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Heat Pump Limit?

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.
Thanks for those details. I knew there was a reason I decided against wintering in Saskatoon.
 
Oct 28, 2019
517
595
Texas
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):

Just finished my first "road trip" and I am not happy with range

the heat-pump needs to run forever to achieve heating in really cold weather. that's why with an auxiliary heating system in a house it kicks in. you don't want to wake up to a 61F house in the morning and then wait for 2hrs+ for the heat-pump to get it to 68F ... hence there is electric auxiliary or gas heating with it. heat-pumps do *not* heat up quickly when it's freezing cold... there simply arent enough BTU in the air to extract.
 

GZDongles

Member
Feb 23, 2020
225
289
Michigan
the heat-pump needs to run forever to achieve heating in really cold weather. that's why with an auxiliary heating system in a house it kicks in. you don't want to wake up to a 61F house in the morning and then wait for 2hrs+ for the heat-pump to get it to 68F ... hence there is electric auxiliary or gas heating with it. heat-pumps do *not* heat up quickly when it's freezing cold... there simply arent enough BTU in the air to extract.
The real question is, what is the total kW/BTU per hour output of the heat pump and how does that compare to the PTC heaters at different temperatures. There are some great videos out there that show how a household heat pump isn't really a good comparison to the Tesla Model 3 heat pump because of the different modes and unique ways it can create auxiliary heat. To be honest, there have been a lot of knee jerk reactions to the idea of a heat pump in a car, but no data that suggests that the heat pump is unable to keep up. There have been a lot of issues with poor quality temperature sensors causing cold air to blow out of the vents, but no reported issues that I'm aware of of the heater not having enough output. I don't expect everyone to watch videos explaining heat pump modes of operation on YouTube, but there are a lot of people making incorrect analogies with household heat pumps here.

For what it's worth, there are a lot of ICE cars that don't do well in those temperatures either if they don't have auxiliary heating. My Honda Civic couldn't get warmer than 50F in the cabin in city driving no matter how long you ran it during the 2013/2014 polar vortex when is was in the -20 to -30 range.
 

MP3Mike

Well-Known Member
Feb 1, 2016
16,853
40,432
Oregon
The real question is, what is the total kW/BTU per hour output of the heat pump and how does that compare to the PTC heaters at different temperatures.

Reports are that the heat pump can draw up to ~7kW, while the PTC heater was limited to ~5kW. They can also run the drive units inefficiently to gain another ~7kW of heat. So if it was programmed to take full advantage of what is available a heat pump Tesla has about 14kW of cabin heating capacity, while a PTC heater Tesla only has about 5kW of cabin heating capacity. (Assuming that no external heat can be brought into the system from the environment and it is running with a COP of 1.)
 

Big Earl

bnkwupt
Supporting Member
Jul 12, 2017
6,123
11,728
Springfield, VA
Reports are that the heat pump can draw up to ~7kW, while the PTC heater was limited to ~5kW. They can also run the drive units inefficiently to gain another ~7kW of heat. So if it was programmed to take full advantage of what is available a heat pump Tesla has about 14kW of cabin heating capacity, while a PTC heater Tesla only has about 5kW of cabin heating capacity. (Assuming that no external heat can be brought into the system from the environment and it is running with a COP of 1.)

On heat pump cars, I don’t think the cabin would be able to take full advantage of heat from the drive units because doing so would likely exceed the capacity of the cabin condenser.

Non-heat pump cars have 6 kW PTC cabin heat and 7 kW (dual motor) or 3.5 kW (single motor) battery heating.
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,177
14,193
San Diego
Would be interesting to know if Tesla's statement that it is "using the compressor as an electrical heater" is actually doing that as the statement implies, or whether they are using the stator heaters (which seems like it would be quite inefficient due to thermal losses when transporting coolant) to actually perform the part of the electrical heater.

