This study presents a prototype of an independent modular air containment (MAC) system that overcomes the limitations of the existing room-based cooling and applies a row-based cooling system for a high-density data center that can meet the requirements of energy efficiency. Furthermore, to improve the cooling efficiency and safety, we developed a novel in-row cooling package with multiple heat-transfer media (a sequential water-to-refrigerant-to-air heat exchange system). While complying with the standard test method, the objective cooling performance and PUE are derived through in-situ measurement in connection with the actual operation of a reference data center, and the energy saving contribution is analyzed. As observed from the result of the experimental measurement for the MAC with the novel in-row cooling package, the thermal balance is maintained between the water to refrigerant primary cycle and the refrigerant to air secondary cycle, and the air temperature in the cold aisle converges to 23 °C, satisfying the ASHRAE thermal guidelines. The energy influence of the in-row cooling package is extremely low with average 0.019 pPUE. For a reference data center, the analyzed energy efficiency can be improved from baseline PUE 1.563 to PUE 1.361 through 43.5% reduction in the cooling system.