Removal of heat generated by IT equipment in a data centre is facilitated by heat exchanging units mounted to back sides of open computer storage racks in which the IT equipment is mounted. One or more fans in the IT equipment generate an air flow across the IT equipment, and a heat exchanging unit mounted to the back side of the rack transfers heat in the air flow to a fluid coolant flowing through the heat exchanging unit. The heat exchanging unit has an air back pressure that does not significantly impede the air flow across the IT equipment, and a low fluid pressure drop for the fluid coolant, so that a cold air exhaust temperature of air exiting the heat exchanging unit is less than or equal to the room air temperature of input air entering the computer rack.