Why does Tesla use a Resistance Heater instead of Heat Pump

[Benjanos]

I need to find a good recipe for a home made ground beef pizza. Any ideas? I like things spicy so any recipe with Jalapenos would be good.

Also need to find a good deep dish pan for cooking pizza at home. Basic oven trays are no good I find.

 

[arnis]

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

Panasonic HZ25UKE gives us COP 5.2 in good conditions. And there are some with a bit better numbers. In real life, usually up to 4 is expected. My calculations on a Leaf give around 300% efficiency.

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?

The fact is, that with cold soaked pack, Model 3 owners have been literally stuck for HOURS at SuperChargers.
There is a real problem waiting Model 3 owners. I hope Tesla can fix it with OTA update, if not, I'm 80-90% convinced once Model 3 enters Norwegian market, there will be #FrozenGate recall/retrofit

 

[mongo]

Panasonic HZ25UKE gives us COP 5.2 in good conditions. And there are some with a bit better numbers. In real life, usually up to 4 is expected. My calculations on a Leaf give around 300% efficiency.

Tried looking that up, but links were non-English. Is that peak COP or seasonal HPSF?

The fact is, that with cold soaked pack, Model 3 owners have been literally stuck for HOURS at SuperChargers.
There is a real problem waiting Model 3 owners. I hope Tesla can fix it with OTA update, if not, I'm 80-90% convinced once Model 3 enters Norwegian market, there will be #FrozenGate recall/retrofit

Yeah, the pack heating for charging may be a problem especially with the surface area, but hours seems extreme...

 

[arnis]

https://www.panasonicproclub.com/uploads/EE/catalogues/18 EN CATALOGUE 18 170818.pdf

Page 57.

 

[AWDtsla]

Tried looking that up, but links were non-English. Is that peak COP or seasonal HPSF?



Yeah, the pack heating for charging may be a problem especially with the surface area, but hours seems extreme...

It is not extreme. That's how it works. How long does it take to heat a pack from -10C to 40C with a 3.5kW heater? Won't take a drop of charge before it's above 0C. What's your 120kW doing for you now????

 

[mongo]

https://www.panasonicproclub.com/uploads/EE/catalogues/18 EN CATALOGUE 18 170818.pdf

Page 57.

Thanks for the link!
If I'm reading correctly, it drops to a COP of less than 3 quite quickly. Still better than resistive, but half its peak value.

COP 2.44 at -7 C (21 F)

 

[mongo]

It is not extreme. That's how it works. How long does it take to heat a pack from -10C to 40C with a 3.5kW heater? Won't take a drop of charge before it's above 0C. What's your 120kW doing for you now????

Super conservative back of napkin math says a 3 pack needs 1kWh to change temp 7C. So 50C is 7kWh, or 2 hours at 3.5kW. But why does the pack need to get to 40C? -10C to 0C would be 1.4 kWh or 24 minutes.

 

[AWDtsla]

Super conservative back of napkin math says a 3 pack needs 1kWh to change temp 7C. So 50C is 7kWh, or 2 hours at 3.5kW. But why does the pack need to get to 40C? -10C to 0C would be 1.4 kWh or 24 minutes.

Rate of charge is 0 (any units) at 0C. Starts climbing from there. You're not getting 120kW at 1C. Maybe at 40C if your SoC is low enough.

Now that I realize you don't own a Tesla, what are you trying to do in this thread? You don't know how to car works, but are asserting all kinds of things about it, that being cold or not having a heat pump, etc, etc, are no big deal. I drive it everyday. It is a big deal. Listen to experience.

 

[mongo]

Rate of charge is 0 (any units) at 0C. Starts climbing from there. You're not getting 120kW at 1C. Maybe at 40C if your SoC is low enough.

Now that I realize you don't own a Tesla, what are you trying to do in this thread? You don't know how to car works, but are asserting all kinds of things about it, that being cold or not having a heat pump, etc, etc, are no big deal. I drive it everyday. It is a big deal. Listen to experience.

I'm on this thread because it is interesting and while I don't have one, I do know a little about HVAC and heat pumps and such and to give counterpoint to HP being an obvious must have. HP are more energy efficient, but also more complicated, especially in a setup where there are different zone of climate control. The thread's title starts with "Why", thus asking, "what are the reasons not to". If you want the thread to just be one post of "They should have, and are stupid not to", imagine that it is.

I'm not here to discount anyone's real world experiences. Did I say it doesn't need to go to 40C? No, I asked why does it need to go 15 degrees above STP after you said people were waiting hours to charge. The pack heating/ charging is a separate issue based on total heat output needed.

 

[JohnnyG]

Now that I realize you don't own a Tesla, what are you trying to do in this thread? You don't know how to car works, but are asserting all kinds of things about it, that being cold or not having a heat pump, etc, etc, are no big deal. I drive it everyday. It is a big deal. Listen to experience.

For what it's worth... @mongo has brought a lot of technical knowledge and thought provoking chat to this conversation. There are Tesla engineers which are designing these cars that don't own/drive them either, so it gives a similar perspective perhaps?

 

[Marc_GA]

Rate of charge is 0 (any units) at 0C. Starts climbing from there. You're not getting 120kW at 1C. Maybe at 40C if your SoC is low enough.

Also keep in mind charging produces excess heat. Charging by itself will warm the pack a good bit faster.

