Through a case study, this research explores an approach, which uses computer simulation technology, to evaluate different energy conservation alternatives and to assist facility managers to select reliable and feasible solutions. The subject facility is located in the Southeast region of the United States. One of the major challenges and operation goals of the General Services Administration, who manages the facility, is for that facility to achieve the Energy Star designation. However, due to the complexity of the facility, the requirements from building occupants, as well as other difficulties, finding a path for optimizing the operation of the facility in order to achieve the Energy Star designation is not always easy. This project uses eQuest, a simulation software tool, to create a "virtual environment", in which the operations of the HVAC (heating ventilation air-conditioning) system and the lighting of the facility are studied. Subsequently, recommendations initially made by experts through traditional energy audit approaches are evaluated in the "virtual environment" in order to determine the best solution to achieve the goal of the facility managers. This paper discusses major aspects of the project, including the challenges, the values and the limitations of applying computer simulation techniques in such a facility with cornplicated structural, occupancy and operation features. (c) 2005 Elsevier B.V. All rights reserved.