Why does Tesla use a Resistance Heater instead of Heat Pump

[mongo]

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.

Electric heat from renewables is not bad for the environment, but it does cost more per BTU.

The 1000W per mile is due to how the calculation handles the preconditioning (or driving really slowly with full heat, sub 15 MPH) the energy spent before the drive starts gets added into the total usage, so the first few miles show energy use that happened when not driving.

Pack should not need to heat when driving unless you are charging or it is sub -30...An insulated garage might be better than letting the car cold soak overnight....

A heat pump works in certain conditions. That doesn't mean it's a good choice for a mass market car.

 

[AWDtsla]

Electric heat from renewables is not bad for the environment, but it does cost more per BTU.

Using 4 times as much electricity as you need is bad for the environment. We're not even close to 100% renewables.

The 1000W per mile is due to how the calculation handles the preconditioning (or driving really slowly with full heat, sub 15 MPH) the energy spent before the drive starts gets added into the total usage, so the first few miles show energy use that happened when not driving.

Wrong wrong wrong. It NEVER includes preconditioning in the drive.

Pack should not need to heat when driving unless you are charging or it is sub -30...An insulated garage might be better than letting the car cold soak overnight....

Wrong again! Regen limiting starts below 15C, active pack heating occurs during preheating up to 12C. Starting preconditioning after the car is "cold soaked" at 8C will draw 11kW to start with. That's still shorts weather for some people.

A heat pump works in certain conditions. That doesn't mean it's a good choice for a mass market car.

We're just going to oscillate between impossible, impractical, and unnecessary until someday they actually implement it. Then you guys will say you knew it all along.

 

[AWDtsla]

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.

This is actually problematic for the Model 3. Smaller pack heater, pack just about the same size, less waste heat from drivetrain. Let's see the complaints streaming in this winter. There were practically 0 Model 3's last winter.

 

[AWDtsla]

PS I heat my pack with "max battery heat" up to 35-40C if heading to a supercharger, for fastest supercharging speeds. Huge amount of energy wasted to do so in the winter. 30-45 minute drive is not enough waste heat even with a P drivetrain to bring the pack to temp.

 

[dgpcolorado]

This is actually problematic for the Model 3. Smaller pack heater, pack just about the same size, less waste heat from drivetrain. Let's see the complaints streaming in this winter. There were practically 0 Model 3's last winter.

With so many new Model 3s out there now, I'll be fascinated to see the complaints about winter driving. The limitation on regen and power will be quite a surprise to many, I would guess.

PS I heat my pack with "max battery heat" up to 35-40C if heading to a supercharger, for fastest supercharging speeds. Huge amount of energy wasted to do so in the winter. 30-45 minute drive is not enough waste heat even with a P drivetrain to bring the pack to temp.

Really? Even 30-45 minutes of driving isn't enough? I've had the cold battery Supercharger limitation on a road trip — I just waited it out — but I don't have any local Supercharger Stations so I've never seen it at home.

 

[AWDtsla]

Even 30-45 minutes of driving isn't enough? I've had the cold battery Supercharger limitation on a road trip — I just waited it out — but I don't have any local Supercharger Stations so I've never seen it at home.

Nope. Sometimes I don't even get out of displayed regen limit with 30 minutes of highway driving. Even if it did, got another 25C to go until optimum supercharging temp. You can of course have some impact on this. Like driving 85 mph with a strong headwind, produces more waste heat. But if you're in traffic going 55-65, not too much is happening.

Even with an ambient temp 40-50F, it takes roughly 10 minutes for the drivetrain loop to be warm enough for warm coolant to be diverted to the battery pack for heating. I didn't have a CAN logger last winter, I'll see how long it takes this winter when the drivetrain is actually cold.

 

[mongo]

Using 4 times as much electricity as you need is bad for the environment. We're not even close to 100% renewables.

The best home heat pump only has seasonal COP of ~3.

Wrong wrong wrong. It NEVER includes preconditioning in the drive.

When did that change?

Wrong again! Regen limiting starts below 15C, active pack heating occurs during preheating up to 12C. Starting precondionting after the car is "cold soaked" at 8C will draw 11kW to start with. That's still shorts weather for some people.

Getting to the temperature to allow regen is a good point in regards to overall efficiency, 30 stops from 30 MPH recovers about the same amount of energy needed to heat the pack 7 degrees C (pure resistive, no ambient losses (seasonal pack insulation seems like it would be a big boost to efficency)).

We're just going to oscillate between impossible, impractical, and unecessary until someday they actually implement it. Then you guys will say you knew it all along.

Knew what all along? It's a design trade off. We are discussing those trade offs.

 

[MP3Mike]

This is actually problematic for the Model 3. Smaller pack heater, pack just about the same size, less waste heat from drivetrain. Let's see the complaints streaming in this winter. There were practically 0 Model 3's last winter.

Technically isn't the Model 3 pack heater larger? Being that the motor/inverter is used for that and it is capable of what 211kW? (Who know at what level Tesla can/will use it as the pack heater.)

 

[mongo]

Technically isn't the Model 3 pack heater larger? Being that the motor/inverter is used for that and it is capable of what 211kW? (Who know at what level Tesla can/will use it as the pack heater.)

Mechanical power output cannot be compared to heat output (unless you pull the heat from the brakes ). If the DU is 95% efficient, it is only built to handle 10kW of waste heat or so.

