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Comment by cmrdporcupine | Hacker News Reader

Your car doesn't feel wind chill.

I drive an EV in Canadian winter all the time. Not at all an issue. Range loss is a thing but it's not like the car stops working. In fact it starts more reliably and heats up more quickly for me. And I start mine remotely while it's still plugged in, so the cabin is warm and ready to go without wasting battery energy. And can do this safely in the garage without concerns of carbon monoxide poisoning or stinking up the garage.

Aside: I wish people in this country would stop reporting wind chill temps as if they're some sort of accurate measure of anything. They're only useful as a relatively subjective measure for people who aren't dressed properly.

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> They're only useful as a relatively subjective measure for people who aren't dressed properly.

That's a bizarre thing to say when to dress properly, you need to know the wind chill.

If it's 25°F out no wind, vs. 25°F out but it's 5°F with wind chill, that's an entire additional layer I need to put on during my morning walk.

Wind chill is a very accurate measure for judging what to wear. How do you think it's not accurate? It's literally an equation that accounts for the fact that wind makes you colder. You can scientifically, objectively measure the faster cooling effect of wind on an object. (Granted there are marginal differences in its effect on a human body depending on one's height and weight, but that still doesn't make it subjective.)

But if you only know the windchill temperature, how do you dress? If it is 10f with wind chill, do you prep for wind or not? I want to know temperature and windspeed, and then I know how many layers of wool I need (from the temperature) and how windproof I need to dress (from the windspeed).

Interesting point: if we need to know two things, one of them being air temperature and the other being [windspeed or windchill], the second thing ought to be whichever delivers more overall value.

If you can figure out how to dress based on either one equally well, then it comes down to what else can be gleaned from windspeed vs from windchill. I would tend to agree that windspeed is more valuable, as it's better at readily telling you if an activity you're planning to do, which is only possible under certain windspeeds (like using a tent or something), will be doable.

Windchill addresses the user request "Don't make me think". Wind speed requires actual thought.

You dress for the wind chill. I'm actually having trouble understanding your question because I can't think of any circumstance where you wouldn't.

I don't care about the wind speed as a separate number because it's useless to me except in how much it converts to wind chill, since I'm not going outside to fly a kite.

Perhaps I simply don't understand the concept of dressing to be windproof or not. Virtually all winter outerwear is "windproof" enough. People aren't usually going outside for an extended period of time in a cable-knit sweater as their outer layer.

Also -- you do understand that the wind still makes you colder regardless of how windproof your clothing is?

> They're only useful as a relatively subjective measure for people who aren't dressed properly.

Depends on your interpretation of "properly". Since 2001, the wind chill numbers for US, CA, and UK are based on a "bare face": https://en.wikipedia.org/wiki/Wind_chill#North_American_and_...

Wanting to know how cold it's going to feel on one's face seems like a pretty reasonable need. At the very least, to know when to break out the balaclava.

Might be more accurate to describe it as cars generate more windchill from driving than the weather station is likely to experience from wind?

Doesn't the cold have the greatest impact when the car isn't moving, because the car warms itself while driving?

And the reported wind chill matters when the car isn't moving.

In the best case scenario where the car is in a garage, I've heard that you can pre-emptively bring it up to temperature on grid power and a great deal of the cold-induced range loss goes away. Might still work for outdoor parking, just a bit less shielded of an environment.

> And the reported wind chill matters when the car isn't moving.

It matters in the sense that a parked car in the wind will cool to ambient temperature faster than it would when the air is still, but not in the sense that it will ever get colder than the actual still-air temperature. Wind chill affects rate of cooling, but (in the absence of evaporation) not the actual low temperature that is reached. Since the concern with loss of range or or starting capacity usually has to do with how the batteries perform at at extremely low temperatures, it's probably closer to true to say that "it does not matter".

Wind chill is mostly a number for TV weathermen to use to hype up cold weather. It does matter to some extent for people in that they may want to be careful to cover exposed skin and wear something windproof. But it's more about dressing for cold windy conditions than about an absolute number.

> Since the concern with loss of range or or starting capacity usually has to do with how the batteries perform at at extremely low temperatures

Isn't heating the cabin also a major component of the concern? That's where heating the cabin on grid power would help get some range back (assuming the battery is fully charged; if it's mid-charge then you're just shifting the grid power from charging to heating so the range will continue to suffer).

Wind chill is because your body heat makes a bubble of warm air which the wind blows away. When you have a full body suit and helmet, wind chill doesn’t matter.

It's always been a pet-peeve of mine. People from the Mid-west of America always use it for hyperbole. -10C is cold, I get it. You don't have to go all dramatic and tell me it's -40C windchill, you're not naked. (if you are, I'm fine with windchill)

Air velocity certainly impacts heat transfer.

Wind chill is a measure of the perception of winter temperatures on human skin.

Certainly the car is affected by wind in cold temps. But that's something else that we would measure entirely differently.

'Feeling cold' is measure of heat flux.

…and therefore your argument is that the wind is somehow blowing on a battery that is enclosed, as are most EV traction batteries?

The air velocity as measured relative to a parked car is not relevant to EV range. When the vehicle is moving the relative air velocity is far different than what it is when parked.

Doesn't the range of an EV drop as the heating load of the cabin of an EV increases?

And doesn't the heating load of the cabin increase as the air velocity over all of its metal and glass surfaces increases? Isn't the shell of the car essentially a giant heatsink with a 70mph relative wind moving across it?

Yes, yes, and yes.

However the speed of air over the car while driving is unrelated to the airspeed that meteorologists use to calculate the wind chill in your local weather report

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