In the climate planning of mines and tunnelling with anticipated poor climatic conditions, and especially in case of longer working shifts, the main question is whether it can be reliably prevented that certain climatic limits laid down be exceeded. Working at high temperature and/or humidity can lead to reduced human working energy - a very important economic aspect - and to a risky lack of concentration on the part of the miners or to heat collapse and extremely dangerous heat stroke. With the Deutsche Montan Technologie GmbH (DMT) climate prediction programs, both the dry and the extremely significant humid heat transfer can be calculated. This is due to the high planning reliability involved. With the help of these climate prediction programs it is already possible to determine the anticipated climatic values for the operation phase as early as the planning stage of new ore or coal fields or of tunnel construction projects and to design the optimum air cooling system for every underground project with due regard to technical and economic aspects.