Data center design point operation is rarely realized and most data center cooling equipment is operated off-design, which has a significant effect on the energy consumption. This paper addresses the development of a thermo-hydraulic model based on an existing ~6 MW data center and chiller plant located in Poughkeepsie, New York. Inherent in this model is the ability to capture off-design operation of the cooling infrastructure caused by changes in ambient conditions, operating strategies and fluctuations in IT load. Collected data is used for validation showing agreement within 5% in the aggregate, at a number of off-design operating conditions.