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Effects of Winter on Energy Consumption

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seanmccutchan

Member
Jul 8, 2013
59
8
Glastonbury, CT
#1
Hello again fellow New Englanders! With the polar vortex visiting us more frequently now, I was a little surprised by just how much the energy seems to go into heating the car on short trips. I wanted to quantify this a bit with the goal of hopefully identifying some improvements. Green car reports noted that the average U.S. automobile trip length is just 6 miles, hence the focus of this study is not on vehicle range but typical energy usage in winter climate.

I ran a little designed experiment (DOE for stats fans) to study the effects of ambient temperature, pre-heating, pre-charging, and climate control on a typical short trip. I wanted to share the results in this smaller audience, and see if anyone is seeing drastically different behavior and collect your feedback.

Some comments before getting to the results:
-We have a MS60, so I expect the thermal energy required to heat the battery may be somewhat less than the MS85.
-The study varied from 4.5-9 mile trips after the vehicle was at rest for more than 4 hours.
-The trips were all on very flat terrain (no more than 40ft elevation change), with speeds less than 40mph as I didn't want drag to be much of a factor.
-I did not put the vehicle settings in "range mode" which has been reported to disable the active battery heating. Honestly, the climate control is too weak in this setting for the general public (e.g. my family members) in extreme weather.
-Anytime climate control was used, interior temperature was set to 70F.

Some general conclusions:
-Initial temperature is a huge effect. Every 10 degree F was worth 60 Wh/mile.
-Turning climate off seems to also disable the battery heating and save copious amounts of energy so long as you can stand the cold.
-Battery pre-warming via charging at 40amps did not show a significant reduction trip Wh/mile (perhaps the MS only heats the battery to ~30F for charging?)
-Preheating the interior saved an additional 111 wH/mile (although this energy is still coming from the wall).
-Energy used in heating the battery plus interior can exceed 2.2kWh for a 6 mile trip at 20F (equivalent to driving an additional 8 miles).
-I'm not hearing a heat pump running, and some rough calculations suggest that resistance heaters could be providing all of the heat.

The 3 factor linear regression equation resulting from the experiment is shown in blue text below. Climate and pre-heat are set to either 0 or 1 for calculating their effect. Whether the vehicle was charging or not did not prior to departure did not show a significant effect and was dropped from the model.

And here is the data collected over the last few weeks, with a linear regression model included.
Screen Shot 2014-01-23 at 10.35.00 PM.png

Screen Shot 2014-01-23 at 11.21.53 PM.png

Screen Shot 2014-01-23 at 10.35.53 PM.png


Regards,
Sean
 
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#4
I find that Eco mode aka Range with a manual override on the fan is best for short hauls. In the 3 miles to my office, I might get a tiny bit of regen, at huge cost in energy.


I'm surprised that you report no benefit from pre-charging. If I've been charging for 30 min or so, I'm usually at 30 kW regen, which seems to be the max you can get from charging alone.
 
#5
Agree Robert, range mode seems to be the best option right now for reducing winter Whm. As stated in your other post, the climate control and battery warming should be separate options. I'll try to add another regression factor for range mode. That said, eco hvac doesn't cut it without pre-heating the cabin.

Pre-heating the battery via charging didn't live up to my hopes for reducing wH/m. Since publishing the DOE, I tried another pre-charging at 40amps for at least 1/2 hr, and saw the power consumption (568 Wh/m) match the regression equation very well (576 wH/m). I'd be curious what difference you find in consumption. Since the cold stuck around late last week, I added points 10 and 11...
Screen Shot 2014-01-26 at 6.24.03 PM.png
 
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#6
Added a few points with Range Mode (EcoMode HVAC) at Roberts suggestion. Looks like about 100 Wh/mile benefit for the two points I collected (27-28F). In this setting, I did find that after 25 minutes of heating at my work parking lot (no plug), interior temperature increased only from 40F to 55F and I used 4 miles of rated range (not a great use of 1.2kWh). So, I counted that trip as a 1/2 preheat. I don't find Range mode that useful unless you can pre-heat on the grid. And, it could be a cause of annoyance when I swap rides with my wife :smile:
Screen Shot 2014-01-28 at 8.13.53 AM.png

Screen Shot 2014-01-28 at 8.09.55 AM.png
 
#8
#12
Great story! I'm looking forward to my first winter and longer trips like that as well. I'm sure it there will be some fun and not so fun driving experiences this winter.

The only part I didn't like is the one with heater off for a while, that seems like a huge inconvenience for longer trips, especially if you have passengers. I've found that the heating system in the Model S is at best mediocre, considering the rest of the components in the car, even at 50 degree weather, as soon as I turn the heat on HI (only setting that actually blows hot air) my consumption jumps up 30-50wh/m, which leads me to believe it's a 3-4kW heating system.

