<10F, Preconditioning helps, but as I see it, even the heat pump can't save range

[TikiSteve]

So I was going on a 10 degree F 200 mile trip starting at 95%, plugged in and preconditioned. I thought I would be golden, and while I did make it in my '23 MYP, the energy app showed I lost 16% rated range to cold (et als). Being preconditioned, I though the loss would be minimal, then the geek in me came through.

1) Started preconditioned is fine, but on a 3 hour trip, the batteries being exposed to the cold, that preheat is going to need to be supplemented.
2) Internal heating on the battery is likely minimal. Discharge rate is probably something like C/5 on the pack, it's snoozing.
3) Ahhh, the heat pump!
a) Lets say the overall system pack to wheel is 90% efficient. Say you are getting 300W/mile, 60 MPH, 18KWH/hour. Thats 1800W/hour losses.
b) Assume 70% of this can be recovered by the heat pump and it has a COP of 2. That leaves 2*.7*1.8KW= 2.52KW/hour of heat available
c) The cabin at 70F in these conditions, must take at least 1KW, leaving 1.5KW to heat the battery
d) The ability to heat 1200# of battery with 1500Watte is not going to be very good
So at the end of the day, I concluded the heat pump helps, but the car is so efficient, even that can't bail you out of loss of range.

I would love is if someone has some FACTS where my assumptions may be incorrect, please link to source.

 

[Goobers]

I don’t get the point of all of this.

The fact you are making so many assumptions already throws out any attempts to prove much of anything. Case in point, I get 400+ whm at about those temperatures at 30-40 mph, let alone 60 mph, so the deviation right there is some 33% already. A quick google shows some sites listing the battery at 1700 lbs, that almost a 50% more than your assumption of 1200. Your assumptions and potential facts vary too much.

The sheer fact it’s colder already has influence on aerodynamics before any thermal efficiencies anyway.

You can’t avoid loss of range. You can only minimize it.

 

[TikiSteve]

I don’t get the point of all of this.

The fact you are making so many assumptions already throws out any attempts to prove much of anything. Case in point, I get 400+ whm at about those temperatures at 30-40 mph, let alone 60 mph, so the deviation right there is some 33% already. A quick google shows some sites listing the battery at 1700 lbs, that almost a 50% more than your assumption of 1200. Your assumptions and potential facts vary too much.

The sheer fact it’s colder already has influence on aerodynamics before any thermal efficiencies anyway.

You can’t avoid loss of range. You can only minimize it.

The point is, even with the heat pump and preconditioning there is loss of range yes! There is not enough waste heat to keep the batteries and occupants 'warm'.

Hmmm, temperature and aerodynamics, good point, a quick google shows it is probably not significant.
>>As the ambient air temperature drops, air becomes denser, which increases aerodynamic drag. For every 10 degree Fahrenheit drop in temperature, aerodynamic drag increases by 2%. Every 2% increase in aerodynamic drag results in approximately 1% decrease in fuel economy.

As for the 400WH/mile at 35ish MPH, feel free to prove me wrong, but I'm inclined to believe the energy meter is fooling you. Do you get the raw data from tessie or other means. The bottom line is that the cells have less CAPACITY at cold temperatures and I believe the energy monitor jacks up the consumption to fool you into thinking it is the overall efficiency that is lower (it should not be). The motor and drives should have HIGHER efficiency in the cold, but this will be small compared to the loss of capacity of the cells.

 

[tga]

So I was going on a 10 degree F 200 mile trip starting at 95%, plugged in and preconditioned. I thought I would be golden, and while I did make it in my '23 MYP, the energy app showed I lost 16% rated range to cold (et als). Being preconditioned, I though the loss would be minimal, then the geek in me came through.

1) Started preconditioned is fine, but on a 3 hour trip, the batteries being exposed to the cold, that preheat is going to need to be supplemented.
2) Internal heating on the battery is likely minimal. Discharge rate is probably something like C/5 on the pack, it's snoozing.
3) Ahhh, the heat pump!
a) Lets say the overall system pack to wheel is 90% efficient. Say you are getting 300W/mile, 60 MPH, 18KWH/hour. Thats 1800W/hour losses.
b) Assume 70% of this can be recovered by the heat pump and it has a COP of 2. That leaves 2*.7*1.8KW= 2.52KW/hour of heat available
c) The cabin at 70F in these conditions, must take at least 1KW, leaving 1.5KW to heat the battery
d) The ability to heat 1200# of battery with 1500Watte is not going to be very good
So at the end of the day, I concluded the heat pump helps, but the car is so efficient, even that can't bail you out of loss of range.

I would love is if someone has some FACTS where my assumptions may be incorrect, please link to source.

So you get to make assumptions, but we can't counter your assumptions with assumptions? Your assumptions are somehow more valid than mine?

2) C/5 is probably low. "Assuming" 25hp steady state to push a car at highway speeds, that's (25*745)W = 18.6kW, or about C/4 for a 75kWh pack.

3a) 90% efficiency is way too high. I've seen detailed estimates in the 70%-77% range for a 3, and the Y will be worse (more frontal area). See:

https://www.reddit.com/r/teslamotors/comments/iws58g

(you need to expand the first set of replies to see the poster's full analysis).

3b) COP is a ratio of (heat moved)/(power used to run the heat pump). Your calculation isn't using the heat pump's power consumption, so COP doesn't come into play here.

3c) Where do you get 1kW to heat the cabin?

 

[Goobers]

The point is, even with the heat pump and preconditioning there is loss of range yes! There is not enough waste heat to keep the batteries and occupants 'warm'.

Hmmm, temperature and aerodynamics, good point, a quick google shows it is probably not significant.
>>As the ambient air temperature drops, air becomes denser, which increases aerodynamic drag. For every 10 degree Fahrenheit drop in temperature, aerodynamic drag increases by 2%. Every 2% increase in aerodynamic drag results in approximately 1% decrease in fuel economy.

As for the 400WH/mile at 35ish MPH, feel free to prove me wrong, but I'm inclined to believe the energy meter is fooling you. Do you get the raw data from tessie or other means. The bottom line is that the cells have less CAPACITY at cold temperatures and I believe the energy monitor jacks up the consumption to fool you into thinking it is the overall efficiency that is lower (it should not be). The motor and drives should have HIGHER efficiency in the cold, but this will be small compared to the loss of capacity of the cells.

Based on your quote, there is a 60 degree drop from assumed 70 f range testing to your 10f condition and that makes 6% already. That’s “not significant”?

Then you argue that my whm is a Tesla trying to fool me? Considering I charge everyday and can see for myself how much I drive verses the amount I charge, I’d say the only one trying to fool anyone is you.

It doesn’t change the fact your assumptions vary too much anyway.

Yeah, time to add another one to the ignore list.

 

[DanDi58]

Thanks, Captain Obvious....