Does Chill mode increase efficiency? Surprisingly, Tesla says yes

Does Chill mode increase efficiency?

This question seems to come up in Tesla circles every so often, and the conventional answer is "no, if you drive exactly the same speeds then acceleration mode does not impact efficiency".

But Tesla has some interesting notes in the manual:

If your vehicle is equipped with a heat pump (to determine if your vehicle has a heat pump, touch Controls > Software > Additional Vehicle Information), you can improve the efficiency of the cabin heating by reducing your selected acceleration mode. This allows the heat pump system to take more heat from the Battery to efficiently heat the cabin, instead of maintaining the Battery's ability to provide peak acceleration performance.

So in weather cold enough to use cabin heating apparently yes it can improve efficiency.

Link to the section for Model 3 (it also exists for S and presumably any heat bump vehicle).

"Tesla Model 3 | E-Cannonball 2018" by JayUny is licensed under CC BY-SA 2.0.
Admin note: Image added for Blog Feed thumbnail

 

[voldar]

I'd be interested to understand why the Engineers designed it that way. It seems like if it was net less efficient to drive in chill mode in very cold temps, at the very least the energy app would say so. Then again, the energy app is also not saying to use chill mode when its very cold.

I can't answer to these questions. The Chill mode was put in place before the heat-pump was introduced in the Tesla lineup.
I doubt either that there are many who are efficiency-nerds and are looking for every electron to squeeze from their battery (like me). It may not be a big difference and we all know that perfection is the enemy of good. Also we know that explaining something in too much details, is like not explaining it at all. So... I don't blame Tesla for this approach. Everyone is entitled to his/hers experience.

 

[voldar]

If you’re accelerating hard enough that you notice the difference between chill and standard modes then efficiency isn’t your primary concern.

I would say it is. Because from my experience, the time to get up to speed doesn't matter in the consumption per se. If you accelerate fast or slow, as long as you want to get to the same speed, the difference in consumption is nothing to write home about. Hard brakes is what makes the difference in efficiency when driving an EV.

 

[dakhlkt22]

Actually you do. Pretty much all lithium-ion battery cells have higher internal resistance at lower temperatures, which means there is a real resistive efficiency loss when the battery is operating in colder weather.

So you really have to balance the energy consumption from heating/maintaining a battery temp, versus the losses from higher internal resistance.

I always thought resistance generates heat. So is that internal resistance from low temperatures heating the battery as a byproduct?

 

[David99]

Because the battery is only heated to 36C when preparing to charge.
For the rest of the time, the battery, while driving, is kept to a very low temperature in cold weather (5C to 10C battery temperature, sometimes even lower, but above 0C). And let me tell you, when your battery is at 2C (Chill mode) and you want to bring it to 36C for an optimal charge, you spend a lot more energy than bringing it from 10C to 36C. But you are free to do whatever you like.

I regularly see it go up to 50 C when preconditioning on a way to the supercharger. There were drives where the car had plenty time to precondition, but stopped at around 45 C. One time it didn't precondition at all on a way to a supercharger, but it turns out it was an urban type station with 75 kW limit. As soon as I changed the destination to a 250 kW V3 supercharger, the car started preconditioning.

I believe the car considers a few things when preconditioning and deciding for a temperature goal.

 

[voldar]

I regularly see it go up to 50 C when preconditioning on a way to the supercharger.

I know EA added the precondition on command and the cell Min temp is 36C when the precondition ends. I am not sure what you are seeing in the ScanMyTesla. When the Min value is 36C the Max value may exceed 50C.

 

[DrGriz]

Actually you do. Pretty much all lithium-ion battery cells have higher internal resistance at lower temperatures, which means there is a real resistive efficiency loss when the battery is operating in colder weather.

So you really have to balance the energy consumption from heating/maintaining a battery temp, versus the losses from higher internal resistance.

You've convinced me that Chill at low temps, by increasing battery resistance, increases available heat to scavenge for cabin heating, making it more "efficient" for that purpose. At the same time it results in efficiency loss for other purposes, that is, range. This is entirely consistent with what Tesla is saying in the manual, which primarily addresses cabin heating.

One reason I still like Chill at cold temps is because it reduces the risk of unexpected tire spinning (and therefore loss of control) during acceleration on ice, one of my real fears (because, it happens). But I can see that on dry/cold roads it would bite more into range and as long as the cabin is warm enough I would turn it off.

