Efficient heating for electric cars

September 2, 2015, Fraunhofer-Gesellschaft

If you don't want to freeze in your electric car, you have to make a few concessions, because heating devours a substantial portion of power supply. Fraunhofer researchers will exhibit the demo model of a highly energy-efficient heating system for electric cars at the IAA: a coated film that produces a broad, radiant heat.

Electric car drivers now have one more reason to love the summer, because in the winter, the vehicle's range declines markedly due to the additional energy demanded by the . Electric cars generate next to no heat as opposed to conventional passenger vehicles, which produce more than enough engine heat to heat the interior. An additional electric heater is required. This is supplied with power by the same battery that provides the engine with energy. "In the most unfavorable case, you can only drive half the usual distance with the car", says Serhat Sahakalkan, project manager at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart.

Researchers at the IPA have developed a film-based panel heater, which quickly provides a comfortable warmth in , which is – particularly on short journeys – more effective than former electric heaters. The heating concept is based on a film that is coated with conductive carbon nanotubes (CNTs). For this, the researchers spray on a very thin layer of CNT dispersion. "The film is glued to the inner door trim and generates a comfortable warmth there in the area of the armrest within a very short time", Sahakalkan explains. The heater functions in accordance with the Joule principle: When electricity flows through the film, it comes across a natural resistance between the individual nanoparticles. These "collisions" generate heat.

Extremely thin film saves energy and costs

Conventional electric resistance heaters of the type used in electric cars, also make use of this principle. Usually, the used is copper wire, which is embedded in silicone mats, for example. The solution of the researchers from Stuttgart, however, offers several advantages: While the copper wire heaters available at present are relatively "bulky" and take up quite some installation space, the film heater consists of a layer of conductive material with a thickness of only a few micrometers. It can be flexibly applied to the most various surfaces and contributes to saving energy and costs due to its low weight. The CNTs themselves have a low heat storage capacity, as a result of which the generated heat is directly released into the environment. As opposed to the wire-based variant, the heat is evenly distributed here over the entire surface of the film, which considerably increases efficiency. When the driver switches the heating off, the material cools down just as quickly. "These fast response times are ideal for short distances such as urban trips", Sahakalkan explains. The desired heating output can be infinitely adjusted by the user. Even isolated defects do not impair functionality. In wire-based heating systems, for example, even minor breaks in the metal can lead to failure.

In order to evenly apply the film to the arched door trim, the researchers divide it into small modules and then glue them to the door trim in sections: "Slight creases arise at the curvatures, which change the spacing of the electrodes. Even heat distribution would then no longer be ensured", the scientist states. In the longer term, the experts from Stuttgart intend to further simplify the procedure and spray the CNT dispersion directly onto the corresponding vehicle components. "This would make the production process considerably more economical – particularly in comparison to wire-based solutions", Sahakalkan says. A first demonstration model of the film heater will be presented by the scientists in September at the IAA in Frankfurt. The trade fair will take place from September 17th to 27th, the press day September 15th and 16th.

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5 / 5 (2) Sep 02, 2015
In colder climates, it's not enough to just keep the driver comfortable with a seat heater or a radiant heater. Water collects inside the car on every cold surface from the occupants breathing and wet clothes/shoes. It fogs and freezes on the insides of the windows, condenses under the floormats etc. which is a problem when you don't have a heated garage.

For safety reasons as well, you need a powerful heater to blow air on the front and side windows, as well as a glass heater at the rear, first to prevent the glass from fogging up, and secondly because in the winter you get freezing rain and sleet which sticks to the outside of the glass and blocks your view instantly if the glass isn't warm throughout.

When it's -15 C outside and people carry in snow with their shoes and generally sweat and breathe out water, it sometimes takes all the power you get from even an ordinary car's heater to keep the windows clear.
not rated yet Sep 02, 2015
Use the AC on recirc to remove internal moisture.
5 / 5 (1) Sep 02, 2015
The heater in a typical vehicle outputs between 1-5 kW of power depending on how high you set the temp and fans.

Consequentally, and because of other factors involved in colder climates such as higher rolling resistance and higher air resistance, the electric cars don't just halve their mileage:


The Renault Zoe which has an advertised driving range of 130 miles couldn't do more than 36.6 miles in the snowy Alps. The Mitsubishi i-MiEV drove 38 miles, just like the BMW i3. The Nissan LEAF managed 42.9 miles, and the Tesla Model S won the comparison test with a range of 128.5 miles.

This test shows the cold reduces an EV's range by more than 50 percent. That's bad but consider that gas cars are even worse: they don't even start when it's too cold.

On the last point I'll give a little cough-bullshit-cough because I've always managed to start cars down to -25 C with no trouble.
not rated yet Sep 02, 2015
Use the AC on recirc to remove internal moisture.

That doesn't work in colder climates because it'll only make the car colder, and you're not supposed to do that when it's well below freezing. The AC can't thaw out and becomes blocked with ice, and may get damaged because the coolant becomes so cold that it stops circulating.

They say you should run it for a couple minutes occasionally to keep the compressor and seals from drying out, but no more.

And for the electric car, it would be outright crazy to run an AC to first cool down air to draw moisture out of it, and then add heat with a heater to keep the passengers happy.
5 / 5 (1) Sep 03, 2015
The heater in a typical vehicle is obscenely overpowered because a fossil car is so inefficient that it has copious amounts of waste heat that it has to dispose of.

All that heat has to go somewhere, it may as well go into your cabin.

You don't need anywhere near that kind of heater power, and even if you did install 1KW, more than enough for a full sized bedroom, you'd still only use a small fraction of the power used for locomotion.

