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Heat Pump Limit?

stopcrazypp

Well-Known Member
Dec 8, 2007
10,955
6,051
It took him about 30 minutes or so to change out the sensor. He did say that he anticipates an entirely different part will be coming at some point but for now he could only replace the failing part with the same part.

View attachment 635058
Thanks for posting the follow up. Yeah, the rumormill is they are working on something that will permanently fix the issue, but currently the sensor swaps are only temporary fixes.
 

Uncle Paul

Well-Known Member
Nov 1, 2013
6,299
7,596
Canyon Lake,CA
3 points.
1. It is good that Tesla has diagnosed the issue as a failed sensor, fixed it, and it should be working better now.
2. Tesla has only been installing these heat pumps for a short time now. Imagine they will continue working on them to make them even better.
3. When Elon was questioned, many years ago, on how his battery powered cars would be degraded at -40F, he cleverly replied that in -40F temperatures most ICE vehicles would not even start.
 
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Justin L

Member
Dec 7, 2020
7
17
Alberta Canada
I am having the same symptoms as the OP. Car gets quite chilly on the highway, but I can switch my commute to through the city and it maintains the temperature much better. Preheating works like a charm, but the cabin seems to get cooler and cooler as I drive home if I take the highway route. Once you get a chance to test it out, report back if the sensor fix did the trick as I'm sure I'll need whatever solution you get.
 
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XPsionic

Member
Jan 20, 2021
79
107
los angeles
I am having the same symptoms as the OP. Car gets quite chilly on the highway, but I can switch my commute to through the city and it maintains the temperature much better. Preheating works like a charm, but the cabin seems to get cooler and cooler as I drive home if I take the highway route. Once you get a chance to test it out, report back if the sensor fix did the trick as I'm sure I'll need whatever solution you get.

Ambient temperature is very important in this conversation. Maybe the sensor issue causes another car to have issues, but since you're in Alberta and it's been -25 to -35c all week, maybe you're discovering the upper limit of how much heat the heat pump could generate?
 

Cybr.Myk

Member
Aug 30, 2020
129
240
Saskatoon
Choose a nearby supercharger. You don't actually have to go there ;)

The car has its own pre-conditioning routine you cannot modify but if you get "close" to the supercharger by chance the battery heating will start. I'm guessing that even before that happens (if it happens), the car will stop scavenging heat from the battery.


Ah, the closest one is over an hour away. It would not start to precondition within my normal commute. I don’t get close enough. I could put it in track mode, I suppose. I don’t think I will but I think that’s another way to get it to heat up the battery.
 

GZDongles

Member
Feb 23, 2020
225
289
Michigan
3 points.
1. It is good that Tesla has diagnosed the issue as a failed sensor, fixed it, and it should be working better now.
2. Tesla has only been installing these heat pumps for a short time now. Imagine they will continue working on them to make them even better.
3. When Elon was questioned, many years ago, on how his battery powered cars would be degraded at -40F, he cleverly replied that in -40F temperatures most ICE vehicles would not even start.

Is #3 actually true? I have only been in -30F for a few days at a time. My 1997 Honda Civic at the time struggled to crank, but it did eventually start and drove fine (I idled it for 20 minutes first to be on the safe side).
 

Gasaraki

Active Member
Oct 21, 2019
2,085
1,446
Syracuse, NY
Hmmm. Time to page @AlanSubie4Life I’m pretty sure he stated that there was a resistance heater to supplement the heat pump, as it just isn’t possible for the heat pump to provide enough heat once it gets really cold out, even when heat is scavenged from the battery and the motors while in heat generating mode.

If we could just get access to the service manual...

If a PTC heater was still in the car to heat the cabin why bother with the heat pump? Well you might say that the PTC heater is a backup in case the heat pump can't produce enough heat. The problem is that Elon doesn't work that way. His thing is "In the case of designing a car, it means the need for every part is questioned. And again as Musk likes to say “the best part is no part the best process is no process."

He is not going to leave a PTC heater in the car when the heat pump is suppose to replace it. Yes, we might disagree but that's how he operates.
 
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Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
5,942
11,157
Springfield, VA
Oh really? So turning on climate control will condition the battery? I had no idea. I assumed the battery was heated up as a side effect of warming up the cabin.

Yes - turning climate on from the app will actively heat both the cabin and the battery when all of the doors are closed. Opening a door will cause it to stop heating the battery. Using Keep Climate On from the touch screen will also actively heat the battery. I think, but I don't remember for sure, that the active heating target for the battery is 20 - 25C. The active heating target when navigating to a Supercharger is 50 - 55C. At 20C, most regen is available.

But again, you will spend more energy heating up the pack than you will gain from increased regeneration. One exception might be if you are starting your trip at the top of a mountain, in which case you might break even. The most efficient way of operating is to preheat only long enough to warm up the cabin, then adjust your driving to maximize the limited regen and minimize brake use (anticipate stops long in advance).
 

GZDongles

Member
Feb 23, 2020
225
289
Michigan
If a PTC heater was still in the car to heat the cabin why bother with the heat pump? Well you might say that the PTC heater is a backup in case the heat pump can't produce enough heat. The problem is that Elon doesn't work that way. His thing is "In the case of designing a car, it means the need for every part is questioned. And again as Musk likes to say “the best part is no part the best process is no process."

He is not going to leave a PTC heater in the car when the heat pump is suppose to replace it. Yes, we might disagree but that's how he operates.
It seems like the compressor for the heat pump has the ability to operate in an inefficient mode to generate heat just like the drive motors. That's the backup. So not a direct PTC heater, but there is a way to actively generate heat to supplement what the system is able to scavenge from outside air.
 
