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Autoweek (and other car news outlets) summarize some independent testing: https://autoweek.com/article/green-cars/how-much-does-cold-weather-cut-electric-vehicle-range-quite-bit-aaa-study-finds
AAA partnered with the Automotive Club of Southern California's Automotive Research Center for its tests, which allowed it to run drive-simulating dynamometer tests in 20-, 75- and 95-degree Fahrenheit temperatures in a controlled laboratory setting. This is way more scientific than anything we'd be able to achieve toodling around in an EV in Detroit the next time a polar vortex hits.
A handful of key points pulled from the report:
- The increased use of HVAC systems in extreme temperatures has a bigger impact on EV range than decreases in battery pack efficiency caused by the temperatures themselves.
- Moreover, while both extremely hot and extremely cold temperatures affect range, you'll incur a significantly larger penalty when heating up a cabin than you will cooling one down. Compare that 41 percent decrease at 20 F to a mere 17 percent decrease at 95 F.
- The BMW i3s saw the biggest reductions in range in both hot and cold conditions, losing 50 and 21 percent of range in cold and hot conditions, respectively.
- The Nissan Leaf was the most versatile, losing 31 and 11 percent of range in cold and hot conditions, respectively.
The other test cars, Tesla S, eGolf and Chevy Bolt fell between these extremes. The article includes a link (pdf) to the original report with many more details. Worth reading if you live outside southern CA and are considering an electric car.
This AC is considering an electric car, and I'm fortunate enough to have an attached garage to keep it warm-ish, probably above freezing, even if the outside temp gets down to 0F (-18C) which is a typical low for my location. That means that any trip will start with a cool (not cold) battery & cabin...but after parking outdoors at my destination(s), I'll have a reduced range for the trip home.
(Score: 3, Interesting) by KilroySmith on Thursday May 16 2019, @05:02PM (12 children)
In the Tesla world, owners mitigate the cold weather range loss by using the seat heaters (and in the Model S/X, the steering wheel heaters) rather than the cabin heater. They say they can be just as comfortable with significantly less power expenditure. Living in Phoenix, I haven't tested this for myself...
The thing that I don't understand is why Tesla uses inefficient resistive heating for cabin heat. In moderate temps (say, above 0C), using the already-installed A/C system as a heat pump to heat the cabin would be much more efficient at a small cost (inclusion of a reversing valve in the refrigerant line). Admittedly, it IS an additional cost because they'd have to have the resistive heater anyway for lower temps, but Tesla isn't about squeezing pennies here and there...
(Score: 3, Disagree) by c0lo on Thursday May 16 2019, @05:17PM (5 children)
Really? I think you'll discover that using electricity to drive a heat pump to heating and using the same electricity through a resistor will favor the latter in terms of efficiency.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 4, Informative) by Immerman on Thursday May 16 2019, @05:46PM
Actually no. It'll depend on just how cold it actually is, but in general a heat pump is much more efficient that direct heating - essentially you're using maybe 100W of energy to move 300W of heat from a cold place to a warm place - giving you 200W of heating for "free".
(Score: 2) by KilroySmith on Thursday May 16 2019, @05:56PM
A heat pump in relatively moderate conditions (0C) will be about 3 times more efficient than electric heating, but rapidly loses efficiency below there. Units can be built to operate much, much colder, but then they don't work (or work well) for cooling.
(Score: 4, Informative) by Arik on Thursday May 16 2019, @06:11PM (1 child)
It doesn't heat or cool, it just transfers hot or cold from one place to another.
If you want to cool, then it needs somewhere to dump heat. A radiator, more or less. It makes you cool by transferring the heat from where you are, to the radiator. The colder that radiator on the outside is, the more efficient this process becomes. But if the radiator is hot, then this doesn't work well at all.
And it works exactly the same in reverse. If you want to *heat* the inside of the car with a heat pump, then you're still going to be using the radiator to do it, only now the HOTTER the radiator the better it works.
In an internal combustion engine, this can still work fine, even in nasty cold weather. That engine has to thermal cycle and build up a good bit of thermal energy to reach operating temperature, and it keeps right on making heat afterwards which must be radiated away. If you don't use that to heat up the car then it will have to be radiated out another way anyway.
One of the nice things about electric motors in other contexts is that they *don't* really put out much heat. Yes, there's friction, there's some radiation of thermal energy, but it's nothing like what happens with an internal combustion engine, there's no getting up to operating temperature and heat radiated is much less. In warm weather this is great, it means you aren't wasting a lot of energy heating up that engine block. In cold weather, though, it means you can't rely on the engine as a source for heat.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by aclarke on Friday May 17 2019, @03:23PM
Air-to-air heat exchangers are pretty well-proven technology. They're a fairly efficient way to heat, even in freezing temperatures, although their efficiency drops with the temperature, just as an air conditioner's efficiency drops as temperature rises.
Perhaps they're too bulky or heavy or expensive to put into a car, but they're used regularly in buildings.
(Score: 0) by Anonymous Coward on Thursday May 23 2019, @09:11PM
LOL.
Reread what you said.
The heat pump IS a "resistor" in terms of converting electricity to heat.
A heat pump running at 0% efficiency is precisely a resistive heater, with 100% electric to heat conversion.
A heat pump running at >0% efficiency and sucking the same juice radiates the same heat due to resistance AND pumps heat in from the outside.
A heat pump, even the literal least efficient so long as it's not being run 'backwards', will ALWAYS outperform resistive heating.
