Why does Tesla use a Resistance Heater instead of Heat Pump

[scaesare]

I want to thank @scaesare and @llavalle for the diagrams, and thank AND apologize to @MP3Mike and @AWDtsla for questioning you.

I came to this thread thinking I had a heat pump, and that waste heat was used for cabin heat. Now I am more educated. Very sorry if I was an @$$ in trying to get real information, but there was a lot more misinformation than knowledge out there, and I just had no idea who to believe.

Cool.... lots of good stuff has been shared on the forums... I learn from folks here all the time.

 

[scaesare]

I was wondering what some of the components (Chiller, Battery Heater etc.) in the diagnostic screen actually look like. This site has quite a few of the components exposed:
Tesla Technology – TesLorean

Oh cool.. I've tried to keep up with his thread here, but missed those pics. Good stuff.

Thanks.

 

[bjornb]

For comparison here is the range increase estimates with and without heat pump for the VW E-golf:

 

[lklundin]

It could be because heat pumps don't work well in colder temps, especially extreme cold. This is why all homes in the northern states have gas furnaces. In order for a heat pump to produce heat on one coil pack it has to make the other coil pack cold and then use ambient air to re-heat/boil the refrigerant so that it can pass through the compressor again. This does not work in freezing temperatures at all and works poorly below ~40 deg F.

Modern buildings can be heated very well with a heat pump, also in cold climates. Optimum efficiency is reached with:
1) Outdoor coil in a high-density heat reservoir, i.e. the surrounding land/ground water or water in a harbour or larger lake, or nearby excess process heat,
2) Indoor coil with low temperature (30C-40C) water, ideally set in a high-mass concrete floor.
3) Solar panels and/or cheap nightly electricity rate, for non-continuous heating allowed by the latent heat of the floor.

This will ensure that the heat pump works with a high coefficient of performance, at a low cost of input electricity.

Here in temperate Bavaria a modern, single family house is heated year round in this manner with a puny 2kW of electrical power, a mere water cooker.

See also,
Geothermal heat pump - Wikipedia

 

[llavalle]

I came to this thread thinking I had a heat pump, and that waste heat was used for cabin heat. Now I am more educated. Very sorry if I was an @$$ in trying to get real information, but there was a lot more misinformation than knowledge out there, and I just had no idea who to believe.

I was in a bit of shock myself when I found out they weren't using the waste heat from the drive unit + battery to heat the cabin. I knew from the start that my car wasn't equipped with a heap pump but figured that it wasn't needed because of the heat transfer. I thought that under -10C the heat transfer wasn't good enough and that's when most heat pump start to be inefficient...explaining the decision of not installing a heat pump.

Driving with the car with the thermal screen opened, I've noticed that when the temps is near freezing, on long drives, the car actually goes into the "passive cooling" target meaning it cools the too hot battery pack / drive unit using outside air on the front radiator. This is such a waste when you consider that you're wasting power on resistive heat at the same time. And it's not like they had to design a special car part for this to work (like they had to do for the heating element for example)... all cars equipped with gas engines have one installed - a heater core in the cabin.

 

[kirkbauer]

How do you access the thermal screen?

 

[AWDtsla]

I was in a bit of shock myself when I found out they weren't using the waste heat from the drive unit + battery to heat the cabin. I knew from the start that my car wasn't equipped with a heap pump but figured that it wasn't needed because of the heat transfer. I thought that under -10C the heat transfer wasn't good enough and that's when most heat pump start to be inefficient...explaining the decision of not installing a heat pump.

Driving with the car with the thermal screen opened, I've noticed that when the temps is near freezing, on long drives, the car actually goes into the "passive cooling" target meaning it cools the too hot battery pack / drive unit using outside air on the front radiator. This is such a waste when you consider that you're wasting power on resistive heat at the same time. And it's not like they had to design a special car part for this to work (like they had to do for the heating element for example)... all cars equipped with gas engines have one installed - a heater core in the cabin.

I think it is actually thermodynamically hard to get good heating from that waste heat. You certainly can't blow hot air based on coolant at the temperature. Of course, IF the car had a heat pump, the heat pump could effectively recover that energy into cabin heating, making it more efficient than the ambient air temperature would allow.

 

[Richard3510]

I was wondering why Tesla doesn't use a more efficient way such as a heat pump for the cabin heater as the resistance heater eats up the Range significantly. I am sure there is a reason other than cost, does anyone know ?

I was wondering why Tesla doesn't use a more efficient way such as a heat pump for the cabin heater as the resistance heater eats up the Range significantly. I am sure there is a reason other than cost, does anyone know ?

dehumidifier

I have been reading some of the topics and find them interesting and informative, even when there is not really good answer. I joined the forum a few minutes ago.

I live in central Texas, we have mild winters and hot summers. Gas heat was the way to go until HEAT PUMPS began to be more efficient.

I have allergies to various ... one being dust mites. Humidity should be less that 50%.

So I set up a small cheep dehumidifier (us$100) to take water out of the air in my home. The air goes in and is cooled and then it is heated, water comes out and is captured in a bucket. The overall result is dryer air that is warmer. Over the past 25 years I have had several dehumidifiers, one that I have could take a lot of water out of the air with not use a lot of kw. Others were not as efficient.

About water and air: When water is added to air it is cooled. The opposite is true when water is taken out of the air. So the warmer air is not all due to the inefficiency of the dehumidifier.

I would assume that with the condenser and the evaporator located in the right places and with the use of resistance heating some smart out-of-the-box thinking person could increase the heating efficiency of an electric car. I think that small multiple units would be used.

