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minus 20 deg. celcius

Discussion in 'Model S' started by NielsChr, Feb 7, 2012.

  1. NielsChr

    NielsChr Member

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    Right now the temp is minus 20 degrees Celsius outside in Denmark, both in Norway, Sweden and some placed in the US/Canada temp will often get below a comfortable. temp.
    I assume Tesla should work well below that - anyone who have seen the beta who know how the heat is transported to the back seats.
    most premium cars have a air flow to the back seats to maintain a decent temp in the car.

    This picture is from a another site regarding a used VW, and shows a Passat witch have been drinking to much water...But it also shows the air pipes below the front seats - these transport hot/cold air flow to the back passengers
    [​IMG]

    Have anyone noticed any similar heating to the back seats passengers in the beta? - any pictures ?
     
  2. doug

    doug Administrator / Head Moderator

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  3. gmontem

    gmontem Model S P01707

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    Are those recessed seat belt locks and chair arms?
     
  4. doug

    doug Administrator / Head Moderator

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    Umm, yes to the seatbelt locks. Not sure about the arm rests. The back seat is pretty much a bench, so they're no loss in head room if you have to sit b*tch since there's no transmission tunnel/center hump.

    Here's another photo:
    attachment.php?attachmentid=2949.jpg
    (Norbert - Photos from Sunday, October 2, 2011 (Model S event))

    Anyhow, for the purposes of this thread, you can see the vents that come out of the front arm rest to provide air to the back seats.
     
  5. Doug_G

    Doug_G Lead Moderator

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    The Roadster has a 3 kW heater, but it's not exactly toasty at -20C. Hopefully the Model S will do a better job... I believe they said it's a heat pump rather than just resistive heaters?
     
  6. Lyon

    Lyon 2016 S P100DL, 2016 X P90D

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    Yes, the heat and AC are supplied via HVAC. Unfortunately, HVAC doesn't do a fantastic job when it's REALLY cold out (or at least that's what I was told in regards to residential heating/cooling).
     
  7. cinergi

    cinergi Active Member

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    My CA (Dan) rides with the HVAC team to work every day and I've given him a LOT of feed back that he's been passing on to the team. So I know they're at least aware of the issues we have with the Roadster.
     
  8. Eberhard

    Eberhard #421 Model S #S32

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    #8 Eberhard, Feb 8, 2012
    Last edited: Feb 8, 2012
    I have good experience with the directed heat pipe, bringing the warm air to the drivers feet. Don't forget to block the passengers outlet.

    But still the best is the heated seat-cover used to keep my feet warm.
     
  9. Discoducky

    Discoducky Active Member

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    I wonder how much heat will dissipate into the cabin from the battery? I hope TM will encourage/allow this on very cold days.
     
  10. stopcrazypp

    stopcrazypp Well-Known Member

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    Given the battery has its own liquid cooling/heating loop (and thus is likely very well insulated), I would expect virtually none. It's better to keep the battery well insulated so that you don't see as big a temperature swing (esp. the resulting voltage sag) from ambient temperature changes. One of the biggest problems in winter for most BEVs is because of voltage sag from low battery temperatures (which affects the range many times more than the heating requirements for the cabin).
     
  11. bolosky

    bolosky Member

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    There's not going to be that much power there to dissipate. The whole drivetrain is supposed to be ~85% efficient. If you assume that the losses are evenly spread between the battery, inverter and motor then 5% of the power draw turns into battery heat. When you're cruising, this probably means < 1kW battery heat. You need several times that power to heat the cabin.
     
  12. Discoducky

    Discoducky Active Member

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    That's a great point, it would appear that even on moderately cool days (10 degrees Celsius) that the battery will need to be heated with such a small amount of waste heat being generated.
     
  13. Doug_G

    Doug_G Lead Moderator

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    Also there is an issue of basic thermodynamics. In order to get heat to flow you need a temperature difference. I don't think my Roadster's coolant has ever been over 41 degrees C.
     
