This car likes it HOT

[gpsman]

For two months I have been driving in the SF Bay area with nights in the 50's and days mostly in the 60's.

My combined city & highway driving is usually right around 4.0 miles per kWh. Exactly the EPA rating.

The past week I have been driving in sunny southern CA with nights in the 60's and daytime temperatures in the 80's. My combined city/highway cycle has been 4.7 to 5.0 miles per kWh. A huge bump upwards.

And I'm not babying the car. I have demo'd the car to family and friends who have never been in an EV so I've been beating this horse more than usual. Lots of Jackrabbit starts. Lots of 10 over the speed limit. I even used the Air Conditioning for 2 hours today when outside air was 82 degrees. The AC only takes about 1000 watts from what I can tell. Still getting high 4's for miles per kWh.

This is an amazing car.

 

[powersurge]

Nice. For a powerful car like this, that is great.

I have a Leaf, and have also found that a low speed A/C also does not take too much battery range away.. Personally, in having my car for 3 years, I think that the majority of the electricity use with heat or A/C happens when you first turn it on. It has to get things either heating or cooling. After it has been working for a while, those systems don't really use too much electrons....

 

[NeilBlanchard]

All cars have lower aero drag in warmer air; and higher humidity and higher elevation also reduce drag.

 

[gpsman]

All cars have lower aero drag in warmer air; and higher humidity and higher elevation also reduce drag.

I understand the heat and elevation lowers air density. I think higher humidity INCREASES density. I think Hot and Dry and High would make the lowest density air.

PLUS the battery cells are at their best at 77 degrees F.

 

[oilerlord]

For two months I have been driving in the SF Bay area with nights in the 50's and days mostly in the 60's.

The past week I have been driving in sunny southern CA with nights in the 60's and daytime temperatures in the 80's. My combined city/highway cycle has been 4.7 to 5.0 miles per kWh. A huge bump upwards.

This is an amazing car.

EV's do amazing things while in that narrow band of perfect temperatures, but more amazing happens with the right driver behind the wheel. To avoid more "what wrong with my range" posts, give yourself some credit. It isn't the car returning 5 miles per kWh - you are.

 

[GetOffYourGas]

I think higher humidity INCREASES density.

I think you have this backwards.

http://www.theweatherprediction.com/habyhints/260/

 

[michael]

Moist air is less dense than dry air because air is mostly nitrogen N2, atomic weight 2 x 14 = 28 and oxygen O2, atomic weight 2 x 16 = 32.

Water is H20, atomic weight 16 + 2 = 18

In moist air, water displaces nitrogen and oxygen, so less dense.

That said, something else is going on....the temperature differences you are describing aren't enough to explain that kind of efficiency difference.

 

[gpsman]

Right Michael.

Thanks for piquing my interest in the subject.
While technically true, in reality, the effects of humidity on your mileage are too small to measure.

At 20'C and below, humidity plays no meaningful role in air density. It's too cold for the air to hold meaningful moisture. Realative humidity, or simply "humidity" is how much water vapor is currently in the air, compared to how much is possible. At 20'C and 100% relative humidity, the actual ABSOLUTE amount of water in the air is slight.

At 30'C and 100% humidity (deep south, tropics, summer) the air is 3% less dense. At a more common 50% humidity, it will be 1.5% less dense.

At 40'C and 100% hunidity (never happens anywhere we drive our cars) the air is 4% less dense. 40'C and 50% humidity would be rare, and net only 2% reduction.

Air temperature alone in dry air changes density from 0.128 to 0.124 pounds per cubic foot going from 60 degrees F to 80 degrees F (15.6'C - 26.7'C).

So it is safe to say both temperature and humidity play a role, temperature much more so, and temperature rise is easily measured and humidity is not. And in general as temperature rises, humidity falls, as on earth, our hottest regions tend to be deserts. :mrgreen:

View attachment IMG_1367.PNG

 

[WetEV]

At 40'C and 100% humidity (never happens anywhere we drive our cars) the air is 4% less dense.

If it does happen, don't turn off the AC for very long.

That temperature/humidity is fatal in a few hours at most. Your skin would lose no heat until warmer than 40C or 104F, your core temperature would rise well above that. Death. Survival limit is near a wet bulb temperature of 35C, will kill in about 6 hours.

http://www.purdue.edu/newsroom/research/2010/100504HuberLimits.html

 

[NeilBlanchard]

All cars have lower aero drag in warmer air; and higher humidity and higher elevation also reduce drag.

I understand the heat and elevation lowers air density. I think higher humidity INCREASES density. I think Hot and Dry and High would make the lowest density air.

PLUS the battery cells are at their best at 77 degrees F.

It is counterintuitive, but water vapor has a lower density than air.

https://en.wikipedia.org/wiki/Water_vapor

Water vapor is lighter or less dense than dry air. At equivalent temperatures it is buoyant with respect to dry air, whereby the density of dry air at standard temperature and pressure is 1.27 g/L and water vapor at standard temperature and pressure has the much lower density of 0.804 g/L.

Another amazing thing is for a typical car, with a frontal area of about 23-25 sq ft - for every mile traveled, the car shifts about FOUR AND A HALF TONS of air out of the way.

Like a snow plow shifts snow - ALL vehicles are air plows.

 

[gpsman]

I drove south in relatively calm conditions.
I drove north in a stiff headwind.

Both trips were ~ Sea Level to Sea Level. No net elevation change.

On the return, I "spent" 15 more kilowatts.
Or 60 miles of range lost on the Anaheim to SF trip compared to the SF to Anaheim trip.

Being aware of the wind, I charged to 93% instead of the typical 80% at the DCFC. And I needed that extra power.

You can't get upset when people stay on a charger past 80%. Even if there is a line (there wasn't today). Sometimes it is absolutely necessary. I had to go 185 miles into a stiff headwind. I made it. Barely. Got to the charger with 1 bar- 5% left.

 

[sgt1372]

The past week I have been driving in sunny southern CA with nights in the 60's and daytime temperatures in the 80's. My combined city/highway cycle has been 4.7 to 5.0 miles per kWh. A huge bump upwards.

And I'm not babying the car. I have demo'd the car to family and friends who have never been in an EV so I've been beating this horse more than usual. Lots of Jackrabbit starts. Lots of 10 over the speed limit. I even used the Air Conditioning for 2 hours today when outside air was 82 degrees. The AC only takes about 1000 watts from what I can tell. Still getting high 4's for miles per kWh.

Interesting. Best I've gotten so far driving really SLOW and EASY around town is 4.2-4.4 m/kwh in moderate SF Bay Area weather.

Took the Bolt on the freeway yesterday (instead of driving on the street) because I was in a hurry to pick the new floor mats and tire inflator kit for the Bolt from my local Chevy dealer.

Total estimated range at the start was a 248 -- 210 on the screen and 38 miles driven at 4.2 m/kwh. After driving just 18 miles, total estimated range was down to 227 -- 171 on the screen and 56 miles driven at 3.6 m/kwh. This was the result of very quick on ramp acceleration 0-70 and freeway speeds varying between 70-90 mph; ave probably around 80 which was the "flow' of traffic in the fast lane.

Lost 21 miles of estimated range just driving 18 miles on the freeway in this way, which is why I try to avoid driving on the freeway with the Bolt.

So, at least in my experience, weather seems to little to do with it my driving "efficiency" numbers. LOL!!!