Cold weather observations

We've recently had temperatures down between -20 to -28 C (-4 F to -18F). We still have the Ecopia tires on with the air pressure set at 40 psi. Our LEAF is kept in an attached garage which stays around 0 C, so that is our normal battery temperature. Of course our range has decreased, quite a bit, from summer highs.

Observation 1:

I'd read a thread here on the forum where a member had installed heating pads on the bottom of his battery to keep it warm, and had noticed that his range was near to his summer normal. I thought I might do the same, but I was held back by the cost of these heating pads. Before spending a lot of money, I thought I'd experiment a bit first. We have a heated workshop, so I turned up the heat to +20 C and parked the car in it overnight for a few nights. (I wired up another NEMA 14-50 plug in the workshop so I could charge there) What I noticed after a few days of commuting is that there was no difference in range whether the batteries were at 0 C or +20 C. Travelling at 100 km/h in -20 C air the energy usage gauge shows that we were using 22-25 kW in both cases (which only makes sense, really, as the air was the same even though the battery was warmer). In +20 C air, it only takes 15-17 kW to travel 100 km/h.

To sum up, winter range reduction was not affected by raising battery temperature to near summer norms. Therefore, the major factor reducing range is the density of the air that you have to push through at -20 C. So, don't spend money on battery heaters.

I should add that our round trip commute is 80 kilometres (50 miles), which is 55 kilometres at 100 km/h and 25 km in city traffic. This means that denser air at highway speeds has more of an impact on our commute than if we were only driving in the city.

Observation 2:

When the weather got colder I would turn up the fan speed to try to keep th interior warm. The energy usage gauge for the HVAC showed that it would consume as much as 4.5 kW with the fan on the highest speed at -26 C. I've found by experimenting that keeping the fan speed at the second lowest setting felt just as warm (less cool air moving around the car) and the energy used dropped down to between 1.5 an 2 kW at the same outside temperature. For our 1.5 hour round trip, this 2 kW reduction means an extra 3 kWh left in the battery to move the car.

So, only use as much fan speed as required because pushing more air through the heater just uses more energy heating that extra air without keeping you noticeably warmer.

People doing electric conversions here in Manitoba typically install 8 kW of heating to keep the cold at bay. If the LEAF had that much, I'd be toasty warm, but I might not make it home.

I'd be interested in other people's experiments and observations for survival in these very cold temperatures.

Bill

BillR said:

So, only use as much fan speed as required because pushing more air through the heater just uses more energy heating that extra air without keeping you noticeably warmer.

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I think it's more a matter of the rate at which warm air is being pushed out of the car and being replaced by intake of fresh (cold) outside air which then has to be heated. Fan speed is one of the things the Auto setting attempts to manage.

Nubo said:

BillR said:

So, only use as much fan speed as required because pushing more air through the heater just uses more energy heating that extra air without keeping you noticeably warmer.

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I think it's more a matter of the rate at which warm air is being pushed out of the car and being replaced by intake of fresh (cold) outside air which then has to be heated. Fan speed is one of the things the Auto setting attempts to manage.

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Like most of us, I don't think the OP is using the Auto setting. It's too dramatic and busy, blasting air one moment and redirecting it the nest. And yes, lots of people have noticed that setting the blower to Low or the next lowest setting seems to be optimum for energy savings. The reason the main factor isn't the air exchange rate is that the air in the whole car is always pretty cold in Winter, so moving more volume through the HVAV unit means it has to work harder to keep that air warm. Even if the car were airtight, radiational cooling would make the interior air cold overall.

LeftieBiker said:

...yes, lots of people have noticed that setting the blower to Low or the next lowest setting seems to be optimum for energy savings. The reason the main factor isn't the air exchange rate is that the air in the whole car is always pretty cold in Winter, so moving more volume through the HVAV unit means it has to work harder to keep that air warm. Even if the car were airtight, radiational cooling would make the interior air cold overall.

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If the car were completely airtight, the fan speed would have little impact on energy use as long as it was high enough to allow the cabin to reach the desired setpoint. Heating a smaller volume of air to a higher vent-temp vs. heating a larger volume to a lower vent-temp... if the cabin temp is the same in both cases, it's basically a wash. Uses the same amount of heat energy.

