Feedback Suggestion For Tesla Cabin Heating with NO Loss of Range

[MitchJi]

Hi,

Reason for this post:
I'm posting this suggestion for Tesla here because at the most recent SH Meeting Elon said that the best way to make a suggestion would be to post it on either the TMC Forums, or the Tesla Motors Forums. He said that they check for popular ideas, so if you would like Tesla to invest the engineering required to determine if this idea can be implemented cost effectively please respond to the poll and reply to the thread if you have any further suggestions or comments you want to add. I hope that I'm making this suggestion in time to be implemented for the M3 Launch. If you agree that this would be a desirable M3 feature please let us know. I believe that if it's feasible, Tesla cculd design a system that can easily be added to all of their cars so even if they have already passed "pencil down", I believe that they could add this feature to the M3 without having a negative impact on their schedule.

IMO at least taking the time to investigate this idea thoroughly is a no-brainer because this would completely eliminate the decreased range in cold weather plus it would provide increased passenger comfort.

The Idea:
This is based on a post, a long time ago (I don't remember where but not TMC), in which someone stated that he heated his EV with a DeLonghi Oil Filled Radiant Heater while his EV was connected to the grid, then on his commute to work the stored heat maintained the passenger compartment at a comfortable temperature.

Tesla's have the ability to preheat or cool the passenger area, while they are connected to the grid. If the car heated containers filled with oil, or phase change materials with sufficient thermal mass to maintain a comfortable temperature for as long as necessary, the range of their cars would be substantially improved in cold weather. For traveling the capability to travel the distance between Superchargers without requiring any supplemental cabin heat would be ideal. The other major benefit would be that radiant heat is a very comfortable type of heat.

Is it Feasible (Cost Effective)?:
Is it possible, and is the solution affordable, to store sufficient heat to maintain a passenger compartment at a comfortable temperature, in a cold climate, for the time it takes to exhaust the batteries of Tesla's? Would it weigh too much? Could the same storage medium be efficiently used to for cooling as well as heating?

Consumer Reports review of the Model S states that:

Drawbacks include tight access, restricted visibility, and range limitations in cold weather.

Implementation Possibilities:
Using phase change materials for thermal storage, seems like a good match for EV heater use, or something simpler, like oil if phase change materials are not cost effective:
Thermal Mass | Sustainability Workshop

Phase change materials are a relatively new class of materials, which are used to add thermal mass without adding weight or bulk. They may replace standard wall board, or may be an additional layer in walls or floors. They are relatively rare but quickly increasing in popularity as technologies improve and prices drop.

In addition to compactness and light weight, phase change materials absorb and release their heat at certain temperatures, just as water boils at a certain temperature. This helps occupied spaces stay at the temperature desired, even as heat is flowing in or out of the space.

Best Approach?:
I can think of two possible approaches, which might be combined.
1. A big slab or slabs of phase change materials, possibly covering the entire floor under the carpets and/or on the doors. This "system" could be as simple heating the space, which would heat the slabs. The disadvantage would probably be (unless the storage medium is insulated) that it would be more difficult to heat the cabin using the on board heating system, if necessary when the car is not connected to the grid.

2. Some approximately brief case sized containers filled with either a phase change material or something simpler, like oil if that will work well enough.

I think that good possible locations for these containers would be one per seat, either on the bottom of the seat, or on the floor beneath the seats. Resting your feet on a warm container would feel great on a cold day!

Insulated Containers?:
I don't know if insulating the containers would be cost effective or not, but insulated containers with vents, which could be opened and closed, would have two advantages. This would allow the thermal mass to be heated to a higher temperature (store more heat), and storing the heat for later use. For example the vents could be opened sufficiently to maintain a comfortable temperature for your morning drive, then closed when you arrive at your destination, then opened again in the evening, with hopefully sufficient stored heat to maintain a comfortable temperature for your return home. If necessary fans could be used to extract hot or cold air more rapidly.

