Heat pump: cabin vs. battery warming?

[scaesare]

So Tesla just released a video on their heat pump.

I question I had some time ago, but never got around to asking is: Does the heat pump also provide heat for the pack in addition to the cabin?

The earlier resistive heater cars (like mine) had separate heaters for the cabin, and the pack. The thermal management system could tie the pack and cabin coolant loops together for some things, but not others (i.e. - the A/C pump cooled both, wheras waste inverter/drivetrain heat could warm the pack, but not the cabin).

I ask because, other than cabin heating, pack heating is the single largest non-locomotive power draw in the cars. I know that the motor can have it's magnetic field energized such that it generates excess heat for the pack. However, the older cars had 2 sources of heat for the pack: waste drivetrain heat AND a resistive heater. If the heat pump is sized to provide pack heat in addition to the motor rotor phase angle heating, that would be significant.

 

[MP3Mike]

I question I had some time ago, but never got around to asking is: Does the heat pump also provide heat for the pack in addition to the cabin?

Yes.

They even go as far as running the HVAC to move the heat from the cabin into the battery after you park, so it doesn't just get lost to the air. Then when you start heating again it pulls the heat out of the battery and puts it back in the cabin. (This works really well with multiple short drives like if you are hitting a number of stores.)

 

[GOVA]

I noticed one thing - once the supercharger trip has been selected and battery needs to warm up, there is more whining from extra resistance from the motors. This generates extra heat which is directed to heat the battery.

This might suffice 100% for that so the heatpump is not used to warm up the battery, but this is just a guess.

 

[ItsNotAboutTheMoney]

I noticed one thing - once the supercharger trip has been selected and battery needs to warm up, there is more whining from extra resistance from the motors. This generates extra heat which is directed to heat the battery.

This might suffice 100% for that so the heatpump is not used to warm up the battery, but this is just a guess.

It's part of the same system, it's just in that case it's pumping heat from motor to battery. The idea of the octovalve is that it can move heat as needed between outside, cabin, motor and battery. The motor is the only one that is consistently a source of heat.

 

[Artful Dodger]

Does the heat pump also provide heat for the pack in addition to the cabin?

This is certainly possible with the octovalve, it should be possible to route heat that way. I'd tag @mongo for the specs. He's got a line on the Tesla parts catalog which may shed some light (and heat).

Cheers!

 

[Cosmacelf]

Yes.

They even go as far as running the HVAC to move the heat from the cabin into the battery after you park, so it doesn't just get lost to the air. Then when you start heating again it pulls the heat out of the battery and puts it back in the cabin. (This works really well with multiple short drives like if you are hitting a number of stores.)

That’s wild. Heat pump usage isn’t free. It does cost energy to run. So after you park, they expend energy to harvest heat from the cabin Into the battery? And then they expend energy again to reverse that?

 

[MP3Mike]

hat’s wild. Heat pump usage isn’t free. It does cost energy to run. So after you park, they expend energy to harvest heat from the cabin Into the battery?

Yep. I assume they have done the math and found it is normally worth it. (Like for trips with a short break between stops, or if you charge after stopping.)

It is probably wasted energy on the last stop of the day when you aren't charging, but I haven't ever monitored it to know how long it harvests heat for. (Which could give an idea of how much energy is used.)

And then they expend energy again to reverse that?

Yep. Well, the cabin was going to be heated anyway, so the heat source would be the air, the motors, or the battery.

 

[mongo]

So Tesla just released a video on their heat pump.

I question I had some time ago, but never got around to asking is: Does the heat pump also provide heat for the pack in addition to the cabin?

The earlier resistive heater cars (like mine) had separate heaters for the cabin, and the pack. The thermal management system could tie the pack and cabin coolant loops together for some things, but not others (i.e. - the A/C pump cooled both, wheras waste inverter/drivetrain heat could warm the pack, but not the cabin).

I ask because, other than cabin heating, pack heating is the single largest non-locomotive power draw in the cars. I know that the motor can have it's magnetic field energized such that it generates excess heat for the pack. However, the older cars had 2 sources of heat for the pack: waste drivetrain heat AND a resistive heater. If the heat pump is sized to provide pack heat in addition to the motor rotor phase angle heating, that would be significant.

