As part of the German Federal Ministry for Education and Research (BMBF) collaborative project Visio.M (earlier post, earlier post), scientists of the TU München have developed an energy efficient solution for passenger climate control in EVs. The researchers are presenting the results of their work, as implemented in the Visio.M prototype vehicle, in the German government stand at the Hannover Messe.
In a combustion-engined vehicle, waste heat could be used to heat the vehicle passenger compartments directly. Many electric vehicles simply took over concepts from the combustion engined vehicles—e.g., a heater and an air conditioner. However, the energy drain of this approach can put a noticeable dent in vehicle range. The Visio.M researchers thus took a new look at all potential solutions, considering their efficiency, comfort and cost.
In their research they quickly determined that cooling in direct proximity to the body provided the most efficient alternative. In contrast to previously deployed solutions, in which the entire interior is cooled or heated to the same temperature, heat is generated or dissipated only where it can actually be felt by the passengers.
Our trials showed that uniform climate control is not necessary. When we heat the seat of a passenger on cold days, passengers find it pleasant. With only a small amount of energy we can significantly reduce the sense of discomfort.—Marius Janta, staff member of the Chair for Ergonomics at the TU München
The temperature control of the seats in the Visio.M is accomplished using Peltier elements—semiconductor elements that can be used for both heating and cooling.
Even though Peltier elements are relatively expensive, they warm up or cool down immediately. Compared to the cold start of a combustion engine in winter, they even improve the level of comfort.—Alexander Präbst, a staff member at the Chair of Thermodynamics at the TU München
Since Peltier elements are light-weight, they are also deployed in the central air conditioning unit which cools the cabin. The installed Peltier elements have a performance capacity of up to 1.6 kW. The elements installed in the seats have a peak performance of 150 W per seat. On very cold days, a supplemental bioethanol heater with a rating of 4.5 kW can be switched on without sacrificing range.
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The Visio.M concept car achieves maximum efficiency not only through temperature control of the passenger space, but also by integrating the performance electronics into a holistic thermal management system. This allows the use of the waste heat from the motor and the performance electronics to heat the entire passenger compartment in the winter while excess capacity of the air conditioning system can also be used to cool the performance electronics in the summer.
The thermal management system is controlled by intelligent, self-adaptive software based on an evolutionary algorithm, developed at Technische Universität München. It evaluates the various sensor signals for temperature and humidity and automatically finds the optimal settings with regard to comfort, safety and efficiency using a simplified computer model.
A further comfort improvement can be achieved using a remote control of the air conditioning system via a smart phone. Thus shortly before his arrival, the driver can start heating or cooling. A preliminary air conditioning during charging could be added as well. Thanks to the open software platform of Visio.M adding of extensions is extremely simple and can take place without workshop visit.
The intelligent coupling of all heating and cooling functions for passengers and performance electronics results in a very compact climate control unit. The approach, the researchers note, can also serve as a model for combustion engine models, as well. In a combustion engine vehicle efficient climate control would generate savings, especially with regard to air conditioning. Beyond that, the compact system requires less space, which provides additional freedom for design and safety.
Participants in the Visio.M consortium were, in addition to the automotive companies BMW AG (lead manager) and Daimler AG, the Technische Universität München as a scientific partner, and Autoliv BV & Co. KG, the Federal Highway Research Institute (BAST), Continental Automotive GmbH, Finepower GmbH, Hyve AG, IAV GmbH, InnoZ GmbH, Intermap Technologies GmbH, LION Smart GmbH, Amtek Tekfor Holding GmbH, Siemens AG, Texas Instruments Germany GmbH and TÜV SÜD AG as industrial partners. The project was funded under the priority program “Key Technologies for Electric Mobility – STROM” of the Federal Ministry for Education and Research (BMBF) for a term of 2.5 years with a total budget of €10.8 million (US$11.4 million).