Winter Range

[ThosEM]

Ok, time to test my confidence:

I'm off on an unplanned trip to the Morristown NJ area along the NJ Turnpike where there plenty of superchargers. The destination is 60 km from the Edison NJ supercharger, and we will need to do some local driving, so the round trip from Edison-Morristown-Edison should not be more than 150 km, barring side trips. No sweat, right? Oh, and overnight at a motel.

But the polar vortex is here and Morristown is predicted to be -20 C on Sat. morning, then warming up for snow. I was unsuccessful finding a motel with an available outlet. So I'm concerned about the overnight cold soak because that is colder than it has been on the mid-coast for many years, and certainly since I've been driving a Tesla.

I'm torn between driving my ICE car, knowing that such temperatures are not an issue for it, or driving the Tesla to see how it fares in the cold soak. It's a weekend trip, so there is only one firm commitment on Sat. mid-day, and then return home, unless we stay another night.

This is a situation in which I would dearly love to have another source of energy, say LP gas, with which to heat the Tesla, so that staying warm would not be in conflict with making the trip.

But I should go for it, right? I understand this is not that challenging compared with -31 C and perhaps worse that you routinely see up in Canada...

 

[Doug_G]

The round trip is no big deal. The local driving might be more of an issue. Each cold soak / heat up the car cycle could easily take 50 miles of range. For sure turn on Range Mode to limit pack heater and cabin heater power draw.

I'd suggest you go ahead, but be prepared to do a side-trip to the Supercharger. And don't try to do that with 60 km of range left. Don't let it go below, say, 120 km before you leave for the Supercharger.

 

[tomas]

Here's a trip I took last week in P85: 79 mi trip each way, 50% hwy 30% rural, 20% city. -20c outbound, -12c return. Not wind chill - air temp. Averaged ~372 wh/mi. Used 75% of available capacity. FWIW, I drive 65 or less on highway, and I think that's critical if you need to conserve.

 

[DMC-Orangeville]

How is the trip? I too may try my luck to Sudbury or North Bay When my 85D arrives in March. A stop at the Barrie Supercharger will be in order.

 

[ThosEM]

Resistive energy waste is costing us

Update: my spouse doesn't want to risk it on our trip to New Jersey in the coldest weather in over 20 years. She doesn't like the competition between getting there and being warm, so it's ICE for this weekend...

The appended is all good and necessary advice, and I follow it myself, though I try to avoid progressing too far down the list, where it borders on desperation. But an 8 point action list reflects a level of effort that is not welcome to the vast majority of drivers. As many others have observed, driving a Tesla under such conditions begins to resemble flying an aircraft that has only very limited touchdown options. It would help quite a bit if superchargers were separated by at most half the rated range less buffer, as they are for our trip, but it still would require a lot more stops and longer travel time in bad conditions.

The problem here is that we are using high quality, high value electricity to generate low quality, low value heat, and we are doing it in the least efficient manner possible, by resistance heating. This is just as bad an idea as using an internal combustion engine to drive mechanical motion. As we all know, that wastes about 80% of the energy on heat. As we also know, resistance heating wastes up to 80% of the heat we could realize by using a heat pump. I will bet that a majority of us, and probably a majority of Tesla engineers, have reversible heat pumps at home to avoid this kind of waste, many of them with ground source heat loops that aren't possible for a vehicle.

I propose that those of us living in cold conditions make a concerted effort to get Tesla's attention on this matter. Ideally I would like to see a retrofittable reversible heat pump that reserves resistance heating for only the most extreme conditions where the heat pump won't cut it. I had thought that this was already in place and that "Range mode" was the disabling of resistance heating, but I eventually was convinced by a member here that is not the case, since the compressor does not run when heating the vehicle. It's really disappointing that Tesla has not implemented a reversible heat pump even on their second vehicle, and it's high time they did.

I've done a 300 km run in horrible weather: -20C, blizzard conditions and arrived with a good safety margin. You do have to be very careful in extreme conditions like this:

