The heat dissipated by data center equipment continues to increase due to the growing server power year by year. Thermal management continually becomes a challenging problem both from the standpoint of maintaining the equipment within a proper and reliable operation environment, as well as from a total energy cost perspective. With the total heat load increasing, as well as local high density heat fluxes, more cooling air flow rates may be needed by the racks which cannot be sufficiently provided by CRAC units. This may occur during peak periods of operation and may also occur in isolated aisles in the data center. Under such circumstances, just changing the air flow rates to specific aisles may cause unanticipated hot air recirculation into cold aisles which may happen during the transients that arise as the load and air flow rates are changing; henceforth, it may even occur in steady state. This could reduce the reliability of the data center equipment. A hybrid cooling strategy, which uses water to air heat exchangers located at the rear of specific racks to assist the air cooling, can be very effective in solving this problem by removing heat from the rack before it is exhausted into the room. This study describes the impact of this heat exchanger strategy on the thermal management of a data center. In this analytical study, the heat removal percentage and working efficiency of the heat exchanger are presented under different water flowrates and water inlet temperatures. Different case studies are conducted, showing that this method can significantly assist the data center air cooling under scenarios such as, power increases or CRAC unit failure. Detailed function of the heat exchanger on impacting the rack inlet temperatures are also discussed in this paper.

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