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.
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.)
@Cybr.Myk can you confirm if turning on climate control warms up your battery as well? Unsure if it does that in the heat pump version.
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.
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."
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: 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).
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? 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. Also posted in this thread!
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).
100% agree. Sounds like it could be very similar. I figured it was not a novel concept being used in the Tesla.
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.
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.
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.
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.