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Cold Weather Range

Discussion in 'Roadster: Performance' started by Doug_G, Feb 3, 2012.

  1. Doug_G

    Doug_G Lead Moderator

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    Today was the first time I did a longer road trip at below-freezing temperatures. Some interesting results.

    attachment.php?attachmentid=4031&d=1328330414.jpg

    The trip was from Ottawa to Kingston and back to Ottawa again, a total distance of 296.1 km. Except for the occasional small town, all the driving was between 80 and 90 kph. I avoided the faster highways to preserve range because of the lack of charging facilities at my destination. (I actually did pick up a few hours of 110V charging, which was nice because it padded my range margin.)

    The total trip time was 4:05 hours, and the energy consumed was 49.31 kWh, for an average of 167 Wh/km.

    Since the trip was going to be a good fraction of the car's nominal range, and conditions were not ideal, I took it easy on heating. I used the seat heater throughout because it's power draw is negligible (can't even see it on the power meter). When I needed to clear the windows I used the cabin heater very sparingly and only at its lowest power setting. I'd ballpark average heater usage at 3 Wh/km. (Continuous full power could have consumed 40 Wh/km, but that would have been too much heat anyway!).

    The main nuisance of driving with the cabin heater off is that air still blows in via the vents. I closed the vents and put the air on the windshield to keep it clear, and turned on recirculation to reduce the flow rate (usually I avoid that in the winter but the Roadster didn't get humid - it was still sucking in quite a bit of outside air). With the seat heater set to low my back and seat were a little too warm, and with cool air bouncing off the windshield made my hands (no gloves) and face a little too cool. The net result was strange because I felt slightly too warm and slightly too cool at the same time; but overall it was reasonably comfortable and I could have stayed that way indefinitely without getting chilled.

    Tesla's efficiency spreadsheet predicted 147 kWh at 90 kph. I've previously found that their estimates are quite accurate - in summer driving conditions, that is. Today's results imply that power consumption was about 14% above nominal. Accounting for heating we're probably looking at 11% in extra losses.

    The temperature ranged from 0C to -5C. If we assume that Tesla's data is for 20C (room temperature) then the increased air density would account for most of the difference. The ratio is 1.316/1.204 (see Density - Wikipedia, the free encyclopedia) = 9.3%. Pretty close.

    We've had a warm winter, and much of the precipitation has been rain instead of snow. Predictably enough a lot of roads around here are in pretty rough shape due to frost heaving. The secondary highways I was driving on were in really bad shape. I wouldn't be surprised if those thousands of bumps added a bit of extra power consumption.

    I'm not sure about the rolling resistance of winter tires versus summer tires, but I don't think that was a big factor.

    So the net result is 11% range loss, plus about 3% for heating. In comparison, Nissan Leaf owners say that they see a 1% loss in range for each 1C below 20C, not including any cabin heat. This would have predicted a 22% drop in range, and implies that the Roadster handles the cold quite a bit better.

    One note: my battery pack was warm throughout. I have previously found that if your pack is cold-soaked well below freezing, you could lose up to 10 km extra during the warmup period.

    Have other people seen similar results?
     

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  2. stenkb

    stenkb Roadster 938 Model S 5957

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    Hey Doug,

    I have seen about 15- 20+ percent more energy used driving in cold conditions compared to warm. Hwy speeds 100/110 with heater on.

    In an extreme case I decided to drive 200 km on clear roads but -20 C weather......what a mistake. To begin with I basically had to have my seat heater and full heat blowing continously - this stopped the uncontrollable shivers - but I was pretty much frozen. -20 C cold air literally blew in from the door sill area on both doors the entire way. I actually stopped and bought a blanket to help finish my trip lol.....

    I love the car but I won't take it at highway speeds again if the weather is much below zero. It just wasn't made for Canadian winter weather IMO.

    Kevin
     
  3. Doug_G

    Doug_G Lead Moderator

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    Curious I haven't noticed air blowing in over the sills. The cold air I was getting was coming in through the ventilation system.

    Another curious fact... of late my Standard Mode charges have been coming in at 294 km, versus 300-301 when it was new. But after the Range Mode charge and road trip, it's back up to 302 km! I guess the rumors that Range Mode charges do more pack balancing are true. It will be interesting to see if that lasts.

    Looks like I'm going to be doing another trip next Friday. Hope the weather isn't too cold!
     
  4. NigelM

    NigelM Recovering Member

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    Yeh, I just drove home from work with the top off, it's 86F (30C) this afternoon. My fans came on when I parked in my garage at home, so even if you lose power in colder weather, I'm still using power in hot weather.

    BTW, I've been doing a lot of city driving recently and find my est range is consistently about 10% higher than my ideal range. Got in the car this morning with a full (standard mode) charge ideal range of 191miles and an estimated range of 211miles.
     
  5. Doug_G

    Doug_G Lead Moderator

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    Show-off!

