Real World Range Questions (Winter)

[darthy001]

I would love some more info about how much power the heater consumes continuously in cold weather. I can't believe it's burning 7.5 kW continuously. That would have to be purely resistive.

Might it be using a resistive device until the heat pump is up and running?

The heat pump in my house produces 3.6 kW of heat at max power, and max power is 600 watts of input. The manufacturer claims it delivers 3.6 kW down to -15 deg C, which seems correct to me. We permanently disconnected 3 kW of electric heating after installing it and burn almost no wood anymore. It's still gushing hot air at -25 deg C, I would guesstimate at least 2 kW.

I'm almost (but not quite) ready to eat my best pair of woolen socks for dinner if it's really using 7.5 kW continuously using only a heat pump.

More or less my initial reaction as well.. 7,5kW continous sounds extremely overkill.

Gonna loose sleep until someone actually are able to do some real-world testing here since I want this car so bad its ridicolous

On a sidenote I believe Tesla will be in big trouble here in Norway if they advertise 300miles of range and you only get around half of that in Winter or Rainy conditions. They will without a doubt see a ****storm of badpress if this turned out to be true. The tabloids and consumer-organisations would be all over that in a split second...

 

[cinergi]

Car heating systems are *VASTLY* more powerful per cubic-foot of air than home heating because they have to be used to quickly change temperatures by a wide margin (home heating is designed towards efficiency and smaller temperature swings). That 7.5kW is at full blast, and you won't be running it full blast for a long trip -- only long enough to get the cabin temp closer to the set point. It then settles down to the ~1kW range when it's ~32F/0C outside (set to 72F/22C inside).
Here's a picture of me turning the car on & heat on when leaving work to go home. You can see how it spikes up and ramps down. This was a cold-soaked ~32F/0C car.

 

[darthy001]

Car heating systems are *VASTLY* more powerful per cubic-foot of air than home heating because they have to be used to quickly change temperatures by a wide margin (home heating is designed towards efficiency and smaller temperature swings). That 7.5kW is at full blast, and you won't be running it full blast for a long trip -- only long enough to get the cabin temp closer to the set point. It then settles down to the ~1kW range when it's ~32F/0C outside (set to 72F/22C inside).
Here's a picture of me turning the car on & heat on when leaving work to go home. You can see how it spikes up and ramps down. This was a cold-soaked ~32F/0C car.

View attachment 12230

What was the average speed approximately? This picture looks more like what I would have hoped to see. You are making a cold(-13,5C here at the moment) norwegian happy with such posts. Gives me a glimmer of hope that my range needs can be met in winter time.

Will be very interesting to see the difference in a car preheated using the mobile app as compared to this graph. That is the more likely scenario for me at least. I would never start a long journey in the winter in a cold car given the impact on range this clearly has.

 

[ChadS]

I noted this already, but just to be clear: the 7,500kW is just a rough number based on one quick measurement. It is also meant to be a worst-case number. It is entirely possible that the heater draw could drop over time, for example if a heat-pump gets going. Or you could simply turn it down if it is too effective! The car's insulation does seem to be very good. I doubt many people would see that kind of draw even if it is possible. I'm sure not seeing anything remotely like it. That's why we'd like to see more measurements from real-world examples.

Incidentally though, that 7,500 wasn't just for the heater - Cinergi, you had the A/C on too, right? That may be necessary at the same time to keep condensation off the windscreen. You don't always need both at the same time; but again, we're trying to calculate the worst case.

 

[eledille]

cinergi: It's very good to see that the heater consumption quickly drops, but I still think this is an incredible amount of power for a heat pump, more than 12 times more than the one I have. Do we know whether it has resistive heaters in addition to the HVAC?

ChadS: Ok. I'm really interested to see what happens when temps reach -20 deg C. 2 kW should impact range by about 10%. I hope it's not much more than that.

I would never start a long journey in the winter in a cold car given the impact on range this clearly has.

This doesn't matter much, it seems like it drops back down within a few minutes. But you could just put a heater in there for an hour to save that kWh.

My personal experience is that bad weather doesn't steal all that much range in Norway, and some conditions can often be countered if you're paying attention. The range killers you can't do much about are mountains, low temperatures and wind.

If it's raining, stay out of the ruts - pushing 2 cm of water away eats range, but the upside is that the hills between the ruts are drier than they would have been if the road surface was flat. If it's really pouring, then you should slow down anyway and that offsets some of the increased resistance.

