Why is the roof black?

[WoodlandHills]

So why does an electric car with limited power and a marginal a/c system have a black roof?

 

[Boxbrownie]

Keeps you warmer on cold days............helps you a lot there doesn't it?

 

[MikeS]

What makes you think the a/c is marginal? Mine works as well as the ones in my other cars.

 

[WoodlandHills]

What makes you think the a/c is marginal? Mine works as well as the ones in my other cars.

We test drove the i3 on a 107 degree day, the car had been sitting in the sun all day, and it took over 30 minutes to cool off the interior. Our smart sat in the sun in our driveway not 4 miles away for the same time and it was cooled off in the 15 minutes it took to drive there. Ditto our Infiniti...... To me that indicates that the a/c could use some help.

BTW, this is typical summer heat where I live, not every single day, but quite common nonetheless. A car designed for city use, ie running errands ought to be able to cool the vehicle between stops and shops. Perhaps they should have Northern and Southern versions?

Maybe when charge points are more widespread people will just keep the a/c running in Precondition mode when parked and plugged in. That way the car would be cool when they came out and that way they could waste more energy than an ICE defeating the purpose of going EV. And why not when power is often free.....?

 

[Boxbrownie]

What makes you think the a/c is marginal? Mine works as well as the ones in my other cars.

Mike...........Southern Calfornia vs Brighton

He may have a point........ :lol:

 

[jackt]

Can't speak about baking heat, but the roof is just clear-coated CFRP it has no paint on it at all.

I suspect its mainly cosmetic, but also maybe problematic to attach a plastic painted panel to the roof :s

If you take a close look it has a cool pattern to it.

 

[i3Alan]

We test drove the i3 on a 107 degree day, the car had been sitting in the sun all day, and it took over 30 minutes to cool off the interior.

Was that with Max AC in Comfort mode? Or, were you in Eco Pro mode, which reduces cooling, and not using the Max setting, which will not engage automatically?

Before I bought mine, I test drove one that had been sitting in 109 sun baking, and it, too, cooled down quite rapidly.

My i3 in Phoenix with 107 and higher temps cools down in a few minutes on Max AC, which is good, because it is too noisy to leave it on Max!

 

[WoodlandHills]

It was in Comfort and Max a/c. The car was a ReX if that makes any difference. It was an extreme test and I expect that the cooling is adequate, but it still wonder why a black roof.

 

[jadnashuanh]

No extra paint on the roof means a few pounds less weight. I think they did it more for the style thing...to show the CFRP. You could always plastic-wrap it in white or a reflective metallic if you wanted to as some have done since they don't like the black hood, either.

 

[i3Alan]

It was in Comfort and Max a/c. The car was a ReX if that makes any difference. It was an extreme test and I expect that the cooling is adequate, but it still wonder why a black roof.

I'm wondering if the REX has less cabin cooling capacity than the BEV. Both the test drive and my i3 are BEVs. I do know there is a difference in the cooling systems between the two.

 

[MurphyDog]

I highly recommend getting your windows tinted. I live in the California Bay Area and we normally see temps in the 90-100's all summer long. I too found the AC being very lack luster until I tinted my windows (35% back, 50% front). Ever since the tinting the I only need to run the AC on low to cool the entire car. Best $250 I ever spent.

 

[MikeS]

What makes you think the a/c is marginal? Mine works as well as the ones in my other cars.

Mike...........Southern Calfornia vs Brighton

He may have a point........ :lol:

Not really - the a/c marginal statement must be a comparison on different car’s a/c effectiveness as I doubt that the OP has tested the car in UK and California :lol:

 

[Boxbrownie]

What makes you think the a/c is marginal? Mine works as well as the ones in my other cars.

Mike...........Southern Calfornia vs Brighton

He may have a point........ :lol:

Not really - the a/c marginal statement must be a comparison on different car’s a/c effectiveness as I doubt that the OP has tested the car in UK and California :lol:

Well it seems he has compared it to other vehicles there, a Smart no less......

I can understand how the AC could be marginal in some circumstances as it has to be running a lower power system to most cars, I am sure it works fine but just takes a bit longer to get into the comfort zone.

