Electric cars and cooling drag

[planetaire]

Originally Posted by JulianEdgar

That information does not tell us what the cooling drag proportion of total Cd is for the listed cars. So basically it’s irrelevant - unless you are suggesting that the change in Cd between the ICE and BEV models is due solely to the change in cooling drag (which it isn’t). The Cruise / Volt comparison is particularly ridiculous - the two cars have completely different shapes.

Again, just sewing the seeds of confusion.

Hi, Julian

It is interesting to compare the vw Up and the e-Up.
First is thermal model, cd 0.32, the second is electric model, Cd 0.308
Vw use exactly the same body for this economical car. They don't add aerodynamic devices. They could have add underbody panel between front and rear wheels, but they don't.
In the electric model they put the battery cells under the front and rear seats. They close the center tunnel that is used for wires and electronic (bms...)
They also permanently partially close the front grill. It is an economical car so they don't add front mobile shutter.
The parts closed are on this picture:


So the difference between this two Cd values are only dues to cooling differences. For the thermal model mainly for the engine and exhaust pipe, for the electric model motor and electronic.

At the "opposite", MB is launching their EBS electric car. Cd goes down to 0.20. It is optimise only for electric, no thermal model.
It is much much more expensive, so they have add a mobile front shutter.
And they said:

The purpose design with smooth underbody and mostly closed radiator shutter as well as the favourable basic shape were a good starting point for the flow optimisation

[JulianEdgar]

Originally Posted by planetaire

Hi, Julian

It is interesting to compare the vw Up and the e-Up.
First is thermal model, cd 0.32, the second is electric model, Cd 0.308
Vw use exactly the same body for this economical car. They don't add aerodynamic devices. They could have add underbody panel between front and rear wheels, but they don't.
In the electric model they put the battery cells under the front and rear seats. They close the center tunnel that is used for wires and electronic (bms...)
They also permanently partially close the front grill. It is an economical car so they don't add front mobile shutter.
The parts closed are on this picture:


So the difference between this two Cd values are only dues to cooling differences. For the thermal model mainly for the engine and exhaust pipe, for the electric model motor and electronic.

Sorry, but again I can't see the relevance to the discussion. If they make underfloor changes to the electric version (as you say they do) then obviously the Cd of that version will be lower, and so it doesn't tell us what proportion of total drag is made up by the EV cooling system on the EV car. This can only be found out by testing the cooling drag of each version and telling us what it is.

At the "opposite", MB is launching their EBS electric car. Cd goes down to 0.20. It is optimise only for electric, no thermal model.
It is much much more expensive, so they have add a mobile front shutter.
And they said:

Nearly all modern prestige cars use cooling shutters - BEV or ICE or Hybrid. It's nothing to do with the car being a BEV.

[planetaire]

Originally Posted by JulianEdgar

Sorry, but again I can't see the relevance to the discussion. If they make underfloor changes to the electric version (as you say they do) then obviously the Cd of that version will be lower, and so it doesn't tell us what proportion of total drag is made up by the EV cooling system on the EV car. This can only be found out by testing the cooling drag of each version and telling us what it is.

They don't change the floor. The difference is only due to the front grill and the exhaust tunnel closed. Two parts that need cooling, more for thermal model

Nearly all modern prestige cars use cooling shutters - BEV or ICE or Hybrid. It's nothing to do with the car being a BEV.

They have. Because the cooling needed is lower for electric (See the e-up for example). So the shutter could be closed most often. If you want to compare the two drags, you need to know how often they will be closed.

[planetaire]

Originally Posted by JulianEdgar

1. Closing off the cooling in low-power electric mode in a Prius tells us nothing relevant to this discussion (which is about BEVs), does it?

I don't agree. I use it as a BEV on our roads. Average power is low, not because electric but because his good aero (cd=0.22). Power is not a part of the BEV definition.

2. Cd values (or percentages of total Cd) are used for cooling systems because it is a coefficient. If we used Newtons, we'd need to specify speed. We can easily work out the force for any car for which we have speed, area and cooling drag Cd.

You are right, newton depend upon speed, then use delta Cd. For example the Up and e-Up have 0.012 delta cd between the two cooling system.
If I compare % upon the two I could may be find that the electric model have more (I am sure not). In my opinion, what is important is that the drag is more important for the thermal model, the Up.

[JulianEdgar]

Originally Posted by planetaire

They don't change the floor. The difference is only due to the front grill and the exhaust tunnel closed. Two parts that need cooling, more for thermal model

I have no idea about the car - I am quoting only what you wrote. And you wrote, "The exhaust tunnel is closed". That will immediately reduce drag, and so the value of overall aero drag we're comparing to has also changed.

