Cold Weather Efficiency Impacts

[AlanSubie4Life]

I wish we could refer to long distance energy consumption concerns as range discussion and around home daily driving as efficiency.

Daily driving and errands mean a high number of initial cabin heating events. Where as a long trip might mean just 1-2 initial cabin heating events for a full charge.

I could claim a 70% range hit in cold weather due to Green Bay getting sub-zero combined with my 7 mile drive. I don't make that claim though because if I am using actual range as in worrying about how far I can go I am not reheating the cabin every 7 miles. On a long trip in single.digits I don't think I saw but a 10-15% hit.

People really want to figure out their theoretical range to make sure they made a good decision, and thus attempt to extrapolate from daily experiences. This goes poorly.

To the point of the OP, he should be accepting only submissions which are from single drives, and clearly indicated as such. The first couple responses in this thread were to the point, and then the thread got derailed by people talking about distance traveled between recharges, which is not helpful.

People need to define their terms extremely precisely.

 

[drotto25]

I know the first few months I was driving the car, we had an efficiency average around 254 wh/km. No that we are in cold weather this has jumped to about 345 wh/km listed in the trip computer. This is going from an average of 60 degrees to around 35 degrees.

 

[AlanSubie4Life]

I know the first few months I was driving the car, we had an efficiency average around 254 wh/km. No that we are in cold weather this has jumped to about 345 wh/km listed in the trip computer. This is going from an average of 60 degrees to around 35 degrees.

Good datapoint. (I'll assume you meant Wh/km as you said...) And that seems like a reasonable result. And you didn't make the mistake of trying to determine how many miles you "could have gone" on a single charge based on the %/km you used between charges!

Worth noting again that your numbers are affected by the type of driving you do (many short trips, etc.). The impact at highway speeds is very unlikely to be this high. At 70mph, 91Wh/km (146Wh/mi) would be (it's not) 10.2kW! The heat pump on a long distance drive in 35 degree weather is likely to be more like 1kW average consumption (I think this might be slightly on the high side, but would be great to get some data - it's quite easy for any owner to determine, with a stationary timed test, counting rated miles/km used), so at 70mph, would be expected to add 1000W/70mph = 15Wh/mi. (9Wh/km).

Your results indicate an average driving speed of closer to 7mph, using that same assumption (or, a bunch of shorter drives, where the initial transient load is higher than 1kW, but settles...so maybe average speed is closer to 15mph). Again, assuming these numbers you quote are Wh/km. Can adjust all the numbers appropriately by factor of 1.61 if they are actually Wh/mi numbers.

 

[acarney]

The heat pump on a long distance drive in 35 degree weather is likely to be more like 1kW average consumption (I think this might be slightly on the high side, but would be great to get some data - it's quite easy for any owner to determine, with a stationary timed test, counting rated miles/km used)

I just switched over to my winter wheels and left the windows down and heat pump blasting on “hi” for about an hour in a closed garage. My charge when from 75% down to about 70%. That means the heating system was using about 3.75kW/h... actually a lot lower than I expected... I though it would be 5kW or so at peak demand...

Edit: That was in a closed garage at ~47F. That makes a lot more sense now, I would imagine 20F or even 30F out would require more energy since there is less latent heat to scavenge...

 

[AlanSubie4Life]

I just switched over to my winter wheels and left the windows down and heat pump blasting on “hi” for about an hour in a closed garage. My charge when from 75% down to about 70%. That means the heating system was using about 3.75kW/h... actually a lot lower than I expected... I though it would be 5kW or so at peak demand...

Edit: That was in a closed garage at ~47F. That makes a lot more sense now, I would imagine 20F or even 30F out would require more energy since there is less latent heat to scavenge...

Rated miles would be easier to calculate. But yes, between 3.3kW and 4.1kW or so.

That’s about what I would expect for heat pump open loop, I guess. It probably varies depending on where the heat is coming from. If you set it to high it should not matter what the outside temp is.

I guess a datapoint closed loop at a given external temp would be helpful as well. It seems like 1kW or less might well be correct at 45 degrees or so.

