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

 

[BitJam]

If you are a physicist as you claim you should recognize the limits of your argument and the fact that no system is perfectly efficient.

Higher acceleration means higher currents and more losses in the wiring and the motors. There will also be increased friction losses in the tires.

I actually did a practical test a year ago or so - I drove the same route twice, once accelerating hard, and once accelerating gently. There was a small but clear increase in efficiency when accelerating gently.

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.

 

[voldar]

I actually did a practical test a year ago or so - I drove the same route twice, once accelerating hard, and once accelerating gently. There was a small but clear increase in efficiency when accelerating gently.

If you drive the same distance in the same amount of time in both cases, there shouldn’t be any meaningful difference in efficiency.

 

[Cubu]

Holy crap, I just lost some brain cells reading the idiocy. Its not brain science, what’s so hard to understand about the car being more efficient when put into chill mode? It clearly states that cabin heating is improved because the battery can be maintained at a lower temperature with chill mode on, more power requires maintaining battery at a higher temp.

 

[gsmith123]

Does chill mode reduce regen? I feel the regen is a little less than what I felt in the test drive. I already set the regenerative braking as “ standard “ ( vs. low).

Chill mode subtly adds a little delay (artificial latency) to the accelerator response. So when you abruptly let off the pedal and let the car apply full regen it takes a little longer to ramp up. To me that often makes it feel like there's less regen but it's just slower. I think peak regen power remains the same.

Same latency applies to applying acceleration as well.

You can visually see this quite clearly if you watch the green bar on the screen while abruptly letting off the accelerator.

 

[flixden]

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.

This is wrong.
No, no, no and nono.

 

[stopcrazypp]

I think the battery heat losses to environment are significant and there isn't significant insulation, and they want it that way. Generally too high temperatures, not low temperatures, are more of a concern as they cause permanent damage to batteries, even though for the short run it's easier to get current out of hot batteries for performance. Consider supercharging (high current going in continuously)---that makes substantial heat which must be removed. I think given their target market (heavy in California) they prioritize supercharging safety (dissipating heat) and low cost over winter efficiency, and so they don't have battery heat insulation.

In the cold the batteries will be higher temperature than the cabin interior.

Unless you are using precondition mode for supercharging, the battery temp targets are substantially lower than the cabin temp (which makes complete sense given the battery doesn't need high temps to discharge).
I don't have a scan tool myself, but according to a quick search, the active heat target is 18.5F for the Model 3 batteries.
Range Loss Over Time, What Can Be Expected, Efficiency, How to Maintain Battery Health

The minimum cabin heating temp target is 60F if I remember correctly, and most people set it substantially higher (70F or even higher, I personally set it to max 60-65F when it's very cold but I'm sure I'm an outlier).

So the cabin tends to be drastically higher temperature than the batteries! That's why I didn't feel like the heat losses via the battery pack would play that big a role.

 

[range269]

Chill mode subtly adds a little delay (artificial latency) to the accelerator response. So when you abruptly let off the pedal and let the car apply full regen it takes a little longer to ramp up. To me that often makes it feel like there's less regen but it's just slower. I think peak regen power remains the same.

Same latency applies to applying acceleration as well.

You can visually see this quite clearly if you watch the green bar on the screen while abruptly letting off the accelerator.

Thanks! It’s possible I was not adapted to regen during the test drive, so the feeling was a little exaggerated

 

[Miata Head]

I started using chill mode when summer started heating up. Seems to be more efficient based on my observations of Wh/mi, even without the heater on. Since most of my driving is city, in Standard mode, I was getting up to 40 faster than necessary, so I'll probably stay in Chill unless I need it on the freeway.

 

[geordi]

I think I might have experienced an aneurysm from this thread. The guy with the PHD likely has forgotten more about physics than any five of the rest of us will ever know. So I’ll defer to his explanations.

But I think there may have been an omission in the discussion - and that is that the source of the heat energy directed to the cabin OR the battery has to come from somewhere - if it is being generated electrically, then that is energy NOT available to the wheels, ergo less range which Tesla may have inaccurately described here as “efficiency” for the non-physics-doctorates among their owners.

