Feasibility investigation on a novel rack-level cooling system for energy-saving retrofit of medium-and-small data centers

Conventional cooling systems in data centers generally adopt computer room air handlers, which have the local hotspot problem and substandard power usage effectiveness. The rack-level cooling system combined with mechanical refrigeration and free cooling is regarded as an effective solution. However, insufficient refrigerant supply and uneven refrigerant distribution problems often occur in the widely-used rack-level system based on backdoor evaporators. To overcome above mentioned shortcomings, a novel rack-level cooling system equipped with an assisted refrigerant pump for backdoor evaporators and a large-capacity reservoir is proposed. Then, the experimental studies are carried out to validate the cooling performance of the proposed system in a self-designed platform, and results indicate that the proposed system can supply sufficient refrigerant, which is beneficial for uniform refrigerant distribution. Finally, the feasibility is investigated for the energy-saving retrofit of the conventional cooling system in typical cities, and results indicate that the proposed system can save 54%, 49%, and 41% of annual energy consumption in Shenyang, Beijing, and Chengdu respectively, and the corre-sponding payback period is estimated at 4, 3.5, and 5 years. Because there is no electronic expansion valve installed in the inlet of every rack evaporator, it is noted that the outlet air temperature of the rack may not be controlled accurately when there is a large load difference among different racks.