GEOTABS combines a GEO-thermal heat pump with a Thermally Activated Building System (TABS). It is one of the most interesting technical solutions for energy efficient and healthy building. The study's objective is to research the characteristics of an optimized GEOTABS office building design. The two most important calculation methods used are the application of dynamic building simulations in TRNSYS and daylight simulations in Dialux. A trade-off of the evaluation variables ‘adaptive thermal comfort’, ‘energy consumption’ and ‘thermal balance of the ground’ has to be made in order to define the optimal solution and desired equilibrium for each specific demand.