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

 

[Cubu]

Sad sad realization of knowing that this is limit of our futures’ cognitive capability.

 

[yessuz]

Bjorn Nyland did test (on YT) - there is no impact on motorway

 

[gsmith123]

Bjorn Nyland did test (on YT) - there is no impact on motorway

Do you have a link? I found this test he did with a 2019 Model 3 (non-heat pump). I love TeslaBjorn, but we should be careful with extrapolating his result to other vehicles, other HVAC systems, other temperature conditions, and other factors like preconditioning / initial battery temperature.

To be fair to Tesla they specifically mention the heat bump, which the car in the video linked does not have.

The temperature was about -9C in his test. That's not super cold.

He was driving at highway speed (albeit slow Norwegian highway speed) so that'll generate more heat in the battery than in stop and go or city traffic.

From his video, I didn't see any different in battery temperatures across chill and sport (about 24C). Isn't it theoretically possible that if the car had a heat bump it would pull down the pack temperature, and moreover pull it down further in chill mode?

Thoughts? Do you think Bjorns evidence can be extrapolated to all cars?

 

[drtimhill]

Chill mode improves efficiency even if you don't have a heat pump. And that's because the simple fact of energy to work relation. The faster work being done the more energy is consumed. This is one of the basic laws of physics.

Chill mode makes the pedal less sensitive. And that increases the time voltage is delivered to the motor. Thus, the more time it takes to do work, the less energy is consumed. It's almost the same principle with gas cars. The lower RPM you drive between each shift, the better gas mileage.

But the point the poster was making (with which I agree), was that even if you are careful with the accelerator to simulate "chill" driving in a non-chill mode you still wont get the same efficiency since the car is keeping the battery at a higher temp just in case you slam on the accelerator, and this consumes more power even if you drive the car as is it were in Chill mode, which is interesting.

 

[E90alex]

Unscientific test with my commute yielded no difference. Usually takes 11% for me to get to work and back (~32 miles round trip).

Tried Chill mode today and was the exact same. Average Wh/mi in the mid 230s like usual. And I’m not shy with the accelerator in either mode.

 

[yessuz]

Do you have a link? I found this test he did with a 2019 Model 3 (non-heat pump). I love TeslaBjorn, but we should be careful with extrapolating his result to other vehicles, other HVAC systems, other temperature conditions, and other factors like preconditioning / initial battery temperature.

To be fair to Tesla they specifically mention the heat bump, which the car in the video linked does not have.

The temperature was about -9C in his test. That's not super cold.

He was driving at highway speed (albeit slow Norwegian highway speed) so that'll generate more heat in the battery than in stop and go or city traffic.

From his video, I didn't see any different in battery temperatures across chill and sport (about 24C). Isn't it theoretically possible that if the car had a heat bump it would pull down the pack temperature, and moreover pull it down further in chill mode?

Thoughts? Do you think Bjorns evidence can be extrapolated to all cars?

Well, that is the video.
However, -9 is actually pretty cold in reality. It is 16 f

The main thing is that during the motorway driving, especially on AP, you are using just a fraction of total power you can pull from engine. Therefore chill has little to no impact to consumption in motorway. But for sure it will be a different situation in city driving

 

[sleepydoc]

Well, that is the video.
However, -9 is actually pretty cold in reality. It is 16 f

The main thing is that during the motorway driving, especially on AP, you are using just a fraction of total power you can pull from engine. Therefore chill has little to no impact to consumption in motorway. But for sure it will be a different situation in city driving

If you're cruising on a highway at a constant speed then it doesn't matter what mode you're using.

The problem with all of this discussion is there are a lot of variables and many of them don't stay constant.

Then there's resistive losses. As others have stated, P=I^2R. Energy = P*t. If you cut the power in half it will take twice as long to reach your target velocity. Except there the effect of heating in the battery, circuitry, etc, decreased motor efficiency and wheel slip. (Yes, Teslas have traction control but if you are constantly gunning it there is microscopic slippage that occurs. We see this as increased tire wear but that wear comes at the expense of decreased efficiency.)

Battery temp can be a net positive or negative, depending on the ambient temperature. If it's cold out then heating up the battery can help, but if it's hot out then the battery overheats and you have to expend energy to cool it. If it's true that chill mode keeps the battery at a lower temperature then there's a constant savings regardless of acceleration.

Below is a graph of motor efficiency vs torque. At higher torques motors become less efficient. (note, this is a generic graph, not necessarily for Tesla's motors but the general principle should apply unless Tesla's managed to develop a motor in which the torque and efficiency curves are matched.)

