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We’ll, I guess that’s why it works when parked and preconditioning, but apparently doesn’t work while driving, since the motors are busy driving… seriously, how hard would it have been to add PTC? Seems a penny wise and pound foolish decision on Tesla’s part. And I’m not sure they’re really saving that much because they have elaborate oil pump and filter system on each motor VW didn’t need.
 

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My 2019 e-Golf SEL Premium had a heat pump. It worked perfectly fine. Excellent in both hot and cold weather, never had a problem with it. I'm not convinced it had much effect on range, but technically it worked great for me. Admittedly I never got to test it in extreme cold though.

I dunno.
 

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We’ll, I guess that’s why it works when parked and preconditioning, but apparently doesn’t work while driving, since the motors are busy driving… seriously, how hard would it have been to add PTC? Seems a penny wise and pound foolish decision on Tesla’s part. And I’m not sure they’re really saving that much because they have elaborate oil pump and filter system on each motor VW didn’t need.
Tesla can use front motors while driving with Model 3 or Y....and switch back and forth if front wheel needs traction .
 

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But how well does it work in the summer when you need AC?

I thought the problem at extremely low temperatures was more of a fundamental one that is due to the laws of thermodynamics. You are trying to extract heat from very cold air, and you have to work like hell to make that happen.
So, the issue with heat pumps in cold weather isn't that there is a fundamental thermodynamics issue with using a heat pump below those temperatures, 0°C is still 273K so there is plenty of thermal energy available, it's that the refrigerant used is no longer in its ideal operating range. If you use the correct refrigerant you can make heat pumps work all the way down to near absolute zero. (Helium is the refrigerant in that case.) The most efficient heat pump systems rely on the refrigerant being able to phase change between a liquid and a gas as they change in pressure and absorb/reject large amounts of heat energy with relatively small temperature differences. Without that phase change you are relying entirely on the pressure change in the system to provide temperature differentials, which uses much more energy. Each refrigerant has a required operating pressure for a given temperature. (Low pressures in a liquid state for the cold side and high pressures in a gas state for the hot side of the loop.) Most of the common refrigerants in use only work well in small temperature ranges. Some will remain a liquid across the evaporator in colder temperatures, others will remain a gas through the condenser in warmer temperatures. To operate over the entire temperature range you find in common weather they would need to be able to not freeze at extreme cold temperatures, be able to transition between a liquid and gas across that entire temperature range at some pressure, and have a system that can handle the pressure at the transition point for the high temperature limit. In the case of some of the refrigerants that can do this we're talking about several thousand psi, and often issues with toxicity. Most of the commonly used refrigerants can only operate well at either the warmer or colder end of the atmospheric temperature scale.
 

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So, the issue with heat pumps in cold weather isn't that there is a fundamental thermodynamics issue with using a heat pump below those temperatures, 0°C is still 273K so there is plenty of thermal energy available, it's that the refrigerant used is no longer in its ideal operating range. If you use the correct refrigerant you can make heat pumps work all the way down to near absolute zero. (Helium is the refrigerant in that case.) The most efficient heat pump systems rely on the refrigerant being able to phase change between a liquid and a gas as they change in pressure and absorb/reject large amounts of heat energy with relatively small temperature differences. Without that phase change you are relying entirely on the pressure change in the system to provide temperature differentials, which uses much more energy. Each refrigerant has a required operating pressure for a given temperature. (Low pressures in a liquid state for the cold side and high pressures in a gas state for the hot side of the loop.) Most of the common refrigerants in use only work well in small temperature ranges. Some will remain a liquid across the evaporator in colder temperatures, others will remain a gas through the condenser in warmer temperatures. To operate over the entire temperature range you find in common weather they would need to be able to not freeze at extreme cold temperatures, be able to transition between a liquid and gas across that entire temperature range at some pressure, and have a system that can handle the pressure at the transition point for the high temperature limit. In the case of some of the refrigerants that can do this we're talking about several thousand psi, and often issues with toxicity. Most of the commonly used refrigerants can only operate well at either the warmer or colder end of the atmospheric temperature scale.
I think that's a good summary. Carmakers can optimize for AC or heat, but doing both well is quite hard. Which may be why the US market doesn't get a heat pump - instead we get a system optimized for AC.
 

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So, the issue with heat pumps in cold weather isn't that there is a fundamental thermodynamics issue with using a heat pump below those temperatures, 0°C is still 273K so there is plenty of thermal energy available, it's that the refrigerant used is no longer in its ideal operating range. If you use the correct refrigerant you can make heat pumps work all the way down to near absolute zero. (Helium is the refrigerant in that case.) The most efficient heat pump systems rely on the refrigerant being able to phase change between a liquid and a gas as they change in pressure and absorb/reject large amounts of heat energy with relatively small temperature differences. Without that phase change you are relying entirely on the pressure change in the system to provide temperature differentials, which uses much more energy. Each refrigerant has a required operating pressure for a given temperature. (Low pressures in a liquid state for the cold side and high pressures in a gas state for the hot side of the loop.) Most of the common refrigerants in use only work well in small temperature ranges. Some will remain a liquid across the evaporator in colder temperatures, others will remain a gas through the condenser in warmer temperatures. To operate over the entire temperature range you find in common weather they would need to be able to not freeze at extreme cold temperatures, be able to transition between a liquid and gas across that entire temperature range at some pressure, and have a system that can handle the pressure at the transition point for the high temperature limit. In the case of some of the refrigerants that can do this we're talking about several thousand psi, and often issues with toxicity. Most of the commonly used refrigerants can only operate well at either the warmer or colder end of the atmospheric temperature scale.
You clearly have a lot of insight into this, so, based on what you know, why do you reckon Tesla's heat pumps are failing and, I know I am asking a lot, would the ID.4's heat pump be more resilient (so far, no known cases of failing ID.4 heat pumps bar a few reports of poor cooling performance)?
 

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The R744 compressor (edit: only in the id.4 with heat pump - not tesla) has to operate at 6-10x the pressure of traditional R1234af AC could lead to a shorter life of components, or reliability problems that won't show up for a while (such as leakage of the refrigerant and having to recharge more often, and may be real expensive for a while since few have the special equipment and training to work with R744 yet.)
 
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Tesla has something that doesn't work right? Say It Ain't So!

I saw a youtube video yesterday concerning their latest OTA navigation system update. The video said "It Sucked".

In the mean time, my ID.4 just keeps on working nicely. It is presently sitting outside in a non-heated carport, but plugged in so I can preheat if I'm going out later. We do have light snow falling. It is 34 degrees so I don't expect any accumulation.
 
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