Abstract: A system for cooling electronic equipment, especially modular electronic units mounted in racks, each having a casing with an air inlet, an air outlet and a fan for cooling the contents of the unit. The system uses a chiller unit, between adjacent racks for returning cooled air to ambient, each of which can be a piping array connected to a supply of chilled water. A baffle backing the piping array improves heat exchange and provides a more uniform transfer of heat to each array, thereby enabling optimum temperature differences to be achieved across each rack. A slidable framework supports the piping array and defines an air space on the cooled air side of the array. An auxiliary piping array extends rearwardly of racks so as to communicate with rear air spaces behind the racks and thereby cool heated air flowing in the rear air spaces.