johnlocke
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Re: Official Tesla Model Y Thread

Thu Mar 19, 2020 9:42 pm

dgpcolorado wrote:
Wed Mar 18, 2020 3:30 pm
LeftieBiker wrote:
Tue Mar 17, 2020 9:55 pm
I'm not entirely following this. Tesla's heat pump scavenges heat from the motors, which are adjusted to produce waste heat for this purpose. At what temp does this process begin? IOW, how low can the heat pump move enough heat from the atmosphere to heat the cabin, without the car having to start "running too lean" as it were, to provide cabin heat? How much less energy does this use at frigid temps than a PTC? Graphs were never my strong suit...
As I understand it, the energy savings of the heat pump (COP >1) depends on both the ambient temperature and the heating load (how much heating is needed). If Figure 32 is representative of the system in the Model Y, the extra heat generation begins to be used in blend mode between 10ºC to -10ºC, depending on load, and is the primary source of heat below -10ºC. At very cold temperatures the efficiency would be much the same as a conventional PTC heater.

It is a bit early to know what the actual numbers on a Model Y will be.
Keep in mind that the motor generates waste heat anyway even if you don't detune it. Using the heat pump to steal that heat is more efficient than stealing it from cold air and cools the motor as well. Detuning to generate more heat is still cheaper than a separate heating system with a resistive heater. Heating and cooling the battery pack is necessary anyway so using a heat pump ought to be a better solution for that too. The heat pump doesn't need to scavenge heat from the air at all. I suspect that the heat pump only dumps heat to the external radiator.
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LeftieBiker
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Re: Official Tesla Model Y Thread

Thu Mar 19, 2020 9:55 pm

The heat pump doesn't need to scavenge heat from the air at all.
Not unless you want heat on a cold morning, from a cold car. What you describe is a system that delivers heat about 10 minutes after driving starts, much like a cast iron ICE.
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johnlocke
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Re: Official Tesla Model Y Thread

Fri Mar 20, 2020 10:53 pm

LeftieBiker wrote:
Thu Mar 19, 2020 9:55 pm
The heat pump doesn't need to scavenge heat from the air at all.
Not unless you want heat on a cold morning, from a cold car. What you describe is a system that delivers heat about 10 minutes after driving starts, much like a cast iron ICE.
Point taken but the motor and coolant still form a large heat sink to draw from and would be at least at ambient temperature or better. Maybe if you were going to preheat the cabin on a cold morning then you might want to use outside air. In either case, the heat pump would start to heat the cabin just as quickly. Car doesn't need to warm up before the heat pump will work. Sucking heat out of cold air is much harder than sucking it out of circulating liquid coolant. Air has a much lower specific heat than water. Using the coolant as a heat source would allow the heat pump to operate efficiently at a lower temp than you could using air as a heat source.
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jlv
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Re: Official Tesla Model Y Thread

Mon Mar 23, 2020 6:26 am

Looks like the Model Y launch was the smoothest ever for Tesla. A whole bunch got delivered up here in MA last Friday.
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dgpcolorado
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Re: Official Tesla Model Y Thread

Mon Mar 23, 2020 9:21 am

jlv wrote:
Mon Mar 23, 2020 6:26 am
Looks like the Model Y launch was the smoothest ever for Tesla. A whole bunch got delivered up here in MA last Friday.
The disappointing thing is that with the factory shutdown those first few thousand cars will be all there are for awhile.
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