Why does Tesla use a Resistance Heater instead of Heat Pump

[AWDtsla]

Humm, Not sure I'm following you here. The Mitsubishi Zuba series has been tested at over 200% efficiency (i.e. COP greater than 2.0) at -15F or -26C. I personally own a Fujitsu 15RLS2 heatpump that has around 1.5-1.6 COP at -4F or -20C

The Lennox XP25 is listed at 2.28 @ 17F or -8.3C. And this is the actual COP of the installed docked system.

There are a couple of easily available options on the market right now with COP > 1.5 at very low temps.

Heat pumps right now have the same problem as EV's do to most people now. "That will never work! It's tiny and slow and has no range!"

Also, as far as I've seen, increasing COP/low temp operation takes no technological breakthroughs. They just keep increasing the size/capacity of the exterior coils. Slightly increased initial cost for better operating capacity/efficiency.

 

[brkaus]

Relax folks, my car will be delivered in a month or so. Then they will start adding new features again.

 

[dhanson865]

So why is there a "loop" for interior heating? Just heat the air.

Air is a poor conductor of heat. For an example put your hand into a hot oven without touching anything solid inside and you won't get burned even though you are exposing your skin to hundreds of degrees short term.

But should something other than air touch that heating element it will absorb that heat quickly and catch on fire. It just isn't very safe to have exposed heating element with airflow.

A coolant loop can shield the heating element from accidental contact and carry the heat away/diffuse it (reduce the maximum temperature) to increase safety and still transfer heat to where it needs to go.

 

[BerTX]

Air is a poor conductor of heat. For an example put your hand into a hot oven without touching anything solid inside and you won't get burned even though you are exposing your skin to hundreds of degrees short term.

But should something other than air touch that heating element it will absorb that heat quickly and catch on fire. It just isn't very safe to have exposed heating element with airflow.

A coolant loop can shield the heating element from accidental contact and carry the heat away/diffuse it (reduce the maximum temperature) to increase safety and still transfer heat to where it needs to go.

I'll buy the safety aspects of your post, but not the "poor conductor of heat" efficiency part. Resistance heat is pretty much power-in makes heat-out. Passing it through water can't really help much. The heat has to be transferred to air at some point.

 

[dhanson865]

But did it actually improve their winter range? How much?

It was an improvement from about 14f to about 68f aka almost room temperature as in the temp where you don't need heat anymore. How much range that saved you just depended on how fast you drive and how long you spend outside in 14f to 68f weather.

It's not the best copy of this graph but Nissan detailed it in a slide showing the resistant heater vs heat pump at various temps.

hard for me to upload from my work PC I'll try to reply with a better copy from home.

 

[dhanson865]

I'll buy the safety aspects of your post, but not the "poor conductor of heat" efficiency part. Resistance heat is pretty much power-in makes heat-out. Passing it through water can't really help much. The heat has to be transferred to air at some point.

If you'll go back and read my post I never used the word efficiency.

Air is poor conductor over time not in terms of efficiency. Energy can't be created or destroyed so air doesn't do magic but try this as a though experiment (don't try both at home)

1. Put your hand inside a 400F oven to see if it is warm
2. Put your hand in direct contact with 400F iron to see if it is warm

One of those will burn you before you can pull your hand away. The other will give you time to think about it but will eventually burn your hand just the same if you don't pull back.

 

[Reeler]

I can say first hand that the heat in the LEAF is much better than the Tesla. My LEAF without the heat pump had horrible range in a cold day in San Diego. In Denver, it was close to 45 miles range.

I think the Tesla's are similarly affected, but with so much battery we don't notice. I hope Tesla solves that with a heat pump as I also believe they are just being lazy.

 

[int32_t]

At my workplace we have a few rooms which require cooling 24/7 to keep them at a reasonable temperature. When it was -30C outside one night, the rooftop compressor unit decided to stop running ... the repair guy says there's nothing wrong with it, just wait for the sun to come up and thaw the coils. Sure enough, it didn't take much sunlight to get it running again. I sure wouldn't rely on a heat pump up here as my sole source of heat, although it might be nice to have a way to pump waste drivetrain heat to the interior of the vehicle when temperatures permit. (Remember, that cooling unit would be heating its coils on the roof, combating the cold, whereas a heating pump would be aggravating the cold weather's effect by cooling its outdoor coils ...)

Weather and locale considerations aside, though, I think Tesla uses a resistance heater for its sheer firepower. You can't beat an 8 kW resistance heater for the amount of heat it will put out for the space it consumes, either. Besides, on a 90 kWh Tesla vehicle, you could run that heater for ten hours at full blast and melt the chocolate bars in the rear hatch area into a puddle. Point being, you don't need all 8 kW all the time so it's not such a significant range hit as, say, ploughing through a snowy road in the winter. The heater's energy usage pales in comparison and becomes almost insignificant.

 

[McRat]

I did not even consider that freezing rain or snow could stop a heat pump in it's tracks.

No airflow, no worky.

 

[ItsNotAboutTheMoney]

Weather and locale considerations aside, though, I think Tesla uses a resistance heater for its sheer firepower. You can't beat an 8 kW resistance heater for the amount of heat it will put out for the space it consumes, either. Besides, on a 90 kWh Tesla vehicle, you could run that heater for ten hours at full blast and melt the chocolate bars in the rear hatch area into a puddle. Point being, you don't need all 8 kW all the time so it's not such a significant range hit as, say, ploughing through a snowy road in the winter. The heater's energy usage pales in comparison and becomes almost insignificant.

There could be a few reason:
- cheaper and simpler to use resistive heat (as you note)
- the colder it gets, the more heat you need, the lower the efficiency of the heat pump; so, a heat pump isn't going to help minimum range much.