There is precious little waste heat available normally, and in winter that would be coveted by the cabin and the battery both - IF the idea then is that the battery is being maintained at X temperature for max power delivery - that would require the heat pump to run continuously. THAT would be costing a substantial amount of electrons! The design of a heat pump is the same as an air conditioner, save for one extra component - a reverser valve that allows the “hot side” and “cold side” coils to swap places. The power consumption rating for the compressor is the same in either mode because it is still doing the same job. The ONLY way to reduce that power consumption is to reduce the demand. In the car’s case, this reduction in demand can come from having more hot water available from the rotor and electronics, OR a colder cabin setting, OR a colder battery setting.

Seems that the last option then is what Tesla was talking about: The variable speed compressor can ramp down to a lower power need if the battery is also allowed to be maintained at a colder temperature.

I do LOTS of highway cruising with my Teslas, and have driven them over 75k miles in the 15 months that I’ve had them. There was not a substantial loss of range in the winter, but there was a loss - now I have an idea why. There however has NOT been a substantial gain in range by running in “chill” mode, and I have tried this over entire battery charges at steady highway speed while crossing the country, and have not seen the wh/mi move in any meaningful way. I have however seen a huge negative impact with other things running more than they should - like the compressor when I had a pinhole leak in an air shock. Of course I’m always searching for more range and capability, but sadly it does not seem like chill mode is it. There just is NOT this magical “accelerate slower and use less total energy” that adds up to a measurable result. It makes more difference on a gasser b/c their engines are so inefficient already, but not on the electrics, and not when we can recover that kinetic energy every time we slow down too. Gassers can’t do that at all.

 

[gsmith123]

I think I might have experienced an aneurysm from this thread.

this whole thread has surpassed my expectations

But I think there may have been an omission in the discussion

I thought we covered it somewhere in the last 4 pages, in between the tangents about other mechanisms chill mode might or might not impact efficiency. Easy to miss

Regardless, I agree. If there's little waste heat generated in the battery then the energy to keep it warm comes from somewhere. I'm still unsure how much or little waste heat actually is generated and someone was speculating earlier in the thread it it's a fair bit...

 

[WyoDude]

Why does accelerating fast use more energy than accelerating slowly?

I'm trying to understand the physics of why accelerating rapidly uses more energy than a more gentle acceleration? Is the motor/inverter less efficient at high current?

teslamotorsclub.com

 

[GBMaryland]

All I can say is:

- If I drive 75 miles an hour to work not using chill mode, the battery goes from 85% to 68%
- if I drive 75 mile an hour to work using chill mode, the battery goes from 85% to 72%

it’s consistent. It does not matter if I use FSDb. If I’m using sport (performance) mode for a trip, the estimate the car gives me is dead on. If I use chill mode, I bet the estimate by 2-5% every time. I never drive under 75MPH. These results are repeatable.

 

[Darmie]

This sounds more like what Range Mode use to do on the older S/X rather than just limiting acceleration.

 

[E90alex]

In theory if you drive identically in both modes (eg accelerate and decelerate at the same rates) then it shouldn’t make a noticeable difference.

In practice, the accelerator pedal is much more sensitive to tiny movements in Normal/Sport which can easily cause you to accelerate or regen too much and then have to correct it by doing the opposite. Even small twitches of your foot or adjusting your foot position can cause the car to accelerate or decelerate a few mph. This all adds up to lost energy because the steadier your speed, is the more efficient you will be. Chill mode dampens out all of these micro movements of the pedal and the car maintains a much more steady speed.

Some people have much better pedal control/modulation than others so results may vary depending on the driver.

Of course if you frequently accelerate aggressively then Normal/Sport can be less efficient than Chill.

 

[DrChaos]

Unless you are using precondition mode for supercharging, the battery temp targets are substantially lower than the cabin temp (which makes complete sense given the battery doesn't need high temps to discharge).
I don't have a scan tool myself, but according to a quick search, the active heat target is 18.5F for the Model 3 batteries.

I assume that's 18.5C and not 18.5F ?

Range Loss Over Time, What Can Be Expected, Efficiency, How to Maintain Battery Health

The minimum cabin heating temp target is 60F if I remember correctly, and most people set it substantially higher (70F or even higher, I personally set it to max 60-65F when it's very cold but I'm sure I'm an outlier).

So the cabin tends to be drastically higher temperature than the batteries!

I don't think that will be true once you start driving and using the batteries.

That's why I didn't feel like the heat losses via the battery pack would play that big a role.

