The Role of CFDs in Containment

The Role of CFDs in Containment

Data center airflow management engineers have used Computational Fluid Dynamics (CFD) programs for years to determine the complicated movement of airflow in data centers. CFD models pinpoint areas where airflow can be improved in order to provide a consistent cooling solution and energy savings.

We interviewed Gordon Johnson who is a certified data center design professional, Data Center Energy Practitioner (DCEP), CFD and electrical engineer regarding the use of CFD’s and containment.

Gordon, what is the principle way CFD’s are used with regard to containment?

We use CFD’s to determine two basic data sets. The first is the baseline, or the current airflow pattern. This initial CFD model shows supply intake temperatures to each cabinet. This model also determines the effectiveness of each AC unit as it relates to airflow volume, return air temperature, delta T, and supply air temperature.

The second model is the proposed design of the CFD engineer who uses the information from the base model to enact airflow management best practices to separate supply from return airflow. Typically several models are created in order to adjust airflow volume, set point temperatures, and adjust individual aisle supply volume.

Gordon, Are there situations in which the CFD engineer does not recommend containment?

Not really, because the entire basis of airflow management is the full separation of supply and return airflow. Anytime these two airflows mix there is a loss of energy and consistent supply temperature to the IT thermal load.

We have seen CFD’s used by manufactures to prove product effectiveness. What are some ways CFD’s are made to exaggerate product effectiveness?

Exaggerations usually stem from the principle known as GIGO, short for Garbage In, Garbage Out. This refers to the fact that computers operate by logical processes, and thus will unquestioningly process unintended, even nonsensical input data (garbage in) and produce undesired, often nonsensical output (garbage out).

Let me give you an example. Recently I recreated a CFD model that was used to explain the effectiveness of airflow deflectors. The purpose of the CFD was to show the energy savings difference between airflow deflectors and full containment. We found that certain key data points were inserted into the models that do not reflect industry standards. Key settings were adjusted to fully optimize energy savings without regard to potential changes to the environment. Any potentially adverse effects to the cooling system’s ability to maintain acceptable thermal parameters, due to environmental changes, are not revealed in the CFD model. Thus, the model was operating on a fine line that could not be adjusted without a significant impact on its ability to cool the IT load.

Can you give us any specifics?

The airflow volume was manually changed from 1 kW at 154 CFM to 1 kW at 120 CFM. Industry standard airflow is 154 CFM. The formula most commonly used is as such:


120 CFM airflow does not give the cooling system any margin for potential changes to the environment.

Another key area of unrealistic design is the placement of cabinet thermal load and high volume grates. The base model places high kW loads in specific, isolated areas surrounded by high volume grates. What then happens, if additional load is placed in areas of low volume airflow? Any changes to the rack kW in areas without high volume grates could not be accounted for. At the end of the day, any changes to the IT load would require an additional airflow management audit to determine what changes would affect the cooling solution. Thus, the proposed model is unrealistic because no data center would propose a cooling solution that would require regular modifications.

Are you recommending a CFD study every time you make changes to the data center thermal load?

No. a full separation supply and return airflow eliminates the guesswork with regards to the effect of air mixture. It also eliminates the need of specific high volume perforated tiles or grates to be placed in front of high kW loads. Instead, a CFD model would incorporate expected increases to the aisle thermal load. This falls in line with the “plus 1” kind of approach to cooling. Creating a positive pressure of supply air has many additional benefits, such as lowering IT equipment fan speed, and ensuring consistent supply temperature across the face of the IT intake.

Data centers should not be operated with little margin for changes or adjustments to the thermal load. That is why I always recommend a full containment solution with as close to 0% leakage as possible.  This is always the most efficient way to run a data center, and always yields the best return on investment. The full containment solution, with no openings at the aisle-end doors or above the cabinets, will easily allow the contained cold aisles to operate with a slightly greater supply of air than is demanded.  This in turn ensures that the cabinets in the fully contained aisle have a minimum temperature change from the bottom to the top of the rack, which allows the data center operator to easily choose predictable and reliable supply temperature set points for the cooling units.  The result?  Large energy savings, lower mean time between failures, and a more reliable data center.