 

[sleepydoc]

Actually you do. Pretty much all lithium-ion battery cells have higher internal resistance at lower temperatures, which means there is a real resistive efficiency loss when the battery is operating in colder weather.

So you really have to balance the energy consumption from heating/maintaining a battery temp, versus the losses from higher internal resistance.

The 'internal resistance' is actually a drop in voltage due to slower chemical reactions. The effect of this is dependent on the amount of current drawn which goes along with chill mode reducing the available current. In any case it is not a huge variation and as the battery passively heats up with use the difference will negate itself.

 

[sleepydoc]

Because the battery is only heated to 36C when preparing to charge.
For the rest of the time, the battery, while driving, is kept to a very low temperature in cold weather (5C to 10C battery temperature, sometimes even lower, but above 0C). And let me tell you, when your battery is at 2C (Chill mode) and you want to bring it to 36C for an optimal charge, you spend a lot more energy than bringing it from 10C to 36C. But you are free to do whatever you like.

The amount of energy required to heat the battery from 10º to 36º C is constant, no matter when you do it. If you actively heat the battery when it doesn't need to be heated then you are simply wasting energy that can either be used to heat the cabin or that will be dissipated into the environment.

I charge in my garage at night with a level 2 charger. By waiting to heat until it needs to it not only saves energy but the heat that is generated goes to heating the garage which is desirable anyway.

 

[sleepydoc]

I would say it is. Because from my experience, the time to get up to speed doesn't matter in the consumption per se. If you accelerate fast or slow, as long as you want to get to the same speed, the difference in consumption is nothing to write home about. Hard brakes is what makes the difference in efficiency when driving an EV.

I've actually tested this - hard acceleration yields a small but definite decrease in efficiency.

I regularly see it go up to 50 C when preconditioning on a way to the supercharger. There were drives where the car had plenty time to precondition, but stopped at around 45 C. One time it didn't precondition at all on a way to a supercharger, but it turns out it was an urban type station with 75 kW limit. As soon as I changed the destination to a 250 kW V3 supercharger, the car started preconditioning.

I believe the car considers a few things when preconditioning and deciding for a temperature goal.

I know EA added the precondition on command and the cell Min temp is 36C when the precondition ends. I am not sure what you are seeing in the ScanMyTesla. When the Min value is 36C the Max value may exceed 50C.

DC fast charging requires temperature optimization so this makes sense. I don't know what the optimal temperature is for the cells in Tesla batteries (it is likely car-dependent as different models use different types of batteries,) but in these cases the optimal temperature is different from that needed for driving.

When you talk about EA adding a precondition command, what car is that for and how is it activated? In Teslas, setting a supercharger as a destination will trigger the car to condition so it is at the optimal temperature on arrival. I'm not aware that you can or how you would do that with EA chargers.

 

[stopcrazypp]

I always thought resistance generates heat. So is that internal resistance from low temperatures heating the battery as a byproduct?

Yes. But then the actual electrical energy you get out would be reduced as a result.

 

[stopcrazypp]

You've convinced me that Chill at low temps, by increasing battery resistance, increases available heat to scavenge for cabin heating, making it more "efficient" for that purpose. At the same time it results in efficiency loss for other purposes, that is, range. This is entirely consistent with what Tesla is saying in the manual, which primarily addresses cabin heating.

One reason I still like Chill at cold temps is because it reduces the risk of unexpected tire spinning (and therefore loss of control) during acceleration on ice, one of my real fears (because, it happens). But I can see that on dry/cold roads it would bite more into range and as long as the cabin is warm enough I would turn it off.

You are making the assumption that resistive heat is the most efficient way to generate heat, but that is not true. Given heat pumps have a COP higher than 1 (meaning they are more efficient than resistive heat) that means its more efficient if that energy instead went to electricity to power the heat pump.

 

[stopcrazypp]

The 'internal resistance' is actually a drop in voltage due to slower chemical reactions. The effect of this is dependent on the amount of current drawn which goes along with chill mode reducing the available current. In any case it is not a huge variation and as the battery passively heats up with use the difference will negate itself.

The internal resistance means you get less electrical energy out of it, meaning it is less efficient. And as noted, given heat pumps have COP higher than 1, you can generate heat more efficiently using electricity than using the waste heat.

