The paper describes a case study of an information technology office building with a radiant cooling system and a conventional variable air volume (VAV) system installed side by side so that performance could be compared. First, an energy model of the building was developed in EnergyPlus, a simulation tool. Second, a base case model was developed to generalize energy saving potential of radiant cooling system. This paper details the calibration of the whole building energy model to the component level, including lighting, equipment, and HVAC components such as chillers, pumps, cooling towers, and fans. The error at the whole building level [measured in mean bias error (MBE)] is 0.2%, and the coefficient of variation of root mean square error (CvRMSE) is 3.2%. The total errors in HVAC at the hourly are MBE = 8.7% and CvRMSE = 23.9%, which meet the criteria of ASHRAE Guideline 14 (2002) for hourly calibration. A base case model was developed by using the calibrated model for quantifying the energy saving potential of the radiant cooling system. It was found that a radiant cooling system integrated with DOAS can save 28% energy compared with the conventional VAV system.