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Heat Pump Limit?

Discussion in 'Model 3' started by Cybr.Myk, Feb 6, 2021.

  1. MP3Mike

    MP3Mike Well-Known Member

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    Actually doesn't it say they are for heating the air in the car? Specifically to help with the temperature difference between the two zones.
     
    • Disagree x 1
  2. Cybr.Myk

    Cybr.Myk Member

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    110 km/h

    that’s probably not an accurate way to look at my driving yesterday though. I was chauffeur-ing my daughter around and I sat in the car with the heat on while she ran into stores. There was a lot of just sitting around burning energy but not moving anywhere.
     
  3. Matias

    Matias Active Member

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    I think COP is at least one, because eventually everything converts to heat. But as I mentioned in the previous post, there is still some absolute amount of heat a heat pump can generate and if OP is outside that envelope, temperature can’t be maintained.
     
  4. SageBrush

    SageBrush REJECT Fascism

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    Agreed, but that does not explain cool air coming out of the vent
     
  5. Matias

    Matias Active Member

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    But if outside air is -38 C and heater warms it to +10 (because its capacity is not enough), it feels cool?
     
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  6. SageBrush

    SageBrush REJECT Fascism

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    Perhaps, but OP was already driving and the car would have been in at least partial re-circ mode.
     
  7. Phlier

    Phlier Bluebird

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    Hmmm. Time to page @AlanSubie4Life I’m pretty sure he stated that there was a resistance heater to supplement the heat pump, as it just isn’t possible for the heat pump to provide enough heat once it gets really cold out, even when heat is scavenged from the battery and the motors while in heat generating mode.

    If we could just get access to the service manual...
     
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  8. Phlier

    Phlier Bluebird

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    If you go to 44 seconds into the second video in @Big Earl ’s post, it does show two resistive heaters adding heat to the system.

    This is supposed to operate at -10C and below.
     
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  9. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    #29 AlanSubie4Life, Feb 7, 2021
    Last edited: Feb 7, 2021
    The compressor operates as a high output heater, with electrical power draw higher than a “typical PTC,” (whatever typical means) according to Tesla:

    https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=51235&flag=1

    Hopefully most of that input power is making it inside the car as heat.

    Page 8 and 9. Videos posted probably also describe it but have not watched them.

    Don’t know what happened here. Seems cold; wouldn’t want to be anywhere near there. Going to be about 70 here today, maybe I will go for a nice bike ride? ;)

    DDDA458E-372D-4221-A408-EB4749662538.png

    Technically true, but misleading, since the heat pump is operating as a resistive heater, apparently. I removed the disagree but tempted to put it back.
     
    • Helpful x 2
    • Informative x 2
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  10. iwannam3

    iwannam3 Member

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    The semi was hauled on a trailer to the midwest, I assume for some cold weather testing to work out things like this. Tesla gets accused of designing cars for CA due to door handle icing, auto wipers, dumping rain into trunk when opening, etc.
     
  11. SageBrush

    SageBrush REJECT Fascism

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    By the people who have never heard of Norway
     
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  12. AlanSubie4Life

    AlanSubie4Life Efficiency Obsessed Member

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    Not quite; as linked above, it seems the heat pump IS a resistive heater with very high capacity (in some scenarios). What disadvantages it may have in place of a PTC, I do not know.
     
    • Informative x 1
  13. Phlier

    Phlier Bluebird

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    Thanks, @AlanSubie4Life , very much appreciated.

    I've owned houses with heat pumps the majority of my adult life. They are fantastic at cooling during our hot desert summers, but they are not effective heaters when the thermostat drops below about 35F. Even between 35F and 45F they're just mediocre. The "Aux heat" (a heat source that supplements the heat pump), whether provided by natural gas or resistive heaters, is run extensively during the coldest months.

    I just can't imagine that even with a couple of relatively minor sources of additional heat, a heat pump by itself would ever be sufficient for a car driving in cold to severe cold conditions. Glad to see Tesla think about this.

    I just wonder what happened to our OP's car? Stuck octovalve? Inaccurate temp sensor? Broken temp sensor? Bad compressor? You'd think the car would throw up a fault code/message for those occurrences, though.
     
  14. dmurphy

    dmurphy Woof.

