A cooling unit is provided to facilitate cooling of coolant passing through a coolant loop. The cooling unit includes one or more heat rejection units and an elevated coolant tank. The heat rejection unit(s) rejects heat from coolant passing through the coolant loop to air passing across the heat rejection unit. The heat rejection unit(s) includes one or more heat exchange assemblies coupled to the coolant loop for at least a portion of coolant to pass through the one or more heat exchange assemblies. The elevated coolant tank, which is elevated above at least a portion of the coolant loop, is coupled in fluid communication with the one or more heat exchange assemblies of the heat rejection unit(s), and facilitates return of coolant to the coolant loop at a substantially constant pressure.