The way I read it, it's the former, but I have no idea whether we have any specific information on that. It seems possible that one could use a compressor as a heater as well, with a special design (since you can do the same with the vehicle motors). And that's what Tesla's comments suggest, although they also reference providing a "controlled environment for the compressor" and thus unlocking "the full electrical input power" [to the compressor]. In the end they say they are using the compressor "like an electrical heater."
 
Would be interesting to know if Tesla's statement that it is "using the compressor as an electrical heater" is actually doing that as the statement implies

Did you watch those 3 videos linked earlier in the thread? The heat pump compressor acts as a heater using the same principle as a fridge with its doors open would warm up the interior of a house. The cold air from the inside of the fridge will cancel out the hotter air being radiated from the coils on the back of the fridge. The only extra heat that ends up warming the house is from powering the compressor.

Basically the energy used to run the heat pump compressor generates waste heat and that's about the only excess heat the interior will get when it's below -10c if the battery and motors are cold soaked. I still haven't seen confirmation that there is a resistive heater in the Model 3/Y or actual documentations of the motors being able to be run in a way to generate waste heat. Glad to see some links on those if you guys have any.
 

stopcrazypp

Well-Known Member
Dec 8, 2007
11,133
6,269
Did you watch those 3 videos linked earlier in the thread? The heat pump compressor acts as a heater using the same principle as a fridge with its doors open would warm up the interior of a house. The cold air from the inside of the fridge will cancel out the hotter air being radiated from the coils on the back of the fridge. The only extra heat that ends up warming the house is from powering the compressor.

Basically the energy used to run the heat pump compressor generates waste heat and that's about the only excess heat the interior will get when it's below -10c if the battery and motors are cold soaked. I still haven't seen confirmation that there is a resistive heater in the Model 3/Y or actual documentations of the motors being able to be run in a way to generate waste heat. Glad to see some links on those if you guys have any.
From the EPA link posted in another thread, absent of the service manual, this is probably the best official information about how the production Tesla heat pump system works:
Tesla’s heat pump uses conventional components with unconventional flexibility or cycle configuration. A heat pump must generally have a low-temperature source from which to draw energy. Tesla’s system enables the heat pump source to be either the power-train coolant loop, e.g., low-temperature waste heat produced naturally by the vehicle while driving, ambient air, the battery thermal mass, the cabin thermal mass, or combinations thereof. Another advantage of this architecture is the ability to reject heat into the battery pack via a liquid-cooled condenser for a limited amount of time during cabin cooling scenarios when the temperature of the battery is modest. Therefore, for most startups with AC on, the relatively cool, well- coupled, large thermal mass serves to lower discharge pressure and therefore reduces compressor input power relative to a conventional air-cooled condenser setup.

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.
https://iaspub.epa.gov/otaqpub/display_file.jsp?docid=51237&flag=1

It's pretty clear that there is no backup resistive heater in the Model Y with heat pump (presumably this won't be any different in the Model 3).
 

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,177
14,193
San Diego
Did you watch those 3 videos linked earlier in the thread?

No, but I just watched the relevant one for mode 4, in part 2 in one of the links above. It left me with a lot of questions, but maybe the details of the compressor are covered in other videos?

The heat pump compressor acts as a heater using the same principle as a fridge with its doors open would warm up the interior of a house. The cold air from the inside of the fridge will cancel out the hotter air being radiated from the coils on the back of the fridge. The only extra heat that ends up warming the house is from powering the compressor.

Sure, I figured it was something like this. Effectively this is a resistive heater though, and it presumably does require a specialized compressor to be able to generate so much heat (it's not pumping much heat from the outside air, though perhaps it has ways of harvesting waste heat around the compressor to still have some decent coefficient of performance heat pumping function which is obviously preferred to the extent it is thermodynamically possible with efficiency greater than 1). Most large and very effective refrigerators do not draw anywhere near a constant 7kW (it's more like 200W)! As we know, the COP of a heat pump doesn't typically drop to 1 until somewhere around 0F, so before that point you'd hope they'd still be using the heat pump to get an efficiency of greater than 1. But that may not be sufficient heat, so you also want to add resistance heat (which sounds like it's coming from the compressor, not the motors).