• Preheat the car while plugged in to 240V power for a full hour
  • Range mode OFF! (Otherwise it limits preheat.)
  • Use the remote app to start the preheat an hour before departure.
  • Crank the cabin heat up nice and toasty
  • After 30 minutes it will automatically shut off - hit it again.
  • Important: this will preheat both the cabin and the battery pack, but only if you use the remote app to do it.
  • If you can do this while the car is protected inside a garage, that's even better. Anything to help it warm up.
• Once you start driving, turn DOWN cabin heat as low as you can tolerate
  • Doesn't hurt to wear warm clothes!
• Crank up the seat heaters as HIGH as you can tolerate
  • Seat heaters take negligible power
  • If you can keep toasty with the seat heater you'll minimize cabin heat usage, which does take lots of power!
• Turn ON Range Mode
  • Range Mode limits cabin heating power. You can do the same thing simply by turning down the cabin heat.
  • As far as I can tell Range Mode doesn't really help that much if you keep the cabin heat down. But it's a good thing to use it if you're pushing distance.
  • Just remember to turn it OFF when preheating because it is counter-productive for that.
• Drive SLOWLY. Try to go 80 kph if the traffic will allow. Don't go over 90 kph.
  • Slower is better because it reduces aerodynamic drag, which is the dominant effect at highway speeds.
  • Better to drive slowly at the start, and then speed up if you have spare power
• If you can, drive behind a large truck.
  • Don't get right up his butt for safety reasons. Yes closer is better in theory, but don't do something dangerous. Maintain a safe following distance.
  • Simply being behind a truck will reduce aerodynamic drag. This is even more important in the winter when the air is denser.
• Use your Energy App and Navigation to keep track of range
  • Set Energy App to 10 km and AVERAGE mode. The "Projected Range" will give you a very good estimate of how far you can drive
  • Use the Navigation to see how far you have to go
  • Maintain a buffer of AT LEAST 30 km
  • If that buffer starts shrinking, slow down
  • If you have lots of spare range you can speed up a little, or use a little more heat
• If you get into trouble, SLOW DOWN
  • The earlier, the better
  • Slowing down is more effective than turning off cabin heat. Reduce speed 5 kph and stay toasty.
  • You can eke out the distance if you do it early. If you wait until you're in trouble nothing will save you except plugging in. Or a flatbed.

Another thing to note - despite all the preheating the car will initially take more power. That's because the drive train is cold. Once it warms up the heat pump will kick in to warm the cabin, and you'll see the cabin heat power draw drop dramatically.

 

[Doug_G]

The Model S heat pump is reversible. It works both for air conditioning and for heating. Heat pump technology has its limitations; some are set by engineering, but major limits are determined by the science of thermodynamics. We can only approach those limits with a real heat pump, of course, but the problem is fundamental: Heat pumps don't work well when trying to pump a very large temperature difference.

In extremely cold areas we either need to have supplemental heat for the very cold days, or as you mentioned use pipes underground as a heat reservoir. The cost of installing such a system is a big reason why most people here are running natural gas furnaces - the payback period is very long.

This is the same reason Tesla uses the drive train coolant as a reservoir. They can't bury pipes in the ground. So there's nothing they can do about a cold soaked car - the heat pump is simply not going to work. When the drive train is cold, they have to use resistive heaters.

 

[tomas]

Marketing 101: when you have a flaw, feature it! If tesla teamed with, say, Barbour to design a very fashionable but functional set of his and hers heated driving boots and matching caps, that plus seat heaters would keep anyone warm with new 60F Eco cabin setting. Include those items plus Barbour carrying satchel in cold weather package. Who could resist the adventure!

 

[ThosEM]

I believe this is incorrect. Did I mention that someone here convinced me there is no heat pump heating, by pointing out that the compressor doesn't run when you turn on the heat? Check it out yourself, or find a place where Tesla states unambiguously that their heat pump is reversible. I could not find such a statement anywhere, and I looked pretty hard.

Good luck! I would be delighted to be proven wrong on this.

The Model S heat pump is reversible. It works both for air conditioning and for heating. Heat pump technology has its limitations; some are set by engineering, but major limits are determined by the science of thermodynamics. We can only approach those limits with a real heat pump, of course, but the problem is fundamental: Heat pumps don't work well when trying to pump a very large temperature difference.

In extremely cold areas we either need to have supplemental heat for the very cold days, or as you mentioned use pipes underground as a heat reservoir. The cost of installing such a system is a big reason why most people here are running natural gas furnaces - the payback period is very long.

This is the same reason Tesla uses the drive train coolant as a reservoir. They can't bury pipes in the ground. So there's nothing they can do about a cold soaked car - the heat pump is simply not going to work. When the drive train is cold, they have to use resistive heaters.

 

[Doug_G]

I believe this is incorrect. Did I mention that someone here convinced me there is no heat pump heating, by pointing out that the compressor doesn't run when you turn on the heat? Check it out yourself, or find a place where Tesla states unambiguously that their heat pump is reversible. I could not find such a statement anywhere, and I looked pretty hard.

Good luck! I would be delighted to be proven wrong on this.

