As a property manager, you are frequently confronted with the need to make energy-use decisions when planning new buildings or redeveloping existing ones. You do not want to spend money for consultants, architects, and construction only to discover that, once built, the building incurs excessive costs for energy or maintenance. These costs directly affect the bottom line of your building. Although most owners pass energy costs on to their tenants, a building with high energy costs is not as competitive in the marketplace as one whose energy costs have been controlled. This article addresses one approach to managing energy costs: previewing the building’s operation, construction, or renovation through use of a computer technique called “building energy simulation”.