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

 

[shahryaran]

You are making the same mistake people tried to explain to you in terms of acceleration. You are doing the same job faster, but the total amount of energy required to do the job is still the same! So you did not consume twice the energy, you consumed the same amount.

Say for example it takes 2 hours to heat up the room with the 1kW heat pump. That means it takes 2 hours * 1kW = 2kWh.

The double heat pumps instead take 1 hour to heat up the room: 1 hour * 2 * 1kW = 2kWh.

The energy consumed is the same!

Incorrect. Using two heat pump is different than using one heat pump under higher load to achieve faster time. If you use one heat pump under higher load to do the job faster, that heat pump would have worse efficiency.
Also, your example of heat pump is irrelevant to OP's concern. We are not adding another motor or battery to the car. We are using the same motor and battery with different power delivery mode.

 

[shahryaran]

Please read the whole thing:

Does rate of acceleration affect the amount of energy used to accelerate?

Assume you start with a car at rest. Then you accelerate the car to 100 kilometers per hour. In terms of the energy needed, does it matter how fast you accelerated the car? In other words, do you...

physics.stackexchange.com

 

[shahryaran]

You are making the same mistake people tried to explain to you in terms of acceleration. You are doing the same job faster, but the total amount of energy required to do the job is still the same! So you did not consume twice the energy, you consumed the same amount.

Say for example it takes 2 hours to heat up the room with the 1kW heat pump. That means it takes 2 hours * 1kW = 2kWh.

The double heat pumps instead take 1 hour to heat up the room: 1 hour * 2 * 1kW = 2kWh.

The energy consumed is the same!

The car literally tells you faster acceleration uses more energy!

 

[stopcrazypp]

Incorrect. Using two heat pump is different than using one heat pump under higher load to achieve faster time. If you use one heat pump under higher load to do the job faster, that heat pump would have worse efficiency.
Also, your example of heat pump is irrelevant to OP's concern. We are not adding another motor or battery to the car. We are using the same motor and battery with different power delivery mode.

The example is to illustrate my point: time efficiency and energy efficiency is different and not the same thing. It's entirely possible to have a system that is significantly more time efficiency while having the same energy efficiency. Do you agree at least with this point?

Your claim in the above is talking about a different point: real world changes in efficiency of the heat pump in response to a different load. As I mentioned, the minor difference in heating capacity from eliminating/reducing the battery heating load is unlikely to change the COP in a meaningful way. It's not doubling the heating capacity or even close.

 

[stopcrazypp]

Please read the whole thing:

Does rate of acceleration affect the amount of energy used to accelerate?

Assume you start with a car at rest. Then you accelerate the car to 100 kilometers per hour. In terms of the energy needed, does it matter how fast you accelerated the car? In other words, do you...

physics.stackexchange.com

The exchange literally disagrees with your point and supports the others! The amount of energy from a first order physics stand point to accelerate a car from a standstill to a given speed is the same whether you take 4 seconds to accelerate or 20 seconds! This is because the formula is (1/2*mv^2) as others pointed out, which has no acceleration time component in it.

The car literally tells you faster acceleration uses more energy!

In a previous thread, I pointed out the reasons why in the real world it tends to use more energy, but it's not for the reasons you describe (not because of less time to do the given work). People aren't disagreeing it would use slightly more energy, they are disagreeing with the mechanism by which it happens!

It depends on what your goal is. If your goal is to accelerate to a target speed (for example during a freeway on ramp) then the energy needed is just the kinetic energy (1/2*mv^2). Using the analysis of force, yes, the acceleration and force is higher, but the distance required for reaching that speed is lower.

Of course when you throw in other increased frictional and heat losses from higher acceleration, you still turn up worse (how much worse is unknown, esp. for EVs). Also those that accelerate fast tend to either overshoot their target speed (causing unnecessary energy loss by having to slow down again) or it leads to excessive braking (like between stoplights).

 

[shahryaran]

The exchange literally disagrees with your point and supports the others! The amount of energy from a first order physics stand point to accelerate a car from a standstill to a given speed is the same whether you take 4 seconds to accelerate or 20 seconds! This is because the formula is (1/2*mv^2) as others pointed out, which has no acceleration time component in it.

I point out the reasons why in the real world it tends to use more energy, but it's not for the reasons you describe (not because of less time to do the given work). People aren't disagreeing it would use slightly more energy, they are disagreeing with the mechanism by which it happens!

But in real world there is time

The exchange literally disagrees with your point and supports the others! The amount of energy from a first order physics stand point to accelerate a car from a standstill to a given speed is the same whether you take 4 seconds to accelerate or 20 seconds! This is because the formula is (1/2*mv^2) as others pointed out, which has no acceleration time component in it.

I point out the reasons why in the real world it tends to use more energy, but it's not for the reasons you describe (not because of less time to do the given work). People aren't disagreeing it would use slightly more energy, they are disagreeing with the mechanism by which it happens!

