Why does Tesla use a Resistance Heater instead of Heat Pump

[AWDtsla]

This entire thread is full of myths about heatpumps. The reason Tesla does not have one is because of laziness.

Modern mass-production heat pumps have design temperatures down to -13F (with performance tapering off below that, but not stopping), with reversing valves so the same unit is the AC in the summer. Even with performance down to -13F, you can keep the resistance heater for backup heat, it's a tiny tiny unit, like 12"x12"x3"


edit - and the conversation about volume is also bunk. Entire homes are heated/cooled via air-source heatpump in very cold climates.

 

[mtndrew1]

My Volts had resistance heating and my Soul has a heat pump and the difference is stark.

The Volt would typically show ~3 kW of draw for the resistance heater in 40 degree F weather where the Soul uses about 500W on-and-off and provides heat MUCH faster than the Volt ever did.

On rainy days or very long drives where defogging is necessary it'll switch temporarily to resistance + heat pump to defog and then it goes back to heat pump. It's wonderful.

It's so efficient I camped in the car one night instead of my tent in a 23 degree snow storm. I set the HVAC to 63 F and it ran for eight hours and used up about 10% of my charge, which would be about 2.7 kWh. The Volt would have used ten times that amount to do the same thing.

I hope the Model 3 has a heat pump + resistance unit.

 

[MP3Mike]

I hope the Model 3 has a heat pump + resistance unit.

The problem is that you would generally need two systems in a car since in most cases when you are heating you always want the defrosters on and you run the A/C to dry the air for that. Maybe you could get away with just heat in cold wet climates but I doubt it.

 

[Uncle Paul]

Some good ideas here.

Believe that Tesla has two settings. A low draw system for normal use and higher range, and a higher draw mode when maximizing range is not an issue, and more comfort is desired.

Tesla has a much larger battery capacity than the Leaf, so maybe conserving the battery draw is less critical.

 

[nwdiver]

The problem is that you would generally need two systems in a car since in most cases when you are heating you always want the defrosters on and you run the A/C to dry the air for that. Maybe you could get away with just heat in cold wet climates but I doubt it.

You don't need a separate HVAC system... you just wouldn't be able to use the heat pump for defrosting.

 

[AWDtsla]

Tesla has a much larger battery capacity than the Leaf, so maybe conserving the battery draw is less critical.

It is not. By Tesla's own standard, 200 miles is the minimum practical range. Well, I get about 130 miles when all is said and done in the winter, cold soaks, battery heating, driving on wet/snowy roads, etc, etc. Model 3 will only be worse as the ratio of miles to kWh gets even lower, it will be impacted harder by losses to a resistance heater.

 

[mtndrew1]

The problem is that you would generally need two systems in a car since in most cases when you are heating you always want the defrosters on and you run the A/C to dry the air for that. Maybe you could get away with just heat in cold wet climates but I doubt it.

But you don't need two systems. When ambient humidity is high the car runs the resistance heater and the heat pump "runs the opposite direction" and behaves as the A/C, thereby drying the air. My car has a small puck on the windshield to measure humidity levels for just this purpose.

In low humidity environments the heat pump alone is fine, providing a substantial energy savings as I've outlined above. It's a win-win, aside from cost (which is probably why it's not there now).

 

[rolson1011]

The leaf does use resistive heating in extreme cold but it switches to a heat pump after a while. Also the peak draw of the leaf heat is 3kw and is VERY hot. The peak draw I've observed in my new S is around 6.6kw and its not terribly warm even with the fan down to 3 or 4. The S does get to temperature but it does so in a lot longer timeframe. I'm just saying that Tesla can't just rest on its laurels and perhaps it can steal some ideas from competitors (or maybe not, I'm not an engineer).

I've noted the same experience with my Kia SoulEV+ and Teslas. The Kia heat pump gets very hot very fast, within 5 sec usually of starting the car. The Tesla is.. meh at best, unless you mash the pedal after a stoplight, it seems to put out some additional heat.

 

[McRat]

My Volts had resistance heating and my Soul has a heat pump and the difference is stark.

The Volt would typically show ~3 kW of draw for the resistance heater in 40 degree F weather where the Soul uses about 500W on-and-off and provides heat MUCH faster than the Volt ever did.

On rainy days or very long drives where defogging is necessary it'll switch temporarily to resistance + heat pump to defog and then it goes back to heat pump. It's wonderful.

It's so efficient I camped in the car one night instead of my tent in a 23 degree snow storm. I set the HVAC to 63 F and it ran for eight hours and used up about 10% of my charge, which would be about 2.7 kWh. The Volt would have used ten times that amount to do the same thing.

I hope the Model 3 has a heat pump + resistance unit.

338 watts load with the IGN on and HVAC on at 40°F delta in windy conditions? Are you sure? Most Kia's use that much power to operate the computers and running lights.

 

[nwdiver]

I've noted the same experience with my Kia SoulEV+ and Teslas. The Kia heat pump gets very hot very fast, within 5 sec usually of starting the car. The Tesla is.. meh at best, unless you mash the pedal after a stoplight, it seems to put out some additional heat.

It'd be surprised if the Kia didn't have a resistance heater for backup and quick heating. As mentioned in earlier posts heat pumps are almost useless below ~10F...

I do agree that it's odd that Tesla lacks a heat pump... it would be interesting to hear the logic from one of their engineers.