Everything shares the same heat pool. Octovalve chooses what outside the cabin gets heat added and what gets heat removed.
The cabin itself is (primarily) heated and cooled by its own refrigerant loops. However, those are also transfering heat from the same coolant reservoir.
Coolant to air heat exchanger is used to cover the difference (beyond stator and heat pump induced inefficiencies).

That’s wild. Heat pump usage isn’t free. It does cost energy to run. So after you park, they expend energy to harvest heat from the cabin Into the battery? And then they expend energy again to reverse that?

Heat pump COP is better at warmer temps, so round trip heat shifting can be better than loss and external replenishment. Plus, the heat pump inefficiency itself adds to the heating, so it's more like single direction, and again, the inefficiency isn't lost (immediately).

 

[lowtek]

Op, love your avatar!

 

[scaesare]

OK, cool... thanks for those that chimed in.

On the heat pump cars, do folks notice if/when the pack is being heated by heat pump vs the motor rotor-phase-angle trick (is there an official name for that heating mode?),

On the resistive cars, you could watch the power usage and be able to tell if the resistive heater was on, or if the pack was (assumedly) just utilizing drivetrain waste heat when the weather was cold. The resistive heater could be 3-5+KW of draw...

 

[scaesare]

Op, love your avatar!

Th-th-th-thanks!

 

[scaesare]

I noticed one thing - once the supercharger trip has been selected and battery needs to warm up, there is more whining from extra resistance from the motors. This generates extra heat which is directed to heat the battery.

This might suffice 100% for that so the heatpump is not used to warm up the battery, but this is just a guess.

I have heard this was audible...

 

[OxBrew]

OK, cool... thanks for those that chimed in.

On the heat pump cars, do folks notice if/when the pack is being heated by heat pump vs the motor rotor-phase-angle trick (is there an official name for that heating mode?),

On the resistive cars, you could watch the power usage and be able to tell if the resistive heater was on, or if the pack was (assumedly) just utilizing drivetrain waste heat when the weather was cold. The resistive heater could be 3-5+KW of draw...

No, can't tell at all. I've done demanding road trips at -7°F, 15, 25, 35F, studying the energy charts and tables, never could tell. I think the heat pump is an excellent solution, really happy with it.

 

[FSDtester#1]

Th-th-th-thanks!

Don't develop Paranoimia...

 

[SageBrush]

There are many very interesting and useful things that the heat pump/octovalve enable, but one I find particularly brilliant and ahead of everybody else in EVs is the the pattern of heat transfer on long trips in the winter:

During Supercharging, the pack is heated up to 50+ C. Then during driving the heat is removed from the pack to protect its health and to heat the cabin The sum result is that cabin comfort is via shore power, and the winter hit to range from cabin A/C is markedly mitigated.

 

[gsmith123]

^ oh that is clever. I mean, it makes perfect sense, but I'd never quite thought of that before. Usually people talk about steady state efficiency and I've never heard this.

 

[SageBrush]

^ oh that is clever. I mean, it makes perfect sense, but I'd never quite thought of that before. Usually people talk about steady state efficiency and I've never heard this.

I haven't had an opportunity to play with this yet, but I suspect that driver behavior can improve utilization. My thought is that the pack has to dump its heat after charging fairly quickly, and the only other heat sink in the car that has enough capacity is the cabin. So it makes sense to me to increase the cabin thermostat to the higher side of comfortable after charging, and then when the cabin is at steady state, to only use recirc at a low level until the passengers want more heat.

 

[mongo]

I haven't had an opportunity to play with this yet, but I suspect that driver behavior can improve utilization. My thought is that the pack has to dump its heat after charging fairly quickly, and the only other heat sink in the car that has enough capacity is the cabin. So it makes sense to me to increase the cabin thermostat to the higher side of comfortable after charging, and then when the cabin is at steady state, to only use recirc at a low level until the passengers want more heat.

