Energy modeling can be a powerful tool for managing energy-reduction concepts for an institution. Different types of energy models are developed at various stages of a project to provide data that can verify or disprove suggested energy-efficiency measures. Education institutions should understand what an energy model can do and, more important, what the limitations of the model are at each stage of design and construction. One of the main sustainability goals for construction projects is to optimize a building's energy efficiency. The reduction of a building's energy usage results in an overall reduction in lifetime owning/operating costs. With so much at stake, energy modeling is a useful tool for school facilities as they make decisions on a project. Building energy modeling enables engineers to model a building's performance mathematically over a period of time to gain an understanding of the potential building energy usage. Energy modeling can be carried out during design, pre-construction and post-construction.