There was a big difference in cool down temps on three of my cars during our summer and all cars are running in tip top regards AC, funnily enough the oldest a Lexus RX was best with the Audi Hybrid second and an '10MY ML trailing, but all worked fine after a while and kept nice and chilly, but I wouldn't be surprised if when we get the i3 the AC is not exactly "the best" as comprimises have to be made.

 

[AlanfromBigEasy]

I painted my roof white. Dramatically cooler in summer and looks better too with my white 2015 i3 !

 

[tjsean0308]

To echo comments here. The roof is just clear coated CFRP. I'd imagine they made the choice for both a bit of weight savings (all be it very minor) and styling. I love the roof and the fact its literal cut-offs from the layup of the rest of the car. If you wanted you could wrap it in a silver or light gray to help reflect some heat.

The BEV does have a heat pump, which generally are more efficient in cooling. I haven't had my car in desert heat, but 100 degrees in the midwest was not a problem with the heat pump. It easily condensates the outside of the windows.

 

[eNate]

The BEV does have a heat pump, which generally are more efficient in cooling. I haven't had my car in desert heat, but 100 degrees in the midwest was not a problem with the heat pump. It easily condensates the outside of the windows.

That's not quite right with respect to the heat pump.

The battery will always produce heat that needs to be stripped away (or "managed," I guess one could say), but will never produce cold.

So the system pumps coolant through the battery tray to carry off the excess heat, just like the coolant system that runs through an engine block.

With the heat pump, the i3 system resembles an ICE car where that heat is then exchanged with the interior system and warms the cabin air, but doesn't cool it. Without this option, that stripped-away heat is shed via a radiator to the outside airflow and "lost."

When the car and battery are parked and cool, this same system will use resistive heating to warm the "coolant" (which instantly becomes an inappropriate name), to bring the battery up to a friendlier operating temperature. But even though this is the reverse of what's described above, it doesn't exchange any cool air with the cabin -- particularly because if the battery is cold and needs to be heated, so too does the cabin.

Put another way, the only thing that cools an i3 interior is the battery-driven AC compressor, and it's identical on BEV and REX.

 

[tjsean0308]

The BEV does have a heat pump, which generally are more efficient in cooling. I haven't had my car in desert heat, but 100 degrees in the midwest was not a problem with the heat pump. It easily condensates the outside of the windows.

That's not quite right with respect to the heat pump.

The battery will always produce heat that needs to be stripped away (or "managed," I guess one could say), but will never produce cold.

So the system pumps coolant through the battery tray to carry off the excess heat, just like the coolant system that runs through an engine block.

With the heat pump, the i3 system resembles an ICE car where that heat is then exchanged with the interior system and warms the cabin air, but doesn't cool it. Without this option, that stripped-away heat is shed via a radiator to the outside airflow and "lost."

When the car and battery are parked and cool, this same system will use resistive heating to warm the "coolant" (which instantly becomes an inappropriate name), to bring the battery up to a friendlier operating temperature. But even though this is the reverse of what's described above, it doesn't exchange any cool air with the cabin -- particularly because if the battery is cold and needs to be heated, so too does the cabin.

Put another way, the only thing that cools an i3 interior is the battery-driven AC compressor, and it's identical on BEV and REX.

I wasn't saying the battery cools the cabin. I was saying heat pumps are generally more efficient at cooling than heating do the thermal operating range of the refrigerant. The i3's heat pump is effective at heating down to 14f, but I notice the resistive heater starting to come on around 22f. This performance is on par with most home heat pumps making it a quite good system.

The i3 doesn't use the heat pump to heat the battery. The i3's battery pack is directly cooled by the HVAC refrigerant not a traditional liquid coolant. It is heated by a resistive battery blanket which was optional on 2014 models and only installed with heated seats as a pseudo cold weather package.

The battery driven AC compressor is the refrigerant pump for the heat pump. A heat pump is essentially a vapor cycle cooling system with a reversing valve to allow the evaporator and condenser to swap roles. That enables the conditioned space to be heated and cooled with the same refrigerant and compressor. There is bit more involved, but that's the basic concept, an air conditioner that can heat and cool. The i3 takes that to the next level with multiple expansion valves and the ability to control which evaporator gets priority.

