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Thread: Heater and air conditioning on the model s

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    Member Merrill's Avatar
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    Heater and air conditioning on the model s

    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.

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    Senior Member steve841's Avatar
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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.
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    Member Merrill's Avatar
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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.

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    Member dbullard's Avatar
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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?
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    Member Merrill's Avatar
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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.

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    Sig 1004 Chgd Up's Avatar
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    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.
    Last edited by Chgd Up; 2013-03-14 at 10:18 PM.

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    S85 - VIN:P05130 - 3/2/13 jerry33's Avatar
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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.
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    Quote Originally Posted by jerry33 View Post
    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.
    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.

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    Senior Member cinergi's Avatar
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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).
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