Research Papers

Effectiveness of Rack-Level Fans—Part II: Control Strategies and System Redundancy

[+] Author and Article Information
John Edward Fernandes

Mechanical and Aerospace Engineering Department,
University of Texas at Arlington,
P.O. Box 19023,
Arlington, TX 76013
e-mail: john.fernandes@mavs.uta.edu

Richard Eiland

Mechanical and Aerospace Engineering Department,
University of Texas at Arlington,
P.O. Box 19023,
Arlington, TX 76013
e-mail: richard.eiland@mavs.uta.edu

Bharath Nagendran

Amazon Lab, 126
Thermal Engineer Enterprise,
Sunnyvale, CA 94089
e-mail: bhanagen@amazon.com

Veerendra Mulay

Facebook Inc.,
Menlo Park, CA 425081
e-mail: vmulay@fb.com

Dereje Agonafer

Fellow ASME
Mechanical and Aerospace Engineering Department,
University of Texas at Arlington,
P.O. Box 19023,
Arlington, TX, 76013
e-mail: agonafer@uta.edu

1Corresponding author.

Contributed by the Electronic and Photonic Packaging Division of ASME for publication in the JOURNAL OF ELECTRONIC PACKAGING. Manuscript received February 19, 2017; final manuscript received September 21, 2017; published online October 27, 2017. Assoc. Editor: Pradip Dutta.

J. Electron. Packag 139(4), 041012 (Oct 27, 2017) (9 pages) Paper No: EP-17-1022; doi: 10.1115/1.4038014 History: Received February 19, 2017; Revised September 21, 2017

Fan efficiency is known to increase with size. In part I of this study, savings in server fan power on the order of 50% were reported by replacing server-enclosed 60 mm fans with a rear-mounted wall of larger fans (80 mm or 120 mm in size). A methodology for row-wise control of such rack-level fans, with the purpose of simulating an actual product, is previewed and savings comparable to part I are reported. Performance under real-life scenarios such as nonuniform computational loads and fan failure is investigated. Each rack-level setup has distinct advantages. Selecting between configurations would necessitate a compromise between efficiency, redundancy, and cost.

Copyright © 2017 by ASME
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Fig. 1

Intel-based open compute server with air duct removed for visual purposes

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Fig. 2

Simplified depiction of the fan wall installed behind the stack for both (a) 80 mm and (b) 120 mm cases with corresponding names for all primary components

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Fig. 3

Simplified depiction of the test setup with control and data acquisition equipment

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Fig. 4

(a) Operating temperatures under 98% load when fan rows are individually run at higher speeds and (b) influence of each fan row on server cooling; used to select coefficients for the control scheme

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Fig. 5

Duty cycle signal from each server is converted into an analog voltage by a low-pass filter and read by the microcontroller board. These inputs are processed by a LabVIEW program and a PWM output is sent to each fan row.

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Fig. 6

Comparisons between (a) cooling power, (b) average CPU operating temperature, and (c) IT power demonstrate that a 7.5% lower bound (LB) in 80 mm fan duty cycle is required to ensure that adequate cooling is provided when compared to the 60 mm baseline

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Fig. 7

Comparison of (a) cooling power, (b) average operating temperature of the stack, and (c) stack IT power consumption for all final configurations under uniform computational loads

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Fig. 8

Locations of simulated individual fan failures for (a) 60 mm, (b) 80 mm, and (c) 120 mm configurations

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Fig. 9

Life expectancy of chosen fans as a function of operating temperature



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