A data center row infrastructure module, comprising: at least two free-standing exhaust plenum structures which establish opposite side ends of an enclosure, wherein each free-standing exhaust plenum structure comprises: a plurality of frame members (322, 324) that provide structural support to the plenum structure, a plurality of wall elements (327, 329), an internal exhaust air plenum at least partially encompassed by the wall elements (327, 329) to restrict flow of exhaust air from the internal exhaust plenum into the enclosure, wherein the internal exhaust air plenum is configured to receive exhaust air from the enclosure via one or more gaps and direct the received exhaust air through an exhaust air outlet on a top end of the free-standing exhaust plenum structure, and a support arm structure; a cooling air plenum; and a plenum module spanning a top end of the enclosure between the at least two free-standing exhaust plenum structures to establish a top end of the enclosure on a lower surface of the plenum module and to establish a bottom end of the cooling air plenum above and separate from the enclosure, the plenum module comprising at least an intake air supply vent configured to supply intake air from the cooling air plenum to the enclosure, wherein at least a portion of the structural load of the plenum module is supported by the support arm structures. at least two free-standing exhaust plenum structures which establish opposite side ends of an enclosure, wherein each free-standing exhaust plenum structure comprises: a plurality of frame members (322, 324) that provide structural support to the plenum structure, a plurality of wall elements (327, 329), an internal exhaust air plenum at least partially encompassed by the wall elements (327, 329) to restrict flow of exhaust air from the internal exhaust plenum into the enclosure, wherein the internal exhaust air plenum is configured to receive exhaust air from the enclosure via one or more gaps and direct the received exhaust air through an exhaust air outlet on a top end of the free-standing exhaust plenum structure, and a support arm structure; a plurality of frame members (322, 324) that provide structural support to the plenum structure, a plurality of wall elements (327, 329), an internal exhaust air plenum at least partially encompassed by the wall elements (327, 329) to restrict flow of exhaust air from the internal exhaust plenum into the enclosure, wherein the internal exhaust air plenum is configured to receive exhaust air from the enclosure via one or more gaps and direct the received exhaust air through an exhaust air outlet on a top end of the free-standing exhaust plenum structure, and a support arm structure; a cooling air plenum; and a plenum module spanning a top end of the enclosure between the at least two free-standing exhaust plenum structures to establish a top end of the enclosure on a lower surface of the plenum module and to establish a bottom end of the cooling air plenum above and separate from the enclosure, the plenum module comprising at least an intake air supply vent configured to supply intake air from the cooling air plenum to the enclosure, wherein at least a portion of the structural load of the plenum module is supported by the support arm structures.