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vba based profiling tool for jbod enclosure system thermal characterization
greg shogan
lsi corp. – esg div., systems architect
austin, tx
abstract
in the advent of any storage enclosure development program the thermal architect/engineer will embark on sizing studies to establish the achievable cooling solutions and respective boundaries based on power, form factor, drive type/protocol, and other relevant packaging related criteria. this effort is typically comprised of a series of fragmented phases consisting of classical calculations, extrapolation of existing testing/emulation data, and numerical analysis (cfd or fea). this is a proven path but historically can be time intensive which does not facilitate today’s fast paced development schedules. a tool that can consolidate power requirements, fan/blower selection, and a resultant comprehensive temperature profile (key components, localized regions, and system level performance) in addition to enabling timely “what if” iterations would add significant value to any development program effort in terms of time and accuracy especially if executed during the architecture/concept phase. additional value would stem from utilization by the design engineer where the steep learning curve, as associated with cfd software tools, would be essentially non-existent. one example of this type of consolidated thermal sizing profiling tool, a vba (visual basic for applications) code based excel add-in, will be discussed as the basis of this paper.
introduction
the thermal characterization process for any enclosure based system can be summarized in the following steps:
- establish the system level heat dissipation based on the
projected power budget
- calculate the system level flow rate required to satisfy
the system level heat load including upper threshold
inlet temperatures and altitude effects (corner cases).
- pre-select blower/fan configurations that satisfy the
system flow rate requirements in the preceding step 2)
- project the system impedance of the system via
cfd analysis, classical calculations, empirical based
calculations, and/or testing methods (flowbench)
to determine blower/fan effective operating point(s) for
each fan/blower configuration considered in step 3)
- determine the acceptable flow rate for each customer
replaceable unit (cru), the hda case temperatures,
the critical localized ambient temperatures, and other
flow/thermal parameters.
- size/select/design heat sinks and thermal interface
materials (tim) that will result in compliant silicon
case/junction temperatures.
the basis of this paper will focus on the tool development integration of the first five steps with the last step to be featured in a future profiling tool release. the functional objective for the profiling tool will be to coalesce the steps in a compact menu-driven based program that will provide the thermal architect or design engineer with the ability to profile various storage enclosure scenarios in a timely fashion.
method
a combination of existing excel based programs were used as the foundation for the solver. these various programs addressed specific steps within the thermal characterization process. the programs were then customized accordingly. figure 1 illustrates an example. the existing programs, driven by classical heat transfer, fluid mechanics, energy balance, and fan performance equations have been validated against actual testing results for accuracy verification. the premise of this paper is the development of an integrated tool versus a dissection of the theoretical backbone. a reference, more applicable to the thermal engineer, is shown below. eq. 1-6 are a sampling of the core equations used in the integrated solver:
the hierarchal menu structure is comprised of three core input value & calculation areas. system flow rate sizing, operating point, and thermal profile maintaining a common submenu structure. albeit basic, this menu structure instills intuitive sequential methodology initiating with system flow rate sizing, followed by operating point verification, and concluding with system level temperature profiling.
figures 2-4 reflect the submenu tree for each core areas. figure 5 illustrates a typical input window. a sample display of input values window is shown in figure 6. figures 7 and 8 are snapshots of typical tabular and graphical results respectively.
fig. 1 sample of existing solver used as foundation for profiler solver/engine
fig. 3 operating point submenu tree
fig. 4 thermal profile submenu tree
fig. 5 system flowrate sizing input (# of drives)
fig. 6 system flowrate sizing display of input
fig. 7 operating point graphical results
fig. 8 thermal profile tabular results
conclusions
results when compared to actual physical testing are consistent and accurate. (refer to tables 1-3). the excel programs that provided the foundation for the integrated solver, have provided quality projections for several years previous to the creation of the vba based thermal profiling tool featured in this paper. although not a direct apple-to-apple replacement for a full-featured cfd tool, it is this author’s opinion that this type of implicitly defined profiling tool is the preferred choice during the architecture definition/concept phase of a program versus the use of an explicitly oriented cfd tool purely on the basis of reduced time/schedule to reach sound numerical conclusions.
table 1 comparison of actual system
test data (3u/16 array) to
storage enclosure profiler
results
table 2 comparison of actual system
test data (2u/12 array) to
storage enclosure profiler
results
table 3 comparison of actual system
test data (2u/24 array) to
storage enclosure profiler
results
future revisions will include a refined ui, include actual flow impedance calculations for the entire system per modified bernoulli [4] equation (versus only impedance input in this revision) including midplane related input, provide import of existing fan/blower pq data files, and provide enhanced graphic based results.
it should be noted that although the application for this paper was storage enclosure centric a similar tool could be developed for server & networking based enclosure architectures .
acknowledgements
i would like to direct a special thanks to my family that was very accommodating during the period of development of this vba based tool and resulting paper.
references
[1] del toro, vincent, principles of electrical engineering, 2nd edition, prentice-hall, 1972
[2] mcquiston, faye, and parker, jerald d., heating, ventilating, & air conditioning – analysis & design, 2nd edition, john wiley & sons, 1982
[3] holman, j.p., heat transfer, 5th edition, mcgraw-hill, 1981
[4] fox, r.w., and mcdonald, a.t., introduction to fluid mechanics, 2nd edition, john wiley & sons, 1978
about the author:
mr. shogan has 22 years experience in product development with the last nine years focused on electronics power/packaging/cooling solutions for server, storage, and networking enclosure platforms. currently, mr. shogan functions as a storage systems architect for lsi corp., esg div. responsible for the development of raid controller & disk array expansion enclosure architectures.
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