Förbättra energieffektiviteten och passagerarkomforten i elfordon

Forskningsprojekt, 2025

The UN SDGs has identified several global challenges. These include an affordable, accessible, sustainable, and safe transport system for all. This system must be low in emission as well as time, energy and cost efficient. Electrification has been one response to this goal. The requirements for the performance of battery electric vehicles (BEVs) are still high to make them an attractive alternative to conventional fossil-fuel vehicles when travelling long distances. One main reason is that BEVs do not have ‘free’ heat from the engine that can be used for climatizing the cabin. This must be provided by the batteries. It is estimated that more than 50% of the battery capacity of city busses is used to keep comfortable interior temperatures, for passenger vehicles and heavy-duty vehicles, these values are 30% and 10%, respectively. This greatly limits the driving range creating a ‘range anxiety’ in BEV users and imposes operational challenges for commercial profitable use in large scale.

The energy spent to climatize the cabin depends on the thermal comfort of passengers which is perceived differently by males/females and elderly/adults/children during winter/summer conditions [1]. This implies that knowledge of thermal management and human factors is needed to further understand and improve the energy expenditure. Reductions in energy usage for climatization can be achieved with insulating materials, by increasing the amount of air cabin recirculation, by localizing heating/cooling distribution to satisfy passenger’s needs, and by recommending that passengers are ‘properly dressed’ with the right amount of clothe layers. Insulation can be costly and unattainable due to packaging. Air recirculation is effective in scaling down thermal loads, but it must be controlled as it increases the CO2 levels inside the cabin causing drowsiness impairing safety and comfort. Right clothing is a simple solution, but uncomfortable during long travelling distances. Localized heating/cooling distribution is an alternative that has been little explored so far.

With this background, the purpose of this project is to increase the understanding of thermal load requirements for cabin climatization in BEVs coupled to safety and perceived passenger thermal comfort under various operating conditions. To enable this, the expertise from the Vehicle Aerodynamics & Thermal Management group at Division VEAS/M2 (Prof. Simone Sebben) and from the Division Design & Human Factors/IMS (Prof. Anna-Lisa Osvalder) is needed. Prof. Sebben has long experience in thermal management issues from her time as an engineer at Volvo Cars and has currently two on-going PhD projects in the area [2,3]. Prof. Osvalder has performed several field user studies related to overall comfort and safety in vehicles for passengers with variations in age, gender, and anthropometric measures. She supervises one PhD-student at Zeekr focusing on NVH and comfort in vehicles, and one PhD-student at Chalmers focusing on objective/subjective methods for comfort studies, and development of a holistic model presenting the complexity of car ride comfort, in collaboration with Volvo Cars, Autoliv, and Delft University (Prof. Peter Vink).

In this pilot project, passenger vehicles are the focus as the cabin size is relatively small, simple, and less costly to simulate in CFD (Computational Fluid Dynamics). Only traditional vehicle interiors will be considered with maximum 2+3 passengers. From the CFD simulations, the temperatures and the estimated passenger comfort obtained using available human comfort models (mostly for males) will serve as input for 1-D thermal simulations to study strategies that reduce the energy required from the HVAC (Heat, Ventilation, Air Conditioning), the system responsible for interior climate. For this, coupled 3D-1D numerical procedures need to be developed. The results from the human comfort model will be compared with available data from literature, and with findings from a field study with passengers (n=18, equal men/women/children), evaluating perceived comfort in the front/back seat during different thermal loads. Methods for evaluation of passengers’ comfort experience in field studies have been developed and used in resent research by Prof. Osvalder [4-6], which can serve as a basis for designing subjective evaluation methods for passengers’ thermal comfort experience in BEVs.

From this collaboration, a numerical methodology for head load reduction estimation will be derived considering thermal human comfort models based on the subjective evaluation obtained in the field study. An increased understanding between the two disciplines and their coupling can improve thermal comfort experience for males/females/children at minimum energy expenditure. Based on the results, the next step is to explore strategies for thermal comfort in commercial vehicles where the challenge is the long-distance travelling. For buses, the challenges are the number of passengers and the continuously opening/closing of doors. Adequate thermal comfort is a crucial parameter to consider if public transportation is to become more attractive. A further step would be to propose alternative vehicle interior designs where sitting positioning could facilitate meeting comfort requirements at lower energy costs.

This project will open for 1-2 collaborative conference papers and a dialogue with industry and Delft University of a joint research project. The relevance of this proposal is confirmed by Volvo Cars, Volvo AB and Zeekr preliminary interest in participating as an observing supporting partner.

Relevance UN’s SDG:

[11]: Promote sustainable cities and communities by facilitating access to energy efficient and safe solutions in the transport sector.  

[12]: Reduce costs of ownership, promote public conscious, safe and comfortable transport alternatives.

[13]: Increasing the attractiveness of BEVs by reducing energy usage and extending the drive range.

References:

[1] Asif, A, et al (2022). Investigating the gender differences in indoor thermal comfort perception for summer and winter seasons and comparison of comfort temperature prediction methods, https://doi.org/10.1016/j.jtherbio.2022.103357

[2] Energimyndigheten P48024-1: Encapsulation of Heat Generating Units for Improved Energy Efficiency and Effective Climatization on Battery Electrical Vehicles.

[3] Energimyndigheten P48024-1: Optimisation of the underhood flow for improving energy efficiency of BEVs.

[4] Makris, M, Osvalder,A-L & Bohman,K (2023). Comfort Experience of Rear Seated Car Passengers Over Time in Stationary and Driven Scenarios. In: Makris, M (2023). How does it feel and how is it measured? Licentiate thesis, Chalmers/IMS, Sweden.

[5] Makris,M, Osvalder,A-L, et al (2024). Unveiling the Complexity of Car Ride Comfort: A Holistic Model. AHFE Conference, Nice, July 24-27.

[6] Wang,X, Osvalder,A-L & Höstmad,P (2023). Influence of Sound and Vibration on Perceived Overall Ride Comfort: A Comparison between an Electric Vehicle and a Combustion Engine Vehicle. SAE Int Journ Vehicle Dynamics, Stability, and NVH, 23802162(ISSN) Vol7.