What do you recommend as to the use of CFD studies and containment?

It’s important to create both an accurate baseline and a sustainable cooling solution design. This model will give data center operators a basis for an accurate representation of how things are being cooled. The proposed cooling solution can be used in numerous ways:

  • Accurate energy savings
  • Safe set point standards
  • Future cabinet population predictions
  • The ability to cool future kW increases
  • Identify and eliminate potential hot spots

Subzero Engineering endorses accurate and realistic CFD modeling that considers real world situations in order to create real world solutions.

Airflow ManagementCFDCold Aisle ContainmentComputational Fluid DynamicsContainmentdata centerData Center Containmentdata center coolingGordon JohnsonHot Aisle ContainmentLarry MainersSubzero Engineering
Two Subzero Engineers Meet Modern Data Center Challenges through DCEP and CDCDP Certification

Two Subzero Engineers Meet Modern Data Center Challenges through DCEP and CDCDP Certification

CDCDP (Certified Data Center Design Professional) – The CDCDP training addresses how to setup and improve key aspects such as power, cooling, security, cabling, safety etc. to ensure a hi-available data center.
DCEP (Data Center Energy Practitioner) – The US Department of Energy has partnered with the data center industry to develop an educational program and accreditation for those working as data center professionals.

Subzero Engineering showcased their continued commitment to saving energy and maintaining best practices by sending two corporate engineers to participate in these advanced learning opportunities and are proud to announce the recent CDCDP accreditation of Rick Lake and the DCEP accreditation of Gordon Johnson.

“Today’s modern data centers are complex and require an enormous amount of knowledge and skill to correctly design, build and operate.  From servers to storage, chillers to cooling towers, efficient utilization of electrical power to industry best practices… all this and more demands that those who design, operate, and manage data centers be fully trained to meet these incredible challenges all while maintaining a competitive advantage.  Contractors and consultants who work in the data center industry face a similar challenge to maintain a current knowledge base and skill set required to service the data center industry in a meaningful way in order to provide products and relevant services for this dynamic industry.

One of the ways that the data center industry has met this challenge is through embracing certification programs that deliver specific training that provide the knowledge and skills necessary to succeed. The Certified Data Center Design Professional (CDCDP) training program is one such program designed to cover all aspects of data centers. The course syllabus includes topics specific to design, cooling, power, IT equipment, and management; taught over a period of seven days through case studies.  The program requires the student to pass a series of five examinations to obtain the certification that is valid for a three-year period, after which refresher courses must be taken in order to maintain the certification.

Subzero Engineering, the industry leader in airflow management products and services, has recognized the relevance of this certification and in 2012 sent two staff engineers to become fully CDCDP certified via the training offered by CNet Services.

As one of those individuals, I am happy to say that the program succeeded in providing relevant and up-to-date information that has increased my knowledge of the data center industry in general.  With this valuable information, I feel fully equipped to assist clients make specific, cost-effective and measurable improvements to their operations.”
Rick Lake, CDCDP / DCIM Manager / Subzero Engineering

“My recent experience attending the DOE DCEP training and certification program in Dallas was exceptional.  I completed and successfully passed the Level 1 Practitioners (Generalists) program and am now looking forward to putting into practice the training and skills received to perform accurate energy assessments in data centers.

The disciplines covered in the training (IT-equipment, cooling systems, air management, and electrical systems) as well as the experience gained using the DC Profiler Tool will be invaluable with my work at Subzero Engineering of data center containment, air flow management, and data center energy efficiency.  Besides having the training and experience now to perform energy assessments in data centers, I look forward to transferring the knowledge received to our customers, data center staff, and my coworkers.

In summary, I feel the recent training and certification received has elevated my standards and awareness in what is necessary in order to further reduce energy consumption levels in data centers and related costs, which in the end translates into more overall savings for our customers.”
Gordon Johnson, EE, CDCDP, DCEP / CFD Engineer / Subzero Engineering

CDCDPData Center ContainmentDCEPDCIMGordon JohnsonRick LakeSubzero Engineering