Anyway, that was the part I was a bit curious about - what features of the compressor are unusual - it doesn't appear to be a "normal" compressor at all (in terms of input rating). I'd be curious if there are HVAC specialists out there who know about home heat pump systems that work similarly (rather than having a pure supplemental resistive heater as an entirely separate element). It may not make sense at the scale of a home heating system, but I have no idea. I'm not an expert on home heating, and how supplemental heat systems work, exactly, to actually talk intelligently about this. My guess is something like this has been done before though. But usually you hear about heat pumps having a supplemental system (as has been mentioned several times here) in addition to the compressor in very cold temperatures - which is not what is happening here, apparently (it's not always using the stator heaters to generate supplemental heat for the compressor & cabin heat, for example). It sounds like the compressor is the resistive heater, operating in an "inefficient" way to generate a ton of resistive heat (electrical energy directly to heat - with minimal pumping action), which I guess is transferred (with minimal loss to the environment hopefully) to the fluid, which is then transferred to the cabin condenser? That's to some extent "different."

Anyway, I have no idea, and hopefully that clarifies what I was curious about.

From the EPA link posted in another thread,

Also posted in this thread!
 
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stopcrazypp

Well-Known Member
Dec 8, 2007
11,133
6,269
Anyway, that was the part I was a bit curious about - what features of the compressor are unusual - it doesn't appear to be a "normal" compressor at all (in terms of input rating). I'd be curious if there are HVAC specialists out there who know about home heat pump systems that work similarly (rather than having a pure supplemental resistive heater as an entirely separate element).
Not a HVAC specialist by any means, but just did a quick google on which are the most efficient heat pump systems available today.

Found this link that mentions there are Mitsubishi units that can maintain a COP of 1.8 down to -18°F (-28°C), which is likely enough to not need any supplemental heat at all when correctly sized.
Do Heat Pumps Work In Cold Climates? | Building Advisor

Mitsubishi's marketing page doesn't say much how it works, just that it maintains 100% heating capacity down to 23°F and 76% capacity down to -13°F, making supplemental heat unnecessary.
Year-Round Comfort, Even Below Zero | Mitsubishi Electric

Googled for how it works:
"Mitsubishi's hyper-heating H2i® compressor motor signals that a burst of heat is needed when the temperature gets below 40°F. Depending on the temperature, the motor revs up accordingly and the system absorbs the additional heat thrown off the compressor magnets. After the extra heat is absorbed, it's funneled to the back of the blower."
That sounds very much like what Tesla describes about using the compressor as a heater.
Hyper Heat Feature Review

Fujitsu's system claims it works down to -15°F but it seems they just do that by having a separate heating system for the base unit that keeps the condensation from freezing (without having to run the unit in AC mode like most heat pumps do to defrost).
XLTH Low Temp Heating: Halcyon™ MINI-SPLIT TECHNOLOGY - RESIDENTIAL - FUJITSU GENERAL United States & Canada
From same blog above:
"Fujitsu's Halcyon™ XLTH Low Temp Heating technology works a little differently. It uses a metal fan guard, a base heater and base drainage holes. The metal fan guard is more capable than plastic guards other heat pumps use to withstand colder temperatures. Including a base heater means when the temperature gets below 36°F, the built-in heater warms the base of the outdoor compressor. Warming the base allows the compressor to capture the warmers' heat, and doesn't allow condensation to freeze - which can damage your compressor. And the drainage holes let melted water (from snow and ice) to drain out of the unit."

So not technically supplemental heat (as it's not warming the air), but it's still using a separate heating system (although it's to heat the equipment).
 
