With the recent development of the IT technology, the demand for data centers has significantly increased, and modular data centers have attracted considerable attention because of their excellent stability, scalability, and economic feasibility. This research quantitatively analyzed the applicability of various air-side economizers and their energy-saving potential in modular data centers. A detailed cooling load estimation process was established for modular data centers, and annual cooling energy simulations were carried out using various air-side economizers. The various air-side economizers yielded cooling coil load savings of 76-99% in comparison to conventional cooling systems in data centers, and the total cooling energy savings of the economizers ranged from 47.5% to 67.2%. Indirect air-side economizers with high-effectiveness heat exchangers were found to yield significant energy saving (63.6%) and have simple system configurations. (C) 2014 Elsevier Ltd. All rights reserved.