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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: 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.