Researchers at the Fraunhofer Institute for Manufacturing Engineering and Automation IPA in Stuttgart have developed a film-based panel heater for electric vehicles. The panel is—particularly on short journeys—more effective than conventional electric heaters. (Electric cars generate little 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; prolonged use of the heater can significantly deplete range.)
The heating concept is based on a film that is coated with a very thin layer of conductive carbon nanotubes (CNTs). 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, according to Serhat Sahakalkan, project manager at the Fraunhofer IPA.
The heater functions—like conventional electric resistance heaters in EVs—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.
|In order to analyze the heating effect of the films for cars, the researchers connected them to a power source and monitored them using a thermo camera. © Fraunhofer IPA. Click to enlarge.|
In conventional electric resistance heaters, the conductive material usually used is copper wire—embedded in silicone mats, for example. The Fraunhofer solution offers several advantages:
While the copper wire heaters currently available 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. Such fast response times are ideal for short distances such as urban trips.
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.—Serhat Sahakalkan
In the longer term, the researchers intend to simplify the procedure and to 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 said.
A first demonstration model of the film heater will be presented at the IAA in Frankfurt.