Data centers are mission critical facilities that typically contain thousands of data processing equipment, such as servers, switches, and routers. In recent years, there has been a boom in data center usage, leading their energy consumption to grow by about 10% a year continuously. The heat generated in these data centers must be removed so as to prevent high temperatures from degrading their reliability, which would cost additional energy. Therefore, precise and reliable thermal management of the data center environment is critical. This paper focuses on recent advancements in data center modeling and energy optimization. A number of currently available and developmental thermal management technology in data centers are broadly reviewed. Computational fluid dynamics (CFD) for raised-floor data centers, experimental measurements, containment systems, economizer cooling, hybrid cooling, and device level cooling are all thoroughly reviewed. The paper concludes with a summary and presents areas of potential future research, which are based on the holistic integration of workload prediction and allocation, and thermal management using smart control systems.
As a common practice in the data center industry, chassis fans are used to direct air flow independent from neighboring servers. However, these fans are less efficient compared to larger rack level counterparts and also operate at higher sound levels. In this study, a novel approach is proposed whereby the smaller chassis enclosed fans are replaced with an array of larger fans, installed behind the stacked servers that share air flow.As a baseline study for comparison of the current scenario, a CPU dominated 1.5U Open Compute server, with four 60mm fans installed within the server, is characterized experimentally for its flow impedance, air flow rate, effect on die temperature and power consumption for various compute utilization levels. Larger fans with a square frame size of 80mm are carefully selected and individually characterized for their air moving capacity and power consumption. CFD is used to simulate the system of stacked servers and larger fans to obtain its flow characteristics and operating points.The fan power consumption of the larger fans is determined experimentally at these operating points replicated in an air flow bench. Comparing with the base line experiments, this study predicts a significant decrease in fan power consumption, without conceding the flow rate and the static pressure requirements of the server.
In general, smaller fans operate at lower efficiencies than larger fans of proportional linear dimensions. In this work, the applicability of replacing smaller, 60 mm baseline fans from within the chassis of web servers with an array of larger, geometrically proportional 80 mm and 120 mm fans consolidated to the back of a rack is experimentally tested. Initial characterization of the selected fans showed that the larger fans operate at double peak total efficiency of the smaller fans. A stack of four servers were used in a laboratory setting to represent a rack of servers. When all four servers were stressed at uniform computational loadings, the 80 mm fans resulted in 50.1–52.6% reduction in total rack fan power compared to the baseline fans. The 120 mm fans showed similar reduction in rack fan power of 47.6–54.0% over the baseline. Since actual data centers rarely operate at uniform computational loading across servers in a rack, a worst case scenario test was conceived in which the array of larger fans were controlled by a single server operating at peak computational workload while the other three in the rack remained idle. Despite significant overcooling in the three idle servers, the 80 mm and 120 mm fan configurations still showed 35% and 34% reduction in total rack fan power compared to the baseline fans. The findings strongly suggest that a rack-level fan scheme in which servers share airflow from an array of consolidated larger fans is superior to traditional chassis fans.
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