 

[austinEV]

You are missing the easiest thing of all. Just preheat the batteries while on the charger. There is your huge slab of thermal mass, and it's just a software fix. I am completely baffled why they don't already do this. If it is a cold morning I can use my phone to tell my car to preheat the cabin, which works ok, but there is little thermal mass heated up. And it doesn't even try to heat the battery. So once you start *driving* the car tells you that regen and performance are limited until the battery heats up, from the battery energy. Just by heating the battery up to nominal heat while on the mains would be an enormous range boost; heating it up to hot summer day is even better. I think that is a way more elegant solution than a new fluid system. The battery is already water cooled, and water is has excellent heat capacity. I think cabin heating is less of a drain than you think, I bet more power is used in heating the battery than you, but I don't have a source on that.

The only reason I can think of that they don't do this is they feel people will waste energy. Owners will want this to be a predictive behavior so a few kWh will be used every morning, even when the driver decides not to use the car. Or people tell their car to warm up with the phone and then change their mind. I bet it's a fair amount of energy wasted from the grid doing this and I suspect TM really doesn't want to get into the business of wasting grid power, green bias and all.

 

[lance p]

Well, the problem is that you'd be adding mass to the car, which you'd be hauling around 24/7, even though you use the feature only part of the year. Also, the creation of heat through resistance is close to 100% efficient, so pre-heating the battery pack while plugged in seems maybe a better option. That way, whatever heat would have been used in heating the pack while driving would be available to heat the cabin.

I am sure that you'd have to have a large mass to provide sufficient heat to keep the passengers comfortable for a prolonged period. Driving an aluminum and glass can at 70 mph through cold air is bound to cause substantial heat loss to that outside air. That is why using the heat leads to significant range loss -- because the car is losing a lot of heat to the environment.

 

[jsrawa]

Not to be a downer here but your poll doesn't really allow for someone to vote that they don't think it's feasible. While your idea isn't bad I just don't see it as something that could be implemented effectively in current EVs. Weight plays a huge factor and your talking about significant weight. Furthermore some climates rarely need extensive heating in their vehicle and for these people it would be unnecessary mass to decrease range.

The idea about preheating the battery seems more effective but I think this would influence battery life negatively. To be fair though I am not a engineer.

 

[David_Cary]

Cold air is denser so aero losses are greater. Cold tires have higher RR. So pre heating the cabin and not running the heat will absolutely not eliminate range loss in cold weather. Reduce it of course but not eliminate it.

My gut feeling is that heating the cabin is only 50% of the range loss but it certainly depends greatly on ambient temp and requested car temp.

 

[Matias]

I don't think there is a need to reinvent the wheel. Many electric cars (Leaf, Prius, Zoe at least) use the heat pump.

According to Renault, the heat pump uses half of the electricity used by a conventional heating system.

The heat pump

 

[jerry33]

If it is a cold morning I can use my phone to tell my car to preheat the cabin, which works ok, but there is little thermal mass heated up. And it doesn't even try to heat the battery.

In my experience, that's not true. There is a big difference in the amount of regen required if I pre-heat compared to not preheating. It's even more if the timer is set so that charging finishes shortly before I start driving. Important: Range mode must be OFF when doing this, otherwise it won't heat the battery enough to matter.

 

[22522]

I expect there is already a battery temperature bias based on ambient temperature. In other words, they are already doing it with software.

 

[brkaus]

I don't think there is a need to reinvent the wheel. Many electric cars (Leaf, Prius, Zoe at least) use the heat pump.

According to Renault, the heat pump uses half of the electricity used by a conventional heating system.

The heat pump

Our home system claims a COP of 4 at 50 degrees outside and 72 degrees target inside temp. So it's 4x more efficient than resistive heat.

Probably couldn't get that efficiency in a small package, but there certainly is some opportunity here for tesla. How about as part of the cold weather package?

 

[David_Cary]

Our home system claims a COP of 4 at 50 degrees outside and 72 degrees target inside temp. So it's 4x more efficient than resistive heat.

Probably couldn't get that efficiency in a small package, but there certainly is some opportunity here for tesla. How about as part of the cold weather package?

brkaus - you know of course that 50 degrees outside means almost zero energy used for heating - car or house. And the COP falls with temperature. If the sun is out, 40 degrees means very little heat for a car.

