Achieving Data Center Containment Through Seismic Requirements13 min read
Conventional wisdom is pretty clear that when it comes to a choice between saving a buck and saving your butt, anatomy takes precedence. Hence, when the fates conspire against us and dictate we must locate our data center on a seismically active plot of real estate, prudence (and sometimes the relevant building codes) typically guides us to focus our energy on designing and building a data center that will stay put on shaky ground and lose sight of the airflow containment strategies that help our operating dollars stay put as well. This is not a necessary compromise. Just as we have previously noted in this space that IT equipment that breathes side-to-side, front-to-side, side-to-back, or even back-to-front is no reason to give up the fan energy savings, chiller plant energy savings, architectural flexibility and access to more free cooling hours resulting from effective data center airflow containment, I assert there is no good reason, period, to compromise on airflow containment energy savings.
Not only are seismic considerations no reason to compromise on airflow containment best practices, there are situations where such compromises are not even allowed. For example, in California, there are very stringent requirements for the seismic sturdiness of data centers in hospitals and other life safety critical applications. These requirements are defined and enforced by the Office of Statewide Health Planning and Development (OSHPD). OSHPD must sign off on building plans as well as actual construction and installation of critical, non-structural equipment, which includes data centers. They will review server cabinets, bracing and anchorage. Specifically, for example, California Administrative Code, Chapter 6, Table 11-1 defines that all communications systems in an NPC-2 building must be braced or anchored in compliance with Part 2 of California Title 24, while exceptions are made for cable trays and ducting in NPC-3 buildings. The point here, however, is that Part 6 of Title 24 dictates that there must be a physical barrier between the supply air mass and return air mass in all data centers with an IT load in excess of 175kW such that the heat load removal path inside the IT equipment is the only path between those two air masses. Data center seismic robustness and energy-efficient airflow containment are therefore required by the same umbrella government regulation. That being said, if you are not building a data center with a life-safety critical mission in California, what are your issues?
Determining Seismic Requirements
First, obviously, we want to determine if we have a seismic requirement. On the seismically active west coast of the U.S., most states and municipalities will have some kind of seismic-related requirement that will typically depend on or be derived from the International Building Code (IBC) and the American Society of Civil Engineers (ASCE). Similar requirements exist in areas of Idaho, Colorado, Wyoming, and Montana under the seismic influence of the Yellowstone caldera. The New Madrid seismic zone affects areas of Illinois, Indiana, Mississippi, Arkansas, Kentucky, Tennessee, and Missouri. While there may not be the same level of regulatory requirements universally applied to this geography as we see out west, the data center builder and the owner should consider the risk factors in their plans. The same can be said for other smaller seismically active areas in Oklahoma and South Carolina. In addition to the external risk, this assessment should also consider what is at risk, and the various building codes will often categorize projects along these lines:
- Am I only concerned about human safety, including ingress/egress?
- Am I concerned about human safety as well as critical equipment survivability
- Am I concerned about safety, equipment survivability and continuous operation of the application/network?
The answers to those questions may either put the builder/owner in a regulatory category or define their own project objectives. In addition to seismic requirements being defined by location, they may also derive from an owner’s specification. For example, there may be government agencies or multi-location enterprises that are looking for the efficiency and cost-effectiveness of a standardized footprint and those specifications might apply seismic-withstanding requirements across the board.
Maintaining the Benefits of Airflow Containment
Once a seismic requirement has been established, the next question addresses how to both meet the seismic requirement and derive the airflow containment benefits. Seismic isolation might be the easiest path. If a building were supported on columns equipped with friction pendulums, the entire building could effectively float above the earthquake movement. This isolation would essentially allow the data center located within such a building to look like any other data center with standard server cabinets and any of the traditional hot aisle containment, cold aisle containment or chimney cabinet airflow separation topologies. When isolating the whole building is not practical, it is also possible to isolate individual server cabinets or small groups of server cabinets from the building movement on bearing-equipped bases.
This approach to isolation probably precludes hot aisle containment because of the potential instability of the large return hot aisle duct. However, if this aisle duct were attached to a seismically ruggedized overhead grid, it might at least satisfy the human safety requirement, though some equipment damage might be predictable depending on event severity. On isolated cabinets, the easiest isolation path is going to be with chimney exhaust cabinets with some sort of pliable extension around the top perimeter of the chimneys. This pliable extension will allow the chimney to abut openings in a return air space and accommodate any vertical movement resulting from the base responding to seismic movement. Aisle containment could also be problematic due to stresses an event might apply to end-of-aisle doors, which could conceivably even be an issue at the lowest human safety level of performance. If the aisle door issue can be addressed, a cabinet supported partial hot aisle containment solution would meet the seismic requirements and deliver some level of energy efficiency containment benefits.
Pre-Approved Seismic Hardware
The other main path to a seismic-withstanding data center with airflow containment is, to begin with as many pre-approved seismically ruggedized pieces of hardware as can be specified that meet the rest of the application performance requirements. One possible starting point would be GR-63 CORE-compliant server cabinets. Such cabinets have been tested on a shaker table under extreme motion conditions and not only have survived but have performed under a tight deflection threshold that assures the survivability of components mounted within and accessories attached externally. Another source of hardware that will offer a little more flexibility and variety will be off the OSHPD Pre-Approval of Manufacturers’ Certification (OPM) list available on the OSHPD website (http://www.oshpd.ca.gov/fdd/Pre-Approval/). This list will not only include server cabinets from multiple vendors, but it will include associated pathways and other ancillary accessories, with bills of material and instructions for anchoring and bracing. At this point, there are no containment products included in the OPM lists, primarily since they are so typically application-specific, so this is where a structural engineer gets involved with the project to use IBC methodology to certify design-specific elements.
This is a calculation method very similar to what manufacturers apply to their OPM products. The calculation includes site-specific variables such as soil classification, maximum ground acceleration, and seismic risk category. It also applies an important factor and calculates amplification based on building height, vertical location in the building of the data center, and weight of the component being evaluated. While that may sound like a cumbersome and expensive process, it is significantly less expensive than a test program for an idiosyncratic solution. The key here is to start with GR-63 CORE or OPM components that have been seismic certified and then have the containment additions certified on site, which will likely require additional anchoring and bracing tactics, which should also be a part of that engineer’s expertise.
Containerized Modular Data Centers
A final approach to incorporating airflow containment into a seismically tolerant data center would be a pre-certified data center in a box. There are available on the market containerized modular data centers that have been certified as a total package to withstand some specified seismic activity level and which include server cabinets pre-installed in an airflow containment array. The lack of access to your own special little-preferred specifications and increment of refresh may be off-putting to some; whereas the no muss-no fuss decision process may be attractive to others.
As always, there are various ways to attack any design problem and no one solution fits all application requirements and addresses all situation obstacles. Some ruggedized seismic products and some applied additional structural engineering expertise will add to the price tag of the data center, but that addition will only delay an ROI payback period very slightly if the benefits of containment are correctly exploited, and should be well within the limits for recovery of most businesses. Finally, the available options for incorporating airflow containment within a data center that meet some level of seismic withstanding compliance means that there really is no good reason for compromising on airflow management.
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