So, if "energy used to accelerate" means "applied force over distance to change speed from vi
to vf
", then the answer to your question is yes.

 

[gsmith123]

I think @shahryaran is just trolling or intentionally being obtuse

The stack exchange answers are quite good and make the same points I and others have been making in this thread.

 

[shahryaran]

The exchange literally disagrees with your point and supports the others! The amount of energy from a first order physics stand point to accelerate a car from a standstill to a given speed is the same whether you take 4 seconds to accelerate or 20 seconds! This is because the formula is (1/2*mv^2) as others pointed out, which has no acceleration time component in it.

In a previous thread, I pointed out the reasons why in the real world it tends to use more energy, but it's not for the reasons you describe (not because of less time to do the given work). People aren't disagreeing it would use slightly more energy, they are disagreeing with the mechanism by which it happens!

You didn't read the whole post

I think @shahryaran is just trolling or intentionally being obtuse

The stack exchange answers are quite good and make the same points I and others have been making in this thread.

I'm done with this post

 

[BitJam]

Tesla is using a different definition of efficiency in context. In context, they are saying the heating may be more time efficient if you use chill mode given there is more heating capacity available. This is a common way "efficiency" is used to describe a heating system (how long it takes to heat up a given space to a given temperature from a given interior/exterior temperature).

That is different from saying that it is making the car more energy efficient (amount of work done for given energy).

I disagree. Tesla is saying they can use less energy to heat the cabin in chill mode. From the Tesla manual quoted in the original post:

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.

Let's assume we're talking about heating the cabin when it's cold outside. Where is the reserve heat in the battery going to go most of time? It's going to be transferred to the cold environment and lost. When Tesla can use this heat to warm up the cabin before the heat is lost to the environment then it's an energy efficiency win.

BTW: the company EVinsulate sells insulation for the bottom of the battery which they say significantly increases the car's efficiency in the wintertime. When combined with their double pane insulation for the roof, they say it reduces your wintertime range loss in half. Clearly, heat lost from the battery reduces efficiency.

Reducing heat lost to the environment by using it to warm the cabin increases efficiency. The energy saved is the energy that would have been lost to the environment divided by the efficiency of the heat pump. Note that a resistance heater is 100% efficient.

This feature might allow the cabin to heat up slightly faster assuming the higher input temperature to the heat pump results in a higher output temperature although the time savings could be hard to measure. The big win is in energy efficiency. The car heats up quickly so most of the time when the heater is on it's maintaining the current temperature in the cabin so most of the time this feature provides no time efficiency win but it always provides an energy efficiency win.

BTW-2: I have the S3XY Button "kick down" feature enabled which causes the car to automatically switch from chill to normal/sport mode when I floor the accelerator. This is a great feature but I now see that in some situations, when it's cold outside, it will result in less acceleration than if the car was always in normal/sport mode because the battery won't be hot enough to provide maximum acceleration.

 

[henderrj]

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.

Depending on the temperature and the wind (the greater effect of the two) a smaller hose could require more water to fill up the pool, as there are evaporative losses as the pool is being filled. More time equals more loss.

Using this illustration the faster a car gets to speed the less time there are for inefficiencies to have an effect. So, it would seem that you would be more efficient by faster acceleration, not less. The effect is going to be extremely small, probably way too small to measure. As mentioned, motor efficiencies under various loads also comes into play.

An interesting theoretical exercise.

 

[stopcrazypp]

But in real world there is time

So, if "energy used to accelerate" means "applied force over distance to change speed from vi
to vf
", then the answer to your question is yes.

See one line above that.
"However, the applied force may not be the net force on the object as there may be, e.g., a frictional force."
"Yes" answer is because there are frictional forces in the real world, exactly as others have claimed! It is not because of time.

The first answer is what others are talking about:
"Does rate of acceleration affect the amount of energy used to accelerate?
The answer is, in a certain sense, no."
And it's no because of the same formula others were talking about.

You didn't read the whole post

I'm done with this post

Yes I did, see above, the points raised in the exchange simply does not agree with your points about time, but rather does with the points others brought up.

 

[gsmith123]

Using this illustration the faster a car gets to speed the less time there are for inefficiencies to have an effect. So, it would seem that you would be more efficient by faster acceleration, not less. The effect is going to be extremely small, probably way too small to measure. As mentioned, motor efficiencies under various loads also comes into play.

This gets slightly tricky and depends on precisely the situation you're suggesting.

Are we comparing just the time while the car is acceleration (lets say 0 - 60 mph)? In that case, yes - faster acceleration reduces the air drag loses incurred! The faster car has been affected by air drag for both less time and less distance.

But the slower car has gone much further distance overall, so this doesn't quite seem like a useful comparison for most real world applications.

