On the path to decarbonizing road transport, electric commercial vehicles will play a significant role. The first applications were directed to the smaller trucks for distribution traffic with relatively moderate driving and range requirements. Meanwhile, the first generation of a complete portfolio of truck sizes has been developed and is available on the market. In these early applications, many compromises were made to overcome component availability, but today, the supply chain has evolved to address the specific needs of electric trucks. With that, optimization toward higher performance and lower costs is moving to the next level. For long-haul trucks, efficiency is a driving factor for the total cost of ownership (TCO) due to the importance of the energy costs [1]. Besides the propulsion system, other related systems must be optimized for higher efficiency. This includes thermal management since the thermal management components consume energy and have a direct impact on the driving range. The main function of thermal management is to protect the components to ensure a long lifetime, especially in the case of the battery. The driver's comfort is another important purpose of the thermal management system (TMS). In the present study, the design development of the TMS layout for an electric heavy-duty (HD) truck is described. The modeled TMS is challenged under different operation conditions, including demanding drive cycles as well as fast charging events. The results are analyzed in terms of energy flows and the usage of the different components of the thermal system. From those results, conclusions are derived for the sizing of components to meet the requirements of electric HD truck applications.