You are correct that they've never put this in writing to my knowledge. Here is some evidence:

1. At the first Fremont Model S event (yes I was there) they had engineers around the skateboard models to answer questions. I found the engineer who was an HVAC specialist and asked him this specifically. He confirmed that the heat pump is reversible and used for heating and cooling. It is essentially a larger version of the heat pump used in the Prius.
2. When the compressor isn't running at full power (it's variable speed) it is not very obvious, so you may not hear it especially from inside the cabin.
3. The Roadster definitely has no heat pump, and in extreme cold conditions it uses nearly 4A (3.6A IIRC) for the heater, and the Roadster cabin is tiny in comparison... and it doesn't get the cabin all that warm. There's no way the Model S could use less power than that to keep the huge cabin nice and toasty - yet once the car is warmed up it most certainly does.
4. The Model S clearly uses much less heater power when the drive train is warmed up then it does with a cold drive train.

If it's not using a heat pump then the motor coolant must get warm enough all on its own... because the power consumption of the car is clearly better than the Roadster, which only has resistive heaters.

 

[ThosEM]

Thanks much! That's very encouraging to hear. I will have mine in for diagnosis of a low power whining noise this week and I will press the service adviser for documentation of this while I'm there.

Update on last weekend's travels:

We took the BMW 328ci to NJ. It was -21C Sat. morning, so quite a deep cold soak, though we would have been ok with Edison less than 60 km away. Our local travels were only about 10 km, but there were two cold soaks of a few hours each before getting back on the road. Still ok.

I'm just as glad we didn't take the Tesla, though, because the winter storm was relentless all the way back to Maryland, some 400 km in totally snow covered roads with very little plowing or salting done by NJ, DE, or MD. The ridges of unplowed snow tugged strongly at the wheel forcing some nervous nellie drivers to take to the most well worn lane and travel at 40 kph with 4 way flashers running. Meanwhile, the competent traffic including trucks and buses were forced to pass in the very snowy lane without being able to see lane markers, if they wanted to get to 60-70 kph that was perfectly safe in the well worn lane. Knuckles were white all around.

My wife commented that she found the lack of road treatment or plowing to be pretty incredible for the main artery on the east coast, especially for a well-predicted storm. Also predicted was a switch to rain during the day, but we didn't see that until we were south of Baltimore, within 30 km of Annapolis. The only thing that was getting attention were the toll booths, where plows were running every which way across and into the oncoming traffic. Even the Delaware Bridge was unplowed, but the toll booths were clear!

The only thing more nuts than making that trip would have been to do it in an spotless aluminum Tesla. Though we were unscathed, we saw at least a half dozen cars in the ditches or collisions, or being towed. Even defensive driving could have failed us in that mess.

You are correct that they've never put this in writing to my knowledge. Here is some evidence:

1. At the first Fremont Model S event (yes I was there) they had engineers around the skateboard models to answer questions. I found the engineer who was an HVAC specialist and asked him this specifically. He confirmed that the heat pump is reversible and used for heating and cooling. It is essentially a larger version of the heat pump used in the Prius.
2. When the compressor isn't running at full power (it's variable speed) it is not very obvious, so you may not hear it especially from inside the cabin.
3. The Roadster definitely has no heat pump, and in extreme cold conditions it uses nearly 4A (3.6A IIRC) for the heater, and the Roadster cabin is tiny in comparison... and it doesn't get the cabin all that warm. There's no way the Model S could use less power than that to keep the huge cabin nice and toasty - yet once the car is warmed up it most certainly does.
4. The Model S clearly uses much less heater power when the drive train is warmed up then it does with a cold drive train.

If it's not using a heat pump then the motor coolant must get warm enough all on its own... because the power consumption of the car is clearly better than the Roadster, which only has resistive heaters.

 

[tomas]

I'll bet those in the ditch were your "competent drivers"! There's nothing wrong with backing it way down on an unplowed road during blizzard. SUVs have created an over confident group of drivers, until they lose traction, wheeee!

 

[ThosEM]

I found this on another thread. It appears from the thermal management patent that the heat pump is used only for refrigeration. Both the cabin and the battery loops contain resistance heaters, the text says nothing about reversibility of the heat pump, nor does the diagram show a crossover valve to run the coolant in the reverse direction. I'd say they are grabbing about 4-5 kW each when running. Very disappointing, but perhaps Tesla judged this to be complex enough without introducing additional valves and switches.

