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Discussion Starter #1 (Edited)
I know there are lots of posts and polls for range but I would like to know if anyone has a good answer for the significant difference in the kWh/mi or kWh/km.

In cold weather I was getting 230 Wh/km and now I'm getting 130 Wh/km. That's huge!

The tire pressure has gone up (10%) due to the warm weather but surely there is a better reason for the difference. Air density cannot be that significant, especially at low city speeds.

There must be some other loss in the system that is not accounted for in the driving/climate/other percentages which effects the driving energy and is temperature related.

Is the battery heating part of "driving %" instead of "other %" for example?

Curious minds want to know!

From the manual...
The Energy Details screen displays how energy is being used since the last time the high voltage battery was fully charged. It includes Driving and Accessories, Climate Settings, and Battery Conditioning. The circle graph displays
these percentages. The total energy used displays at the bottom of the screen.
Screen shot 2016-05-20 at 11.11.03 PM.jpg
The manual seems to indicate that battery conditioning is under "Other". I guess the question is what accessories are using significant power when it's cold which does NOT include climate settings or battery conditioning?
 

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In addition to battery heating (and overall efficiency differences between cold and warm weather which are applicable to all cars) cabin heating is the other big reason for increased KwH usage in cold weather. I've driven Volts through four Colorado winters. I always drive with the climate set at Auto, Comfort (which is "Max" on my 2016) 68 degrees in winter and 70 degrees in summer. For the 2012-2015 Volts I would get around 4.4 miles per KwH in Summer and down to 3.8 in winter. The 2016 is more efficient. I'm now getting 5.1 miles per KwH and was getting 4.4 in winter.
 

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The resistive heater uses much more battery power than the air conditioner. You only have the one big battery providing power for both traction and comfort.
 

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To elaborate on that article: Yes, cold temperatures degrade battery performance - but that's not the direct cause of poor range in cold weather. Degraded battery performance is why the battery has to be heated. GM did a good job of insulating the battery very well, but obviously, the colder it is, the more energy is required to heat the battery (and cabin). Which is why range gets worse as the temperature declines.

I'm actually still surprised by the range difference in cold vs warm weather. Here in NY, on the coldest days I was sometimes barely getting 40 miles of EV range - in fact, I think it was down at 36. That was with "Eco" mode heat at 74 and ambient temperatures just above the threshold for ERDTT (15 degrees F). Today, the first 75 degree day, I'm on track for a 69 mile range - nearly DOUBLE the worst range I got in winter.
 

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In cold weather I was getting 230 Wh/km and now I'm getting 130 Wh/km. That's huge!
Sounds about right.

Cabin heating, plus damp road surfaces. When the sun is out on a cold day but has baked the road completely dry you might have noticed you mileage shoot up. A damp road can account for 10~20%. It is shocking the scale of the impact, but bear in mind everything else has been totally optimised, transmission, aerodynamics, etc.. There's very little else to improve on, so when something comes along with a significant impact then it can have a very large, disproportionate effect.

Bear in mind something else with the Volt - don't hold me to this but I think this is what I saw someone else's data from MGV app - the battery coolant will be heated up to ~9C when it is plugged in on charge, but once you are driving it'll then heat the battery coolant up more. Very frustrating it doesn't draw on the domestic supply to get the battery pack up in temperature. This can account for a sudden 0.5~0.8kWh loss in the first few miles, it seems, which obviously hits the energy economy hard especially if you are doing short journeys.
 

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Discussion Starter #7
Lots of people are replying with cabin heating and battery capacity. I'm looking for an explanation of driving energy. I'm getting ~14 kWh usable capacity cold or warm. I would expect the battery heating to be filed under "Other" in the cold so I'm hoping someone can explain where the difference is coming from. I can't believe there is almost 100% change in driving efficiency from the power train due to temperature so some other power loss has not been mentioned. Maybe it is battery heating! Can someone confirm?
 

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Lots of people are replying with cabin heating and battery capacity. I'm looking for an explanation of driving energy. I'm getting ~14 kWh usable capacity cold or warm. I would expect the battery heating to be filed under "Other" in the cold so I'm hoping someone can explain where the difference is coming from. I can't believe there is almost 100% change in driving efficiency from the power train due to temperature so some other power loss has not been mentioned. Maybe it is battery heating! Can someone confirm?
Ottawa has variations in conditions about as extreme as any of our forum members see. The results you are getting don't surprise me.