Heavy, falling snow is really bad, but only as long as it hasn't yet been compacted by passing cars. Stay in the tracks. Thick slush is bad and harder to avoid.

We don't have much wind in eastern Norway, I don't think that is going to be much of a problem.

Darkness doesn't matter at all, the motor can gobble up more power than an AC/DC concert, and a few watts for the headlights is completely irrelevant. Another way of looking at it is that the battery has enough energy to power two 50 W bulbs for 35 days.

You can also probably get a fuel powered heater installed. I have one in my EV, and it works really well. I buy about 20-30 liters of diesel for it per year, and I can live with that when the alternative is to burn 1000 liters per year in an ICE.

 

[cinergi]

I noted this already, but just to be clear: the 7,500kW is just a rough number based on one quick measurement. It is also meant to be a worst-case number. It is entirely possible that the heater draw could drop over time, for example if a heat-pump gets going. Or you could simply turn it down if it is too effective! The car's insulation does seem to be very good. I doubt many people would see that kind of draw even if it is possible. I'm sure not seeing anything remotely like it. That's why we'd like to see more measurements from real-world examples.

Incidentally though, that 7,500 wasn't just for the heater - Cinergi, you had the A/C on too, right? That may be necessary at the same time to keep condensation off the windscreen. You don't always need both at the same time; but again, we're trying to calculate the worst case.

The A/C made a negligible additional impact on the power draw (I did let heat run full blast, watched it, and wondered what turning the A/C on would do ... barely noticed a difference). You're not likely to need it if it's REALLY cold out (e.g. 0F) since the (heated) air will be so dry.

- - - Updated - - -

cinergi: It's very good to see that the heater consumption quickly drops, but I still think this is an incredible amount of power for a heat pump, more than 12 times more than the one I have. Do we know whether it has resistive heaters in addition to the HVAC?

My previous apartment - 800 sq ft - had only a heat pump (using the building's pre-conditioned water feed on the other side as opposed to a coil to the open outside air). One a 240/208v 30a circuit. It didn't produce anywhere near as much heat. Guessing its max draw was 5kW (24a * 208v).
No idea what the Model S has. I CAN tell you that if you cycle it off and back on, it takes a while (minute?) to recover -- the air goes cold and slowly comes back to warm; the power used reflects that as well. Which makes me think no resistive heating (that it's protecting the compressor from a fast cycle). *shrug*

 

[darthy001]

My personal experience is that bad weather doesn't steal all that much range in Norway, and some conditions can often be countered if you're paying attention. The range killers you can't do much about are mountains, low temperatures and wind.

Same here. I automatically drive more defensively in winter anyway due to less grip etc so I have never seen a significant rise in average consumption. Last winter I actually had just the same average as my last trip a few weeks ago, and that wintertrip was with a roofrack and box. Of course i probably used 30minutes longer on the trip, but that is expected.

Cant wait to test the car next week here in Oslo and hope the cold weather lasts so I can see som realworld datahere

 

[eledille]

My previous apartment - 800 sq ft - had only a heat pump (using the building's pre-conditioned water feed on the other side as opposed to a coil to the open outside air). One a 240/208v 30a circuit. It didn't produce anywhere near as much heat. Guessing its max draw was 5kW (24a * 208v).

It can't possibly have had that high max draw, that would have produced something like 20 kW, which would have made a 75 m[sup]2[/sup] apartment into a sauna.

I posted about my heat pump here last year. This is the one, MSZ-FD25VA. My house is built to Norwegian standards and well insulated, but it's some thirty years old, so not that well insulated. It's a little over 100 m[sup]2[/sup] and the heat pump does most of the heating even at a 45 °C temperature differential - with 0.6 kW max draw.

I completely agree that cars need incredible amounts of heating compared to a house, but at 0 °C, 7.5 kW input should today produce at least 30 kW of heat, and that is far and away too much. I don't think it's possible to fit a 7.5 kW compressor in a car either, that's a pretty hefty chunk of hardware:

No idea what the Model S has. I CAN tell you that if you cycle it off and back on, it takes a while (minute?) to recover -- the air goes cold and slowly comes back to warm; the power used reflects that as well. Which makes me think no resistive heating (that it's protecting the compressor from a fast cycle). *shrug*

Agree that points to heat pump only, but the incredibly high startup spike puzzles me. I think they must have done something clever to kickstart the heater. I'm just curious, I actually think that would be a good idea. The startup spike doesn't really matter as long as average power is low.