So there is no way, no how that your heat pump is 4 times more efficient than resistance. 3 times perhaps.

I think people are mostly concerned with range when you are down in the 20s. Then you are going to get COPs in the 2 range in automotive application.

For you own house, you do have to balance the improved efficiency with possible duct and air movement losses that resistance doesn't usually have. This coming from someone with heat pumps at home but I also have NG for backup when the COP drops too much.

 

[ecarfan]

I hope that I'm making this suggestion in time to be implemented for the M3 Launch.

Too late. Elon has stated that the Model 3 design was finalized last month, "pencils down". Tesla is going into production next year and the design had to be locked down.

And your proposal does not make sense to me for a variety of reasons.

 

[brkaus]

brkaus - you know of course that 50 degrees outside means almost zero energy used for heating - car or house. And the COP falls with temperature. If the sun is out, 40 degrees means very little heat for a car.

So there is no way, no how that your heat pump is 4 times more efficient than resistance. 3 times perhaps.

I think people are mostly concerned with range when you are down in the 20s. Then you are going to get COPs in the 2 range in automotive application.

For you own house, you do have to balance the improved efficiency with possible duct and air movement losses that resistance doesn't usually have. This coming from someone with heat pumps at home but I also have NG for backup when the COP drops too much.

Agree 100%. 50 is typical in our area, so used that as an example. My COP is 3 around 38 and 1.7 at 20.

Automotive system is much more size constrained so I would bet 2.0 would be best possible and only go down from there. Might help in more temperate areas, but probably not much in the cold north.

I guess geothermal is out of the question for car applications

 

[Matias]

I guess geothermal is out of the question for car applications

 

[Matias]

I'm surprised, that Tesla at the moment doesn't have heat pump. Car could use it also for battery heating besides cabin heating.

 

[Topher]

Feel free to put a 5 gallon bucket full of melted wax in your car every morning.

Probably the best is to add 3 more 100 Watt mobile heaters to the car (aka passengers).

Thermal mass in a car is tricky since all the thermal mass in on the outside of the insulation (which is minimal), and any added thermal mass or phase change material adds weight, which lowers range.

[If people beg, I will do the math, but my intuition is that you are better off with my first two suggestions]

Thank you kindly.

 

[austinEV]

In my experience, that's not true. There is a big difference in the amount of regen required if I pre-heat compared to not preheating. It's even more if the timer is set so that charging finishes shortly before I start driving. Important: Range mode must be OFF when doing this, otherwise it won't heat the battery enough to matter.

I think you are saying the regen line is different for pre-heating vs not pre-heating. That may be, but why would the battery be cold at all? I get that heating it up to "hot" is probably a heat cycle stress that the pack could do without, but heating it up to room temp should be a no-brainer.

 

[jerry33]

I think you are saying the regen line is different for pre-heating vs not pre-heating. That may be, but why would the battery be cold at all?

My guess would be that if the battery was kept warm all night there would be many complaints about increased vampire drain. The aluminum bottom gets radiates heat rapidly.

 

[Lex]

Love that the first posts are from California, Texas, etc. Here in Toronto we nearly always have weather on the mind and winter is coming.

There is already liquid coolant in this system, so as with others I agree that we just need the ability to warm-up everything via shore power.

For some reason it is not there today... the app's cabin pre-heat is not even half the story. Never mind pack heating, you can't turn on the rear defroster until you're in the car (and then mine takes 10 minutes to get started defrosting).

If they're worried about 12V drains then let us only use it when on shore power...

I've asked for this a few times here as have many others.

 

[Mario Kadastik]

I want an option that this is a bad idea...

Also, set your car to charge so that it finishes charging right around when you leave and voila, warm battery, nomregen limits and no big consumption change.

Trust me, I live in the north and have weathered 3 winters including weeks of -20C

 

[Lex]

Yep, that was my 1st winter workaround last year, I tried to remember to do the last 1 or 2 hours of charging in the early AM and it helped but did not eliminate the limited regen (though the updates at the end of winter really seemed to reduce the issue). Just weird we have to work with workarounds for something so basic.