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).

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[shahryaran]

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:



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).

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.

 

[rjpjnk]

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:



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).

Interesting. I think Tesla is saying that the cabin will heat up faster in chill mode because it is allowing the battery to remain colder. But in what sense is this more efficient?

 

[israndy]

Ha ha, more heat in chill mode

The only improvement I am jealous of, but I'll take my original TM3 over a Model S/X with heat pump but all that extra weight. I do love bopping into a Supercharger and heading out before any of the bigger cars have moved.

 

[gsmith123]

But in what sense is this more efficient?

At the beginning of a drive the car doesn't need to spend as much energy warming up the battery. Similarly, after a DC fast charging session the battery is hotter than ideal and the car can pull more energy out of it.

That's all "free" energy in the sense that otherwise it would just be dissipated away to the air at the end of the drive.

It also reduces heat losses while driving. The hotter something is the faster it dissipates energy to the environment (meaning the hotter the battery is the more power the car uses to keep it at that temperature).

Interestingly all of these (except the fast charging one) can apply to a non-heat bump car too in cold enough conditions.

 

[rjpjnk]

The car may be more efficient in chill mode, I just don’t think that quote from tesla says that. I think you may be making the assumption that the battery is maintained at a lower winter temp in chill mode overall, and not just at startup.

 

[gsmith123]

The car may be more efficient in chill mode, I just don’t think that quote from tesla says that. I think you may be making the assumption that the battery is maintained at a lower winter temp in chill mode overall, and not just at startup.

I am making that assumption, yes - do you think that's wrong? My interpretation is that Plaid/Insane/Sport acceleration mode sets a higher target temperature for the battery throughout the drive, not just at startup. Tesla's wording seems to support that notion:

...maintaining the Battery's ability to provide peak acceleration performance

And that makes sense. The car is trying keep itself ready to give you full power at any time.

If you think Tesla isn't saying the car will be more efficient, how do you interpret the section quoted below? They literally say it makes cabin heating more efficient, I'm not quite sure what else they could mean. More efficient as in it takes less time to heat, perhaps?

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

 

[BitJam]

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.

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.

 

[rjpjnk]

I am making that assumption, yes - do you think that's wrong? My interpretation is that Plaid/Insane/Sport acceleration mode sets a higher target temperature for the battery throughout the drive, not just at startup. Tesla's wording seems to support that notion:

I don't know if that assumption is right or wrong. Could go either way. I assume that as the car eventually reaches full operating temperature there is still an excess of heat (produced by battery and motors) even on a winter day with the cabin fully heated. I could be wrong, but that is my current assumption. If this is the case, it will be necessary to vent some of this surplus heat to the atmosphere. But before they would vent this heat I would assume they first use it to raise the battery to the ideal operating temperature even if chill mode is selected. That's why I assumed it was just at startup. By "efficient" I think it is just Tesla's way of saying "In chill mode the cabin heats up faster because we let the battery warm up more slowly". But this is complete speculation on my part of course.

 

[shahryaran]

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.

So you are saying a car going 0 to 60 in 10 seconds uses the same amount of energy compare to another car going 0 to 60 in 4 seconds?

 

[shahryaran]

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.

You have to spend more energy to do the same work faster. Time does matter

 

[gsmith123]

As a physicist I strongly disagree with this. Conservation of energy tells us there is no inherent inefficiency when expending energy more quickly.

Agree with everything in your post - the previous commenter was sloppy at best in their application of physics.

That said, their conclusion might still be right (albeit for the wrong reasons), because of the heating losses (as you mention). There are two contributors to those (two that I can think of at least!):

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.

Motor efficiency

Electrical motor efficiency varies somewhat, by both speed and torque (source). The sweet spot is somewhere near the middle; full power is not the most efficient.

So you are saying a car going 0 to 60 in 10 seconds uses the same amount of energy compare to another car going 0 to 60 in 4 seconds?