    My foot is too heavy for that. Just ask my rear tires...
     
  6. NigelM

    NigelM Recovering Member

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    #6 NigelM, Feb 5, 2012
    Last edited by a moderator: Mar 13, 2016
    This is why we live in Florida......:cool:

     
  7. Doug_G

    Doug_G Lead Moderator

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    #7 Doug_G, Feb 5, 2012
    Last edited by a moderator: Mar 13, 2016
    Yes, it's so much better there.

     
  8. NigelM

    NigelM Recovering Member

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    #8 NigelM, Feb 5, 2012
    Last edited by a moderator: Mar 13, 2016
    Umm, yeh cos' you never had storms like that in Ontario.....

     
  9. Doug_G

    Doug_G Lead Moderator

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    I've been doing some more investigation into winter driving range. I'm not happy with my earlier back-of-the-envelope estimates; I simply assumed aerodynamic losses were the dominant factor; in fact, at this speed they're not.

    I was seeing around 160 Wh/km at 85 kph, with no cabin heat. Interpolating Tesla's efficiency spreadsheet, at that speed I should nominally be seeing:

    Aero 54.1 Wh/km
    Tires 34.8 Wh/km
    Anciliary 2.1 Wh/km
    Drivetrain 47.9 Wh/km
    Total 138.9 Wh/km

    The point here is that at this speed, aerodynamic drag is NOT dominant. Drivetrain losses are almost the same.

    Let's assume the aero goes up by 9.3% due to the denser air. That's only an extra 5 Wh/km. I'm seeing about 20 Wh/km. Where is the rest going?

    The battery pack started at 13C and rose to 26C over the trip. The PEM started at 8.5C and rose to 26C by the end. The motor spent most of the trip at 40C. They're all in perfectly normal ranges; I don't see how they would affect anything.

    I'm wondering if the loss was due to the rolling resistance of the winter tires. Does anyone have any experience with that?
     
  10. dhrivnak

    dhrivnak Active Member

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    I do think it is more due to running cabin heat that anything else. I go from about 250w/mile to 300w/mile running the heat. So my results are very similart to Doug_G.
     
  11. Doug_G

    Doug_G Lead Moderator

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    Clearly running the heater full blast can add 50 Wh/mile, but that data was taken with the heat OFF.
     
  12. neroden

    neroden Happy Model S Owner

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    Thanks for the cold weather range testing.
     
  13. drees

    drees Active Member

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    Both tire drag and drivetrain drag will go up in cold weather as well. Tires are less flexible so "bounce" back less readily. Grease / gear lube is also thicker when cold.

    Depends highly on the tires in question. The PriusChat guys have varying results, but Nokian tires in particular seem to have low rolling resistance and typically nearly match the stock all-seasons. I would imagine that similar Nokians would at least match the sticky stock Roadster rubber in rolling resistance.
     
  14. Doug_G

    Doug_G Lead Moderator

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    I'm running the Pirelli winter tires. I just did a second road trip, with similar results to the first one. The temperature was not quite as cold this time, and the pack was also warmer when I first set out. I'm really thinking the range difference is mainly due to the winter tires, not the temperature.

    On both trips the VDS reported higher-than-normal power consumption at first - 200 Wh/km versus 170 Wh/km after the No-Regen light went out. I was maintaining the exact same speed. Is this a Range mode thing? I must confess that on previous road trips I've not looked closely at the power consumption early on.
     
  15. Brian H

    Brian H Banned

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    About the heat: someone found that blocking the passenger vent greatly increased the driver's comfort, without affecting the passenger noticeably. Should translate into lower power drain.
     
  16. dj905

    dj905 Member

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    I did this and while it helped the driver's side head, I had an overheating situation where the heater shut down completely while my car was sitting still for a few minutes with the heater on. I have since removed the passenger side blocking, and have had no further overheating problems. I would not recommend blocking this completely.

    David
     
  17. S-2000 Roadster

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    Hmm, does turning the heat down save electricity? ... or do you really need to shut the heat off completely?

    With an ICE vehicle, the knob controls the rate of flow of engine coolant, which is vastly different from what is happening in an EV. The Roadster is using 400 V for the heater, but does it throttle the current or pulse-width modulate it when you turn down the cold/hot knob below full? Would the heater use any power at all if turned on with the knob rotated fully counter-clockwise?
     
  18. donauker

    donauker Member

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    Yes, the Roadster does regulate the power to the heater based on knob setting just as it will vary the speed of the A/C compressor to regulate cooling level based on the knob position. I believe the heat is more of a thermostatically controlled on/off cycle rather then a PWM control but I am not certain.
     
  19. Doug_G

    Doug_G Lead Moderator

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    The heater power level definitely can ramp up and down; I think it actually is PWM controlled.

    Also note the maximum amount of heat it will provide depends on the fan setting. (I recently noticed that one of the firmware upgrades appears to have changed this behavior somewhat, but I haven't explored that yet.)
     

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