With a length of more than 55 km, the Brenner Base Tunnel (BBT) connecting Austria and Italy will be one of the world’s very long tunnels in the future. During the construction phase, climatic conditions need to be maintained fulfilling the occupational health requirements, assuring the functionality of the machinery and allowing the intended construction processes. In view of the extended construction time of the BBT lasting several years and the long tunnel sections of more than 10 km, a sound planning of the preliminary ventilation and cooling systems is required. The proposed paper shall address the related requirements, the design methodology, the simulation tools and the results of the design process. In addition to the general methodology for the assessment of the tunnel environmental conditions, particular aspects shall be highlighted such as the heat and emission sources during the construction phase. The concepts for ventilation and cooling as well as the performance data of their key components shall be presented. As another topic, the impact of tunnel logistics and the need for flexible enlargement of the underground ventilation and cooling network shall be addressed.