You have to spend more energy to do the same work faster. Time does matter

If you ignore inefficiencies, it takes exactly the same energy. It takes however much kinetic energy the car has at 60 mph.

 

[gsmith123]

@shahryaran respectfully, you should review some basic thermodynamics, conservation of energy principles, and the differences between power, energy, and work.

 

[BitJam]

So you are saying a car going 0 to 60 in 10 seconds uses the same amount of energy compare to another car going 0 to 60 in 4 seconds?

Yes! Of course there are losses due to friction and so forth and the losses may be greater in one situation but the inherent amount of energy needed in both situations is the same.

If you want to learn more about this I suggest doing a search for "conservation of energy high school physics" without the quotes.

 

[shahryaran]

Agree with everything in your post - the previous commenter was sloppy at best in their application of physics.

That said, their conclusion might still be right (albeit for the wrong reasons), because of the heating losses (as you mention). There are two contributors to those (two that I can think of at least!):

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.

Motor efficiency

Electrical motor efficiency varies somewhat, by both speed and torque (source). The sweet spot is somewhere near the middle; full power is not the most efficient.





If you ignore inefficiencies, it takes exactly the same energy. It takes however much kinetic energy the car has at 60 mph.

They would have the same kinetic energy once they reach 60 mph. But it takes different energy to get them to 60. Because the work in being done is different. Working faster takes more energy.

Yes! Of course there are losses due to friction and so forth and the losses may be greater in one situation but the inherent amount of energy needed in both situations is the same.

If you want to learn more about this I suggest doing a search for "conservation of energy high school physics" without the quotes.

Tesla Model 3 travels 606 miles on a single charge in new hypermiling record

Hypermiling is the practice of driving vehicles as efficiently as possible in order to achieve the longest distance possible on...

electrek.co

 

[BitJam]

You have to spend more energy to do the same work faster. Time does matter

If you do the same work faster you are expending energy at a higher rate for a shorter period of time so the total amount of energy is the same.

It's like filling up a pool with a wide hose and a narrow hose. The wide hose will fill the pool faster using more water per second but the total amount of water that ends up in the pool is the same.

 

[shahryaran]

If you do the same work faster you are expending energy at a higher rate for a shorter amount of time so the total amount of energy is the same.

Higher rate for a shorter time means higher energy consumed in addition to the total energy consumed. The inefficiency of a system becomes greater when time is involved.

 

[gsmith123]

I assume that as the car eventually reaches full operating temperature there is still an excess of heat (produced by battery and motors) even on a winter day with the cabin fully heated.

Ah, gotcha. Yes, agreed. If your assumption is true, then either way the battery should reach ideal operating temperature... I'm a bit skeptical the battery and motors generate that much waste hit but that's admittedly a complete guess. Hmm.

Working faster takes more energy.

Higher rate for a shorter time means higher energy consumed

^ These statements just aren't necessarily true ^

100 watt * 1 second = 100 joules
200 watt * 0.5 second = also 100 joules

 

[BitJam]

They would have the same kinetic energy once they reach 60 mph. But it takes different energy to get them to 60. Because the work in being done is different. Working faster takes more energy.

Tesla Model 3 travels 606 miles on a single charge in new hypermiling record

Hypermiling is the practice of driving vehicles as efficiently as possible in order to achieve the longest distance possible on...

electrek.co

That article says:

The attempt basically consists of driving at extremely low-speed in order to get the most efficient driving speed for the vehicle while also not using power consuming onboard features like climate control.​

​

It does not say they got better efficiency by limiting their acceleration.

 

[shahryaran]

Ah, gotcha. Yes, agreed. If your assumption is true, then either way the battery should reach ideal operating temperature... I'm a bit skeptical the battery and motors generate that much waste hit but that's admittedly a complete guess. Hmm.





^ These statements just aren't necessarily true ^

100 watt * 1 second = 100 joules
200 watt * 0.5 second = also 100 joules

That's theoretical. The system producing 200W now likely has less efficiency than 100W