 

[DrGriz]

You are making the assumption that resistive heat is the most efficient way to generate heat, but that is not true. Given heat pumps have a COP higher than 1 (meaning they are more efficient than resistive heat) that means its more efficient if that energy instead went to electricity to power the heat pump.

Thanks for clarifying. Bottom line the same, right? Chill mode to more efficiently heat the cabin, but compromising range/acceleration?

 

[sleepydoc]

The internal resistance means you get less electrical energy out of it, meaning it is less efficient. And as noted, given heat pumps have COP higher than 1, you can generate heat more efficiently using electricity than using the waste heat.

But it’s a catch 22 - in order to use the more efficient heat pump you need to get the energy out.

 

[voldar]

When you talk about EA adding a precondition command, what car is that for and how is it activated?

It is Tesla and it is Europe, where Tesla can charge on other DCFC stations and as we all know, the preconditioning to charge doesn't work when navigating to non-Tesla DCFC.
EA = EnhAuto and their S3XY buttons.

 

[David99]

It is Tesla and it is Europe, where Tesla can charge on other DCFC stations and as we all know, the preconditioning to charge doesn't work when navigating to non-Tesla DCFC.
EA = EnhAuto and their S3XY buttons.

OH!! EA in the US usually means 'Electrify America', which is a charging network. I was so confused.

I have the S3XY buttons and I think it is helpful to manually start preconditioning in some situations. #1 when navigating to CCS stations that one can use with the official adapter. The other useful situation I can think of is kind of inspired by this discussion. If I charge at home on AC and it's a very cold day, I can precondition the battery which makes it extra warm. Since I'm still charging, the extra energy needed comes from the grid. In essence I can take with me heat energy stored in the battery. The car can use that energy to heat the cabin. One degree (Celsius) difference in battery temperature is approx 0.5 kWh of energy. Having the battery at 50 C (the typical precondition target I have seen) would have 15 kWh of heat energy available compared to say 20 C which is average charging off AC on a cold day. That's the equivalent of 50 miles of range. Not bad.
If you don't have the S3XY buttons but a performance car, turning on track mode will also heat up the battery.

 

[voldar]

The other useful situation I can think of is kind of inspired by this discussion. If I charge at home on AC and it's a very cold day, I can precondition the battery which makes it extra warm. Since I'm still charging, the extra energy needed comes from the grid.

I doubt it would be possible, but needs to be tested. AFAIK the preconditioning for charging is only allowed when the car isn’t plugged in. Yes, you could precondition for 20-25 minutes unplugged then you plug the car and refill it, but … needs to be tested.

 

[voldar]

Thanks for clarifying. Bottom line the same, right? Chill mode to more efficiently heat the cabin, but compromising range/acceleration?

Yes, in cold weather at least. In temperatures above freezing, Chill mode only compromises the acceleration.

 

[stopcrazypp]

Not quite, it will give you more max heat output (since you now have max heat pump output+waste heat), so it can heat up the cabin more quickly or maintain a larger heat differential, but that doesn't necessarily mean it is more efficient (as in energy in versus useful work out gotten out of it) than maintaining a higher target temp and lower resistance. Whether that is true depends on how much the higher resistance "costs" versus the energy spent keeping the battery warm. If you are running high per loads (like accelerating), it will cost more in energy efficiency.

 

[David99]

OH!! EA in the US usually means 'Electrify America', which is a charging network. I was so confused.

I have the S3XY buttons and I think it is helpful to manually start preconditioning in some situations. #1 when navigating to CCS stations that one can use with the official adapter. The other useful situation I can think of is kind of inspired by this discussion. If I charge at home on AC and it's a very cold day, I can precondition the battery which makes it extra warm. Since I'm still charging, the extra energy needed comes from the grid. In essence I can take with me heat energy stored in the battery. The car can use that energy to heat the cabin. One degree (Celsius) difference in battery temperature is approx 0.5 kWh of energy. Having the battery at 50 C (the typical precondition target I have seen) would have 15 kWh of heat energy available compared to say 20 C which is average charging off AC on a cold day. That's the equivalent of 50 miles of range. Not bad.
If you don't have the S3XY buttons but a performance car, turning on track mode will also heat up the battery.

I'll give it a try. I'll also try turning on 'track mode' while charging to see if that works.