If the intent were just pack cooling, they also have the radiator to dump heat with.
The pack is a huge thermal mass, so if it is cold out, it may not be getting to temperatures that impact pack life, especially if charged to less than 90% and/ or immediately driven.
https://www.sciencedirect.com/science/article/pii/S1002007118307536
The patent called out 85 Wh/degree C (for some pack size), so freezing to 50 C would be over 4kWh.
US20190070924A1 - Optimal source electric vehicle heat pump with extreme temperature heating capability and efficient thermal preconditioning - Google Patents

[ 0103 ] Although it is useful to heat the battery system 106 , particularly when the battery system 106 is very cold , it is often more beneficial from a range perspective to use part or all of the available thermal energy ( from driving or stored in the battery system 106 thermal mass ) to heat the cabin . The vehicle heat pump system 202 can efficiently source this low - grade thermal energy from the battery system 106 / powertrain coolant loop to efficiently heat the cabin ( COP > > 1 ) . However , this in - turn would slow down heating of the battery system 106 ( or even cool it down ) . In other words , we can trade efficient cabin heating ( improved range ) against a colder on - average battery system 106 , which has downsides that depend on context . The trade - off strongly depends on the balance between cabin heating needs , dis sipation available naturally ( driving profile ) , battery perfor mance requirements ( driving profile ) , and initial battery temperature ( stored thermal energy ) . The utility of heating the battery system 106 is particularly complex , and is a strong function of temperature , drive profile , state of charge , anticipated charging needs , and age . At the cold extreme , the battery system 106 will not accept charging ( or will charge extremely slowly ) , has low discharge power capability , low regen capability , higher electrical resistance , and potentially ages more rapidly . As the battery system 106 warms up , these issues each diminish separately ; heating the battery system 106 from 0 to 10° C . requires the same energy as 20° C . to 30° C . , but the impact on driving experience and range are immensely different . In other words , the sourcing scheme must consider many objectives and adjust accordingly .
[ 0104 ] It is clear that when both the cabin and the battery system 106 are soaked to extremely cold temperatures , e . g . , - 10° C . , both are in dire need of heating and cabin heating efficiency ( but not comfort ) should be sacrificed in an effort to heat both the battery system 106 and the cabin as quickly as possible . However , when the cabin is cold or needs heating , but the battery system 106 is at an intermediate temperature , there are significant opportunities . In cold conditions , the battery system 106 ( a massive thermal mass at 85 W - h / ° C . ) is usually warmer than ambient at the start of the drive because it is relatively well isolated from ambient and therefore takes a long time to reach thermal equilibrium . Although the battery system 106 effectively already serves as a natural thermal reservoir , it can also function as an artificial thermal reservoir . The vehicle heat pump system 202 architecture provides a new way to efficiently utilize it as more deliberate energy storage medium . The battery temperature can be efficiently ( COP > > 1 ) topped up and drawn down to provide more efficient cabin warm - ups .

 

[Cosmacelf]

If the intent were just pack cooling, they also have the radiator to dump heat with.
The pack is a huge thermal mass, so if it is cold out, it may not be getting to temperatures that impact pack life, especially if charged to less than 90% and/ or immediately driven.
https://www.sciencedirect.com/science/article/pii/S1002007118307536
The patent called out 85 Wh/degree C (for some pack size), so freezing to 50 C would be over 4kWh.
US20190070924A1 - Optimal source electric vehicle heat pump with extreme temperature heating capability and efficient thermal preconditioning - Google Patents

Wow, that patent excerpt is fascinating. I think I now know why the latest battery pack tear down done by Munro showed so much lightweight foam everywhere. It’s there for thermal insulation! Munro’s guys appeared mystified why there was so much pink foam everywhere (And it was a pain in the butt to get rid of it).

I also now know why regen gets limited even in fairly mild temperatures (like 50 degrees F or 10 C). They might be harvesting heat from that pack to heat the cabin, and then eventually the pack warms itself up and the motors generate heat too. Talk about not leaving anything on the table. I doubt we will see this level of heat harvesting efficiency from other vehicle manufacturers for the next ten years!

 

[beatle]

I also now know why regen gets limited even in fairly mild temperatures (like 50 degrees F or 10 C). They might be harvesting heat from that pack to heat the cabin, and then eventually the pack warms itself up and the motors generate heat too. Talk about not leaving anything on the table. I doubt we will see this level of heat harvesting efficiency from other vehicle manufacturers for the next ten years!

Well, regen is limited below battery temps of 67F even on the cars with resistive heat and no heat scavenging. I think it's more to protect the battery from the inrush of power while the battery is cold more than anything else.