The current methods of building energy simulation that designers and engineers (D&E) use in order to find the energy performance of a building do not take into account the real behavior of the people who will use the building. The main aim of this paper is to show how by merely including the real behavior of people in building simulations there may be differences of up to 30%, through the study of a real pilot site simulation with existing software. These data confirm the possibilities of energy and money saving that energy simulation programs bring about when they include schedules of true use of the building (BIM). (C) 2013 Elsevier Ltd. All rights reserved.