I think you are misunderstanding or underestimating the energy cost of keeping us comfortable in the winter. Of that 14kWh quite a bit does go to warming the cabin (as opposed to the battery). In an ICE car or ERDTT mode this is done by recovering waste heat from the engine. In an EV, or in EV mode, this energy can only come from the battery and there are not any very efficient ways of converting it to heat.

Then, of course, there are all the other draws brought on by the cold, common to any car. Think about the fuel mileage hit you are used to in the winter, and then add in extra for electric cabin heating.
 

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Discussion Starter #9
Ottawa has variations in conditions about as extreme as any of our forum members see. The results you are getting don't surprise me.

I think you are misunderstanding or underestimating the energy cost of keeping us comfortable in the winter. Of that 14kWh quite a bit does go to warming the cabin (as opposed to the battery). In an ICE car or ERDTT mode this is done by recovering waste heat from the engine. In an EV, or in EV mode, this energy can only come from the battery and there are not any very efficient ways of converting it to heat.

Then, of course, there are all the other draws brought on by the cold, common to any car. Think about the fuel mileage hit you are used to in the winter, and then add in extra for electric cabin heating.
The car displays the percentage used for driving / heating / other so the math is quite simple to figure driving Wh/km. It seems that the driving percentage includes something other than just driving. This is what I'm trying to determine. My only guess is that additional battery heating is significant after unplugging and included in "driving" and not "other".
 

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I'm puzzled by your reference to "driving/climate/other". In the end, there is one battery with a specific capacity - 14 kWh in your case. That has to supply all consumers - motive power, battery and cabin heating, parasitic losses. When you compute the kWh/km, you have simplified all the variables into one. So if the heating and parasitic consumption goes up (as it does in cold weather), your kWh/km will rise correspondingly. Electric heat is expensive in every sense. Your experience is typical. So the simple answer to your question is "yes" - everything is part of the "driving %".
 

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The car displays the percentage used for driving / heating / other so the math is quite simple to figure driving Wh/km. It seems that the driving percentage includes something other than just driving. This is what I'm trying to determine. My only guess is that additional battery heating is significant after unplugging and included in "driving" and not "other".
I didn't know you could break down your usage that way. Still, a winter/summer ratio of 230/130, overall, is more or less in line with what I've seen over the past four winters in the slightly milder GTA climate.
 

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Discussion Starter #12 (Edited)
I'm puzzled by your reference to "driving/climate/other". In the end, there is one battery with a specific capacity - 14 kWh in your case. That has to supply all consumers - motive power, battery and cabin heating, parasitic losses. When you compute the kWh/km, you have simplified all the variables into one. So if the heating and parasitic consumption goes up (as it does in cold weather), your kWh/km will rise correspondingly. Electric heat is expensive in every sense. Your experience is typical. So the simple answer to your question is "yes" - everything is part of the "driving %".
From the manual...
The Energy Details screen displays how energy is being used since the last time the high voltage battery was fully charged. It includes Driving and Accessories, Climate Settings, and Battery Conditioning. The circle graph displays
these percentages. The total energy used displays at the bottom of the screen.
Screen shot 2016-05-20 at 11.11.03 PM.jpg
The manual seems to indicate that battery conditioning is under "Other". I guess the question is what accessories are using significant power when it's cold which does NOT include climate settings or battery conditioning.
 

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You should take into consideration the fact that on colder weather, the tire pressure also goes down --> a greater "print" surface on the road --> more power needed to move forward --> more battery used to travel the same amount of miles. This and all the other little things like:
- battery conditioning
- warming the cabin
- denser air resistance
- road surface friction coefficient going down
- stiffer tires surface
- etc.
 

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You should take into consideration the fact that on colder weather, the tire pressure also goes down
Not if you keep the tires properly inflated. When I do my monthly once-over of my car I find I have to add air during the fall months and release it through the spring so as to maintain the target pressure.
 

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I have experimented with tyre pressures extensively, and it is bogus. It makes no difference you would be able to tell.

LRR tyres work by having more elastic side-walls. (A side-effect is they tend to be weaker and more prone to side-wall blowout initiated from side damage - DON'T drive up kerbs with LRR!!!) It is part of the design that these flex, whereas in a conventional tyre you get more losses if the side-wall flexes.

It's nonsense. Leave your tyre pressures where they give you the best ride.

... If anyone has EVIDENCE to the contrary, not anecdote, then I'd be happy to see it.
 