Admittedly, the higher air flow would result in some additional thermal losses by eliminating boundary-layer effects near the windows and allowing more warm air to contact the cold glass. But by far the bigger factor is the amount of heat energy simply being blown outside.

When the fan is pulling in outside air, an equivalent amount of heated cabin air is being blown out of the car. I think a lot of folks don't realize how much air is being blown outside all of the time. It's worse than having a small window open. It's like having two small windows open, with a fan in one of them! You don't notice it so much because that cold incoming air is going straight through the heater before it gets into the cabin. Consuming gobs of energy as it does so.

Yes it is a lot of "fresh" air that has to get heated from ambient outside, 15F or -10C to 80F or 26C to feel warm. Then if the cabin is warm that same amount of warm air you just heated up is leaking out the back

The flip side is you need this fresh air. If I switch to recirculate the windows start to fog in a few minutes and start to ice over on the inside and then there is no keeping up with it so I have to leave recirculate off to keep the windows clear. With just me in the car I can typically leave the heat on the lowest fan setting set for 80F and at my feet. With the kids in the car I have to switch to the split, foot and windshield or just windshield depending on how cold it is and how wet they are after swim practice.

ECO mode reduces heating, no? Try no-ECO and D mode to see if heating improves.

Last winter when it was -15 celcius i tried recirculate and medium to high fan speed with good result(almost no fogging and half energy consumption vs fresh air)
It takes 5-10min before the heater consumptions lowers.
Works best on highway.

I find it funny that everyone that has posted a comment on this topic is about the fan speed. No one has commented about the heat pads on the battery. This is the part of the article that I find quite hard to swallow. I understand that this is his observations and all, but I guess I would have to test this theory for myself in order to believe it. We all know that a warm battery can hold more power than a cold battery so in theory you should have better range with a warm battery than a cold one. I know cold air is thicker and therefore harder to cut through the air, but I just don't buy that it's that much thicker to reduce the range so much that a warm battery is not of benefit. Without actually doing this test myself (which I'm not going to since my car goes back in two months) I call heating the battery not helping with range total bluff. My opinion.

CRLeafSL said:

I find it funny that everyone that has posted a comment on this topic is about the fan speed. No one has commented about the heat pads on the battery. This is the part of the article that I find quite hard to swallow. I understand that this is his observations and all, but I guess I would have to test this theory for myself in order to believe it. We all know that a warm battery can hold more power than a cold battery so in theory you should have better range with a warm battery than a cold one. I know cold air is thicker and therefore harder to cut through the air, but I just don't buy that it's that much thicker to reduce the range so much that a warm battery is not of benefit. Without actually doing this test myself (which I'm not going to since my car goes back in two months) I call heating the battery not helping with range total bluff. My opinion.

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I did find this part of your experiment interesting. One question I have is whether you monitored the battery temperature throughout the commute. If the battery temperature dropped quickly to ambient levels during the commute then the benefit of pre-heating the battery would be minimal.

Honestly I don't have any real data to go on, but based on a lot of anecdotal experience if the battery temperature gauge shows two bars or lower I do experience a noticeable reduction in range even if the heater is off and at lower speeds (factoring out air resistance). So I think it has *some* impact but I can't quantify how much.

I started messing with this as well. Our attached insulated garage does't get below freezing even when it's -10F or -23C. When I leave home to go to work and back the trip is almost the same and I have been keeping track of my summer kW/mile and even though I start out at 35F and come home after sitting 12 hours at 5F the mile per kwh is about the same. I know some of my drop is the snow tires. Yet the trip on the way there right after charging, 4 bars on the dash and coming home, 2 bars on the dash is almost identical. So I don't think warming the batteries is going to help. Now this might not be true when it starts to get colder, but I will keep track and see.

When having your car in the garage at 20C, did you check your battery temp in the morning? If it was starting at -20C, it might not have completely warmed during the night. Think of how long it takes for a big block of ice to melt.

I would also cover the front grill (on top of the pads). you want to stop the air cooling of the battery when its cold out. That will quickly take your battery temp back down when you leave.