Here is a video from the Munro labs tear down where the talk specifically about the refrigerant cooling on the i3's pack. Tesla's and others have liquid managed packs, but the i3 is refrigerant only in the pack. https://www.youtube.com/watch?v=pgu6mkKZwNg&feature=youtu.be&t=329

Here is a pamphlet from BMW showing all the heating and cooling system components. You can see on page 37 the battery in particular and the refrigerant lines that are in the pack. The only coolant is for the electric heater and the drive motor itself because liquid is much more efficient to heat with a resistive heater.
https://www.speakev.com/attachments/08-i01-heating-and-ac-systems-pdf.79217/

There was a very useful FAQ from a BMW engineer on the sadly dead now, BMWiForum that clarified all this and confirmed the HV battery is refrigerant cooled and resistively heated. That is why the battery preconditioning lead time is a minimum of three hours because it's only a 1kW blanket of sorts that heats the battery. It's pretty plan to see when you have cold soaked the car and are on reduced power. Even driving the wheels off it, it takes about 30-40 minutes to start recovering the power back and usually I'm still reduced by the time I get home from work when it's been a cold night. (I work 24 hour shifts so the car is cold soaked overnight a few times a month)

Edit: Clarity.

 

[Deutsch100]

I highly recommend getting your windows tinted. I live in the California Bay Area and we normally see temps in the 90-100's all summer long. I too found the AC being very lack luster until I tinted my windows (35% back, 50% front). Ever since the tinting the I only need to run the AC on low to cool the entire car. Best $250 I ever spent.

Sorry to be resurrecting such an old post, but I do have to confirm that tinting the windows in the i3, makes a HUGE difference. In my 2019 i3S and now my new 2020 i3S, I tinted all side windows, rear window and even the glass moonroof with CERAMIC window tinting, and it has made the A/C incredible now, as the the cabin is not heated much at all with heat coming through the glass.

In the past, I always just used standard 3M tint, as the cars I had came with thermal/UV glass from the factory, but since the i3 does not (and being an EV, it should), the ceramic tinting for the i3 is the best thing ever!!

I did 35% ceramic on all side windows and the rear and did 15% ceramic on the glass moonroof. Amazing, honestly!

 

[AlanfromBigEasy]

I first had the high end 3M tint applied, but it was not enough for New Orleans summers parked outside. So I had my roof painted (NOT wrapped which only lasts a few years) BMW White to match my car.

The white roof reduced inside temperatures significantly better that the window tint AND the car looks much better. I have had some questions from other people that know i3s, asking what year is it ?

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[alohart]

I first had the high end 3M tint applied, but it was not enough for New Orleans summers parked outside. So I had my roof painted (NOT wrapped which only lasts a few years) BMW White to match my car.

The white roof reduced inside temperatures significantly better that the window tint AND the car looks much better.

In the tropics where the average sun angle is quit high, heat being radiated down from the roof feels more intense than that entering the vertical windows. If ours was a Capparis White i3, I would have had the roof painted as you did. However, a white roof on an Arravani Gray i3 would have made it a 3-tone car which I don't think would be very attractive. Instead, I felt that a silver chrome vinyl wrap might look better and would reflect infrared radiation even better than white. However, local car wrappers wanted over $500 to wrap the roof which was more than I wanted to pay, especially because the wrappers told me that silver chrome vinyl film on a horizontal surface would likely degrade within a couple of years.

Instead, I bought some inexpensive silver chrome vinyl film to install myself. I had hoped that the roof was flat enough that I would not have to heat and stretch a large piece of vinyl film to avoid wrinkles along the edges. Unfortunately, that wasn't the case, so my installation looks terrible. However, it does reduce cabin heating noticeably when strong sunlight shines on the roof. I will probably remove the film as winter approaches, but probably won't pay to have it wrapped professionally because our i3 isn't driven much (only ~11k miles in 6 years) and is parked out of the sun in our apartment parking garage.