 

[AWDtsla]

Technically isn't the Model 3 pack heater larger? Being that the motor/inverter is used for that and it is capable of what 211kW? (Who know at what level Tesla can/will use it as the pack heater.)

If I recall correctly its heat output is rated at 3.5kW, vs 5.5kW for S/X. When I heard about this design, I was hoping for something more like 20+kW. There are probably limits to how inefficient you can make the waveform before suffering side-effects.

A Model 3 owner could confirm the power draw pretty easily.

 

[MP3Mike]

Mechanical power output cannot be compared to heat output (unless you pull the heat from the brakes ). If the DU is 95% efficient, it is only built to handle 10kW of waste heat or so.

How can you know that? It could be 95% efficient when operating in normal driving mode, but Tesla can purposely run it in a lower efficiency method and could have built the cooling system to handle a much larger load. (Which it likely is as it has to be able to cool both the motor and inverter.)

How much heat is created from the invertor/motor combination if you command 10kW to create 0 torque?

 

[AWDtsla]

The best home heat pump only has seasonal COP of ~3.

white goods manufacturers cheaping out. Innovation only forced by increasing government regulations. Not state of the art, by any means.

When did that change?

It has ALWAYS been this way. You have the car. Do the experiment. Do the math. Precondition for 6 hours if you have to. Car reports a fraction of total usage to the driver.

 

[mongo]

How can you know that? It could be 95% efficient when operating in normal driving mode, but Tesla can purposely run it in a lower efficiency method and could have built the cooling system to handle a much larger load. (Which it likely is as it has to be able to cool both the motor and inverter.)

How much heat is created from the invertor/motor combination if you command 10kW to create 0 torque?

Sure, they could oversize the cooling system for the times when it is a heating system. I'm saying the ability to convert electrical energy to mechanical energy is not indicative of the ability to convert electrical energy to heat energy. The only load they have is the stator coils and rotor reluctance (like an inductive cooktop). If the rotor is not coaxially cooled like the S/X, then use of rotor heat is severely limited is out.

 

[mongo]

white goods manufacturers cheaping out. Innovation only forced by increasing government regulations. Not state of the art, by any means.

If it is not cost effective for a white goods/ house scenario, why would an automotive OEM go that extreme to develop it? Packaging alone for the heat exchangers needed would be a challenge.

For reference, the maximum theoretical COP for a 35C output from -20C input (95 F, -4 F) is 5.6 (no fans, no losses, ideal gas, yada yada yada).

It has ALWAYS been this way. You have the car. Do the experiment. Do the math. Precondition for 6 hours if you have to. Car reports a fraction of total usage to the driver.

Can't, don't have one. Had just read about people getting really high first mile or two readings after getting service or such. Maybe it's while on, but not driving?

 

[eml2]

Just want to point out that when comparing the efficiency between PTC and HP, one needs to take the weight of such system into account since it needs to be carried around by the car.

 

[Benjanos]

Bottom line, heating in an EV consumes energy, so people need to adapt. You cannot expect to drive around with the cabin heat on as you would in the past with an ICE. These ICE cars have a ridiculous amount of waste heat from the motor that they can use for heating the cabin. Its a key downside/upside of comparing ICE/EV.

If you stand back and consider it properly as an EV driver, you realize how much waste there is in an ICE car.

My last 2 cents.

 

[E-Ryc]

Just want to point out that when comparing the efficiency between PTC and HP, one needs to take the weight of such system into account since it needs to be carried around by the car.

HP is usually there already (A/C), maybe some valves need to be added. So there is probably no reason not to have both (PTC weighs and costs pretty much nothing).

 

[AWDtsla]

If it is not cost effective for a white goods/ house scenario, why would an automotive OEM go that extreme to develop it? Packaging alone for the heat exchangers needed would be a challenge.

Blowing Hot and Cold

These guys already designed a new AC system. It's like about 5% work for 100% upside.

For reference, the maximum theoretical COP for a 35C output from -20C input (95 F, -4 F) is 5.6 (no fans, no losses, ideal gas, yada yada yada).

Look at historical weather data for your average winter temperature. It's way, way, way, above -4F. You can as well look at design basis temperature, which is used for HVAC sizing in houses. Of course there's always a PTC backup, so not even that matters. Only average.

Can't, don't have one. Had just read about people getting really high first mile or two readings after getting service or such. Maybe it's while on, but not driving?

It's barely a blip, next to nothing. It's some sampling error (every tenth of a mile) plus cold tires plus idling time between entering drive and cruising speed.

 

[AWDtsla]

Just want to point out that when comparing the efficiency between PTC and HP, one needs to take the weight of such system into account since it needs to be carried around by the car.

All the weight is in the compressor. Coils are thin wall aluminum. Weight has negligible impact on Tesla energy usage anyway.

 

[Reeler]

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.

The ski resort I have a pass for is about 80 miles from my home. They have some slow level 2 chargers that are frequently occupied so no guarantee I would get one. Round trip is 160 miles so you might think that is no problem for a day trip to the slopes. But, several times each year the normal 90 minute one-way commute stretches to 4-6 hours uphill as they meter traffic. When that is really cold and in the snow, I have been there freezing and avoiding any use of the heater. Minus 20 F one time in heavy snow while it was 5 hours to get to the continental divide. Not fun at all.

To have a resistance heater offends my sensibilities. There is plenty of time on one of those days to become a hater as one contemplates lazy HVAC design.