 

[AWDtsla]

I've noted the same experience with my Kia SoulEV+ and Teslas. The Kia heat pump gets very hot very fast, within 5 sec usually of starting the car. The Tesla is.. meh at best, unless you mash the pedal after a stoplight, it seems to put out some additional heat.

Tesla's problem is entirely their software. The resistance heater will go to max power immediately if you let it, but it takes several minutes for the software to turn it on. Mashing the throttle has nothing to do with it.

 

[zentage]

This entire thread is full of myths about heatpumps. The reason Tesla does not have one is because of laziness.

Modern mass-production heat pumps have design temperatures down to -13F (with performance tapering off below that, but not stopping), with reversing valves so the same unit is the AC in the summer. Even with performance down to -13F, you can keep the resistance heater for backup heat, it's a tiny tiny unit, like 12"x12"x3"


edit - and the conversation about volume is also bunk. Entire homes are heated/cooled via air-source heatpump in very cold climates.

I second this. In norway more than 50% of all houses has a heatpump. The modern ones are rated to deliver efficent heating down to -30 celsius.
Considering the Model S to be a premium car I would say they certainly took the easy way by just installing a resistive heater. Lets face it, its nothing more than a heating element and a fan - as cheap as they get.

In my opinion the resistive heater should be installed to be used during startup until the heat pump could take over, and thats it. It would have made many KWH's difference on a long drive.

In my house (remember, thats a HOUSE) the heat pump is rated to use 1 kwh to deliver 6 kwh of heat.

 

[mtndrew1]

338 watts load with the IGN on and HVAC on at 40°F delta in windy conditions? Are you sure? Most Kia's use that much power to operate the computers and running lights.

Yep, I'm sure. I didn't make it a scientific thing so there are no hard data points but I had an 80 mile drive home and made it, so power usage was minimal.

With the Soul in Park and with lights/wipers/seat heaters/infotainment off the car uses less than 100W at idle. I've confirmed this with Torque Pro.

In any event, the heat pump uses a huge deal less power than the resistance heaters in my Volts did, whether camping in the car or during regular drives. It's a feature I want in my next car and I'd be happy to pay the added premium, even if it were an extra-cost option. It's a stark contrast to the Volt both in consumption and performance, though the lowest temp I've used it at is the example referenced above (23F).

 

[nwdiver]

I second this. In norway more than 50% of all houses has a heatpump. The modern ones are rated to deliver efficent heating down to -30 celsius.
Considering the Model S to be a premium car I would say they certainly took the easy way by just installing a resistive heater. Lets face it, its nothing more than a heating element and a fan - as cheap as they get.

In my opinion the resistive heater should be installed to be used during startup until the heat pump could take over, and thats it. It would have made many KWH's difference on a long drive.

In my house (remember, thats a HOUSE) the heat pump is rated to use 1 kwh to deliver 6 kwh of heat.

Hmmm.... I admire your enthusiasm but I don't think your numbers are correct... the best heat pumps available have a COP of ~4.0 at ~0C and that's being generous. That COP slowly falls to ~1.0 at -5C.

Next-Gen CO2 based heat pumps show tremendous promise but they're not very common now.

 

[McRat]

Now I want a heat pump! I take 1 kwh of power, put it into a heat pump, then boil water, drive a steam engine with the 6 kWh of heat.
Even if my steam engine is only 33% efficient, I double my range and get free heating in the process.

 

[AWDtsla]

Hmmm.... I admire your enthusiasm but I don't think your numbers are correct... the best heat pumps available have a COP of ~4.0 at ~0C and that's being generous. That COP slowly falls to ~1.0 at -5C.

Next-Gen CO2 based heat pumps show tremendous promise but they're not very common now.

http://www.nrel.gov/docs/fy11osti/52175.pdf

Page 10. Measured COP of 2 at -5F, for models from 6 years ago.

Note F not C!

 

[stopcrazypp]

Now I want a heat pump! I take 1 kwh of power, put it into a heat pump, then boil water, drive a steam engine with the 6 kWh of heat.
Even if my steam engine is only 33% efficient, I double my range and get free heating in the process.

I don't think that is possible since the temperature doesn't get over boiling. You would need some kind of heat based generator that can work at much lower temperatures.

 

[BerTX]

Now I want a heat pump! I take 1 kwh of power, put it into a heat pump, then boil water, drive a steam engine with the 6 kWh of heat.
Even if my steam engine is only 33% efficient, I double my range and get free heating in the process.

And a solar panel on the roof to drive it all!

 

[mtndrew1]

Supposedly the Prius Prime debuts a twist on the heat pump that makes it more efficient at low temps but I don't quite understand how it works. Something about "gas injection" or some such. With the many bright minds here I doubt it will be long until someone gives a detailed explanation of its improvement and whether or not such an improvement would make it viable in a Tesla (or other BEV).

Edit: Found a link.

 

[llavalle]

Hmmm.... I admire your enthusiasm but I don't think your numbers are correct... the best heat pumps available have a COP of ~4.0 at ~0C and that's being generous. That COP slowly falls to ~1.0 at -5C..

Humm, Not sure I'm following you here. The Mitsubishi Zuba series has been tested at over 200% efficiency (i.e. COP greater than 2.0) at -15F or -26C. I personally own a Fujitsu 15RLS2 heatpump that has around 1.5-1.6 COP at -4F or -20C

The Lennox XP25 is listed at 2.28 @ 17F or -8.3C. And this is the actual COP of the installed docked system.

There are a couple of easily available options on the market right now with COP > 1.5 at very low temps.