Bottom line, there are many factors involved, but several that can contribute to decreased efficiency with more aggressive acceleration. As I said above, I did my own, semi-scientific test. driving the same route under hard and gentle acceleration and there was a small but clear decrease in efficiency with hard acceleration.

 

[stopcrazypp]

Well, that is the video.
However, -9 is actually pretty cold in reality. It is 16 f

The main thing is that during the motorway driving, especially on AP, you are using just a fraction of total power you can pull from engine. Therefore chill has little to no impact to consumption in motorway. But for sure it will be a different situation in city driving

Yeah, -9C is pretty cold already. But the non-heat pump version of the Model 3 had no ability to use waste heat from the battery and it was not connected to the cabin heating loop, so whatever the heat pump can do does not apply to it.

 

[yessuz]

Yeah, -9C is pretty cold already. But the non-heat pump version of the Model 3 had no ability to use waste heat from the battery and it was not connected to the cabin heating loop, so whatever the heat pump can do does not apply to it.

if you watch the video till the end, you will notice that he also ran the test without HVAC on

 

[Cubu]

nvmpm

if you watch the video till the end, you will notice that he also ran the test without HVAC on

Maybe take a mental break before you hurt yourself.

 

[Cubu]

But the point the poster was making (with which I agree), was that even if you are careful with the accelerator to simulate "chill" driving….

If you're cruising on a highway at a constant speed then it doesn't matter what mode you're using…..

Both of you cut it out, what are you two even doing here? Y’all don’t belong here, take your common sense, comprehension, and basic knowledge where it’s welcome. The audacity of some folks flaunting their brain, think of others you selfish lizards.. y’all are causing mass depression and just created 7 new genders with y’all’s BS.

 

[Tom Sagrak]

Sorry, am I missing an important point in this discussion - what does the Tesla SOFTWARE do when the car is in chill vs standard mode? It might have been programmed to (let's say) maintain 20 degrees C in chill mode and 35 in standard mode, and just THIS could be the main efficiency difference while changing the driving mode?

 

[drtimhill]

Unscientific test with my commute yielded no difference. Usually takes 11% for me to get to work and back (~32 miles round trip).

Tried Chill mode today and was the exact same. Average Wh/mi in the mid 230s like usual. And I’m not shy with the accelerator in either mode.

Interesting but what was the ambient temp? If this is related to battery heating then the surrounding temperature will be a factor.

 

[E90alex]

Interesting but what was the ambient temp? If this is related to battery heating then the surrounding temperature will be a factor.

mid 70s ish.

 

[DrChaos]

Sorry, am I missing an important point in this discussion - what does the Tesla SOFTWARE do when the car is in chill vs standard mode? ]

It limits the maximum power output and changes the mapping from pedal depression angle to power output.

 

[drtimhill]

Sorry, am I missing an important point in this discussion - what does the Tesla SOFTWARE do when the car is in chill vs standard mode? It might have been programmed to (let's say) maintain 20 degrees C in chill mode and 35 in standard mode, and just THIS could be the main efficiency difference while changing the driving mode?

Basically yes .. the speculation is that driving with a "light foot" in non-chill mode wont be as efficient as driving the same way in chill mode, since in sport etc modes the car maintains the battery ready for more aggressive acceleration, which requires heating the battery == more energy consumed "just in case" you slam your foot down compared to chill mode (which doesn't have to be ready for instant power).

 

[gtae07]

Basically yes .. the speculation is that driving with a "light foot" in non-chill mode wont be as efficient as driving the same way in chill mode, since in sport etc modes the car maintains the battery ready for more aggressive acceleration, which requires heating the battery == more energy consumed "just in case" you slam your foot down compared to chill mode (which doesn't have to be ready for instant power).

This statement from the MY owner's manual under "acceleration modes" would seem to agree...

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. This helps to maximize driving efficiency in colder weather. Note that when subsequently increasing the acceleration mode, the Battery requires time to warm up before the increased level of acceleration is available.

 

[sleepydoc]

Gosh, I thought I addressed this quite well in the very post you quoted. I said:

Fast acceleration might be slightly less efficient if heating losses are a slightly greater percentage of the energy expended. You could also lose a tiny bit of efficiency because you are spending slightly more time at higher speeds and because you will be more likely to need to use the friction brakes to slow down.​

​

Please note that higher currents and higher heating losses in the wires and motor don't necessarily result in lower efficiency. Believing otherwise is a common misconception. If the losses and the power delivered scale equally with current (which they do over a wide range of currents) then the efficiency does not change. It's only when the losses are a greater percentage of the energy expended that efficiency decreases.