I have been dreaming about having an road worthy electric car for over 50 years. We discussed how cars could be powered in some of my sources in school, at the time we did not come up with anything better that a diesel engine. Also the highly efficient diesel sometimes does not have enough wast heat available to heat other spaces.

I think that I will be buying a Tesla within the next 2 to 6 months. I will be looking at the X in the near future, and I expect that I will end up with an upper end S.

 

[GlmnAlyAirCar]

Umm, no that is an AC loop with the whole purpose being to cool things. It isn't a heat pump.

When did I claim it was a heat pump?

 

[scaesare]

When did I claim it was a heat pump?

Perhaps it was unwittingly, but when you referred to waste heat being transferred to the AC loop via the exterior condenser coils at the top of the diagram:

That's not how I am reading the diagram. Looking at the top, we have the waste heat loop being cooled by ambient (or fan-driven) air. It also shows the AC loop being cooled the same way. This is open to interpretation, but this diagram implies that waste heat can be transferred to the AC loop, allowing it to be used as heat for the cabin.

The only way heat applied to AC coils and transferred in to the cabin is if the system were configured to operate as a heat pump.

 

[GlmnAlyAirCar]

Here's a few other from my car. Sorry for the LONG post

I don't suppose you would be willing to divulge how you gained access to these screens?

 

[GlmnAlyAirCar]

Perhaps it was unwittingly, but when you referred to waste heat being transferred to the AC loop via the exterior condenser coils at the top of the diagram:



The only way heat applied to AC coils and transferred in to the cabin is if the system were configured to operate as a heat pump.

I suppose that's true. But my intent certainly wasn't to claim there is a heat pump in the system. I am just trying to pull together what sources I can to learn how this thing operates.

 

[scaesare]

I suppose that's true. But my intent certainly wasn't to claim there is a heat pump in the system. I am just trying to pull together what sources I can to learn how this thing operates.

That's the only way it would work as you suggested. A standard AC system won't transfer heat to the interior in that manner.

So now you know a little better "how this thing operates".

 

[GlmnAlyAirCar]

That's the only way it would work as you suggested. A standard AC system won't transfer heat to the interior in that manner.

So now you know a little better "how this thing operates".

You must have been reading something into what I wrote. I was referring strictly to a heat exchanger using air as the medium.

 

[scaesare]

You must have been reading something into what I wrote. I was referring strictly to a heat exchanger using air as the medium.

Those sets of coils you refer to are the exterior condenser coils for the AC system. How does exchanging heat in to them get heat in to the cabin if you weren't suggesting the system was a heat pump?

 

[llavalle]

I don't suppose you would be willing to divulge how you gained access to these screens?

You got that right

 

[tyson]

Modern buildings can be heated very well with a heat pump, also in cold climates. Optimum efficiency is reached with:
1) Outdoor coil in a high-density heat reservoir, i.e. the surrounding land/ground water or water in a harbour or larger lake, or nearby excess process heat,
2) Indoor coil with low temperature (30C-40C) water, ideally set in a high-mass concrete floor.
3) Solar panels and/or cheap nightly electricity rate, for non-continuous heating allowed by the latent heat of the floor.

This will ensure that the heat pump works with a high coefficient of performance, at a low cost of input electricity.

Here in temperate Bavaria a modern, single family house is heated year round in this manner with a puny 2kW of electrical power, a mere water cooker.

See also,
Geothermal heat pump - Wikipedia

Right, without doubt geothermal systems are able to make this work but there is no such resource in a moving vehicle.

I would agree that a heat pump could be utilized as long as the evaporator side of the coil pack (the one that is outside the car during heat mode) has a resistance heater on it or some other way to ensure ice does not form on the pack during what is sure to be already cold weather and at times very damp environment. Without this the coil pack would freeze up during extended runs in damp conditions. Whether or not all this work is worth the added efficiency I do not know. I do know that it would be more complex and since the AC is about the loudest thing on my S already idk that I really want a heat pump in place of the resistance heater unless it can be shown to add at least 5% to the range and even that is a stretch since I rarely need to reach that deep into the pack that 5% makes a difference.

 

[wdolson]

I don't suppose you would be willing to divulge how you gained access to these screens?

Those are maintenance screens used by service. I've read you access them by holding down the T on the screen for a few seconds and a box asking for a password pops up. There are some easter eggs enabled by typing in some known passwords, but the maintenance passwords are a relatively closely held secret. Some non-Tesla people know them, but so far they have been tight lipped about revealing them to just anyone, probably because Tesla would change them if they became publicly known.

Personally I would love to know how to get into those screens too. I am a bit of a data junky, but I don't ask because I don't expect the information to be forthcoming.

That may change when Tesla allows people to access the shop manuals:
Charged EVs | Repair your Model S under a shade tree? Tesla plans to open up its policy

 

[jaguar36]

Those are maintenance screens used by service. I've read you access them by holding down the T on the screen for a few seconds and a box asking for a password pops up. There are some easter eggs enabled by typing in some known passwords, but the maintenance passwords are a relatively closely held secret. Some non-Tesla people know them, but so far they have been tight lipped about revealing them to just anyone, probably because Tesla would change them if they became publicly known.

Its not a single password, its specific to the car and changes over time.

I also don't think its used much anymore, as the service techs usually just use the Toolbox to do any diagnostic work.

 

[llavalle]

Its not a single password, its specific to the car and changes over time.

I also don't think its used much anymore, as the service techs usually just use the Toolbox to do any diagnostic work.

Correct. The car generates a new set of password every ~24h or so and sync them to the mothership..