Why does Tesla use a Resistance Heater instead of Heat Pump

[wdolson]

I agree. But Tesla's most problematic region is the heating up. Battery and cabin. Insulation doesn't change that.
Tesla owners, on average, do not drive long distances. Therefore insulation has mediocre effect.
Björn from Norway does long distances and... well... after heating up the vehicle, consumption of heating is acceptable.
Though before INSULATION... they MUST HAVE SHADES. Especially roof, incl half of Model X windshield and half on 3 back window.

Americans tend to drive longer distances than Europeans and that's true for Tesla owners too. A few years ago superchargers in California were wearing out prematurely because they got such heavy use.

Well... newest and cleanest (and more efficient) refrigerant is R744. We know it as CO2. Technically it is not a new gas. Just newest system.
Merces already makes few models with this carbon dioxide as refrigerant. System costs slightly more but is also more efficient,
including heating cycle... that is definitely good news for EV's.

This gas is ideal for cold and mild climates but doesn't actually work when external temps are very high (30+C for example).
Therefore, again, one system for the whole world is definitely NOGO.
1234 gas for hot climates and not heat pump. CO2 based heat pump system for climates where temps go below freezing. Usually both extremes are not happening.

VW id3 - soon on the market, will have both options. Heat pump (R744 based) and regular.

There are quite a few places in the US where winter temps can easily get very cold in the winter and very hot in the summer. In Minneapolis, Minnesota, the average high temperature in January is -5C, with the average low -13C. Average summer highs can be 30C and I've been there when it was close to 40C (though that was close to an all time record). Reno, Nevada (near the GigaFactory), the winters don't get as cold, but the average low in the winter is around -4C, and the average summer high temps are in the high 30s C.

Where I live near Portland, OR it's a mild climate compared to most of the rest of the US, but winter daytime high temps are usually around 5C going down to 0 at night, but most winters we have 20 days or so where it's below freezing all day and in the summer we almost always have a few days above 35 C.

Driving between climate extremes can also be very common in the US. It's not unusual for people in Phoenix to go skiing in the winter in Northern Arizona or Colorado. Flagstaff is only a couple hour drive. In Seattle and Portland a large percentage of the population goes skiing every winter in the nearby mountains. Tesla put in a supercharger outside of Portland that is really only useful for people going skiing on Mt Hood.

So heat pumps with one or the other may not be an issue in some parts of the world, it would be a big deal in large parts of the US.

 

[Saimaannorppa]

I agree. But Tesla's most problematic region is the heating up. Battery and cabin. Insulation doesn't change that.
Tesla owners, on average, do not drive long distances. Therefore insulation has mediocre effect.
Björn from Norway does long distances and... well... after heating up the vehicle, consumption of heating is acceptable.
Though before INSULATION... they MUST HAVE SHADES. Especially roof, incl half of Model X windshield and half on 3 back window.

Well, some of us also drive mainly from warm garage to warm garage. And if heating up is done plugged in, insulation surely improves heating performance, perhaps even more than a heat pump could.

I have a free idea for Tesla (next one costs a Roadster): have a team of SpaceX engineers design an insulation package for the cars, and sell the option with SpaceX branding. Cheap closed cell foam for profit (maybe a bit of aerogel to make it space tech). No other car maker could do it.

Btw. I have insulated my car as a by-product of hi-fi/road noise project, and I’m seeing a 3% reduction in consumption over a full season. Weather and driving styles not constant, for sure.

 

[mongo]

I think I heard the answer from Elon at the Starship update:

The best part is no part.

 

[Legen---dary]

I think I heard the answer from Elon at the Starship update:

The best part is no part.

People have a hard time with that and typically can't grok the concept.
It's why I'm suggesting high pressure hydrogen/helium without a phase change in a sealed Stirling engine for use as an HVAC heat pump.
Way less parts. Better efficiency. It also sees -40 as balmy with plenty more degrees to work with before absolute zero.
If any company can engineer a compact and highly efficient Stirling heat pump, it's Tesla/SpaceX. Maybe a two stage series pump with displacers running in opposite directions to dampen harmonics and increase efficiency.
Improved seat heaters would also go a long way to prevent cranking the air temperature so high.
A windshield with insulation would also be a breakthrough. An air gap might mess up optics too much, so the insulator would need to be a layer, or multiple thereof, of some sort. Beyond insulation this world help a great deal with fogging issues.
Much room to optimize heating and cooling.