Patent US20100025006 - Electric vehicle thermal management system - Google Patents

The Model S heat pump is reversible. It works both for air conditioning and for heating. Heat pump technology has its limitations; some are set by engineering, but major limits are determined by the science of thermodynamics. We can only approach those limits with a real heat pump, of course, but the problem is fundamental: Heat pumps don't work well when trying to pump a very large temperature difference.

In extremely cold areas we either need to have supplemental heat for the very cold days, or as you mentioned use pipes underground as a heat reservoir. The cost of installing such a system is a big reason why most people here are running natural gas furnaces - the payback period is very long.

This is the same reason Tesla uses the drive train coolant as a reservoir. They can't bury pipes in the ground. So there's nothing they can do about a cold soaked car - the heat pump is simply not going to work. When the drive train is cold, they have to use resistive heaters.

- - - Updated - - -

Agreed, but we didn't see any trucks or buses in the ditch or jack knifed. In the well worn lane, 65 kph was no sweat. Out in the soft stuff, I'm sure it helped to be heavy. Possibly interesting sidelight: after all that snow and rain, there was hardly any salt on my car. Wiped it down and it looks clean!

I'll bet those in the ditch were your "competent drivers"! There's nothing wrong with backing it way down on an unplowed road during blizzard. SUVs have created an over confident group of drivers, until they lose traction, wheeee!

 

[Albatross]

Hi
i do find this range concerning. I drive every weekend 190km one way from Ottawa to Tremblant. There were so many days this year of -25-30C. A friend has an S85 and barely made it one way (with heat off driving slow etc). My P85D is on order and I'm worried won't be up for this regular trip.

 

[tomas]

Hi
i do find this range concerning. I drive every weekend 190km one way from Ottawa to Tremblant. There were so many days this year of -25-30C. A friend has an S85 and barely made it one way (with heat off driving slow etc). My P85D is on order and I'm worried won't be up for this regular trip.

You will need to pre-heat car while plugged in prior to departure, do full range charge completing just before departure, and manage HVAC. What I usually do is charge to 90% overnight, then reset to 100% range charge and restart charging 1 hour before departure to get the last 10% and heat the battery.

If you are talking about air temp (NOT wind chill) of -30c for entire trip, it might be tight. That is rare, though. Darned weather broadcasts - in order to be spectacular - seldom talk air temp any more when it is much more exciting to talk wind chill! If air temp averages, say, -15 this trip should be easily doable with margin. Of course, I do not know what your elevation change is. I'm sure some natives will chime in.

 

[mknox]

You will need to pre-heat car while plugged in prior to departure, do full range charge completing just before departure, and manage HVAC. What I usually do is charge to 90% overnight, then reset to 100% range charge and restart charging 1 hour before departure to get the last 10% and heat the battery.

Yep, I do the same and it does help a lot. One other thing I'll mention is that on longer drives, even when it's cold, your energy consumption is not as bad as it would be on a shorter trip. Once the battery, inverter and motor get humming along, they generate a bit of heat themselves which is circulated and managed very well by the car. I've done long winter trips to a rental property I own and may see only 15% more consumption than I would in ideal temperate seasons. If I'm doing shorter trips, I may see consumption double or more than it would be in the summer.

 

[clea]

Hi
i do find this range concerning. I drive every weekend 190km one way from Ottawa to Tremblant. There were so many days this year of -25-30C. A friend has an S85 and barely made it one way (with heat off driving slow etc). My P85D is on order and I'm worried won't be up for this regular trip.

I have made the Laval - Mont Tremblant trip a few times in the winter with an overnight stay before returning without plugging in. The worst time was when the car was completely cold soaked and the weather was not just cold but windy and snowing and I still made it home with electrons to spare without needing to change my driving habits beyond what the weather dictated. I know that Laval - Tremblant is shorter than from Ottawa but it is not half the distance so one way should be easily doable.

 

[Albatross]

I have made the Laval - Mont Tremblant trip a few times in the winter with an overnight stay before returning without plugging in. The worst time was when the car was completely cold soaked and the weather was not just cold but windy and snowing and I still made it home with electrons to spare without needing to change my driving habits beyond what the weather dictated. I know that Laval - Tremblant is shorter than from Ottawa but it is not half the distance so one way should be easily doable.

Thank you. That is helpful. My garage at Tremblant is heated so that should help once here. We had something like 20 plus days with air temps below -20C. There were a couple trips below -30. With windchill much lower (was-52 with windchill top of mountain one day).

I have to think 200 km is doable.

 

[wayner]

One thing that kills you is freezing rain or snow that freezes on your windshield as you have to run your front defroster at full heat almost 100% of the time which really saps the range. Absent that you should be able to make it for 190km.