I think I might have experienced an aneurysm from this thread. The guy with the PHD likely has forgotten more about physics than any five of the rest of us will ever know. So I’ll defer to his explanations.

get ready for your arteries to pop, there's >1 with physics PhD here

Seems that the last option then is what Tesla was talking about: The variable speed compressor can ramp down to a lower power need if the battery is also allowed to be maintained at a colder temperature.

exactly yes. The battery could be damaged by asking for a very high current when it's too cold.

I do LOTS of highway cruising with my Teslas, and have driven them over 75k miles in the 15 months that I’ve had them. There was not a substantial loss of range in the winter, but there was a loss - now I have an idea why. There however has NOT been a substantial gain in range by running in “chill” mode, and I have tried this over entire battery charges at steady highway speed while crossing the country, and have not seen the wh/mi move in any meaningful way. I have however seen a huge negative impact with other things running more than they should - like the compressor when I had a pinhole leak in an air shock. Of course I’m always searching for more range and capability, but sadly it does not seem like chill mode is it. There just is NOT this magical “accelerate slower and use less total energy” that adds up to a measurable result. It makes more difference on a gasser b/c their engines are so inefficient already,

almost but in a LICE car the thermodynamic efficiency at high power is significantly less than at lower power levels (but above idle)---for modern EVs with good control the efficiency of the operating point is high and flat across most of the space of output parameters (RPM and load)

but not on the electrics, and not when we can recover that kinetic energy every time we slow down too.

also true---the main human-alterable driving parameter for efficiency is high speed, not high accleration primarily. A 65 MPH speed limiter would increase range much more than chill mode.

 

[DrChaos]

Unless the chill mode limits the power to the wheels by half, I doubt it is more efficient than the normal/standard mode.

Chill mode does reduce max power output. Not quite a half but significantly.

 

[E90alex]

Chill mode does reduce max power output. Not quite a half but significantly.

Depending on the car it can be more than half. It seems Tesla targets 0-60 of about 7.5 seconds in Chill mode regardless of vehicle.

 

[voldar]

Chill mode does reduce max power output. Not quite a half but significantly.

I didn’t know this. Thank you !

 

[Max Spaghetti]

Electrical Losses (outside the motor)

Electrical losses scale as P = I^2 * R (source). Note how current has an exponential contribution! And faster acceleration requires higher current.

Very happy to get an opinion from the resident physicists on this little point!

The best my non-physicist brain can come up with is as follows:

For the following, let's disregard all losses with the exception of a randomly chosen parasitic resistance of say 0.1 ohm in the power circuit. This also means that constant speed requires zero energy, so we are only looking at acceleration.

From the above observation (P = I^2 * R), it is valid to say that if you double the power, say from 100kW to 200kW, then for a constant voltage, you also double the current, so the resistive losses increase four-fold.

To pick an example with easy hypothetical numbers given P=EI, a 400V battery will supply
100kW at 250A, and
200kW at 500A.

If the total parasitic resistance is 0.1 ohm, then resistive loss (I^2 * R) is
250^2 *0.1 = 6.25kW at 100kW, and
500^2 *0.1 = 25kW at 200kW (a four-fold increase, as previously noted)

However! To get the car to the same desired speed (say 60 mph), we only need to supply 200kW for half the time (kinetic energy = power x time) - both cars end up with the same kinetic energy at 60 mph, so doubling the power will halve the time.

If 100kW gets us from 0 to 60 in say 10 seconds, then 200kW gets us from 0 to 60 in 5 seconds

Now we're actually interested in energy consumed (power x time), which we normally measure in watt-hours (Wh), but for simple maths, lets use units of kilowatt-seconds (kWs).

0-60 at 100kW consumes 100x10 = 1000kWs, with a resistive loss of 6.25x10 = 62.5kWs (6.25%)
0-60 at 200kW consumes 200x5 = 1000kWs, with a resistive loss of 25x5 = 125kWs (12.5%)

This is, of course, slightly inaccurate because not all our energy actually made it to the motor.

However, the approximate conclusion I'm trying to reach is that our resistive loss has actually doubled (rather than quadrupled), for the same energy delivery. Whether the actual value is significant to the topic is another question. Probably not, because my hypothetical 125kWs translates to a mere 0.035kWh.

 

[gsmith123]

I believe that’s all correct! Thanks for going through that in detail, I admittedly hadn’t really thought through the math of if the losses would 2x or 4x.

So double the acceleration doubles the loses. Very tidy!