  14. eledille

    eledille TMS 85 owner :)

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    #14 eledille, Feb 9, 2012
    Last edited: Feb 16, 2012
    That used to be true, but things have improved. My HVAC is producing a lot of heat even when it's -24 degrees C outside, which is the coldest we've seen since we installed it last winter. The manufacturer claims it works well down to -35 C.

    Correction: The manufacturer claims it works well to -25, but practical experience in Norway indicates it still works well at -30 C.
     
  15. Lyon

    Lyon 2016 S P100DL, 2016 X P90D

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    That's great to hear! I doubt that I'm going to be driving my Model S around in temperatures that low, but it's gotta be able to keep me warm below freezing.
     
  16. KBF

    KBF Model S 2017

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    When it hits - 35C we stop BBQ' ing outside in Manitoba, but we still have to drive to work. Of course, that's also why we have electric block heaters - I don't see any serious issues unless you let the charge get really low and don't plug in at work.
     
  17. neroden

    neroden Happy Model S Owner

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    Last I read, heat pumps start getting less efficient than resistive heating around -20 C and below, but will still work down to significantly lower temperatures. I don't remember the exact reasons or numbers.
     
  18. eledille

    eledille TMS 85 owner :)

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    #18 eledille, Feb 15, 2012
    Last edited: Feb 20, 2012
    That's exactly what I meant when I said "used to be true". Our HVAC is clearly much more efficient than resistive heating even at -24, at that point it's still blowing a huge quantity of very warm air. Its output is actually much warmer at -24 than at -15, simply because at -15 full power isn't required to maintain 20 C indoor temperature. I'd estimate it replaces at least 2 kW of electric heating and it saves stacks of firewood to boot. Max consumption is 600 W. The manufacturer claims it delivers more heat heat energy than the electricity it consumes at much lower temperatures than that, and it's not enormously expensive either. I think you can get even better models now.

    Condensation releases heat, evaporation absorbs heat, and you can change the boiling point of a substance by altering the pressure. The heat pump uses a combined pressure/vacuum pump and a valve to create a partial vacuum in the outside evaporator and high pressure in the inside condenser. That causes the refrigerant to cool to whatever boiling point the pressure dictates, -40 or so, as a part of it boils after having passed through the valve into the low pressure evaporator. The rest of the refrigerant then evaporates while absorbing heat as it flows through it. The refrigerant then passes through the pump into the high pressure zone, where it becomes hot due to the compression. The boiling point is also much higher at the higher pressure, +50 or so, so it becomes liquid again in the condenser while releasing the heat that was absorbed earlier.

    The reason for the falling efficiency at lower temperatures is that the pump must perform more work when the temperature differential is larger, as more vacuum and higher pressure is needed to evaporate and condense the refrigerant. When more heat from the pump is lost in the evaporator than the small amount of refrigerant still being moved can transport, you are losing energy compared to resistive heating.

    I believe the recent performance increase is due to inverter controlled brushless pump motors, digitally controlled release valves which allow precise control of pressure in both halves of the loop and new, better refrigerant (R410A).

    This doesn't mean that Model S' HVAC can do the same, of course, only that it's possible. Also, there are much tighter space constraints in a car. This is the model we bought.
     
  19. VolkerP

    VolkerP EU Model S P-37

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    thanks eledille for real world description & theoretical background. One more thing to add:
    Performance of heat pumps is measured in a dimensionless number named COP. Top notch residential heat pumps come with a COP of 4, meaning it uses 1kWh of electricity to extract 3kWh of heat from the (outside) heat source and transform it into 4kWh heat at desired temperature. The COP depends on input and output temperatures and varies with season, thus a formula is used to calculate a year-round average value.
     
  20. dpeilow

    dpeilow Moderator

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    Who was it said here they also use the ground as a sink to store heat from summer months to use in the winter?

    I was also going to say that some Japanese manufacturers are claiming a COP of 5, but eledille has one.
     

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