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Jul 2021
11:34am, 19 Jul 2021
10,519 posts
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jda
I think the main problem with ICE at low speeds isn't absolute engine efficiency per se but idling and braking wasting a lot of energy. Ie it's urban driving, rather than a steady slow pace. Whereas electric can just sit waiting quietly at stops, and use regenerative braking.
I could be wrong about that though.
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Jul 2021
12:35pm, 19 Jul 2021
39,240 posts
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HappyG(rrr)
Yes jda, that may well be part of it.
Re WLTP, yes, those are better tests, but who understands them?!
I understand the figures that I read when I buy an ICE car (new or used)
'maximum' 37 mpg
'urban' 18 mpg,
'extra-urban' 35 mpg
'combined' 26 mpg
It might say 37 mpg, but I know I'm never getting that! Town driving half that, motorway driving, most of that, on average somewhere between the two. If I am a salesperson doing 90% motorway miles I can assume near the top figure. If it is my shopping and family taxi car, then I need to half that! It matters, imho.
If I had the same for an EV, I would find that useful.  G
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Jul 2021
9:07am, 20 Jul 2021
39,250 posts
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HappyG(rrr)
After yesterday's pootling down to the gym and shops, range estimate has gone back up again.
100% charged, range estimate instead of being 290 miles, was showing 268 miles, so it had given me a more "realistic" range estimate based on the last (or average?) type of driving. I assume that after my more normal pootling for rest of week, that it will go back to estimating 280 plus. We shall see! G
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Jul 2021
2:27pm, 20 Jul 2021
15,874 posts
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Garfield
How does aircon affect potential mileage?
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Jul 2021
2:52pm, 20 Jul 2021
15,136 posts
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larkim
I've not noticed it having a measurable impact, but then I've not tried driving in a sweltering car with it turned off to give me a reasonable comparison.
I've read that it can be significant, but I *think* because newer ones use heat exchangers they are a lot more efficient than they would be if they used the more traditional heater / refridgerant approach that a car would traditionally use.
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Jul 2021
3:38pm, 20 Jul 2021
39,257 posts
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HappyG(rrr)
I can't give you any stats either Garfield, but "not noticeable" is what I would say. This doesn't mean that I just am oblivious to all mileage by the way! As evidenced by my watchful eye on the difference between motorway battery consumption vs. town/local driving.
But I haven't done an hour with aircon vs. an hour without. If it was supping down the battery though in any significant way, I think I would have noticed, as the "miles per kWh" display is pretty prominent and obvious in my car.
Larkim's explanation sounds good for perhaps how they've made it less of an issue.
Here's one that made me laugh, in the category of "stuff that's different with an electric that I wouldn't even that thought of" - there's no heat, unless you turn on a heater! When you say internal temp e.g. 21C, and outside it's say 15C (very common in Scotland, more than aircon!) nothing happens. You have to actively turn on the heater. In fact, think of it like the aircon button in an ICE car. There's a point below which it can't cool down unless you hit the aircon on button.
Of course, it's because an ICE car just passes the external air over the engine to heat the inside of the car. Can't do that with EV!! G
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Jul 2021
4:18pm, 20 Jul 2021
15,137 posts
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larkim
Exactly. Spare heat in an ICE is either wasted or recycled to heat the cabin, that's why there is a general "thing" with EVs that the advice is to heat the more local area (e.g seat or wheel) rather than heat the whole car as heating is costly in terms of battery drain - and also why pre-heating the car in winter before you drive if it is plugged into the mains before you set off is "efficient" (in the car's terms anyway) as it doesn't need to blast out heat by draining the battery to get the car feeling warm inside. The electricity cost is the same, but if range is the concern then you'd rather have the car heated via the mains than the battery.
But isn't that sort of concept of "just get me to 21 deg whether the car is hot or cold" what "climate control" effectively is in an ICE car? In the peugeot I have it set to auto at 19deg so whether it's hot or cold, the air system moves it to that temperature without me having to switch on or off the heating / cooling independently.
In terms of pre-heating / cooling the car, the Pug can only be set to 21deg (i.e. you can't say "turn on air con remotely and get to 16degC", it just achieves 21deg without any user choice. Seems to work OK though - 21degC is warm enough not to feel stifling and in this week's weather it's substantially cooler than the cabin would be having sat in broad daylight!
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Jul 2021
4:31pm, 20 Jul 2021
10,527 posts
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jda
I'm sure that aircon must have a significant effect on mileage, especially if you have if running on urban journeys where you may be stationary. It will surely be using at least a few hundred watts of power, possibly kilowatts (but I wouldn't expect it to run continuously flat out even if it's a 3kW system).
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Jul 2021
5:15pm, 20 Jul 2021
39,258 posts
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HappyG(rrr)
jda, I think 3kW is more like a house aircon unit. I don't believe it's anything like that for a car aircon. As far as I know it runs off the 12V system, not off the main motor / battery circuit. However, that's conjecture.
The real world impact seemed very low. However, as I say, I'm in Scotland. Even just now in our "heat wave" it's been 20C and a bit for last couple of weeks. I put the aircon on for a couple of minutes and the car is cool. Then I turn it off again! So I am probably not a good tester. I am content that so far neither the heater nor the aircon function have severely depleted my range.
However, trying to outdrag a Ford Fiesta ST or a big Audi, or sitting at 80mph on the motorway (ahem, I mean legally on an autobahn in Germany of course) did (would!) severely deplete my range.
I actually quite liked setting cruise to 65mph and not doing any faster to be honest. G
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Jul 2021
9:20am, 21 Jul 2021
7,196 posts
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paul the builder
My 'test' of aircon effect on fuel efficiency would be to sit at about 60mph on a long drive with it on for (say) 15min, and then off for the same period, and watch the 'miles per kWh' instantaneous value (or whatever the analogous unit to mpg is for EV). In fact I'd probably also re-set the average at the start of each 15min too.
And do this multiple times - whenever I get the chance. Yes, I'm an engineer.
My tests with a diesel ICE suggest that aircon is quite 'expensive', slicing about 5mpg (or 8-10%) off fuel economy.
I reckon (different set of trials) that the effect of sticking a massive roof box on the car is about the same cost.
lark - normal AC systems have a heat exchanger; it's the condenser. What's the new tech of which you speak?
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