump work.

 

[dgpcolorado]

Yes it does. Electric heat is very expensive, and therefore bad for the environment. Not only heating the cabin, but the pack. City driving is dominated by climate control. Will see 1000+Wh/mile in 1-2 months.

I don't know what's up with this thread. We can put a car in solar orbit and land rockets, but we can't make a heat pump work.

If efficiency is the goal, the Model 3 is considerably more efficient than the Model S — that would be way more energy savings than a heat pump in the Model S best to eliminate the Model S entirely.

I don't use the heater much because I am already dressed for winter — snow here yesterday — so the heater is often unnecessary. Since this is sunny Colorado, not the frozen north, I guess it doesn't really count. Nevertheless, I power my car with solar panels, so even an energy hog Model S is better than an ICE car in my view. However, any car is far worse for the environment than no car, so there's that. Back to bicycle commuting I guess — I have many tens of thousands of miles of experience with that, much of it at night in winter.