 

[AWDtsla]

Also keep in mind charging produces excess heat. Charging by itself will warm the pack a good bit faster.

How does that help you if you can't charge because the pack is under 0C? If you're above 0C, how long do you have to sit at the supercharger before you get to actual supercharging speeds or you complete charging? The "hours" mentioned above is correct.

I really really really hope Tesla solved the design error with the Model S/X that wouldn't let you turn on the pack heater from shore power if the pack can't charge. Although there was one report from last winter where it seems they didn't.

 

[RobS87]

Near instant heat with resistive heater. Light weight. Great package.

 

[mongo]

How does that help you if you can't charge because the pack is under 0C? If you're above 0C, how long do you have to sit at the supercharger before you get to actual supercharging speeds or you complete charging? The "hours" mentioned above is correct.

I really really really hope Tesla solved the design error with the Model S/X that wouldn't let you turn on the pack heater from shore power if the pack can't charge. Although there was one report from last winter where it seems they didn't.

Hard to implement but effective: liquid cooled cables that also connect to vehicle coolant system. Superchargers could then use all their waste heat to warm the packs of cold cars. Partly lines up with the under connection charger patent Tesla has.

 

[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...

And so it begins...

Regenerative braking off

 

[arnis]

As of right now, Tesla has really bad hardware for battery heating and even worse software.
Luckily they should be able to fix the latter in november-december.
Step 1) heat the pack if navigation is set for any rapid charger, incl ChaDeMo.
Step 2) dump all "unable to regen" load into a resistive heater or motor windings so retardation* would be fully available not
only with pack that is below freezing but also with 100% charged pack.
In case of warm pack, dump the heat with regular glycol radiator, in case of cold pack, circulate into the pack glycol loop.

Show energy dumping in another color on that same regen display. Proceed right on the dotted line up to normal maximum amount.



*not technically regen as energy is being converted into heat, not back where it came from.

 

[WeberAuto]

Here's a few other from my car. Sorry for the LONG post

Taken back in August. Outside temp was 4.0C (40f).
HVAC was off. Battery was pretty cold (between 9.5C and 12C) so the cooling loop was in series with the drive unit (basically heating the pack from the heat of the DU). You can confirm that by checking the 2 temps.
-Just under "Battery Heater" (which is off in that pic), 17.5C entering the pack (this screen is animated, trust me on the flow direction)
-Left side, out of the pack and 2nd pump, 14.6C.

i.e. Coolant gets cooler as is go through the batteries. Note that the top right valve is bypassing the center radiator at 100%

Another one, taken in December. A lot colder outside. Battery pack is REALLY cold, almost below freezing. -15C outside (5F). System is running the pack heater and the cooling (well, heating in that case) loop only goes though the pack, the DC-DC and the Heater. It bypasses the chiller (that's the heat exchanger from the AC and the battery loop when supercharging)

And here's the raw data :
You can see that the PTC heater (that's the cabin heater) is running at 90% capacity. Outside air is at -15.6C but evap temp is -12C because AC is actually working in COOLING mode to dry the air. Note that in that mode, the AC compressor pulses on & off so that pic was taken when the compressor was at 0%

In all cases, the only time there is coolant in contact with the AC heat exchange is when the chiller is in use and the system runs. There are no coolant loop connected to anything inside the cabin. The only way to get heat is to use the PTC. The only way to get cold is to use the AC

Example of use of chiller during supercharging session :
EAC (AC compressor) running at 100%, both AC coil fans running at 100%, evap at 107.4. Chiller in use, pushing coolant at 28.6C in the pack.. cells steady at 41-45C. Pump running at 100%. Drive unit pump running at 0%.

How do I access the thermal data on my Model S?

 

[David99]

How do I access the thermal data on my Model S?

It's not available to owners. To get this screen, a service technician must be connected to the car with a laptop.

There are other ways, though. You can get to the CAN bus data, though. Requires a few steps and some hardware.

 

[WeberAuto]

Thanks @David99

 

[Galinette]

My two cents: I bet that they did not use a HP because as every automakers, Tesla relies on OEMs for many, many parts including AC. And as on ICEs a heating source is not required, AC heat pumps are cooling only. Tesla had to use these HP. as it was probably much more expensive to make an OEM develop a dedicated reversible one. This may change in the future with growth of EV market. A reversible heat pump would for sure lower a lot energy drain when heating the car in cool (but not freezing) climates.
Small series are costly for an OEM part, and 200k/year is a small serie in the automotive industry. Remember, even for the Model S wheel selectors, Tesla had to reuse the ones from Mercedes.

Now when it comes to heating the battery pack. A heat pump is more efficient than a battery pack. The efficiency is lower on cold temperatures, but will generally still stay better than a resistor. BUT, the heating power will be also very low. For instance, a 3kW resistor will produce 3kW of heat whatever the conditions. A 1kW heat pump may generate 4kW of heat at 20°C, 2.5kW at 0°C and 1.5kW at -20°C (numbers are illustrative only). Wich means, that at -20°C, it's still slightly more efficient than a resistor, but the heating power is very low. And thus, initiating a battery charge will be super long.

The best world would involve both a reversible heat pump and a resistor. The resistor costs virtually nothing, but it adds some complexity to the wiring and design.

So the reasons why they do not have a reversible heat pump are:
1) This is not a standard OEM part as the ICE cars doesn't have one.
2) A resistor is still required, which adds to the overall complexity.

Cheers!