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Heater and air conditioning on the model s

Discussion in 'Model S: Interior & Exterior' started by Merrill, Mar 14, 2013.

  1. Merrill

    Merrill Active Member

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    This may have been talked about, but cannot find it. We were driving to San Francisco today and my wife asked me how the Tesla S gets it heater and air conditioning. We know how an ICE works from coolant and a/c compressor, but could not explain to her how that works on an all electric car. Can someone explain.
     
  2. steve841

    steve841 Active Member

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    Ask your wife how the a/c in the house is able to work without a V8 attached....

    Concept is pretty much the same in an EV.
     
  3. Merrill

    Merrill Active Member

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    So we had discussed the heat pump concept, but want to know more detail on how that transfers to the EV. What components are used on the Tesla.
     
  4. dbullard

    dbullard Member

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    Think of exactly a normal A/C in an automobile. Now, take the gas engine out of picture - it was turning the A/C pump via a belt. Replace that belt and engine with an electric motor. That's your A/C. Add a small radiator up front to act as the heat exchanger.

    Add a valve with a selenoid to control it, make the freon go in reverse, it's now a heat pump.

    Basically, and A/C IS a heat pump, it's just moving the heat from inside to outside. Heat pumps just let you run the cycle in reverse, so you move the heat from outside to inside.

    The biggest problem with a heat pump is that at low temperatures, there is less heat available in the ambient air, so they need an auxiliary source, either electric or waste heat from something else.

    Does that clear it up?
     
  5. rlpm

    rlpm S P85 | Sig X _P90D_

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  6. Merrill

    Merrill Active Member

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    Thanks for the information, I was just trying to understand what acts as the condenser, heater core and evaporator in the ICE.
     
  7. Chgd Up

    Chgd Up Sig 1004

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    #7 Chgd Up, Mar 14, 2013
    Last edited: Mar 14, 2013
    As noted the Model S has an electric AC compressor located under the frunk. You can hear it running if you turn on/off the climate control set on Lo setting with AC on. It slowly speeds up. I'm not sure there is a conventional evaporator for cabin cooling it may evaporate through a heat exchanger in the liquid heating/cooling loop as the AC compressor can be tied in to cool the powertrain through the liquid cooling loop. The Model S has 3 radiators up front a larger center one and two on each side under the headlights these side radiators are behind adjustable louvers in the chrome fins on the lower marker lights.

    There is a very elaborate set of coolant/heat liquid loops. Heat is not generated from a heat pump cycle but only from two sources: the first is powertrain waste heat from the motor, inverters and batteries. All of which are far more efficient than an ICE but still not 100% efficient so there is some heat available. This is also used to heat the batteries under cold conditions. The second heat source when the powertrain does not provide enough heat is a resistance electric heater. It can provide up to 6kw of additional heat. In the Econ mode the use of this resistance heater is minimized to save power.
     
  8. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    It's also very likely a variable speed scroll compressor rather than a standard automotive piston compressor. Scroll compressor are much more efficient and by varying the speed to suit the amount of cooling needed, a lot of energy can be saved.
     
  9. DFibRL8R

    DFibRL8R Member

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    I've actually wondered about this myself, not knowing much about how the ac is working. My impression is in a typical ICE vehicle, the AC is either on or off and any adjustment in temperature with AC on was achieved by adjusting fan speed and mixing in heat. This would seem very wasteful in an EV. The reason I am curious is I would like to know when I am trying to extend range on a hot day, is a warmer cabin setting (but AC is on) going to consume less energy than a cooler setting? Seems like it should but I don't fully understand how the AC works in the Model S at various set cabin temperatures.
     
  10. cinergi

    cinergi Active Member

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    It will save energy, yes -- but you probably won't notice the impact of setting it a few degrees warmer. Pre-cooling the cabin will help the most (get the interior components of the car cooler -- not just the air, but the interior objects as well).
     
  11. jerry33

    jerry33 S85 - VIN:P05130 - 3/2/13

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    1. You can demonstrate that the a/c compressor is variable speed easily. If it was just on and off it would always make the same sound when on, but it doesn't.

    2. A particular cabin temperature isn't the deciding factor, instead it's the difference between the actual cabin temperature and the set temperature. The software figures out the difference and then adjusts the fan and compressor speed. The greater the difference, the faster the compressor will run.

    3. There are two ways to look at a/c energy use: A. Total power used. B. Battery power used. Most people are concerned with B because that affects range. Of course, sometimes you can't pre-cool from shore because you aren't plugged in (at the end of the work day for instance). So to minimize battery usage I've found a method that works well is to start with the temperature set high (e.g. 26 when the temperature shows 35). This setting will have the fan at two blades. Then when the initial heat is gone, lower the temperature one click, and repeat every so often. If the car has been parked in the sun, have the windows open a bit at first to let out the superheated air.

    4. I did try the range setting, but it used more energy than the normal setting. Perhaps it works better with the heating rather than the a/c.
     
  12. DFibRL8R

    DFibRL8R Member

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    I have recently noticed something else that I find odd. I do tend to drive a fair amount with the AC turned off and just the fan moving air from the vents. Periodically, despite the fact that the AC is turned off, I can tell the air starts getting cooled (noticeable drop in air temperature and humidity coming from vents). This lasts for a few minutes then goes back to what feels like regular, non-conditioned air from the vents. I've even noticed it if I have the car in range mode which is supposed to limit HVAC settings to conserve charge. One thought was the AC is kicking on to cool the battery pack coolant and there is spillover into the climate control system.
     
  13. DFibRL8R

    DFibRL8R Member

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    I just discovered an interesting link to Tesla's patent for their cooling/heating circuit posted on the Tesla forum.

    Patent US20100025006 - Electric vehicle thermal management system - Google Patents

    Very interesting (and complicated) patent. I wonder if this is actually the system being used in the Model S or if the system differs. If the patent system is accurate, the 3 loops (battery cooling, motor cooling and cabin cooling) should be separate and I shouldn't feel Cabin AC if the cabin AC is turned off.
     
  14. ThosEM

    ThosEM Space Weatherman

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    Thank you so much for this. I'd been looking everywhere, and while I'm very disappointed to learn that the heat pump is not used for heating of either the cabin or the battery pack, I'm glad to see it laid out definitively.



     
  15. scaesare

    scaesare Active Member

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    Interesting old resurrected thread.

    While it's been suggested that a heat pump would be an efficient part of the heating system it seems that there's some consensus that the S does not have one, and that the cabin heating is purely resistive electrical (and to a lesser extent wast heat from the battery cooling loop".

    Does anybody have any specific evidence pointing to the inclusion of a heat pump in the S?
     
  16. W0QR

    W0QR Member

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  17. grichard

    grichard Member De-Luxe

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    It's hardly definitive, but when I pre-heat the cabin on cool mornings, the car is almost silent from the outside. But when the A/C is running, it's fairly loud. Seems to me a heat pump would be loud, as the compressor would be running and doing its Carnot-cycle business. So I assume the heater is just resistiive...
     

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