With the growth of information technology applications, the high energy consumption issue of data center cooling systems has drawn more attention. Existing cooling systems in data centers mostly adopt room air conditioners, which can easily cause local hot spot issues with low energy efficiency. By contrast, the rack-level cooling technology, which adopts on-demand direct cooling, is regarded as a promising solution. Aiming at rack-level cooling technology, some studies have been carried out from the aspect of design, performance analysis, and operation regulation. However, there is still a lack of systematic reviews to analyze existing deficiencies and to explore future development tendencies. Firstly, the different types of existing rack-level systems are investigated in detail. Then, the impact factors and operation performance are analyzed based on the existing studies. Furthermore, limitations and opportunities of the rack-level cooling technology are demonstrated in aspects of operation control, reliability, and energy-saving retrofit. Finally, technological limitations including the determination of optimal filling ratio, matching control for inhomogeneous load distribution, multi-rack integration model for solving redundancy problem, and opportunity in energy-saving retrofit are pointed out for promotion and application of rack-level cooling technology. This review is expected to contribute significantly to achieving green, sustainable, and energy-efficient data centers.

中文翻译：

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数据中心机架级冷却技术——全面回顾


随着信息技术应用的增长，数据中心冷却系统的高能耗问题越来越受到关注。数据中心现有制冷系统多采用机房空调，易造成局部热点问题，能效低。相比之下，采用按需直冷的机架级冷却技术被认为是一种有前途的解决方案。针对机架级冷却技术，从设计、性能分析、运行调节等方面开展了一些研究。但目前仍缺乏系统的综述来分析现有的不足并探讨未来的发展趋势。首先，详细研究了现有不同类型的机架级系统。然后，在现有研究的基础上，对影响因素和运营绩效进行了分析。此外，机架级冷却技术在运行控制、可靠性、节能改造等方面也表现出了局限性和机遇。最后，指出了最佳填充比例的确定、负载分布不均匀的匹配控制、解决冗余问题的多机架集成模型以及节能改造的机会等技术限制，为机架级制冷技术的推广应用提供参考。此次审查预计将为实现绿色、可持续和节能的数据中心做出重大贡献。