Last edited:

AlanSubie4Life

Efficiency Obsessed Member
Oct 22, 2018
11,177
14,193
San Diego
Mitsubishi's hyper-heating H2i® compressor motor signals that a burst of heat is needed when the temperature gets below 40°F. Depending on the temperature, the motor revs up accordingly and the system absorbs the additional heat thrown off the compressor magnets. After the extra heat is absorbed, it's funneled to the back of the blower."
That sounds very much like what Tesla describes about using the compressor as a heater.
Hyper Heat Feature Review

100% agree. Sounds like it could be very similar. I figured it was not a novel concept being used in the Tesla.
 

SageBrush

REJECT Fascism
May 7, 2015
12,791
17,101
New Mexico
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.

Cue HVAC for dummies time, please
 

68882

Member
Jan 19, 2020
43
51
Victoria BC
People should remember that Musk has said that based on Tesla’s work the heat pump market is ripe for improvement. You have to wonder how good Tesla’s Heat Pump engineering is as compared to the residential market offerings.

Not a HVAC specialist by any means, but just did a quick google on which are the most efficient heat pump systems available today.

Found this link that mentions there are Mitsubishi units that can maintain a COP of 1.8 down to -18°F (-28°C), which is likely enough to not need any supplemental heat at all when correctly sized.
Do Heat Pumps Work In Cold Climates? | Building Advisor

Mitsubishi's marketing page doesn't say much how it works, just that it maintains 100% heating capacity down to 23°F and 76% capacity down to -13°F, making supplemental heat unnecessary.
Year-Round Comfort, Even Below Zero | Mitsubishi Electric

Googled for how it works:
"Mitsubishi's hyper-heating H2i® compressor motor signals that a burst of heat is needed when the temperature gets below 40°F. Depending on the temperature, the motor revs up accordingly and the system absorbs the additional heat thrown off the compressor magnets. After the extra heat is absorbed, it's funneled to the back of the blower."
That sounds very much like what Tesla describes about using the compressor as a heater.
Hyper Heat Feature Review

Fujitsu's system claims it works down to -15°F but it seems they just do that by having a separate heating system for the base unit that keeps the condensation from freezing (without having to run the unit in AC mode like most heat pumps do to defrost).
XLTH Low Temp Heating: Halcyon™ MINI-SPLIT TECHNOLOGY - RESIDENTIAL - FUJITSU GENERAL United States & Canada
From same blog above:
"Fujitsu's Halcyon™ XLTH Low Temp Heating technology works a little differently. It uses a metal fan guard, a base heater and base drainage holes. The metal fan guard is more capable than plastic guards other heat pumps use to withstand colder temperatures. Including a base heater means when the temperature gets below 36°F, the built-in heater warms the base of the outdoor compressor. Warming the base allows the compressor to capture the warmers' heat, and doesn't allow condensation to freeze - which can damage your compressor. And the drainage holes let melted water (from snow and ice) to drain out of the unit."

So not technically supplemental heat (as it's not warming the air), but it's still using a separate heating system (although it's to heat the equipment).
 
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dmurphy

Active Member
Supporting Member
Dec 7, 2018
3,925
5,551
New Jersey - Morris County
People should remember that Musk has said that based on Tesla’s work the heat pump market is ripe for improvement. You have to wonder how good Tesla’s Heat Pump engineering is as compared to the residential market offerings.

Once Tesla home HVAC is a thing, I’ll be customer #1. My system absolutely sucks and I can’t wait to get rid of it. Problem is, it works. Inefficient and dumpy as it is, the house is warm in winter and cool in summer, so replacing it with another run-of-the-mill unit doesn’t make sense. But a Tesla unit? That’ll change the equation completely.
 

keith4909

Member
Aug 28, 2020
28
14
Sf bay
Fancy engineering doesn’t mean anything if it doesn’t work. Test the product in the development phase. Installing untested tech just makes Tesla look bad and makes future potential owners question whether to buy or not. It’s on my mind and I have one on order.
The HVAC system should be able to produce heat in all weather conditions. If yours is having performance issues, let Tesla know.

