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Old 03-22-2021, 08:40 PM   #1 (permalink)
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Electric cars and cooling drag

I've noticed that a few people here seem to believe that the cooling system drag of battery electric vehicles is very low, or even zero.

I don't think that is right.

In the research for my upcoming book on car aerodynamic history, I've looked at the percentage cooling drag of the Tesla Model S and the Porsche Taycan.

The Tesla's cooling drag calculates at 8 per cent, and the Taycan's at 16 per cent.

Obviously, these - and other modern cars - can decrease that when cooling isn't needed by closing shutters. But the fact remains that cooling drag on electric cars appears to be similar, or even greater, than on traditional internal combustion engine cars.


Last edited by JulianEdgar; 03-22-2021 at 09:54 PM.. Reason: typo
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Old 03-22-2021, 09:54 PM   #2 (permalink)
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Quote:
But the fact remains that cooling drag on electric cars appears to be a[sic] similar, or even greater, than on traditional internal combustion engine cars.
I'm available for proof-reading (structure, not content).
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Old 03-22-2021, 11:27 PM   #3 (permalink)
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Julian, your cooling numbers don't wash. A modern EV wastes only 7-15% of the energy taken onboard, and a lot of that is during charging i.e. when sitting still. There is cooling for A/C, of course, but ICE cars have that, too.

Typical ICE cars waste about 75% of the energy taken onboard, so they have to shed a lot more energy as heat than they use to move the vehicle.

In addition, a typical EV only has the equivalent of about 1-2 gallons of gasoline onboard. So, it is impossible for an electric car to shed anywhere near as much heat as an internal combustion car.
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Old 03-23-2021, 01:02 AM   #4 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Julian, your cooling numbers don't wash. A modern EV wastes only 7-15% of the energy taken onboard, and a lot of that is during charging i.e. when sitting still. There is cooling for A/C, of course, but ICE cars have that, too.

Typical ICE cars waste about 75% of the energy taken onboard, so they have to shed a lot more energy as heat than they use to move the vehicle.

In addition, a typical EV only has the equivalent of about 1-2 gallons of gasoline onboard. So, it is impossible for an electric car to shed anywhere near as much heat as an internal combustion car.
I didn't say that a battery electric vehicle needs to dissipate as much heat as a internal combustion engine car.

I said that the proportional drag of the cooling system appears to be at least as high, if not higher, in battery electric cars as it is with internal combustion engine cars.

Happy for someone to check my figures:

Tesla Model S -

Palin, R., Johnston, V., Johnson, S., D'Hooge, A. et al., The Aerodynamic Development of the Tesla Model S - Part 1: Overview, SAE Technical Paper 2012-01-0177, 2012

Porsche Taycan -

Hinterbuchinger, M., Aerodynamics, electrified - Porsche Taycan Turbo, 12th FKFS conference, 2019
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Old 03-23-2021, 07:58 AM   #5 (permalink)
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Quote:
Originally Posted by JulianEdgar View Post
I didn't say that a battery electric vehicle needs to dissipate as much heat as a internal combustion engine car.

I said that the proportional drag of the cooling system appears to be at least as high, if not higher, in battery electric cars as it is with internal combustion engine cars.

Happy for someone to check my figures:

Tesla Model S -

Palin, R., Johnston, V., Johnson, S., D'Hooge, A. et al., The Aerodynamic Development of the Tesla Model S - Part 1: Overview, SAE Technical Paper 2012-01-0177, 2012

Porsche Taycan -

Hinterbuchinger, M., Aerodynamics, electrified - Porsche Taycan Turbo, 12th FKFS conference, 2019

I understand what you were saying in the first post.
In the leaf the charging system really builds heat in the summer under the hood.
That may be the main reason for the what seems like an overly large cooling system opening.
The first year I had the leaf it was a pretty normal summer, had a lot of 7 temperature bar days. On the hottest days the radiator fan kicked on to cool the charging system while it was active. Then I started opening the hood on hot days like that, with the hood up I had fewer 7 bar days and never heard the fan kick.
With a tiny opening the heat build up woud be far worse.
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Old 03-23-2021, 10:29 AM   #6 (permalink)
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I think the key here is "proportional" - most EVs have lower overall drag than their ICE counterparts. Which is not to say cooling drag can't still be significant. I think Julian brings up a good point.

On the other hand, variants of the Tesla (Model S?) can have over 1000hp. It would be interesting to look at the Cd and percent drag of cooling for vehicles with comparable power figures.
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Old 03-23-2021, 10:31 AM   #7 (permalink)
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Interesting, could be because you have less temperature difference between the heat source and ambient. I don't know what temps motors are run at, but I know you wouldn't want your battery at 100⁰C.
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Old 03-23-2021, 10:33 AM   #8 (permalink)
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Quote:
Originally Posted by jakobnev View Post
Interesting, could be because you have less temperature difference between the heat source and ambient. I don't know what temps motors are run at, but I know you wouldn't want your battery at 100⁰C.
I was thinking the same thing.
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Old 03-23-2021, 11:55 AM   #9 (permalink)
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Obviously the overall drag on ICE cars is much higher and they require more cooling (larger grills). I'm with Neil-- I don't quite buy it.
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Old 03-23-2021, 12:43 PM   #10 (permalink)
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EVs don't have the air intake, so that may be where your "proportional" qualifier comes into play. But the air intake is small compared to the radiator, I think.

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