Get Leaf Pro to watch your battery temp while you drive. The battery temp (not outside air temp) is the biggest factor in my experience.

DougWantsALeaf said:

When having your car in the garage at 20C, did you check your battery temp in the morning? If it was starting at -20C, it might not have completely warmed during the night. Think of how long it takes for a big block of ice to melt.

I would also cover the front grill (on top of the pads). you want to stop the air cooling of the battery when its cold out. That will quickly take your battery temp back down when you leave.

Get Leaf Pro to watch your battery temp while you drive. The battery temp (not outside air temp) is the biggest factor in my experience.

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I do have the grill blocked. I hadn't thought of actually looking at the pack temp in Leaf Pro, I have that so I will take a look when I get home and again when I leave. I would assume some of the warming is charging right before I leave as well.

often wondered what the trade offs would be to make all the glass in the LEAF heated? seems to be a much smaller energy footprint and I think could contribute significantly to less defrost usage and less cold transfer from the outside thru the glass

My cold weather observation is that using the charging timer to finish charging just before leaving results in better efficiency than charging the day before. I assume this is because the battery has been warmed by 2-3 hours of charging. I have a 20 minute, 10 mile rural/city commute so it may not have the same effect for longer and/or highway trips.

I've been collecting daily data for my commute for the last few months now and have really watched the HVAC energy consumption with interest as the temperatures dropped through the fall. I don't have time to dig out numbers right now, so will only put out my anecdotal thoughts and values.

First, I agree that having the charge end right before the drive starts does allow for a small amount more energy to be available for the trip, but it doesn't seem to impact efficiency, only available range.

Second, I have come to the same conclusion regarding fan speed; after some experimentation, I now run it at the lowest speed (which is usually sufficient for just me). I also only set the heat to 18C and just use the heated seat and steering wheel. I was trained to drive wearing a winter coat, boots, glove and toque, so this heat setting is more than sufficient for me (if you go off the highway in the winter and are stuck for a few hours in the car [literally stuck, as in pinned by the steering wheel or something], you don't want to be in a t-shirt!)

Third, I've tried running the fan in recirculation mode with mixed results. Yes the energy draw is lower (I recall about 1/2 to 2/3rds consumption of using fresh air); however, it is almost averaged out by needing to turn it to fresh-air periodically. YMMV of course, depending on the RH in the car, outside and temperature. The big annoyance with this idea is that you can't do this on defrost mode, only on foot/vent mode! It would work much better if you could run it on defrost.

Fourth, when we had -10C for a few days, I drove with ONLY the fan on, just enough to keep the window clear. I did not preheat the car, and only used the heated seat and steering wheel. By the end of the drive I was getting a bit chilled, but managed ok. Amazingly my efficiency was very similar to that of my early fall commute (within a few %), when I also didn't use any AC or heat (+15-20C). My Nokian R2's must be pretty good in the rolling resistance department!

Finally, for my area and typical moist rainy/snowy winter, I am finding that:
- at about +1 to 3 C, I use about 250W
- for 0 to -2 C, it nudges up to 500W
- for -2 to -5C, around 750W
- somewhere after this point it starts to steepen dramatically, by -10C I am using 1.25 - 1.5 kW

achewt said:

I agree that having the charge end right before the drive starts does allow for a small amount more energy to be available for the trip, but it doesn't seem to impact efficiency, only available range.

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I think many are thinking about this question the wrong way, and the above quote sums it up well. Nobody is claiming that a warmer battery would make your car more efficient. The claim is that it can hold more energy. Your miles / kWh will not be affected, but if the battery holds more kWh, you can travel more miles. This is the claim.

Given the poor quality of Nissan's sensors, I just don't trust the dash readings or Car Wings to answer this question. I feel that you would need to do an actual range test. For example, drive with a cold battery to LBW in a controlled loop. Then repeat the same loop (with same outside conditions: temperature, wind, etc) with a warm battery.

Edit: Nissan put a battery heater in 2012+ Leafs. The heater only comes on at something like -4F to prevent the battery from freezing. Has anyone tried to hack the controls for this heater and run it off of wall power when the temperature is, say, less than 32F?