And yes, there is an optimal temperature. Probably on the bad side of the curve below 35 degrees or so.

 

[acarney]

Rated miles would be easier to calculate. But yes, between 3.3kW and 4.1kW or so.

That’s about what I would expect for heat pump open loop, I guess. It probably varies depending on where the heat is coming from. If you set it to high it should not matter what the outside temp is.

I guess a datapoint closed loop at a given external temp would be helpful as well. It seems like 1kW or less might well be correct at 45 degrees or so.

And yes, there is an optimal temperature. Probably on the bad side of the curve below 35 degrees or so.

Maybe I’ll park the car outside in 20F and measure how much energy it uses for an hour at a “realistic” set point of 70F inside or something. I usually live in the world of percentage rather than displayed miles but maybe I can switched between them if I remember. I’ll also look at Teslafi on how much energy is used to recharge again afterwards. I know there is some losses associated with charging but that should get a rough ballpark as a double check.

 

[Fizzyo]

NOOB here...picked up my new M3 LR and spent 2 days in the mountains...On the way back from Calgary, temp was 1below C (30F) charge read that I needed 51% and it was charged to 64%. 1 hour into the 2 hour trip the temp had dipped to -8C (17F) a;d I received a message stating that I would need to travel no faster than 125km/hr (78mi) to get there w8th 5% to spare. Driving into my garage, temp is -10C (14F) it stated that I had a critical 2% and that I needed to plug in to avoid damage to battery. Still awaiting delivery of my 14-50 adapter so waiting to see what 120 does in an unheated garage.
Should I have allowed for a greater buffer in cold weather?
Thanks,
Cal

 

[MP3Mike]

Should I have allowed for a greater buffer in cold weather?

Larger buffer, or drive slower.

 

[Fizzyo]

Larger buffer, or drive slower.

Ah, you definitely have something on the drive slower MP3Mike...must admit that I was opening her up on the hiway. Thanks

 

[AlanSubie4Life]

Should I have allowed for a greater buffer in cold weather?

It seems like you did fine. 2% is enough arrival charge, especially with the margin you started out with (you do have a small buffer below 0% but don’t count on it). You’re definitely going to need that faster charging! However, in Calgary, in remote areas, maybe allow even more margin, given the dire consequences of running out of charge.

A few other things:

Are you running snow tires? If so, consider swapping your wheel configuration to 20” wheels in the GUI settings. This will make the trip planner baseline estimation of consumption higher, and will better account for the higher rolling resistance of some winter tires. The predictions will therefore be better. Eventually Tesla will hopefully allow even more tire choices here.

The other thing you can do is turn down the heat, though obviously at those temps there are limits to what you can get away with.

Slowing down will help, but when the heat is blasting, slowing down will help less than it does in summer (since the heat will have to be on for longer). Following the guidance is good here. It will start bugging you when your arrival charge is predicted below 5%.

If there was traffic, tucking in (at about 3 seconds following distance) behind a van or truck would also help a little (at the expense of possible rock chips).

In summer, I typically charge enough to get to the destination with 10%-12% or so left. That usually gives me enough margin to really gun it. Usually I really get on it the closer I get, to try to get that arrival charge below 5% (with varying success).

In winter, more margin would be nice. For trips with minimal unknowns, I would allow for 15% arrival charge. In more dire circumstances, give yourself more margin and definitely pack your emergency kit for cold weather, in case of becoming stranded.

 

[Hmalc]

A lot of these posts are really off from my experiences as a new Canadian MY owner. And if fact reading this stuff really worried me early on.

In my experience winter range is much better than I expected. I got my car in November but it was a demo, and the lifetime efficiency is 195wh/km which I assumed a was mostly done with warmer temps.

Using best practices, such a 20 mins of preheat, keeping heating set to 18C, and using seat heaters (I find this setup most comfortable since I’m already layered up) and driving somewhat sensibly (sport mode with a light touch and a few fast accelerations from a light) I have consistently stayed below 200wh/km, even at -20C

Generally my efficiency will start around 400wh/km and then very quickly drops to just over 200wh/km after a mile or so. Around town I do 150wh/km as per the energy meter and on the freeway I drive the speed limit of 110km and it maybe averages around 200wh/km even in very cold (-10C)

 

[Fizzyo]

It seems like you did fine. 2% is enough arrival charge, especially with the margin you started out with (you do have a small buffer below 0% but don’t count on it). You’re definitely going to need that faster charging! However, in Calgary, in remote areas, maybe allow even more margin, given the dire consequences of running out of charge.