 

[Big Earl]

Oh my god. It is not good to state things that are out of someone's expertise.

All these components exist on vehicles with no heat pump. All vehicles with AC have those things. Because heat pump is the same thing as air conditioning. Difference is in few valves that redirect refrigerant to run in reverse. There is one evaporator but it is inside a HVAC box and will never be damaged in reasonable car crash.

Also your 4-degree celsius story is nonsense. Or it might be Zoe specific due to some defect or software problem.

It isn't that simple. A heat pump system in a vehicle with a liquid cooled battery requires several additional changeover valves in order to work properly. In addition, if you want to dehumidify in the cabin without making it colder or adding electric reheat to keep supply temperature comfortable, you need to add a condenser to the HVAC box and the refrigerant control valves to make it function like a dehumidifier, isolating the exterior heat exchanger. System design and control logic starts to get complex very quickly, adding cost and maintenance concerns.

So yes, a simple heat pump is the same as an air conditioner (plus a reversing valve), but what's needed for today's EVs is much more complex.

 

[dgpcolorado]

The insulation thing is why I wanted a solid roof when I was shopping for a car. Cooler in summer, warmer in winter and better sound insulation year 'round. I was disappointed when Tesla got rid of the solid roof and went with all glass, although I understand that it made assembly easier.

 

[Legen---dary]

The insulation thing is why I wanted a solid roof when I was shopping for a car. Cooler in summer, warmer in winter and better sound insulation year 'round. I was disappointed when Tesla got rid of the solid roof and went with all glass, although I understand that it made assembly easier.

You could always use some foam rubber, like mousepad material, and cut it to shape then stick to the glass. I've been waiting to see someone do that. Make the upper side reflective.

 

[mongo]

The insulation thing is why I wanted a solid roof when I was shopping for a car. Cooler in summer, warmer in winter and better sound insulation year 'round. I was disappointed when Tesla got rid of the solid roof and went with all glass, although I understand that it made assembly easier.

My general theorectical thoughts with zero real world experience.

I'm not sure on the overall advantage. Glass thermal conductivity is 1 W/(m K) versus steel at 40 W/(m K) and the glass is thicker. The headliner is the biggest factor which you could retrofit with a sun shade if you wanted.
Solar helps in winter/ hurts in summer.

The radiative effects may have more comfort impact than the conductive due the percentage of remaining glass.

 

[dgpcolorado]

My general theorectical thoughts with zero real world experience.

I'm not sure on the overall advantage. Glass thermal conductivity is 1 W/(m K) versus steel at 40 W/(m K) and the glass is thicker. The headliner is the biggest factor which you could retrofit with a sun shade if you wanted.
Solar helps in winter/ hurts in summer.

The radiative effects may have more comfort impact than the conductive due the percentage of remaining glass.

The Tesla headliner and insulation on the solid roof are really quite robust, although I guess you would have to see/feel it to appreciate it. There is enough glass in the Model S to give plenty of solar gain in winter, assuming that the sun is out, as is often the case in sunny Colorado. I generally park facing south to use my sunshade to reduce heat on the dash (and MCU) and general heating in the car most of the year — It is very effective.

I don't use heat much in winter because I always wear warm winter clothes and my garage doesn't go below freezing, so the car usually starts out at 1º to 4ºC — I just leave the seat heater at setting one all winter. Around here, temperatures of -20ºC aren't all that common and generally happen only at night/early morning. For me the cabin heat is mostly used to briefly defog the windshield, as needed. On the other hand, the battery heater is often on and I am regen limited for most of the year due to a cool battery. So far as I can determine, regen limitation starts at a battery temp of about 15ºC and I need regen to descend a steep hill every time I leave home, although 20kW is sufficient if I am careful with speed entering steep (14% grade) hairpin turns.

