A modular data center (MDC) has an air handling system that air cools a volumetric container and heat-generating equipment contained in externally attached equipment panels. Heat-generating information technology (IT) component(s) are positioned within the volumetric container with a cold aisle defined on one side and a hot aisle defined on another side of the IT component(s). The IT component(s) has air-cooling air passages that fluidly communicate between the cold and the hot aisles. A cooling unit pressurizes the cold aisle with supply air and draws return air from the hot aisle. The equipment panel(s) are externally attached to an exterior wall of the volumetric container. A supply air conduit directs supply air from the cold aisle into the equipment panel(s). A return air conduit directs air warmed by the heat-generating equipment inside the equipment panel into the hot aisle from the equipment panel(s) that receives the supply air.