How to design resilient power systems in data centers

Power insights

• Data centers employ sophisticated backup power systems to ensure uninterrupted operation during power outages.
• To enhance resiliency, data centers are designed with multiple utility sources and robust backup generators to protect against losses caused by natural disasters.

Respondents:

• Amanda Carter, PE, Electrical Discipline Lead, Stantec, Chicago
• Brian A. Rener, PE, LEED AP, Mission Critical Leader, Smith Group, Chicago
• William Kosik, PE, CEM, LEED AP, Lead Senior Mechanical Engineer, kW Mission Critical Engineering, Chicago

Courtesy: WTWH Media

Are there any issues unique to designing electrical/power systems for these types of facilities? Please describe.

Amanda Carter: One unique and costly issue is related to underground power installations. Unlike commercial facilities, which often use significantly less power than NFPA 70: National Electrical Code (NEC) load calculations would imply, data center facilities often operate at 95-100% of their capacity. Because of this, any power feeders that are installed underground require Neher-McGrath calculations to ensure the feeder temperature does not exceed the temperature rating of the feeder insulation. This is done using computer programs capable of modeling and running these complicated calculations based on the installed condition. These calculations often reveal that alternate backfill materials, such as concrete or engineered backfill, will be necessary, driving up costs. They also often require much larger feeder sizes than the minimum allowable by NEC.

What types of unusual standby, emergency or backup power systems have you specified for data centers? Describe the project.

Amanda Carter: Unlike commercial facilities that often have one utility source, and possibly a generator source or an uninterruptible power supply (UPS) in between for “critical” loads, data centers often employ multiple layers of backup power protection. On the medium voltage (MV) side, this is often done using redundant MV feeders from the substation, or with MV distribution to the switchgear. In addition, we can also create MV loops with groupings of MV switchgear. On the low voltage side, this is often done through a “catcher” system, where you have N+1 systems and the +1 system stands by to “catch” a load if its primary source is lost. Another typology often deployed on the low voltage side is a “distributed redundant” N+1 system, where the loads are evenly distributed across N+1 systems. If a source is lost, the loads from that source redistribute themselves across the remaining N systems. Both systems require coordination with mechanical to ensure the same N+1 strategy is being employed.

What are some key differences in electrical, lighting and power systems you might incorporate in this kind of facility, compared to other projects?

Amanda Carter: Some key differences in the electrical systems provided by data centers have to do with the associated controls. The switchgear specified at a data center often has electrically interlocked breakers that are part of a larger redundancy scheme controlled through the electrical power monitoring system (EPMS). From a lighting perspective, it is more about function than look and feel. For general power systems, you will see a lot of UPS-backed and dual-sourced loads for items critical to data center operation, such as anything supporting the EPMS.

Figure 1: Example of heat recovery system at National Renewable Energy Labs ESIF HPC data center. Courtesy: SmithGroup.

Brian A. Rener: Right now, there are two major pushes for back-up power in data centers. First is meeting decarbonization goals through the use of alternative cleaner fuels, like hydrogen and hydrotreated vegetable oil that replace traditional diesel fuel. The technology is improving to generate hydrogen on-site. Secondly, there are applications of large-scale utility grade BESS, which not only provide clean back up power to a data center, but also can work with local utility grids to help manage power stabilization regionally by supplying power back into the grid.

How does your team work with the architect, owner’s rep and other project team members so the electrical/power systems are flexible and sustainable?

Brian A. Rener: We are a fully integrated architectural engineering company, which means our electrical and mechanical engineers help lead our data center design. The most important early part in preparing for future flexibility and growth revolves around space planning for mechanical, electrical and plumbing equipment. The engineers must lead this discussion.

“Resilient” or “resiliency” is a buzzword when discussing data centers. What are owners requesting to make the building meet resiliency goals? How are you designing data centers to be more resilient?

Amanda Carter: When a client is discussing “resiliency,” they are often looking for ways to harden their facilities against utility losses. Whether it’s an ice storm, hurricane or any other uncontrollable disaster leading to a utility outage, clients want to have an overall distribution that will be unaffected by said event. If they are impacted, they want to be able to protect their facility during the outage. The first line of defense is to try to provide a utility substation that has feeders coming from multiple utility sources, preferably completely different high-voltage substations for the most critical facility types. The next line of defense is the use of generators, whether they are used to back up the entire facility, as is often seen in colocation facilities, or simply the critical loads to protect the facility during a utility outage, such as security and basic operations functions. In this case, there is an understanding that these types of clients are often capable of shifting their IT load to another unaffected facility entirely.

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