Energy saving strategies for electric vehicles operating in cold climates

Doktorsavhandling, 2024

Electromobility has gained significance over recent years in an attempt to reduce greenhouse gas emissions contributing to climate change. The requirements for the performance and efficiency of electric vehicles are high to make them an attractive alternative to conventional fossil-fuel-driven vehicles. Lithium-ion batteries are excellent energy storage systems when operated under conducive conditions, i.e. a temperature range of 15°C to 35°C. Their performance and cycling life are drastically affected when operated outside this range. In cold climates, the battery packs need to be heated for optimal performance. Additionally, the passenger cabins must be climatized. The energy for battery and cabin heating is derived from the packs, which consequently results in reduced driving range.

This work is concerned with strategies for reducing these heating loads. Three methods, namely cabin insulation, cabin air recirculation, and battery pack thermal encapsulation, have been investigated to estimate heating load reductions and their influence on vehicle range. 

Cabin insulation was investigated on a passenger car cabin and a truck cabin using computational fluid dynamics (CFD). Insulating the cabin reduced the heat losses, heating the cabin faster and to higher mean temperatures than the non-insulated configuration under a constant heating load. An adaptive cabin air recirculation strategy was used to control the return-air ratio such that window fogging was avoided, and good air quality could be maintained. Numerical simulations using a coupled CFD-thermoregulation model were performed on the truck cabin with cabin heating and recirculation controllers. Combining the two strategies (cabin insulation and air recirculation) further decreased the cabin heating energy consumption. 

Thermal encapsulation of battery packs as a means of passive battery thermal management was tested to improve the battery performance and decrease the heating demand for climatization after long parking periods in cold climates. Several levels of insulation on a calibrated battery pack model were studied under cool-down scenarios. With sufficient thermal resistance, the heat loss from the pack was minimized and the packs were kept at near-optimal temperatures. 

Finally, vehicle simulations were performed for a truck under parking-driving scenarios to investigate the effectiveness of all the strategies combined at various ambient temperatures. The cabin heating load decreased significantly, and the battery heating load was eliminated for all low ambient temperatures. Their combined effects led to the increase in vehicle range at low ambient temperatures, up to 7% at -20°C.