When it comes to cabin heating concepts of future EVs, we are convinced that only a smart combination of conventional (convective) heating and surface heating will serve both energy efficiency as well as passenger thermal comfort targets.

Amongst others, thermal comfort is one of the most important interfaces between the human and the machine. If we don’t feel comfortable, we tend to dislike the whole product, independent on other aspects. The vehicle attribute “passenger thermal comfort” must be engineered like any other attribute employing state of the art development methodology.

However, since the human organism is not able to feel temperatures but interprets heat flux as a warm or cold feeling, we need to rethink current target functions which are based on temperatures in the cabin once we introduce surface heating. This goes hand in hand with new development methodologies that need to account for those updated target functions since common methods of measuring thermal comfort are based on temperatures instead of heat flux.

The conventional development process for passenger thermal comfort engineering is based on simulation (Computational Fluid Dynamics coupled with radiation solvers) and testing. Testing employs human manikin methods as well as temperature sensors which are placed inside the cabin based on VDA guidelines and customer specific norms. However, measuring each kind of heat transfer mechanism, quantifying the passenger thermal comfort and putting that in relation with energy required (which equals impact on driving range) is a complex and challenging task.

ATT develops, industrializes and manufactures intelligent heating systems based on printed polymers. Whenever possible, we try to introduce intelligence to heating systems, as we believe in on-demand heating to be one answer to the question “how can we save energy to maximize driving range of electric vehicles?”

We are highly involved into thermal comfort engineering projects in different industries (Automotive, Aerospace and Rail) and we know how to develop and exactly specify surface heating systems to optimize thermal comfort with an energy saving potential of up to 30% compared to purely convection driven concepts.

For us, thermal comfort is a predictable parameter, which we exactly engineer based on given limits and boundaries. ATT is the turn-key solution for thermal comfort. As a one stop shop, we engineer the solution, manufacture the required heating elements and provide the tools to measure thermal comfort.

We use a highly sophisticated virtual representation of the human organism to run our thermal comfort analysis. Seat heating or steering wheel heating for example have a very interesting impact on the thermal comfort sensation. They both have a very positive impact on the sensation even if the individual feels very cold overall. But as soon as the seat heating becomes too warm, the positive sensation flips into a negative one. Even effects like this can be modeled and predicted precisely.

Our process for thermal comfort engineering focuses on a comparison between the baseline version of the vehicle’s HVAC (pure convective heating – no surface heating installed) with the configuration including surface heating elements at different location. Besides objective comfort criteria, we calculate the overall energy consumption and savings based on different target functions and operating strategies and thus help to define location, quantity, power requirement and control strategies for surface heating systems to be implemented in an existing convective system.

The following image shows a representative result of a passenger thermal comfort analysis, comparing the baseline of the vehicle with convectional heating (left) with the configuration including surface heating elements (right). It can be clearly seen that the required power for the overall system is reduced considerably due to the optimized system.

After performing a depth analysis of the collected data, we are able to precisely predict how a human being would thermally feel being exposed to the defined environment. The charts below show the thermal comfort sensation of the driver and the passenger with and without the integration of heated surfaces. We analyse in detail the thermal response and the thermopsychological interpretation of the human body dependent on different thermal load cases and dependent on the body region. Data like these form the fundament of a consequent thermal comfort engineering process.