What if we say the cars accelerate to 60 mph and then drive to a point that is 1 mile from the initial starting point? In that case the faster accelerating car has a higher average speed over the 1 mile and incurs higher air drag loses.

 

[stopcrazypp]

I disagree. Tesla is saying they can use less energy to heat the cabin in chill mode. From the Tesla manual quoted in the original post:

Let's assume we're talking about heating the cabin when it's cold outside. Where is the reserve heat in the battery going to go most of time? It's going to be transferred to the cold environment and lost. When Tesla can use this heat to warm up the cabin before the heat is lost to the environment then it's an energy efficiency win.

I'm assuming the battery is well insulated enough, a large enough thermal mass, and the cells are oriented to reduce thermal loss on the bottom, so that it wouldn't be losing much thermal energy to the environment through the bottom, as opposed to the cabin losses (which has a lot of glass and relatively poorly insulated panels). Of course if thermal losses are huge through the battery, that may change things, but I don't think people did an analysis of that.

Also for the heating differences I assume it is cold enough there is practically no excess heat from the battery left, but rather any heat generated is used to maintain the battery temp. I'm assuming it's cold enough that the heat pump may even need to occasionally deliver heat to the battery, so the difference between chill mode on/off is the heating capacity difference between delivering heat to the battery vs to the cabin related to the higher target temp.

BTW: the company EVinsulate sells insulation for the bottom of the battery which they say significantly increases the car's efficiency in the wintertime. When combined with their double pane insulation for the roof, they say it reduces your wintertime range loss in half. Clearly, heat lost from the battery reduces efficiency.

While the roof insulation may help a bit, a brief search shows the company quotes zero empirical measurements for either modification, so very hard to tell what real world advantage either would provide. It might shed some light on how the OEM pack insulation is, but unfortunately they seemed to have done no empirical measurements.

EVinsulate. Better range during cold weather. Is this the real deal?

I was informed yesterday that this was available for our vehicles. Do you guys think this works and if it worth it? Tesla Model 3 Clear Sunroof Insulation Panels

teslamotorsclub.com

Reducing heat lost to the environment by using it to warm the cabin increases efficiency. The energy saved is the energy that would have been lost to the environment divided by the efficiency of the heat pump. Note that a resistance heater is 100% efficient.

This feature might allow the cabin to heat up slightly faster assuming the higher input temperature to the heat pump results in a higher output temperature although the time savings could be hard to measure. The big win is in energy efficiency. The car heats up quickly so most of the time when the heater is on it's maintaining the current temperature in the cabin so most of the time this feature provides no time efficiency win but it always provides an energy efficiency win.

BTW-2: I have the S3XY Button "kick down" feature enabled which causes the car to automatically switch from chill to normal/sport mode when I floor the accelerator. This is a great feature but I now see that in some situations, when it's cold outside, it will result in less acceleration than if the car was always in normal/sport mode because the battery won't be hot enough to provide maximum acceleration.

 

[mjwojtukiewicz]

I've always drive in chill mode and the other day it was in the 70s, no AC, no driving like a nut and I got the trip meter down to 146kWh

 

[DrChaos]

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.

In a dual motor car, one motor is permanent magnet and the other is induction. The induction motor is typically used only for higher acceleration as it's less efficient, as it needs to consume and dissipate electricity to magnetize the rotor, whereas in an permanent magnet motor (with either permanently magnetized rotor or switched reluctance and permanent stators) that isn't needed.

So a moderate acceleration will more likely operate in the most efficient parts of the battery drive system.

It's also possible there will be more tire losses in higher acceleration.

 

[DrChaos]

I'm assuming the battery is well insulated enough, a large enough thermal mass, and the cells are oriented to reduce thermal loss on the bottom, so that it wouldn't be losing much thermal energy to the environment through the bottom, as opposed to the cabin losses (which has a lot of glass and relatively poorly insulated panels). Of course if thermal losses are huge through the battery, that may change things, but I don't think people did an analysis of that.

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.

 

[sleepydoc]

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.

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.

 

[voldar]

I think the only reason for a more efficient drive in chill mode rather in normal mode is related to the fact that most people don't have a good control over the way they accelerate. I drive my Tesla in standard mode and I am sure that I have the same efficiency as I would drive it in chill mode. The Bolt EV I owned for 4.5 years had also the normal and the sport mode. The sport mode maps more agressive the acceleration as you press the pedal, but in both cases, the max kW output is the same in both modes. You reached it at half press in sport mode and full press in normal mode. It’s all about how much pressure you put on the accelerating pedal in the end.
Unless the chill mode limits the power to the wheels by half, I doubt it is more efficient than the normal/standard mode.

 

[range269]

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).

 

[sleepydoc]

Incorrect. If you do the same job faster, your efficiency is worse because you consumed twice the energy by doubling the heat pump

Your conclusion is correct but your reasoning is faulty