A space-saving, high-density modular data center and an energy-efficient cooling system for a modular data center are disclosed. The modular data center includes a first cooling circuit including a primary cooling device and a plurality of modular data pods. Each modular data pod includes a plurality of servers, a heat exchange member coupled to the first cooling circuit and a second cooling circuit coupled to the heat exchange member and configured to cool the plurality of servers, the second cooling circuit including a secondary cooling device configured to cool fluid flowing through the second cooling circuit. Each modular data pod also includes an auxiliary enclosure containing at least a portion of a distributed mechanical cooling system, which is configured to trim the cooling performed by a central free-cooling system.