A cooling approach is provided for cooling an electronics subsystem, such as an electronics rack. The cooling approach includes a coolant conditioning unit and a thermal capacitor unit. The coolant conditioning unit has a heat exchanger, a first cooling loop and a second cooling loop. The first cooling loop receives facility coolant from a facility coolant source and passes at least a portion thereof to the heat exchanger. The second cooling loop provides system coolant to the electronics subsystem, and expels heat in the heat exchanger from the electronics subsystem to the facility coolant in the first cooling loop. The thermal capacitor unit is in fluid communication with the second cooling loop to maintain temperature of the system coolant within a defined range for a period of time upon shutdown or failure of the facility coolant in the first cooling loop, thereby allowing continued operation of the electronics subsystem.