Here is a great three-part video series about how Tesla’s new heat pump system works. It’s pretty slick.

part 1:

part 2:

part 3:
 

Phlier

Bluebird
Jun 12, 2019
2,166
4,030
Utah
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?
If this was what we think of as a traditionally setup heat pump, I'd agree. But take a look at what @AlanSubie4Life posted.

Tesla is planning on selling this car in places that have extremely cold weather. There is no way they would ever attempt to sell a car in those markets that lack the ability to heat the cabin appropriately.

This is simply a case of a combination of: 1. Tesla factory assembly not hooking up the sensor on many cars 2. A poor quality part (temp sensor) that has already been superseded with a replacement part number.
 

Cybr.Myk

Member
Aug 30, 2020
130
240
Saskatoon
Sorry I’ve been away from this thread for a bit. We had a COVID scare and we all needed to get tested and shut things down for a few days. I wasn’t able to go out and do the highway test that I wanted to after service replaced the sensor until this morning.

the good news is that after 45 minutes on the highway everything was still warm. It’s not as cold as it has been but it’s still -38 with the wind chill.

so the sensor seems to have fixed my issue.

however (separate issue), I did notice that as soon as the car hit 20% state of charge, the heat dropped significantly. I had the auto climate in the cabin set to 23 and the app showed 19. It doesn’t seem to be a sensor issue but a state of charge issue where it diverts heat from the cabin and directs it to the battery. It’s also painfully slow in this temp at under 20% battery…embarrassingly slow.

for the guy that asked what this temperature feels like…the ground freezes my French bulldog’s paws in 30 seconds so she hates going out to pee right now. I bought her boots, which she also hates, but at least she can go out long enough to poop without getting frostbite.
 

Venom

Leo Hates You Club Scout
May 29, 2019
764
1,522
Chicago, IL
Sorry I’ve been away from this thread for a bit. We had a COVID scare and we all needed to get tested and shut things down for a few days. I wasn’t able to go out and do the highway test that I wanted to after service replaced the sensor until this morning.

the good news is that after 45 minutes on the highway everything was still warm. It’s not as cold as it has been but it’s still -38 with the wind chill.

so the sensor seems to have fixed my issue.

however (separate issue), I did notice that as soon as the car hit 20% state of charge, the heat dropped significantly. I had the auto climate in the cabin set to 23 and the app showed 19. It doesn’t seem to be a sensor issue but a state of charge issue where it diverts heat from the cabin and directs it to the battery. It’s also painfully slow in this temp at under 20% battery…embarrassingly slow.

for the guy that asked what this temperature feels like…the ground freezes my French bulldog’s paws in 30 seconds so she hates going out to pee right now. I bought her boots, which she also hates, but at least she can go out long enough to poop without getting frostbite.
Yep it’s embarrassingly slow at 20% SoC. The Long Range smokes the performance at a lower SoC

 
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Sorry I’ve been away from this thread for a bit. We had a COVID scare and we all needed to get tested and shut things down for a few days. I wasn’t able to go out and do the highway test that I wanted to after service replaced the sensor until this morning.

the good news is that after 45 minutes on the highway everything was still warm. It’s not as cold as it has been but it’s still -38 with the wind chill.

so the sensor seems to have fixed my issue.

however (separate issue), I did notice that as soon as the car hit 20% state of charge, the heat dropped significantly. I had the auto climate in the cabin set to 23 and the app showed 19. It doesn’t seem to be a sensor issue but a state of charge issue where it diverts heat from the cabin and directs it to the battery. It’s also painfully slow in this temp at under 20% battery…embarrassingly slow.

for the guy that asked what this temperature feels like…the ground freezes my French bulldog’s paws in 30 seconds so she hates going out to pee right now. I bought her boots, which she also hates, but at least she can go out long enough to poop without getting frostbite.
I'm the guy who had asked. I was also wondering about the dogs - so I got my answer.

I'm so bored with Covid I thought it would be interesting to spend a few days tooling around the tundra. But with the USA / CN border closures... oh well on that one.
 
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