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Oct 28, 2019
462
530
Texas
If a PTC heater was still in the car to heat the cabin why bother with the heat pump? Well you might say that the PTC heater is a backup in case the heat pump can't produce enough heat. The problem is that Elon doesn't work that way. His thing is "In the case of designing a car, it means the need for every part is questioned. And again as Musk likes to say “the best part is no part the best process is no process."

He is not going to leave a PTC heater in the car when the heat pump is suppose to replace it. Yes, we might disagree but that's how he operates.

there's a reason residential heat-pumps include a gas furnace / auxiliary electrical heating units ... because once you go below 30F it becomes *really* hard to heat the place via a heat pump ... under 25F nearly impossible...
 

stopcrazypp

Well-Known Member
Dec 8, 2007
10,955
6,051
there's a reason residential heat-pumps include a gas furnace / auxiliary electrical heating units ... because once you go below 30F it becomes *really* hard to heat the place via a heat pump ... under 25F nearly impossible...
My understanding is that the heat pump still functions even at low temperatures, just that the COP is more like 1, which makes it so the heating capacity is well below what the user is typically expecting from the system (basically it'll never be able to reach the set temperature in the thermostat). So Aux heat (usually resistive) comes in to supplement. It's not that there is zero heat being generated.

In this case, the OP's issue was a defective sensor like most cases. So we have yet to see the true limits of Tesla's heat pump system (which as others point out has other ways to provide supplement heat).

Edit: someone in other thread provided EPA link that provides a very good description of how Tesla's production heat pump system works. On page 9 it addresses the issue of aux heat (bolded part about using the compressor as a substitute for a PTC heater):
Modern automotive heat pump systems using an HFC/HFO refrigerant suffer from low heating capacity in extremely cold ambient conditions, e.g., minus 10°C and below. Therefore, these conventional systems retain an expensive high‐voltage cabin heater to cover heating deficits whenever the heat pump capacity is insufficient. Tesla’s heat pump system also provides ways to remove a cabin air high voltage PTC heater completely by using the compressor as an electrical heater in specific scenarios. In fact, the electrical power draw capability of the compressor significantly exceeds a typical HV cabin PTC heater capability. This last point is accomplished via Tesla’s unique architecture – the cycle is configured in such a way to provide a controlled environment for the compressor, regardless of ambient conditions, and ultimately unlocks the full electrical input power. Therefore, Tesla’s thermal system can sometimes operate like a heat pump (heat efficiently) and sometimes like an electrical heater when heat pump capacity is not sufficient for comfort – using the same compressor.
Just finished my first "road trip" and I am not happy with range
 
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tstolze

Member
Oct 9, 2020
297
432
OFallon, MO
My understanding is that the heat pump still functions even at low temperatures, just that the COP is more like 1, which makes it so the heating capacity is well below what the user is typically expecting from the system (basically it'll never be able to reach the set temperature in the thermostat). So Aux heat (usually resistive) comes in to supplement. It's not that there is zero heat being generated.

In this case, the OP's issue was a defective sensor like most cases. So we have yet to see the true limits of Tesla's heat pump system (which as others point out has other ways to provide supplement heat).

^^^^This ^^^^^
Newer Heat pumps can produce heat at or below zero and still be as efficient as resistive heating, then you take the heat that it has access to from 1 or 2 drive motors, the battery, and the compressor itself, while I believe isolating the transfer fluid from the radiator.
 
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XPsionic

Member
Jan 20, 2021
79
107
los angeles
^^^^This ^^^^^
Newer Heat pumps can produce heat at or below zero and still be as efficient as resistive heating, then you take the heat that it has access to from 1 or 2 drive motors, the battery, and the compressor itself, while I believe isolating the transfer fluid from the radiator.

There's no heat to be had from the battery and motors when driving at -35c, in fact the heat pump has to do double duty and heat up the battery as well as the cabin.
 
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Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
5,942
11,157
Springfield, VA
There's no heat to be had from the battery and motors when driving at -35c, in fact the heat pump has to do double duty and heat up the battery as well as the cabin.
I suggest you check out the videos in this post
Heat Pump Limit?

You’re both right.

The system can scavenge heat from the motors and battery if they contain enough heat. If they don’t (-30C cold start, for example), the compressor must generate heat for both the cabin and the battery pack at a COP of 1, the same as resistive heat in non-HP cars.
 

Justin L

Member
Dec 7, 2020
7
17
Alberta Canada
So as a clueless Californian, I am wondering... what does -36 feel like ?

Is it painful just to stand outside ? Can you actually feel the difference between - 20 and -30 for example ? Does the family dog just sit inside for a month or two ?

Below -25°C it gets really hard to feel any difference. There's very little moisture in the air, so the heat loss in a "dry" cold helps a bit. At -25°C I can start to feel my nostrils stick a bit when I'm breathing through my nose. If you're dressed well, generally you stay pretty warm, but any exposed skin hurts, it's not a cold feeling per se, it just hurts. The colder you go and windier it gets the faster it hurts. You can get into trouble if it stops hurting, that means it's starting to freeze and it's time to deal with it. With good gear, it can be a lot of fun to go skiing or biking, but there's no half assing it with the gear. Everything has to be covered.

One other really interesting thing is the way planes sound going overhead. With no moisture in the atmosphere to attenuate the sound, you get a much higher pitch to a jet engine and it sounds more like it's ripping it's way through the sky.
 

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