Effects of airflow on the thermal environment and energy efficiency in raised-floor data centers: A review

Airflow is crucial for air-cooled data centers. Its flow path and distribution influences the thermal environment and energy efficiency of raised-floor data centers. This paper provides a review of the topic including the aspects of airflow factors, numerical study, airflow performance metrics, and thermal optimization. Based on the multi-scale characteristics of the data center, the thermal environment is categorized into room-level, rack-level, and server-level environments. For the room-level thermal environment, the main factors include layout, raised floor plenum and ceiling height, and perforated tiles. For the rack level, the effects of the porosity ratio of rack door, airflow rate/temperature, server population, server arrangement and power density are considered. For the server level, airflow rate and server fan speed are investigated. Moreover, numerical studies have been widely employed to understand the thermal environment of data centers. The selections of simulation tool and the methods for simplifying and validating the models are key to predicting the data center's thermal behavior correctly. In addition, airflow performance metrics and multi-scale thermal optimization are summarized and discussed. This review aims to emphasize the importance of the airflow in data centers and thus serve a guiding reference for airflow design and energy efficiency in data centers. Some recommended topics for future research are also provided.