A few other things:

Are you running snow tires? If so, consider swapping your wheel configuration to 20” wheels in the GUI settings. This will make the trip planner baseline estimation of consumption higher, and will better account for the higher rolling resistance of some winter tires. The predictions will therefore be better. Eventually Tesla will hopefully allow even more tire choices here.

The other thing you can do is turn down the heat, though obviously at those temps there are limits to what you can get away with.

Slowing down will help, but when the heat is blasting, slowing down will help less than it does in summer (since the heat will have to be on for longer). Following the guidance is good here. It will start bugging you when your arrival charge is predicted below 5%.

If there was traffic, tucking in (at about 3 seconds following distance) behind a van or truck would also help a little (at the expense of possible rock chips).

In summer, I typically charge enough to get to the destination with 10%-12% or so left. That usually gives me enough margin to really gun it. Usually I really get on it the closer I get, to try to get that arrival charge below 5% (with varying success).

In winter, more margin would be nice. For trips with minimal unknowns, I would allow for 15% arrival charge. In more dire circumstances, give yourself more margin and definitely pack your emergency kit for cold weather, in case of becoming stranded.

Thank you for your post.
I am running winter tires so will change size to 20”.
Just day 2 with the car so heavy foot, though fun, may have been a factor.
Appreciate the advice and the time taken to respond.
Happy New Year!

 

[Fizzyo]

A lot of these posts are really off from my experiences as a new Canadian MY owner. And if fact reading this stuff really worried me early on.

In my experience winter range is much better than I expected. I got my car in November but it was a demo, and the lifetime efficiency is 195wh/km which I assumed a was mostly done with warmer temps.

Using best practices, such a 20 mins of preheat, keeping heating set to 18C, and using seat heaters (I find this setup most comfortable since I’m already layered up) and driving somewhat sensibly (sport mode with a light touch and a few fast accelerations from a light) I have consistently stayed below 200wh/km, even at -20C

Generally my efficiency will start around 400wh/km and then very quickly drops to just over 200wh/km after a mile or so. Around town I do 150wh/km as per the energy meter and on the freeway I drive the speed limit of 110km and it maybe averages around 200wh/km even in very cold (-10C)

Thank you for these tips...I’m still struggling to get my head around thinking in wh/km and figuring out it’s significance. So thank you for sharing that too; I can see how it could play an important role in determining distance and efficiency.
Happy New Year

 

[ratsbew]

Lots of short trips kill range in the winter (50% like you said). Long highway drives are closer to 80% rated range.

 

[AlanSubie4Life]

Thank you for these tips...I’m still struggling to get my head around thinking in wh/km and figuring out it’s significance. So thank you for sharing that too; I can see how it could play an important role in determining distance and efficiency.
Happy New Year

It’s super easy and straightforward. Convert your displayed rated range to kWh by multiplying the range at 100% by the vehicle constant (see elsewhere here 137Wh/rkm, 220Wh/rmi for 2021 AWD). Then divide by your average displayed Wh/km to get your expected range for a given efficiency.

Do note that ranges calculated this way will assume full use of the buffer. So multiply the result described above by 95.5% to get approximate “usable” range, for a given displayed efficiency. That will be within 1-2% of correct.

 

[WattsappMTL]

I wish we could refer to long distance energy consumption concerns as range discussion and around home daily driving as efficiency.

I disagree - I think that efficiency is the correct term for every drive. Range is just a result/projection from initial and final battery charge, combined with efficiency for a particular drive.