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    Sure - but my original point was that there is no PTC heater in 3 or Y. It's all being done by the heat pump. If it has some internal resistive strips, it's still not heating the air blowing into the cabin, but rather, the coolant. Still not as instant-on and as direct as a PTC cabin heater. More efficient, sure, and helps with warming the battery and the motor ... but less direct heat into the cabin. Better for the car, worse for my fingertips. :)
     
  15. Phlier

    Phlier Bluebird

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    OK, so after re-reading OP's post, and watching the videos posted by @Big Earl , it looks like @Cybr.Myk 's car was operating in "Heating Mode 5," which is at the 3:30 point in the second video. In this situation, the compressor is supplying heat for both cabin heating and battery heating. IMO, the OP found himself in a cold enough situation that the heat supplied by the compressor (and the drive motor(s))just wasn't enough to heat both the battery and the cabin.

    Bjorn Nyland did take a heat pump equipped Model 3 car camping in -25C in Norway. He has a video about it that's worth watching. In this situation (car stationary), the heat pump kept the interior toasty warm. It also kept Cybr.Myk warm during stop and go driving.

    So the difference appears to be highway driving. Is the system capable of bypassing the radiator? At first glance, it looks like there is just too much heat lost through the radiator at highway speeds for the system to keep up when heat is being called for at the battery and the cabin at very low temperatures. Tesla drivers might have to start borrowing a page from ICE (and especially diesel) drivers, and blocking off the radiator. Although doing so in our cars might have more negatives than positives. Personally, I'd bring blankets along before making any alterations to the heating/cooling system of our cars.

    Hmmm... This whole situation has me intrigued, but not quite intrigued enough to leave my wonderful winter desert temps to venture to the ice planet of Hoth (aka, "Canada") to find out. 65F today. While you guys are keeping warm inside your Tontons, I'll be washing my car here shortly.:p
     
    • Like x 1
  16. XPsionic

    XPsionic Member

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    I don't think OP's car is malfunctioning.

    Is there anything to suggest that the model 3 heat pump + resistors have enough capacity to overcome to heat loss at highway speeds at 110kph? I think it's just really frigging cold, like -30c or lower, and therefore the system struggles to keep up. It can happen to gas cars too, if they don't generate enough waste heat (super efficient 4 cyl, especially hybrids) you don't get a lot of heat in the cabin.
     
  17. Phlier

    Phlier Bluebird

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    I can't speak to the others, but for me, it's because I'm a huge nerd. I love to learn everything I can about everything I drive (or fly), and it's fun to learn not only about the systems themselves, but also what their limits are... what scenarios they excel in, which ones they don't, how to get the most out of them. Some would call it a "hobby." Others would call it a "sickness." ;)
     
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  18. XPsionic

    XPsionic Member

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    hehe, not a problem. I just don't really see it as an actual malfunction in this case. There's only so much heat the car could produce and it wouldn't surprise me that a California designed car doesn't make enough heat at highway speeds at -35c.
     
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  19. Big Earl

    Big Earl bnkwupt

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    #39 Big Earl, Feb 7, 2021
    Last edited: Feb 7, 2021
    In those conditions, covering the roof and the rear side windows with something like Sunshades for Tesla Model Y would probably make a big difference in the amount of cabin heat loss.


    I agree with you about the system being overwhelmed when it’s attempting to heat both the cabin and the battery in extreme cold (heating mode 5). It seems to me that Tesla needs to make a mode 5+ where the drive units can provide boost heat (like they do for heating Model 3 battery) in these edge cases. That would, of course, make energy consumption even worse in those conditions.

    Edit: that might not work if the heat pump is at its BTU/hr capacity limit. The waste heat it scavenges from the drive units makes it more efficient, but it wouldn’t increase its capacity. If you’re using the drive units as boost heat, you’re neither increasing efficiency nor increasing the capacity of the heat pump. If there was an additional octovalve mode that would isolate the battery and drivetrain from the heat pump and cabin, the compressor could dedicate its entire output to the cabin while the drive units heated the battery, but that’s not really possible.

    I wonder if the 12 volt boost heaters are active in mode 5. If not, they could be added through a software update.

    I’m not an engineer but there is a Holiday Inn Express down the street.
     
  20. TheRFMan

    TheRFMan Member

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    I don't think the car is malfunctioning. I just think most people here have never experienced that level of cold. It's also exceptionally windy out in the prairies. Skin freezes in a few minutes. Most of Canada does not get that level of cold. I drove from Calgary to Ottawa in winter about 10 years ago in a RAM pickup with he 6.7L Cummins diesel, and that truck struggled to keep the cabin warm on the prairie highways as well.
     
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