 

[Saimaannorppa]

You could always use some foam rubber, like mousepad material, and cut it to shape then stick to the glass. I've been waiting to see someone do that. Make the upper side reflective.

I've done that as part of my project, with main motivation in improving car audio.

It came out better than expected. Could have used OEM alcantara if I had known it works so well.

Upper layer is reflecting and strong aluminium paper. I glued closed cell foam on it, and upholstered with black car interior felt. The closed cell foam is molded in shape with heat and the felt is tucked under headliner. It needs only a couple of 3M Command picture hangers to stay on. Can be removed in a minute, and tucked back in in 10 minutes.

Bad picture, but it was hard to photo black on black thingy without light.

 

[arnis]

So yes, a simple heat pump is the same as an air conditioner (plus a reversing valve), but what's needed for today's EVs is much more complex.

If that was true then sub 40k EV's would not have heat pumps.
What you just said is almost FUD

There is no NEED for dehumidification capable heat pump capability. Just use PTC. This function is rarely necessary and if it is, it is not at sub-freezing temps when HP actually matters a lot.

 

[mongo]

If that was true then sub 40k EV's would not have heat pumps.
What you just said is almost FUD

If that statement "So yes, a simple heat pump is the same as an air conditioner (plus a reversing valve), but what's needed for today's EVs is much more complex." is almost FUD, please list some sub 40k EVs with simultaneous HP sourced heat and cool functions which is what he was refering to.

There is no NEED for dehumidification capable heat pump capability. Just use PTC. This function is rarely necessary and if it is, it is not at sub-freezing temps when HP actually matters a lot.

Totally incorrect. People track snow into the car, the heater melts the snow, raising the humidity. Water vapor condenses and you can't see very well.
The colder it is outside, the lower the temperature of the inside of the glass and the lower you need to keep the interior humidity to avoid this issue.
ICE cars have had to increase the AC capacity due to finding this problem in cold weather testing.

Edit: (sure you could source outside air to dehuminify since it is dryer, but then you are heating a large flow from below freezing)

 

[arnis]

sure you could source outside air to dehuminify since it is dryer, but then you are heating a large flow from below freezing

And this is exactly how things actually operate. Fresh air from outside. Fresh cold air that is extremely dry anyway.

Like I said, things are not like you said, that "today's EVs need to have HP capable doing both simultaneously". No they DONT.

I lived in a wet winter region (slushy months each year) for 5 years with HP vehicle. I KNOW HOW THINGS WORK.
Yes dehumidification function is helpful, but not requirement. It's like another premium function.
There is no need to excuse for not having "first level premium function" (HP capability)
with statements that "second level premium function" is complex/expensive.
Do one step at a time. Have HP, then we can discuss second level premium function (dry+heat HP).

Also in real life, AC is not ever running on Tesla (or any other vehicle) in winter (sub-zero temps) if recirculation is deactivated.
And AFAIK, nobody runs their vehicle on recirculate in winter months (incl Tesla HVAC control software).

 

[Toumal]

I lived in a wet winter region (slushy months each year) for 5 years with HP vehicle. I KNOW HOW THINGS WORK.
Yes dehumidification function is helpful, but not requirement.

NO YOU DON'T. So first of all, don't go all caps. Second, don't berate others for their alleged stupidity when you disagree. You may well just be wrong, like now.

Dehumidification is not necessary? It's absolutely vital when temps drop below 0. You have a damp human sitting in that car. True, depending on the car's design the effect may vary, but for example in my Zoe it's a matter of being able to drive, and not being able to drive. It's that simple, and no amount of "I know this" will change this.

I do not claim to be an expert in the heating/cooling system of the Model 3. I know enough to know that I don't know enough. The superbottle is a heat exchanger, which by definition can also be called a heat pump. But is it the same as a classic automotive heatpump? I'd say absolutely no. I know the Zoe's system pretty well. I agree that the talk about dehumidification is kinda off topic. But here's the thing: If the Model 3 used the superbottle for cabin heating, it would take around 1-2kW while heating like the Zoe, and not 4.5kW as measured by Bjoern. That number tells me that the PTC heats the air directly.