This whole article is focusing on a non-issue they just made up to try to convince people that an electric car can't possibly meet their needs.

They do. Get over it. If you want to pay more for your car, buy a guzzler. Stop standing in the way of me saving money on clean energy vehicles.
5 / 5 (2) Sep 03, 2015

On the last point I'll give a little cough-bullshit-cough because I've always managed to start cars down to -25 C with no trouble.

-25C Pff. That's nothing. Haven't you ever been anywhere cold? I spent 3 months in Yellowknife where it was -45C as a HIGH for 3 weeks straight. Gas cars? Well unless you left it plugged into a block heater overnight your oil has turned to gel. If you don't stop your radiator fan or block it's airflow it'll never make enough heat to warm the cabin.

And I went to a 30ft office trailer, 8 ft wide, 10 ft tall with 1" of insulation and single pane window. 3KW of heat was enough to make it toasty warm inside.

Tell me again how you need a 5KW heater to keep 2 cubic meters of air warm at -25C.

I get it. You want to destroy the planet. Well use your own money to do it and get out of the way of people trying to save money with green energy solution to your backwards world view.

not rated yet Sep 03, 2015
As usual Eikka you are brilliant at pointing out the flaws in an article or idea. Great points about the need for a real heating system when driving in wintery conditions.
not rated yet Sep 04, 2015
The heater in a typical vehicle is obscenely overpowered because a fossil car is so inefficient that it has copious amounts of waste heat that it has to dispose of.

On the contrary. Small TDi cars often struggle with providing enough heat in the winter. The reason is that most of the waste heat in an engine goes out the tail pipe, and only a small portion is left to be extracted out of the engine block and the coolant loop. An efficient small turbo diesel barely heats up the block.

And I went to a 30ft office trailer, 8 ft wide, 10 ft tall with 1" of insulation and single pane window. 3KW of heat was enough to make it toasty warm inside.

That's because it wasn't moving. The air blast on the front window will easily overpower a 3 kW heater.

Tell me again how you need a 5KW heater to keep 2 cubic meters of air warm at -25C.

Because you need to exchange the air to carry away moisture. If you put it on recirculate, the windows will fog up.
5 / 5 (1) Sep 04, 2015
And you're not heating just 2 cubic meters of air. You're heating the seats, the panels, the windows... it's the cold objects around you that make you feel cold, because the air itself is an insulator: it only transfers heat by direct touch, so its heating effect on you is dwarfed by your radiative heat loss to the cold interior of the car.

When the car around you has warmed up, it begins to return that heat radiation, and that's when you begin to feel warm. That's the point of the article - to install radiative heaters in the interior panels.

It works for comfort, that I'll give, but it still does nothing to the water problem. Water melts and collects wherever it's still cold, and if you don't get the car heated thoroughly to evaporate and drive the water out, you'll be scraping ice off the windows both inside and outside in the mornings and your electronics start to corrode.

I get it. You want to destroy the planet.

Don't shoot the messenger
5 / 5 (1) Sep 04, 2015
Ironically, in the colder climates in Scandinavia, electric cars have fuel operated heaters:


Volvo C30 electric vehicle uses ... ethanol for heat

At zero degrees Centidrade or slightly colder, you lose about 35-40 percent of the range if you use electricty [to heat the battery and or the cabin]. What we decided is we can have the opportunity to have this fuel-operated heater, which has a capacity of about six kilowatts

The system is a gasoline heater that was adapted to burn E85.

Volvo, being a Swedish manufacturer, pretty much knows what they're doing when it comes to driving in cold weather.
not rated yet Sep 04, 2015
spent 3 months in Yellowknife where it was -45C as a HIGH for 3 weeks straight

Almost forgot to add: lithium batteries stop working well before -40 C


a tenfold increase in resistance relative to room temperature has been measured in commercial cells at −20◦C

The internal resistance of the cells increase and the current output diminishes, and the efficiency of the battery drops, which results in diminished capacity. That's why electric cars sacrifice some energy to heat up the battery when the temperature is below freezing.

At -40...-45 C an electric car would simply refuse to charge or turn on unless you heat the battery up.

But those environments aren't really made for electric cars anyhow, because in Canada or Alaska, or Russia etc. where it really gets that cold you don't have the infrastructure to drive an electric vehicle. The distances are too great and you can't carry electrons in a jerry can
not rated yet Sep 06, 2015
you can't carry electrons in a jerry can

Sure you can. Every conventional car has an alternator, doesn't it?

Take this approach further and you have onboard power generation via an engine. You combine the efficiency of an electric motor with the energy storage, and the widely available and fast refil, of gasoline etc.

Taken to the extreme you'd probably want a small gas turbine for the electricity generation.
not rated yet Sep 06, 2015
Get over it. If you want to pay more for your car, buy a guzzler.

VW egolf price: 37 000€, electricity price for 100km = 2,25€, given 140km range (190 km is advertised but the ranges advertised are never reachable). I want to have the car for 7 yrs and travel 15 000 km a year; then sell it for i dont know how much but judging from the normal used cars market for ~7k. So, 37 000 + 7 x 150 x 2,25 - 7 000 = 32 352 €. The same golf, only petrol: price 17k, 6l/100km @ 1,35€/l = 8,1€, sold for 7k = 18 505€. And for that, almost half the cost, i get a complete car, not an EV.
The comparison would be even more ridiculous in the US with their dirt cheap petrol price and would be somewhat better, but i still doubt on par, in some eco crazed countries like netherlands and norway coz of taxes.

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