Why does Tesla use a Resistance Heater instead of Heat Pump

[scaesare]

I believe that example is not steady state so can't apply to a long trip, and unlike the Leaf examples, they weren't measuring purely the power demand from the heating/AC systems. That means there are other non-heating related factors that can play into the efficiency numbers. Basically the comparison is a lot more useful if you just compare power in kW and don't conflate miles into it. This is because heating demand varies with time, not directly with miles.


The problem with your calculation is you were essentially assuming that there is no consumption by the heat pump, which is far from the case. What matters is the difference.

Right, I acknowledged both that it wouldn't be steady state, and that the heat pump wouldn't use zero energy in my post that you quoted.

So I agree it's the delta that matters. I suspect that delta would be large enough to be useful. Now as to if the implementation cost makes that an attractive option, I don't know.. but given the relatively easy process of adding heat pump functionality to an existing A/C system, along with the success other low-cost EV's have had with implementing them, I suspect it might be.

 

[dhrivnak]

...:

Not apples to apples - but we had a 3.5 ton ac unit [undersized for the house sadly] that died after 16 years. I replaced it with a 4 ton heat pump. It was easily twice the footprint of the old unit [sure, refrigerant type made it so] but that unit would not be able to heat a 2800 square foot house under 45F no matter how long it ran at 15 seer.

. There are many variables as I have a 3 ton unit for 2600 sqft and even at 5F the back up heat has yet to come on. If you have backup heat below 45 you have a problem with your unit.

PS mine has been running for over 17 years now. And the Leaf with a HP gets several more miles on a charge and I hear it warms up faster.

 

[GlmnAlyAirCar]

I understand what he means, however, the original statement from another user put forth the thesis that running a heat pump improves the cars range when in fact running a heat pump consumes energy. There is no free lunch. Pumping energy from a source to a sink against the nominal thermal gradient costs energy, the COP has nothing to do with improving range, but simply the efficiency of producing the heat energy to heat the cabin.

Running a heat pump intrinsically does not improve range, running a heat pump as opposed to resistive heating uses less energy and therefore retains more range relatively speaking. But it does not create energy out of thin air.

I got into this discussion a few years back. Hey, it may have even been in this thread. In any case, when people claim these >100% efficiencies, they typically omit the fact that they are treating the heat pump as an open system. If treated as a closed system, yes >100% efficiency is impossible. But for practical purposes, the exterior of the car can be treated as an infinite heat source, hence these large efficiencies.

 

[tyson]

Tell us, how easy it is with those two and then I tell you how it will work with heat pump
I'll give you a hint, this is Tesla Model S resistive heater.

So that was not a troll or anything... genuinely curious.. I would assume that you can just run both the a/c and the resistive heater and divert the airflow as needed. But I don't know the HVAC system of the S to that level

 

[arnis]

I have a heat pump on my in-ground spa. It's a piece of shizzle, breaks down all the time and needs constant service. A resistive heater is much simpler and just works.

Has absolutely nothing to do with anything else than your spa.
Tesla's heat pump will be exactly as reliable as Tesla's AC. Which is far from perfect, but has nothing to do with your spa

I would assume that you can just run both the a/c and the resistive heater and divert the airflow as needed.

That would be the simplest way. Some of the airflow is bypassing the fins. Most likely AC coil is not bypassed on Model S but that can be changed.

 

[mongo]

Tesla's heat pump will be exactly as reliable as Tesla's AC.

It may be highly reliable, it may be sufficiently reliable, but two systems with different part counts and types will most likely not be bold-font-exactly as reliable.

 

[comanchepilot]

. There are many variables as I have a 3 ton unit for 2600 sqft and even at 5F the back up heat has yet to come on. If you have backup heat below 45 you have a problem with your unit.

PS mine has been running for over 17 years now. And the Leaf with a HP gets several more miles on a charge and I hear it warms up faster.

