A data center immersion cooling system is described. The system comprises: an immersion tank; a heat exchanger to extract heat from heated coolant and transform heated coolant into cooled coolant; a coolant supply line to supply the cooled coolant from the heat exchanger to the immersion tank; and a coolant return line to return the heated coolant from the immersion tank to the heat exchanger, wherein the immersion tank further comprises: a plurality of equipment compartments that accommodate electronic devices; and a heated coolant reservoir disposed around the plurality of equipment compartments, wherein the cooled coolant enters the equipment compartments from the bottom, wherein the heated coolant in the equipment compartments exits the equipment compartments at the top, and is collected into the heated coolant reservoir, and wherein the heated coolant in the heated coolant reservoir is returned to the heat exchanger via the coolant return line. The heated coolant reservoir also provides a buffering function to the systems which is needed in several operating scenarios.