If my balance between being clear and being pedantic didn't suit you, I apologize. I got a PhD in theoretic physics from the C. N. Yang Institute of Theoretical Physics in Stony Brook NY. Nobel Laureate C. N. Yang was the chairman of my thesis defense. I think that qualifies me as a real physicist. They gave out two awards to graduate students. One was voted on by undergrads for the best teaching assistant. The other was for getting the highest score on the qualifying exam. I won both awards my first year.

Believe it or not, even real physicists make mistakes. So I appreciate corrections. But I think the post you quoted is both correct and clear. My main point was that the laws of physics do not tell us that doing work faster necessarily uses overall more energy. I even added a caveat about some ways in which faster acceleration will cause a slight drop in efficiency similar to and overlapping with the ones you claim I omitted. Nowhere did I say or assume that real world systems are 100% efficient.

Sorry, I missed that part of your reply. As to the other aspects, see my reply above.

You are of course correct, P=I^2*R and E=P*t, but there are other areas in which it matters.

Another aspect is that since neither the batteries nor the motors are 100% efficient at converting electricity to motion and vice versa, you're better off braking slowly and letting the intrinsic resistances (wind, wheel friction, etc) do more of the braking. (This goes for all cars, not just EVs) Driving more calmly is, in general, easier on other mechanical components as well.

 

[DB288]

As a physicist I strongly disagree with this. Conservation of energy tells us there is no inherent inefficiency when expending energy more quickly. Most of the electric energy spent in accelerating a Tesla is converted into kinetic energy which you can recover with regenerative braking.

The inherent amount of energy needed to roll a ball up a hill or accelerate a car from 0 to 60 is independent of the time you take to do it. The energy needed is given by the formulas mgh and mv^2/2. Time does not enter into these equations. The inherent energy needed is simply the energy of the final state minus the energy of the initial state.

Fast acceleration might be slightly less efficient if heating losses are a slightly greater percentage of the energy expended. You could also lose a tiny bit of efficiency because you are spending slightly more time at higher speeds and because you will be more likely to need to use the friction brakes to slow down.

but as a theoretical physicist (you brought it up not me) you know that real world non-thought experiment empirical measurements need to be modeled using the actual system one is studying…

1. we do not live in that perfect frictionless F=ma world

2. the battery connected to motor with computer control does not have to be linear with respect to energy usage…you used no parameters of the battery; motor; system that drives the wheels; wheels moving on pavement; suspension system to model your assertions

antecdotally:
1. clearly driving fast with friction/wind mf resistance lowers efficiency
2. i believe rapid acceleration def uses more energy than slow stead acceleration..,

i have ben using autopilot a lot and watching my Wh/mile

autopilot/chill accelerates slowly (sometimes embarrassing slow for cars behind me) and i get <215 Wh/mi through a range of conditions (no a/c or heat) and around town at 35mph autopilot i have gotten <200 wh/mi

but it a punch it and have a high rate of acceleration …260 wh/mi

i def think chill + autopilot/slow acceleration enhances range

 

[stopcrazypp]

but as a theoretical physicist (you brought it up not me) you know that real world non-thought experiment empirical measurements need to be modeled using the actual system one is studying…

1. we do not live in that perfect frictionless F=ma world

2. the battery connected to motor with computer control does not have to be linear with respect to energy usage…you used no parameters of the battery; motor; system that drives the wheels; wheels moving on pavement; suspension system to model your assertions

antecdotally:
1. clearly driving fast with friction/wind mf resistance lowers efficiency

Yes driving fast does, but this is not talking about driving fast. This is talking about accelerating to the same speed (for example at an on-ramp). If the average speed about that same, that largely reduces that contribution.

2. i believe rapid acceleration def uses more energy than slow stead acceleration..,

Was mentioned in the other thread years ago, this is mostly the case because most people when doing rapid acceleration overshoot the target speed and then will waste more energy slowing back down. The main energy lost there is from going a higher speed and wasting energy slowing back down, not necessarily from the acceleration. It largely depends on what assumptions you make.

i have ben using autopilot a lot and watching my Wh/mile

autopilot/chill accelerates slowly (sometimes embarrassing slow for cars behind me) and i get <215 Wh/mi through a range of conditions (no a/c or heat) and around town at 35mph autopilot i have gotten <200 wh/mi

but it a punch it and have a high rate of acceleration …260 wh/mi

i def think chill + autopilot/slow acceleration enhances range

AP vs manual driving has the same issue as mentioned above. Most people have a harder time manually staying below a set speed and maintaining it with little variation (that's what cruise control is generally good at). So when driving manually, people tend to go faster than necessary, then slow down too much, then need to speed up again. So there are major differences from that, vs necessarily that it has to do with chill.
If you want a test solely about chill vs normal, then only do that. For example, manual driving chill vs regular. AP chill vs AP regular. Not having two different variables being changed.