Buildings and their various subsystems often do not perform as well as intended at the design stage. Building energy performance suffers from insufficient documentation of design intent, inadequate building commissioning, and a lack of robust methods for short term and continuous performance tracking. This paper discusses how calibrated models can be used to track building systems and component performance from design, through commissioning, and into operations. Models of the chillers energy use and efficiency were developed and used to evaluate energy performance and control changes to minimize energy use. The example discussed is based on an actual university building. A detailed discussion of the extrapolation and associated uncertainty of using six months of data to develop annual energy use scenarios from various chiller models is included. An important lesson concerning the design is that there was significant oversizing of the chillers resulting in poor part load performance and over $3,000 year of annual energy cost increases. The oversizing is related to extremely high estimates of office equipment loads. The oversizing also causes frequent cycling of chillers, which shortens chiller life. Due to the lack of careful start-up procedures, it appears construction debris fouled one of the new chillers, resulting in about $5,200 year in energy increases. Additional comments on design and commissioning issues are included. The monitoring, modeling, and software development efforts were developed to demonstrate the value of collecting and organizing information regarding design, commissioning, and ongoing performance. This case study is part of a larger effort to examine methods and technologies to improve buildings performance and develop interoperable Building Life-Cycle Information Systems (BLISS).