How do you know @ 5F your back up has not come on? relying on your electric bill? doesn't it run through the same HVAC coil? In TN I imagine that back up is purely resistive -

 

[dhrivnak]

How do you know @ 5F your back up has not come on? relying on your electric bill? doesn't it run through the same HVAC coil? In TN I imagine that back up is purely resistive -

Yes we have electric resistance back up and you can tell by the vent temperatures and from the control module if it has been switched on. I also watch my electric bill quite close, and my record winter high has been $107 with 4 of us in the house, or less than 1/2 of any of my neighbors and we had 4 of us. Heat pumps are MUCH better now than they were in the past. And it helps that we have a well insulated home.

 

[jlarmstr]

I got into this discussion a few years back. Hey, it may have even been in this thread. In any case, when people claim these >100% efficiencies, they typically omit the fact that they are treating the heat pump as an open system. If treated as a closed system, yes >100% efficiency is impossible. But for practical purposes, the exterior of the car can be treated as an infinite heat source, hence these large efficiencies.

Hahaha, yes, someone who understands ... thank you.

 

[mpt]

It seems that the debate is looking for a binary output - HP or no HP. I'm actually going to come down on the no-HP side after years with, and years without HP but, only because the circumstances are right for no HP in the Model 3.

I don't think the heating tech is super important, after all resistive is cheap, fast and 100% efficient at converting battery power to heat but HP uses less power as it steals the heat from the rest of the world rather than creating it in-house though I don't find it to be a nice heat particularly.

What I think is the real decider is the cars cabin thermal performance.

Here's the history for me:

• Tesla Roadster - No HP, leaked cabin air like a sieve, no insulation, weak heater compared to job at hand. => adding a heat pump would have improved range in the winter.
• MINI E - Massive resistive heater but actually vented cabin air through the batteries and out the back !?!!?!?! => Heat pump would have helped because, like the Roadster, the heater was running flat out all the time.
• i-MiEV - Small resistive, large cabin, not much insulation => HP would have helped range I'm sure.
• BMW Active-E - Modest resistive, good cabin insulation => HP might have helped but it was always cosy and it stayed warm for a long time.
• Focus Electric - Same as BMW Active E => HP might have helped but it was always cosy.
• SmartED 2015 - Small cabin, chunky resistive, so-so insulation. It's a car that gets too warm too quickly (yeah I know, and it's an EV!) => The heater impacts range at startup but seems to trail off after the car is warmed up. Not sure if HP would help much as all the heavy lifting is done at the start.
• BMW i3 - Has HP and good insulation. => Not totally convinced it's needed. The range still falls in winter like the Active E did but it's slow to warm up and never really felt 'toasty'.
• SmartED 2017 model - 3kW resistive (it actually shows heater consumption in real time) small cabin + mega insulation => I don't think it'd benefit from HP at all. Looking at the power consumed by the heater (it's -16℃ here today) I see that yes, there's a hit at startup; 3kW for ten mins but afterwards or, all the time if I pre-condition first, it's floating around 0-1kW. Most of all though, it feels toasty and warm - heck, I was coat off, bare arms yesterday at -14℃.

If you need a lot of heat all the time because of a large or lossy cabin, get a heat pump as the efficiency will help range, if your car is smaller and/or well insulated, spend the money elsewhere.

If the Model 3 has a big battery and modern insulation which I suspect it has, I'll stick with no HP, and that surprises me after all the excitement I experienced in the run-up to the i3 arriving.

 

[Reeler]

Good synopsys, but no contrary data in your analysis. What I like about my heat pump LEAF is that I don't have to do anything special or adjust my thinking about range when driving in the winter. To appeal to the non-EV-geek crowd, I think one less thing to understand is a good thing.

I will add contrary data to your glowing review of resistive heating cars. I had a couple RAV4 EVs V.2. I would use them to drive from Denver to the mountains for skiing. I usually would make it, but on a particularly cold day I saw my 25 miles of range with 9 miles to go before the continental divide before the glide to my cabin downhill. Suffice to say, I ran out of juice in the one mile long Eisenhower Tunnel a few hundred yards from the downslope on I-70. Very scary.