To answer the OP, I have been driving my 2021 Y with 19" wheels for 2000 km around Montreal, including two 550km round-trips to Kingston. My cumulative energy efficiency so far is 222 Wh/km (355 Wh/mi). I have been amazed at the large variation of average efficiency readings I've seen on the Energy display. Highway value has been around 230 with temps in the -5C to 0C range, and I hit over 290 in -15C weather driving around town. EPA rating is 168 (160 city, 179 highway) so both of my numbers are way above that. Even though it feels a bit distressing to find that the energy efficiency is so much worse than advertised, I guess (hope?) it's explainable and the overall $ impact isn't too significant. It's comforting to see that my experience is not out of line with others in these conditions. Can't wait for warmer weather to see the numbers go down though!

What has also struck me is the huge variation in regen limitation dots. I've seen as many as 25 after parking outside for a while at -18C (0F). Sometimes parking the car inside and preconditioning before departure doesn't seem to give the benefit I would expect. In addition, I don't understand what criteria trigger the warning on the driving display. It seems to pop up randomly without any correlation to the actual number of dots, and even stayed on while I was driving once.

 

[SSedan]

@WattsappMTL yes efficiency certainly fits the technical definition for both, but we need to differentiate somehow, what do you suggest?

 

[Fizzyo]

It’s super easy and straightforward. Convert your displayed rated range to kWh by multiplying the range at 100% by the vehicle constant (see elsewhere here 137Wh/rkm, 220Wh/rmi for 2021 AWD). Then divide by your average displayed Wh/km to get your expected range for a given efficiency.

Do note that ranges calculated this way will assume full use of the buffer. So multiply the result described above by 95.5% to get approximate “usable” range, for a given displayed efficiency. That will be within 1-2% of correct.

Thank you for this...will play around with the numbers until I get more proficient at it

 

[WattsappMTL]

@WattsappMTL yes efficiency certainly fits the technical definition for both, but we need to differentiate somehow, what do you suggest?

I'd suggest just highway and city efficiency, same as the EPA rating does. These are single numbers that can be compared to see the impact of outside temperature, driving style, speed, preheating/conditioning and heater usage. Wind and elevation effects should roughly average out for roundtrip travel. Achieved range adds the variables of starting and ending charge level. EPA range sounds impressive, but I've realized it will seldom be reachable because it would require ideal conditions and availability of recharging right at the end of the trip. Based on my experience, I just won't plan legs over 275 km between charges in winter, because I'll be getting nervous about charge level after that. In addition, functions like Dog Mode won't work below 20% which might affect how far I want to push it.

If I'm not mistaken, energy efficiency calculated by the vehicle doesn't take into account the power used for pre-conditioning while plugged in. Does this consumption get included in any of the values accessible through the touchscreen? It's a recommended procedure for improving battery efficiency and regenerated power, but it does artificially improve the displayed efficiency values.

Good news for my car - cumulative average continues to drop below 220 Wh/km and I've sometimes achieved 50 km values around 180 despite the winter conditions.

 

[cdam44]

Been lurking here for a while but wanted to weigh in on some of the things I’ve been following re: winter driving/range based on my experiences. Took delivery in September on MYP, 20” induction (no pup),live in MA, drive to Maine pretty regularly. In September and October was making it door to door ~ 205mi with 15-20% range left, typically not starting at 100% SoC. Well under 300wh/mi. It’s roughly 1/2 highway/numbered routes, 75-80 mph easy on highway/ 50-60mph other, plus some city. Last week went on the same trip but added a loaded car/Yakima roof box (skybox 16) plus it was below freezing the whole trip. While we were there it was single digits over night. I wouldn’t say it was 1/2 the rated range but it was pretty close. I left time to supercharge both ways, so just makes it a different trip, wasn’t the end of the world. I estimate if I drove 65mph and started from 100% I could probably still make it but I’ll never have the nerve to test that theory, plus it would be 4.5 hour trip

Set the trip odometer and round trip 453mi, 174kwh, 384wh/mi.. highway I noticed well over 400wh/mi but knowing I was going to super charge I kept 70-80mphpretty much the whole time.

also had an 8” plus snow storm, +1 on the need for a basic snow mode. Did fine overall, not a ton of fishtailing, but I would say it was more me knowing the roads and taking every precaution than the car being a tank. Coming from Jeep Cherokee and before that an mdx, def felt less in control...