The role of occupants and their interactions with the building envelope and systems represent a key factor of uncertainty when predicting building energy use with simulation tools. The aim of this simulation-based study is to contribute to gaining further knowledge on how much the deviation between occupant-related input by (i) Swiss national and European standards (or suggested comfort categories), (ii) selected developed stochastic models in literature for window, blinds, light control behaviour and (iii) assumptions based on tracked employees' presence might impact predictions of heating/cooling needs in offices. The case study for the simulation is an open space office located in Geneva, Switzerland.