I can tell similar stories waiting in traffic approaching the tunnel. A couple times with more than 5 hours of uphill traffic on the way back to Denver on Sunday night to catch a flight. Running the heat as little as possible in the hopes to make it home. A few stories like that will hurt adoption.

 

[arnis]

If the Model 3 has a big battery and modern insulation which I suspect it has,

Well.. battery is bigger. But insulation is way way worse than average. Mostly due to being aquarium. There is no roof. And roof is where the warm air is hiding. And single layer glass is not going to insulate. Model X is a good example (range loss in cold).

We've already "figured out" that not having a frking valve to reverse AC gas is unjustified in not hot climates.
And it's not just about range, it's about lifetime efficiency.

 

[croman]

Tesla doesn't understand how to insulate or what cold is. Heat pump is necessary, model 3 or not, if you need to heat.

 

[arnis]

Definitely agree.
Proof:

how to insulate

Tesla - none. Others:
One part:

Windscreen:

what cold is

Well, they understand what cold is. They don't even charge the battery when it is below 0*C (which is weird).
But they don't know/want to make that heat efficiency. Making it with drivetrain is still 100% efficient.
Actually, less than 100%, because drivetrain loses heat even before that heat is transferred to battery.

I think it would be reasonable to add one extra subscore in addition to city, highway, combined EPA ratings.
How about combined winter. Test done at -10*C, dry road, all else same. It also applies to non-EV's.

 

[Reeler]

MPGe should account for heater usage. Car makers are avoiding the heat pump out of laziness, but if MPGe ratings penalized them, I bet they would quickly change their tune.

 

[AWDtsla]

Jaguar I-pace uses a heat pump to heat the cabin and the battery pack.

Clock is ticking Elon...

I-PACE Concept | Thermal Management Systems | Jaguar

The impact of the heat pump is considerable. When the outside temperature is between 10°C and 15°C, the use of the heat pump rather than power exclusively from the battery can extend I‑PACE Concept’s range by up to 50km (30 miles).

 

[Carl Brandon]

I just saw this thread, and wanted to respond to the general info about heat pumps. I'm a college physics professor, have a Model S for two years, live in Vermont, have two Powerwalls, heat my house with a heat pump (with NO BACKUP), and heat the house fine at -40F. I use a Mitsubishi heat pump for my house with four interior units and one exterior unit. To do this at low temperatures, you need a Mitsubishi Hyperheat outdoor unit. They have only been available for two and 1/2 years (I got the first one in Vermont). Non Hyperheat models do not work at low temperatures. I keep the living room at 75F when it is -40F outside, with no other heat source. My overall efficiency for the entire season is 500%, and all my energy for my house and car come from PV panels.

 

[arnis]

Air-Air heat pumps do not operate at -40*C (same as -40*F) outside. Regular refrigerant is not suitable for that.
Nor do they get 500% efficiency at cold temperatures (below freezing).

 

[AWDtsla]

Air-Air heat pumps do not operate at -40*C (same as -40*F) outside. Regular refrigerant is not suitable for that.
Nor do they get 500% efficiency at cold temperatures (below freezing).

And electricity doesn't cost exactly the same amount all the time, it actually varies wildly from very high numbers to negative every few minutes. Yet you still pay 1 or 2 constant rates. What point are you trying to make? One that hasn't been covered in the last 300 posts?

 

[arnis]

Yet you still pay 1 or 2 constant rates.

No. I pay exactly what it costs. Price fluctuates every hour from almost zero up to half euro per kWh.
Market data | Nord Pool
Example:
Tomorrow, at 2-6am electricity costs 0,36cents/kWh, and 10,0cents/kWh at 10-11am.

My point is exactly what I said.
500% efficiency is unheard of. And air-air heat pumps do not work at -40 at any reasonable efficiency.
I believe I explained myself well enough.