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You keep going back to pictures from the owners manual... where are the pictures from your car in winter and summer? Without those we can't tell you where your power went.

Interesting mind F for you! The faster you drive in winter the less affect cabin heating has on your range... cabin heating is fairly constant per unit time.... weather the car is sitting in your drive way or driving 80 mph it will still use the same KW per hour of energy on cabin heating. My car being a 2011 doesn't have a power usage display, so I can't give you accurate numbers and I don't want to make up some SWAG numbers on the issue :)

My personal experience in my 2011 is that summer range on non-lrr all season tires on my typical drive to work and back round trip was 28 miles and I had 12 miles of range left... so 40 miles range at the speeds I drive on my commute. In winter on non-lrr snow tires following the same route using just seat heaters and freezing I could barely make the drive all electric. If I wanted to be comfortable and be able to see out of my windows I would do about 24 miles on electric and 4 miles on gas for my commute.
Translated into percentages, added drag from higher air density, thicker fluid in the planetary gearset, thicker wheel bearing grease, stiffer sidewalls on tires, stiffer tread on tires, battery heating, damp roads, all together dropped my range to 70% of its summer time high. Add in some heater use to avoid hypothermia and death and you get down to 60% of summer time range.

Keith

PS: This is why people in California don't really "get" the desire for 200 mile BEV's.... for California the new Leaf with around 120 miles range is fine... for those of us with this thing called "Winter" we need a 200 mile BEV to get 120 miles of range for around a quarter of our year.
 

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So using the example in your manual screenshot, if only 93% of the battery capacity was used for motive power, ie "driving %"; then your traction battery capacity is effectively 14*.93=13 kWh. No matter what the weather conditions are, that will not take you as far as 14 kWh. In cold weather your "driving %" will be much lower because "heating %", in particular, will be much higher. In the end, at -20c, you're looking at something like 14*.6=8.4 kWh battery capacity available for "driving %". That's right in line with your results.
 

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Discussion Starter #19
So using the example in your manual screenshot, if only 93% of the battery capacity was used for motive power, ie "driving %"; then your traction battery capacity is effectively 14*.93=13 kWh. No matter what the weather conditions are, that will not take you as far as 14 kWh. In cold weather your "driving %" will be much lower because "heating %", in particular, will be much higher. In the end, at -20c, you're looking at something like 14*.6=8.4 kWh battery capacity available for "driving %". That's right in line with your results.

The units of Wh/km or Wh/mi is independent of range or capacity. The question is why does the driving Wh/km seem higher in the winter since the change appears more significant than air density and tire pressure should contribute.

Maybe the thicker oil in the planetary gears?

You keep going back to pictures from the owners manual... where are the pictures from your car in winter and summer? Without those we can't tell you where your power went.
I've actually been recording some of the data when I charge at night. This is not controlled test data so average speed and the resolution of the percentage (quantization) can cause some error but the conditions are largely similar. My ERDDT was at -10C so I'm not posting trips when ERDTT was active.

Screen Shot 2016-05-21 at 10.09.48 AM.jpg

Really some controlled tests and multiple readings for averages would be best but this is what I have to work with and from my observation something significant is missing which effects our driving efficiency. Curious minds want to know!
 

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I have experimented with tyre pressures extensively, and it is bogus. It makes no difference you would be able to tell.

LRR tyres work by having more elastic side-walls. (A side-effect is they tend to be weaker and more prone to side-wall blowout initiated from side damage - DON'T drive up kerbs with LRR!!!) It is part of the design that these flex, whereas in a conventional tyre you get more losses if the side-wall flexes.

It's nonsense. Leave your tyre pressures where they give you the best ride.

... If anyone has EVIDENCE to the contrary, not anecdote, then I'd be happy to see it.
Does anyone else hear echoes of the "*olting" donnybrook? You're challenging time-honoured conventional wisdom. It's going to take a carefully designed and executed experiment to refute it.

My non-researched assumption is that LRR tires (Tyres if you want, I was English educated too) compensate for the lighter sidewalls by running at increased pressures. Lower pressures inevitably increase the contact patch area, with extra deformation of the sidewall and the tread. It takes energy to overcome that distortion.

The OP says he has controlled for pressure anyway. He is apparently running the same tires winter and summer, which in Ottawa could be a temperature variation of 70 Celsius degrees. If anything I'd expect the tires to be almost solid in the winter and have less rolling resistance. They certainly would have less traction but that's another discussion.
 
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