Your turn. But not in all caps please.

 

[arnis]

Dehumidification is not necessary? It's absolutely vital when temps drop below 0

It it was true then a) there would not be vehicles on our roads that do NOT have AC at all. Like...there is no compressor from factory and b) those vehicles that have AC (like BMW 5-series or Tesla model S) would actually run compressor when outside temps fall below 0*C ALL THE TIME. But almost ALL THE TIME these vehicles have air mixture flap on "fresh air".
VITAL, like you mentioned, function is almost NEVER used. Like...EVER... omg
Most people have their HVAC on AUTO. And that means AC compressor is offline. So ZERO dehumidification.
Whoever doesn't agree, wait for the winter and just stick your hand next to HVAC air intake under the windshield.

heat exchanger, which by definition can also be called a heat pump

Heat exchanger doesn't pump heat from one side to another. Superbottle is a heat exchanger.


* - caps means emphasized text, read loudly and clearly, 20% slower that normal.

 

[Toumal]

Oh but a heatpump also contains a heat exchanger. See I can use your style of argumentation too. Oversimplification on one hand, overspecification on the other, as needed.

My point stands: I am glad the model 3 doesn't have a system like the Zoe. And you skipped on the energy consumption, which to me makes it rather clear that you're incorrect.

Also, on the internet, caps is the equivalent of shouting. If you want to emphasize a point, there are better tools.

 

[arnis]

Oh but a heatpump also contains a heat exchanger.

You mean condenser and radiator? Well pipework itself is heat exchanger between pipe and air surrounding it.

I'm also glad that Zoe system is not on Model 3. But I'm sad that that Model 3 doesn't have a HP as good as on Ioniq or i-Pace.

 

[Legen---dary]

I've done that as part of my project, with main motivation in improving car audio.

It came out better than expected. Could have used OEM alcantara if I had known it works so well.

Upper layer is reflecting and strong aluminium paper. I glued closed cell foam on it, and upholstered with black car interior felt. The closed cell foam is molded in shape with heat and the felt is tucked under headliner. It needs only a couple of 3M Command picture hangers to stay on. Can be removed in a minute, and tucked back in in 10 minutes.

Bad picture, but it was hard to photo black on black thingy without light.
View attachment 460672

Would be amazing to see some video of install/removal of that. Nice work!!

 

[taraquin]

I don't have nearly all the technical insight as many of you have, but after driving a lot of EVs with and withput heatpump, there is a major range difference from 10C and down to - 5C, below that the difference becomes much smaller. Tested the Kia Soul a few days ago again and when outside temp is 0-5C it uses about 0.5kW avg to keep cabin warm. In my Model S it uses about 2kW to do the same. Insignificant some might say, but I sometimes drive long trips where there are no SC and miss the heat pump. One of my standard trips is 160km long, it takes about 2 hours and climate uses 4kWh, in the Soul I use about 1kWh. Where I live avg temp from September to May is -5 to 10C which is perfect for a heat pump. The e-Golf used to have a option of heat-pump (it costed about 800usd) before it became standard. I don't think VW subsidized it so it means the extra cost is quite small considering the extra range most of the year. Living in California I can understand that a HP is a waste of money, but Canada, northern USA, most of europe would benefit a lot. The extra range a HP gives much of the year is a lot cheaper than adding extra capasity to the battery.

 

[Saimaannorppa]

Would be amazing to see some video of install/removal of that. Nice work!!

I will try to document if I’m to make another revision of it.

I can second @dgpcolorado comment on solid roof. My friend has one, and we contemplated insulating and deadening it, but when we peaked under headliner, we concluded it is already reasonably well done from the factory, and not worth extra effort.

Solid roof was dropped from European cars already a long time ago, since gluing the glass roof at Tilburg assembly gives them some % of credit in building the car in EU. This is my guess.