This case study describes how a global financial services firm made energy-efficiency improvements in their legacy data center environments, which can be applied to other facilities with traditional chilled-water cooling designs. The facility power usage effectiveness (PUE) ratio was 2.3 at the start of the program and was reduced by 34% to 1.49, resulting in significant energy and operational cost reductions and enhanced rack densities and system capacities. This was achieved through an energy assessment and data hall air temperature survey, operator education workshops, implementation of air management improvements, optimization of cooling unit fan control, a gradual increase in air and chilledwater temperature setpoints (to ensure energy savings did not compromise reliability), and installation of a free cooling circuit.