A Seattle-based EV battery and range analytics company called Recurrent has reportedly tested thousands of vehicles in various weather conditions. It found that many vehicles experienced “significant declines” in their range as temperatures rose. Some apparently suffered a 31% drop when temps got about 100 degrees Fahrenheit.
DB2
I have two comments on this:
First, on my recent trip to Glacier NP in Montana I monitored the wh/mile in my model 3 fairly closely. The temp was normally about mid 80s to mid 90s. But on the return between Winnemucca and Reno it hit over 100F. There was no significant change in efficiency on that segment, maintaining just over 250 wh/m (while driving 80 mph most of the time). The whole trip average was ~250 wh/m.
Second, the article says this:
Auto News says that in order to calculate these average temperatures, Recurrent used a blend of data from the 17,000 vehicles the company keeps track of. This data includes 65 EVs and plug-in hybrid models that include mainstays like Tesla’s entire lineup, the Chevy Bolt EV, Hyundai Konda, Nissan Leaf, Ford F-150 Lightning and Mustang Mach-E.
Unfortunately, we don’t know which models did the worst in terms of range loss. However, Recurrent did say that all four of Tesla’s vehicles had the smallest range degradation, but they also had the widest gap between their real-world range and the EPA’s estimates. Part of the reason for their resistance to range loss may be because of their heat pumps, Recurrent’s CEO Scott Case told AutoNews. They’re apparently much more efficient at cooling than standard automotive air conditioners.
My Model 3 is from 2018 before the heat pump. Maybe someone with more expertise can comment, but isn’t an A/C a heat pump? The advantage of switching to a heat pump in an EV is for heating not cooling. This prevents needing the inefficient resistive heat. So if Auto News is going to monitor 17000 cars, including just 65 EVs perhaps they should be able to explain why a heat pump running in cooling mode is any different than an A/C. Maybe the heat pump version is a bit more efficient in cooling mode, but it is nothing like the heating improvement I would think.
Mike
Apparently, a heat pump is both more efficient for heating and more efficient for cooling. Also, Tesla touted their heat pump design as even more efficient than usual because it has more than one “sink” and more than one “source” to move hot/cold around. I’m quite sure I am not explaining it correctly, so search online for the Tesla presentation about it from a few years ago.
Not an expert, but my understanding is that is roughly correct. The main difference being that a heat pump has the capability to move heat in two directions and the AC only one.
But back to range and heat, I would not be surprised by range loss in heat, especially if using real world observations. Actual users - as opposed to researchers - are going use their AC more when it gets hot. And the AC has to work harder when it’s hotter. Both of those will take more energy out of the battery, reducing range.
—Peter
If battery temperature isn’t controlled, you can expect a loss of efficiency at both temperature extremes. I believe Tesla’s regulate their battery temperature. But that also requires energy, so expect some losses there.
I have an ID.4, and now that it is AC weather (Phoenix), the range has gone down about 20%. Just from the onboard AC.
AC will, of course, drop the range (mpg) on gas cars as well of course. It takes energy to cool cockpit air. But why is the hit more on an EV?
The hit on an EV is the same (approximately) in absolute terms. However, since gas cars waste so much energy (lost as engine heat) that as a percentage it is more on an EV.
Note that most ICE cars have a belt driven A/C compressor which is less efficient than an electric compressor.
Mike
Has the AC induced drop in range in ICE vehicles been measured? I have never heard of such a measurement. If measured in MPG, has it been translated into range? If not then assuming that ICE vehicles are more efficient is just a guess.
Thanks for this info.
The Captain
“Switching on your car’s air conditioning system will use some gas. There are estimates that the air conditioning system will lower mileage by about 3 MPG. “
Fuel-Efficient Ways to Run a Car's AC | Chapel Hill Tire.
How many gallons in your tank? 20? Range reduced by 60 miles.
Thanks.
The Captain
9 8 7 6 …
“In a test conducted by Consumer Reports, they drove a Honda Accord at 65 mph and found that using the air conditioner reduced fuel mileage by 3%.”