I have little experience of course, so take my observations with a grain of salt. I've contacted Tesla in Watertown already about the heating issue in my car and was told to use the heating on HI(as the system they said isn't so good) and that they will pull up my logs to see if there are any anomalies there, since I can't seem to "make" the car push hot air on 70+ settings, when outside temperature is 45-50 degrees. It's been a week and they haven't contacted me, so I would assume there aren't any abnormalities.
 
#13
Robert.Boston said:
Cottonwood's write-up is great. Note, though, that he was driving in the Rockies. As he states, the thinner air reduces aero drag losses. We're 5000' lower in the atmosphere and will see worse Wh/mi as a consequence.
Click to expand...

Actually, my lowest altitude on that drive was about 7,000 feet, 2,100 meters, MSL, most of the drive was higher than that, up to over 11k at Fremont Pass. Those altitudes reduce aerodynamic drag by 20% or more, as well as thermal conductivity to the low temperature air outside, a big advantage.
 
#14
I found that during the major "arctic blast" last winter I was dropping by about 20% of range with the heat set to 66f and on range mode (for AC, though also with a range charge). My ride from my home in southwestern, CT to my second home in VT (Stratton) got very dicey at 185 miles. I did a range anxiety charge in Northampton, MA when it was really cold. The charger at the fire department is across from an all you can eat Chinese place that my kids loved! There are others as well, but that was my preferred option.

With the superchargers going in West Hartford and West Springfield it opens up a large area of ski-country. That said, if you don't have decent destination charging options you may be in for a stressful and long ride home. I have an uninsulated garage in VT, and due to wiring was only able to put in a NEMA 14-30 where I can only pull 24amps. My charge rate was effectively halved due to the extreme cold - below 10f. I ended up putting an electric space heater in the garage and that seemed to help. The vampire loss was also pretty bad. There have been several updates to the software since then, so my hope is those are now moot points. Still, it was not a fun thing to wake up with half the added range you anticipated!

As for driving without the heat on, my car predates the winter package, and my kids were in the back seat, so that wasn't tenable for us. I do agree that a 5mph reduction in speed will go a long way to keeping the range up, but it also goes a long way to your kids kicking a hole in the back of the driver's seat due to the extended drive time. The PlugShare integration makes planning stops really easy. Save them on the app or desktop site and then log in from the car and find a good bathroom / food stop. I did a run up to Augusta, ME in June and was able to have a nice meal and add 20 miles or so while we ate. In the end I didn't need it (barely), but in winter I certainly would have!



My final winter advice (two winters under my belt already) is snow tires. You want them. The car is passable in snow with all seasons, but the snow tires really helped.
 
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#15
Mike - Thanks for the write-up. I too live in southwestern, CT and have a second home in VT (Mount Snow.) My drive from Stamford to VT is 182 miles. I picked up the car in Mid-Sept so I haven't yet done the trip. My intention is to install a NEMA 14-50 plug at my VT home so I don't have to worry about stopping on the way up and will have a full charge for the ride home. That said, I am thrilled about West Hartford and West Springfield as they provide options for charging if needed for any reason.

I have also been thinking about the need for snow tires and will probably take your advice and get them.
 
#16
@Shelbri, if you need a VT based electrician PM me and I'll send you who I used. Decent guy, did good work.

As for snows, yeah, get them.

I have chains as well, as my driveway is utter crap. I generally won't take the Model S if there is snow in the forecast, but you never know what will happen. The time I did get stuck I was able to get out with pushing and grunting and criticism from my wife, and since then have kept them in the car during winter.
 
#19
You have to laugh a bit at how in a thread titled "energy consumption" we wandered to range, snow tires, superchargers, electricians.

Seriously though, anyone see improvements over my numbers from this winter? My study was last winter, and I'm curious if software or hardware updates have made any improvements.
 
#20
Sean,

I don't have the detailed information you provided but I can provide a little that suggests my numbers are in line with yours. I have been in VT since Christmas. This morning the temperature was 13F when I left to drop my son off at the mountain. I preheated the car for about 10 minutes while she was still plugged in so I assume this means the energy for preheat was from the house and not the battery.

Anyway - when I got in the car, both screens had a warning indicating that the regenerative braking was disabled. I presumed this was due to the cold and the need for the battery to warm up first. Very odd going back to a car that coasts down a hill after driving with standard regen for the past 3+ months. This heavy car has quite a bit of momentum for coasting with regen off.

After 2 miles into the drive, my consumed wh/mi was about 1,200. Regen came back on about 4 miles into the ride but at very low kWh. Just below the 0 line. After completing the ~12 miles round trip my wh/mi since last charge had dropped to around 500. Well above my normal consumption but not surprising given the cold and the fact that my heater was on.
 
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