The only argument you could POSSIBLY make against them is that they take material to make and to lug around, and maybe they're too heavy to be practical (not the case, but you could argue it).
Learn some basic physics. Heat pumps don't violate conservation of energy.
(Score: 2) by bussdriver on Thursday May 16 2019, @05:51PM (2 children)
Resistance heating wastes almost no energy... a heat pump loses a fair amount of energy pumping gas into liquid and I suppose you could put the motor into the car so the lost heat goes into the car (not helping in summer.)
More fundamental: heat pumps MOVE temperature. In summer, you have cool air rushing past a radiator at high speeds so moving heat away is easy to do that is FREE cooling (within the loop; obviously ignoring that the car has to move itself.) In winter, you have cold air rushing past a radiator trying to extract heat so the compressor has to work more to get less. You can't place the warm loop into the ground to get FREE heat because it's a car. Best you can do is place a black glass covered radiator on the roof of the car (solar heater.)
(Score: 3, Informative) by Immerman on Thursday May 16 2019, @06:39PM
It's true there's little waste - heating is typically very close to 100% efficient, because heat is the thermodynamic waste-pit of the universe.
However, being 100% efficient at what it does (generating heat), doesn't mean that what it's doing is the most efficient way to accomplish what you actually want (heating an area). A heat pump can be much more efficient because rather than generating heat, it's consuming energy to move heat from someplace cool to someplace warm. So long as that temperature difference isn't too great (and humans can't actually survive a very large temperature range), 1kW of mechanical work can move several times than much heat.
(Score: 5, Informative) by KilroySmith on Thursday May 16 2019, @06:53PM
Resistance heating has an efficiency of 1 or 100% (kinda by definition). Every watt of power going into it generates a watt of heat.
Within their rated temperature range, a heat pump has an efficiency of 3 to 6 - 300% to 600%. Every watt of power going into it (compressing and pumping gas) generates the equivalent of 3 to 6 watts of heat/cold. In Phoenix, all of our Air Conditioners (kinda required for summer) are Heat Pumps, and are used for heating the houses in the winter. Older models used to have resistance heaters piggy-backed on that only ran when the temperature got below freezing - and boy did people hate it when the electric bill came. Newer units continue to operate down to the lowest temperatures we see out here (maybe 25F) so the resistance heaters have disappeared.
(Score: 2) by Immerman on Thursday May 16 2019, @06:55PM (2 children)
>using the already-installed A/C system as a heat pump
The question I would ask is, is the AC actually a viable heat pump? In theory there's very little difference between a refrigeration unit and a general-purpose heat-pump, but in practice... practical design choices and optimizations (like the optimal thermal range of the refrigerant) can often make a refrigeration unit unsuited for pumping heat in the other direction. Rather like a claw hammer and a crowbar - both do basically the same thing, pounding on things and pulling them apart, but they're optimized for opposite jobs, and you have to work way too hard to use the one where the other is called for.
My understanding is that a bi-directional heat pump is typically considerably more expensive than a dedicated AC - and I assume there's good reason for that. And as you allude to, heat pumps become a lot less effective when it gets really cold, which means you still need all the resistive heating in addition to a more expensive heat pump.
(Score: 2) by Arik on Thursday May 16 2019, @07:40PM (1 child)
Sure, and the reason you mentioned (optimal refrigerant for cooling versus compromise choice that will work for both) may well be part of it, it makes sense. But a bigger part is on the external end. For ideal efficiency you want both a hot source and a cold source. A shaded radiator and blower outside normally works fine for just cooling, but the problem is when you want to heat in the winter that's not very efficient at all. So what do you do? Add an entirely different endpoint for heating in winter? A lot of extra work and material but ok, where, how?
A thermosolar collector, for instance, would work well during the day, but it would cool down mighty quickly after sunset. You can moderate that effect by including a really big heat sink, but of course that makes it all the more expensive.
If you happen to have built next to a hot spring, well that's just great, use that, but most places that's not an option.
So what you might see in a high end system is they'll bury the radiator several feet underground. Actually works pretty well, the temperature stays pretty consistent if you bury it nice and deep, in a range where it can both cool in summer and heat during winter with reasonable efficiency. Helps to narrow down the range of temperatures your refrigerant will encounter too, I would imagine. But it's expensive, and difficult to access for maintenance or repair.
Now, in a conventional car, with an ICE, it actually makes a lot more sense to just use two endpoints. You have a hot engine block and a cool radiator very close together.
It makes sense, but I'm not sure how often it's really done. As far as I know car heaters more often just intake hot air from off the engine block instead of using a heat pump. I'm far from expert on cars though.
With an electric vehicle, however, you don't have that engine block for a ready source of heat, so in that case it doesn't even make sense.
If laughter is the best medicine, who are the best doctors?
(Score: 2) by dry on Friday May 17 2019, @06:01AM
Cars usually are water cooled and have plumbing and a small radiator in the cab or firewall area with a fan that blows air through the small radiator (heater core) into the cab. Vans and such might have pipes going to the rear and another heater core back there. There's also a thermostat that isolates the radiator until it's needed to cool down the engine. In really cold conditions, the radiator might never get hot.
I'm old enough to remember the original Volkswagen Beetles with air cooled engines, total bitch to heat, they actually had gas (petrol) powered heaters. This might be another option, an alcohol or such powered auxiliary heater in really cold climates.