My Volvo has a 17.8 gallon gas tank and I get about 30 mpg in my driving.
Range = 17.8 x 30 = 534 miles
Range with AC = 534 x 0.97 = 518 miles
Reduction = 16 miles
DB2
That is exactly what I was wondering. Why only a 3% hit to fuel mileage, but a 20% hit to battery range? Does not make sense.
Perhaps it is because EVs take multiple hits when it is hot. There is the obvious loss to AC (in common with ICE vehicles) plus the fact that battery chemistry does not operate as well at high temps. If you want to minimize that hit you have to cool the battery which takes energy and reduces range.
DB2
Not an expert but in general, batteries can lose charge in extreme temps from self-discharge (why you should store any batteries in your home in a temperature regulated environment and not in a place like your garage). Perhaps that self-discharge is increased if the battery is in use during the extreme temp.
Per Tesla’s owners manual, their batteries do indeed self-discharge over time.
High Voltage Battery Information.
Even when Model 3 is not being driven, its Battery discharges very slowly to power the onboard electronics. The Battery can discharge at a rate of approximately 1% per day, though the discharge rate may vary depending on environmental factors (such as cold weather), vehicle configuration, and your selected settings on the touchscreen. Situations can arise in which you must leave Model 3 unplugged for an extended period of time (for example, at an airport when traveling). In these situations, keep the 1% in mind to ensure that you leave the Battery with a sufficient charge level. For example, over a two week period (14 days), the Battery may discharge by approximately 14%.
Of course ICE vehicles do this too since they have a battery. shrug
Yes, but ICE cars don’t depend on batteries for their range (assuming the car will start).
DB2
Just to make up some reasonable numbers, for easy math.
Assume an EV with 400 mile range and a 100 kwh battery (a bit bigger battery and bigger range than a Tesla Model 3)
With A/C on let’s say it consumes 20 kwh to drive to empty.
Thus a 20% penalty
Let’s compare to a 25 mpg ICE car with 400 mile range. So a 16 gal tank.
At 33.7 kwh/gal equivalent this means the tank holds about 540 kwh of energy.
The same A/C would consume 3.7% of the tank’s energy…pretty close to the 3% others measured.
Again, the ICE car wastes about 65-70% of the energy as waste heat, while the EV only loses about 10% (typical number from battery to wheels)
This is after the battery is charged or the tank is full, not a complete well-to-wheels comparison.
So of the 540 kwh in the gas tank 378 kwh heats the engine and the air, while 162 kwh makes the car go and runs the A/C
The higher number to make the ICE car go is just that I picked some approximate numbers, but also the ICE car probably has more air resistance compared to a typical EV. And I just guessed at the 70% waste heat.
Mike
Then this 3% is a measure of the energy density of the fuel, not the efficiency of ICE propulsion in other respects. Even so it’s a negative for the practical use of EVs.
The Captain
Under very hot conditions, AC use can reduce a conventional vehicle's fuel economy by more than 25%, particularly on short trips.https://www.fueleconomy.gov/feg/hotweather.shtml
At 55 degrees Fahrenheit, the difference in fuel economy was minimal. But as temperatures pushed into the low 70s and peaked in the high 80s, the vehicles gas mileage took a dip, reducing the mileage between one and four mpg.https://www.jiffylubesocal.com/jiffy-lube-blog/2014/08/does-using-the-ac-hurt-gas-mileage/
So it appears the answer is “it depends”. It depends on the car, on the speed of the car, the temperature, whether the windows are open, how hard you make the air conditioner work, and the price of cheese in Chelsea.
Not really. The ~3% for ICE compared to the ~20% for EV is just a mathematical result of the fact that an ICE engine is so inefficient that the 70% waste heat masks all other auxiliary loads. The energy density of another liquid fuel could be one half of gasoline and require a twice as large gas tank and you’d end up with the same numbers.
Note. To test this, just reduce the waste heat in 10% increments and see how the 3% for the A/C increases and increases.
Mike
mike
Please keep pounding on this crucial thermodynamics point.
That’s it!
david fb