You are right, newton depend upon speed, then use delta Cd. For example the Up and e-Up have 0.012 delta cd between the two cooling system.

I am not sure if you're trying to be misleading but that statement is quite incorrect. The delta Cd between the two cars is that, not their cooling systems. We have no data at all on their cooling systems!

If I compare % upon the two I could may be find that the electric model have more (I am sure not). In my opinion, what is important is that the drag is more important for the thermal model, the Up.

I don't know what that means.

[JulianEdgar]

Originally Posted by planetaire

I don't agree. I use it as a BEV on our roads. Average power is low, not because electric but because his good aero (cd=0.22). Power is not a part of the BEV definition.

That is true - but no mainstream BEV will ever be sold with as little power as an electric-only Prius. So it's a bit cute saying you can run with its cooling reduced to zero - and drawing any comparison with a proper BEV.

The cooling drag on my electric bicycle I once made was very low, but it's irrelevant to the discussion.

[JulianEdgar]

TBH, I wonder a bit if people even understand my argument.

Let's put it this way.

1. We have a ICE vehicle. We measure cooling drag by blocking the cooling intakes (a little more to it than that, but that will do for now) and measuring the change in Cd. We then compare that change in Cd with the overall Cd. From that we get cooling system percentage of overall Cd.

2. We then do exactly the same with a BEV. It doesn't have to be the same car in ICE and BEV forms - that's not even particularly relevant as both overall Cd and cooling drag are likely to have changed between the two car versions.

I have seen ICE cooling drag figures from less than 1 per cent to 14+ per cent. The only BEV figures I have seen are 8 and 16 per cent.

So to say it all again:

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.

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.

I'd love to see some other figures on the measured cooling drag proportion of some other BEVs.

[planetaire]

Julian,

My question is : do you want to study only very high powered electric car ? Or do you give numbers about these sort of cars because you don't find others ?

So you want a percentage of the total drag.

This value will be high for a (very) high power car having a low cd and no front shutter. Some Tesla model for example. Without grill shutter they have to handle the worst case possible: a lot of air goes always through the front grill.

At the middle you will have a lot of cars where makers don't give data. Today you can find Cd, it is more difficult to find frontal area, but cooling drag never.
Some guys in priuschat forum have tested blocking totally the front grill. I remember 4% cd decrease. Here they found 3%

At the low side you will find low power (Or medium powered used at low power) car with grill blocking for which during most of the time the cooling drag will be near zero. The drag losts will depend upon road conditions. This drag will increase if you climb stepped hills and get some energy back going down (What ice don't do)

And at a very low side your bike that have a tiny cooling drag.

This study show cooling data.

Of course you don't have the exhaust pipe and his cooling in BEV cars.

[JulianEdgar]

Originally Posted by planetaire

Julian,

My question is : do you want to study only very high powered electric car ? Or do you give numbers about these sort of cars because you don't find others ?

So you want a percentage of the total drag.

This value will be high for a (very) high power car having a low cd and no front shutter. Some Tesla model for example. Without grill shutter they have to handle the worst case possible: a lot of air goes always through the front grill.

At the middle you will have a lot of cars where makers don't give data. Today you can find Cd, it is more difficult to find frontal area, but cooling drag never.
Some guys in priuschat forum have tested blocking totally the front grill. I remember 4% cd decrease. Here they found 3%

At the low side you will find low power (Or medium powered used at low power) car with grill blocking for which during most of the time the cooling drag will be near zero. The drag losts will depend upon road conditions. This drag will increase if you climb stepped hills and get some energy back going down (What ice don't do)

And at a very low side your bike that have a tiny cooling drag.

This study show cooling data.

Of course you don't have the exhaust pipe and his cooling in BEV cars.

I am afraid your post shows a lot of misunderstandings eg high car power does not equal a higher proportion of cooling drag. Just look at a variety of ICE car data to see that - one of the lowest ICE cars I can find for cooling drag proportion is a very powerful car! (Guessing is not a very good research approach.)

And your post provides no new data on percentage cooling drag for any BEVs, so it takes us basically nowhere.

[planetaire]

Originally Posted by JulianEdgar

I am afraid your post shows a lot of misunderstandings eg high car power does not equal a higher proportion of cooling drag.

That's not all what i wrote.
I said high power car having a low cd and no front shutter.
You want a percentage of the total cd. It will mathematically increase if the cd is lowered.

And your post provides no new data on percentage cooling drag for any BEVs, so it takes us basically nowhere.

Sorry, i give you a real example in one of my previous posts.

Of course you may ignore real examples.
It depend on:

My question is : do you want to study only very high powered electric car ? Or do you give numbers about these sort of cars because you don't find others ?