I'd like a heat pump as a way to improve energy efficiency (and range and travel time on long trips) overall, but I doubt they'll add one at this point.

 

[croman]

I did not even consider that freezing rain or snow could stop a heat pump in it's tracks.

No airflow, no worky.

Never had a problem in 3 winters in Chicago. 2014 Leaf SV. It gets COLD in Chicago and it snows. It is quite windy though

The point is that even though a Tesla has a larger battery, it could really make a large efficiency gain by adding a heat pump without a big negative. The Leaf (and apparently the Soul) are good examples of how smaller BEV do more with less. I would love to maintain a semblance of efficiency in my driving. I notice in winter that I get around 315wh/mi if I am on a highway vs. 400 if I am driving local. The opposite of what it should be solely because the energy draw of the heater is spread over miles faster on the highway than on local roads where I might sit at a red light for 2 minutes. The Leaf was horrible on the highway but killed it on local driving, regardless of season.

 

[Reeler]

Running electric heat in a house in a cold climate makes no sense. We pay to put electrons in our Tesla to run electric heat, which doesn't make sense in Colorado. For my place in San Diego, electric heat is fine because I almost never use it.

 

[stopcrazypp]

There could be a few reason:
- cheaper and simpler to use resistive heat (as you note)
- the colder it gets, the more heat you need, the lower the efficiency of the heat pump; so, a heat pump isn't going to help minimum range much.

I'd like a heat pump as a way to improve energy efficiency (and range and travel time on long trips) overall, but I doubt they'll add one at this point.

That's what I'm thinking too. The ones that have the heat pump and see a huge improvement largely see it in more moderate cold. But for extreme cold, the efficiency of the heat pump approaches that of the resistive (and many heat pumps fall back on a resistive element at that point). So for the same amount of space, Tesla can shove in a larger resistive heater, and given the large battery the impact isn't as much. The complexity of the coolant loop may also have to do with it given Tesla uses waste heat from the motor (which I don't believe the other examples do).

This is way different in a Leaf since that has such a tiny battery in comparison that the heating load makes up a huge portion.

 

[JOEV1]

That's what I'm thinking too. The ones that have the heat pump and see a huge improvement largely see it in more moderate cold. But for extreme cold, the efficiency of the heat pump approaches that of the resistive (and many heat pumps fall back on a resistive element at that point). So for the same amount of space, Tesla can shove in a larger resistive heater, and given the large battery the impact isn't as much. The complexity of the coolant loop may also have to do with it given Tesla uses waste heat from the motor (which I don't believe the other examples do).

This is way different in a Leaf since that has such a tiny battery in comparison that the heating load makes up a huge portion.

Very well put! In other words: the bigger Delta - t .... the lower the COP. Resistive heating is the simplest and most reliable form of heating!
Specially when it is really cold outside. My suggestion is to preheat while plugged-in at home in the garage (set the timer) and one will use less energy when finally on the road

 

[BerTX]

If you'll go back and read my post I never used the word efficiency.

Air is poor conductor over time not in terms of efficiency. Energy can't be created or destroyed so air doesn't do magic but try this as a though experiment (don't try both at home)

1. Put your hand inside a 400F oven to see if it is warm
2. Put your hand in direct contact with 400F iron to see if it is warm

One of those will burn you before you can pull your hand away. The other will give you time to think about it but will eventually burn your hand just the same if you don't pull back.

You are correct, I misread your meaning. At least you didn't tell me to go stick my head in the oven.

My original question was facetious, because I think the MS DOES use waste heat to help in heating the car. The argument was being made that the only source of heat was the resistance heater in a liquid loop. I was asking why have the liquid loop at all.

I don't really know how the heating system works, and haven't heard anyone comment here who does. I have looked at the Tesla patent discussed previously in this thread, and Im going with that as the way the system works until somebody can prove otherwise.

 

[AWDtsla]

You are correct, I misread your meaning. At least you didn't tell me to go stick my head in the oven.

My original question was facetious, because I think the MS DOES use waste heat to help in heating the car. The argument was being made that the only source of heat was the resistance heater in a liquid loop. I was asking why have the liquid loop at all.

It DOES NOT use waste heat to heat the cabin, nor does the glycol fluid loop enter the cabin HVAC. The charger(s) are sitting under the rear seat and can give off some heat while charging, but basically insignificant.

I don't really know how the heating system works, and haven't heard anyone comment here who does. I have looked at the Tesla patent discussed previously in this thread, and Im going with that as the way the system works until somebody can prove otherwise.

Direct to air 400V PTC resistive heating element, in cabin.

Patents don't mean a damn thing.

 

[Lloyd]

If you make the AC into a heat pump, then you loose the ability to remove moisture from the air to defog the windows. That might be an issue!!

 

[AWDtsla]

I'm going to go with there's a teapot in orbit on the earth until somebody can prove me wrong.

If you make the AC into a heat pump, then you loose the ability to remove moisture from the air to defog the windows. That might be an issue!!

I have the AC manually disabled all winter, I force on outside air occasionally to defrost. Otherwise the penalty is too high. 1000 watts for the AC 3000 watts for the heater (at least). No useful range.

 

[Bangor Bob]

Just out of curiosity, do you notice the Leaf running defrost cycles on the coils during cold+damp conditions? That's my one complaint with my Mitsubishi MUFZ-series heatpumps. Turn up the temperature on them in cold temps and they immediately decide to go to defrost mode for 10 minutes before generating any heat.

 

[croman]

Just out of curiosity, do you notice the Leaf running defrost cycles on the coils during cold+damp conditions? That's my one complaint with my Mitsubishi MUFZ-series heatpumps. Turn up the temperature on them in cold temps and they immediately decide to go to defrost mode for 10 minutes before generating any heat.

No. At least I've never seen that.