Energy storage by eutectic materials for the air conditioning of an electrical vehicle

Energy usage optimization is a crucial issue in electric vehicles, especially for energy consuming services such as air cooling, because vehicle autonomy is solely related to battery capacity. Positive phase change eutectic materials can be used to store thermal energy by exchanging latent heat; when phase change occurs around a "comfort zone" (i.e. about 20°C) those materials can be effectively used to control air temperature. Starting from components of natural origin, we exploited an eutectic material melting at about 22°C with high latent heat, to improve the performances of an electric cooling system, mounted on a fully electrical minibus. We measured time evolution of air temperatures inside the vehicle, as well as the electrical consumption of a cooler; tests have been carried out in a climatic chamber in order to simulate operational conditions in the summer season. Measures have been performed by installing into the vehicle 16 metal containers filled with the eutectic material, previously solidified; measures have been compared with available results from similar tests carried out without the material. The cooler alone was unable to maintain an inside temperature lower than 33°C, due to the standard insulation of the vehicle (e.g. windows made of standard glass, without any specially designed solution). By using the cooled eutectic material we obtained two main results: As first the temperature difference (outside/inside) ΔT = 13°C was reached and maintained for about 90 minutes without the need of active cooling; when turning on the electric cooling system, we maintained a ΔT = 13°C for about 6 hours.