 

[cinergi]

FWIW, it'll stay at 7.5 kW as long as it's running full-blast. The taper-off only happens as output is reduced.

 

[RDoc]

The heating system could be heat pump plus resistance, perhaps with a de-humidifying circuit in the cabin to dry out the air for the windshield de-fogger. The 7.5 kw would be the resistance heater plus the heat pump, but once the cabin was up to temp, the resistance shuts off and the heat pump maintains it. As the temp drops there's going to be more heat loss so the duty cycle of the heat pump will increase. The dehumidify function wouldn't add much since the only load is condensing the moisture.

Using cinergi's number of 1 kw at 32F and a bunch of other guesses for increased drag and increased heater load as the temp drops, my estimate is that for highway speeds you'd need to slow down by about 1 mph for every 7 degrees drop from 70F to maintain range. So roughly 5-6 mph for 32F and 10 mph for 0F. At lower speeds, it's much worse as the watts/mi from the heater goes up. As always, YMMV :wink:

This all still seems to me to point to heated rear seats as a very good potential option for cold climates.

 

[eledille]

FWIW, it'll stay at 7.5 kW as long as it's running full-blast. The taper-off only happens as output is reduced.

OK, thanks. Like RDoc, I'm guessing heat pump plus resistance. That seems like a good choice for quickly warming the car up, but still having high efficiency on average. But it doesn't explain why it needs time to recover from a cycle. Hmm.

 

[TonyWilliams]

Higher air density probably has a much higher affect on us drivers in the USA as it sounds like our average speeds are much higher.

Just to clear up any confusion, the air density has nothing to do with USA drivers going faster or slower. Air density is a factor of air pressure, elevation, and air temperature, and to a far lesser degree, humidity. That is the same anywhere on planet earth.

The issue you are referencing is aerodynamic DRAG. Higher speeds produced exponentially more drag. However, decreased air density at a high elevation, hot ambient temperature, high humidity, low pressure location (Salt Lake City in August just before a huge thunderstorm) will have significantly reduced drag at the same speed.

That same speed in Norway at sea level on a really cold, high pressure day will have far greater drag than your USA driver in Salt Lake.

Hope this helps.

 

[darthy001]

New(?) range-tool on teslamotors.com is quite interesting:

20miles of difference in range when choosing night-time with lights. But still within my needs here. Getting even more curious on real-world tests now.

 

[SteveH]

I with the speed dial went a bit higher. Plenty of roads around here with higher speed limits and I'd like to see how steep the range drop is going from say 70 to 80 mph.

 

[eledille]

That same speed in Norway at sea level on a really cold, high pressure day will have far greater drag than your USA driver in Salt Lake.

Plugging in some extreme, but not off-the-scale values (960 hPa, 30 °C vs. 1050 hPa, -20 °C) into this air density calculator I get a difference of 32% - much more than I would have guessed. The difference between +20 and -20 °C alone is 16%!

20miles of difference in range when choosing night-time with lights. But still within my needs here. Getting even more curious on real-world tests now.

I get 1 mile difference.

 

[mnx]

Can someone post a link to the range calculator? I can't seem to find it on the website...

 

[darthy001]

Plugging in some extreme, but not off-the-scale values (960 hPa, 30 °C vs. 1050 hPa, -20 °C) into this air density calculator I get a difference of 32% - much more than I would have guessed. The difference between +20 and -20 °C alone is 16%!


I get 1 mile difference.

Get the same now, but if you look at my screenshots I originally might have clicked 21" rims on the night-mode didn't notice that it actually changed the range. If correct this tool is great and it would seem that my concerns aren't valid!

 

[eledille]

Can someone post a link to the range calculator? I can't seem to find it on the website...

Your Questions Answered | Tesla Motors

 

[clea]

Can someone post a link to the range calculator? I can't seem to find it on the website...

it is not available in the Canadian pages you must switch to be from the US to see it.

 

[RDoc]

Plugging in some extreme, but not off-the-scale values (960 hPa, 30 °C vs. 1050 hPa, -20 °C) into this air density calculator I get a difference of 32% - much more than I would have guessed. The difference between +20 and -20 °C alone is 16%!

That's true, but keep in mind that not all the loss is from drag. At 65 mph the drag is about 60% of the total resistance so the range difference due to air density is about 10%.

Using some guesses and cinergi's heater number my very rough estimate is that at 65 mph going from 70F to -4F there's about a 30 wh/mi difference due to air density and only slightly less due to the heater. Don't take these numbers too seriously though.