How to design data center electrical and power systems

An expert panel provides engineering and design tips for electrical, power and lighting systems in this Q&A

By Consulting-Specifying Engineer April 28, 2021


  • Peter Czerwinski, PE, Uptime ATD, Mechanical Engineer/Mission Critical Technologist, Jacobs, Pittsburgh
  • Garr Di Salvo, PE, LEED AP, Associate Principal – Americas Data Center Leader, Arup, New York
  • Scott Gatewood, PE, Electrical Engineer/Project Manager, Regional Energy Sector Leader, DLR Group, Omaha, Neb.
  • Brian Rener, PE, LEED AP, Mission Critical Leader, SmithGroup, Chicago

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

Brian Rener: The amount of power and the reliability are unlike most other facilities. The fast deployment timelines of many of these mission critical facilities requires the electrical engineer to quickly design and specify primary equipment and their space needs and often prepare to purchase this equipment due to the long lead manufacturing times for this equipment. Also, very early conversation and planning is essential with the local utility power company to determine the capacity and sources of power to the site.

Peter Czerwinski: Although standby generators are a common feature of data centers, the startup time for the generators must be considered when deciding which cooling components to put on uninterruptible power supply power. If generators take several seconds to start and apply power, that is time that chilled water pumps could shut off and fans could ramp down, possibly allowing the data hall’s air temperature to increase above the desired limit.

Scott Gatewood: The uniqueness of electrical design infrastructure for data center designs might cluster around four factors: Concurrently maintainable, resilient, physically separate and expandable. Insuring independently produced power flows while servicing or replacing equipment that, should it fail, it does no harm but to itself and remain expandable for future efficient power flows, is an artform. Sure, there is a great deal more here but accomplishing these feats puts the cost within budget constraints.

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

Brian Rener: Diesel generators have long been the backbone of data centers. As power demands have risen, we have seen the size of the generators continue to rise. This not only includes the size but the use of paralleling and also medium-voltage rated generators. However, sustainability is driving the need for more environmentally friendly solutions, which at times includes consideration of natural gas generators and most recently even large-scale utility grade and utility interactive battery systems as alternatives to generators.

Garr Di Salvo: One of the areas where we’ve seen the greatest diversity in approach is in ensuring smooth and continuous power to IT equipment. The best accepted criterion for power continuity is the Information Technology Industry Council curve, which describes the tolerance of PC power supplies to voltage sags and the equipment supply. UPSs provide capacity to ride through utility voltage dips and outages (allowing for startup of standby power systems). Although in-rack backup power can help reduce common mode failures and Day One costs, centralized solutions are more common. Double-conversion UPS are prevalent in North America, whereas rotary and diesel rotary systems are more common in the rest of the world. One interesting deployment we’ve seen involved a hybrid system that employs rotary UPSs along with batteries to extend the ride-through capabilities.

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

Peter Czerwinski: Equipment yards in data centers commonly contain rows of isolated pieces of equipment that may cause shadows and blind spots at night. Care must be taken to design exterior lighting to meet code and safety requirements. Consider specifying lighting to be installed on the equipment by the equipment manufacturers.

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 Rener: It is important to work closely with the client and their IT professionals to understand the phased implementation and growth of the computer equipment so that the right “modules” of electrical power can be designed. These power modules must be designed and installed to allow the owner to grow their load without interruption of any previously installed data center systems.

“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?

Scott Gatewood: Resiliency can apply to every facet of infrastructure design including the serving utilities, the security perimeters, the building envelope and physical program spaces. Literally, every element can be evaluated for its threat to operational integrity. Carefully asking after and listening to the client’s goals and infrastructure risk tolerances is a primary goal.

Peter Czerwinski: Standards such as Uptime Institute and TIA-942 are straightforward road maps on how to achieve a desired level of resiliency. Sometimes a data center owner requires a Tier II minimum resiliency, but still wants to implement certain features found in Tier III facilities. Certain power and cooling technologies are easier and less expensive to achieve Tier III’s concurrent maintainability with than others.

Garr Di Salvo: The industry’s view of resiliency has become much more sophisticated over the course of my career. Reliability is still a critical design criterion but competes with others, like time-to-market and life cycle costs. Owners are now looking beyond simple stratagems like Tier III, system plus system or distributed redundant in system architecture. Instead, they’re seeking tangible justification for design decisions. In response to this, we’ve incorporated probabilistic modeling of building system availability as a supplement to point of failure and fault tree analysis techniques.

Brian Rener: Climate change is on the minds of many data center owners. We are seeing records for flooding and unusually high temperature and also low temperature “design days” as we saw this winter in Texas. You want the facility and the electrical power systems designed to accommodate these new environmental stresses. This may mean things as simple as designing to a 500-year flood or increased utility outage times.

When designing lighting systems for these types of structures, what design factors are being requested? Are there any particular technical advantages that are or need to be considered?

Scott Gatewood: Lighting design factors requested for data halls balance efficiency for the task at hand with getting light levels deep within the cabinet rows. Typically, operational light levels can be low (20 foot candles) for typical management. However, for buildings, light levels should be elevated (50 foot candles) to permit detailed tasks deep within cabinets where indirect illumination is nearly zero due to the tall cabinets and supporting infrastructure above. Consequently, luminaires nearer to the cabinet elevation are optimal.

Garr Di Salvo: With the wide variety of solutions available on the market, it’s easy to specify high-efficiency lighting fixtures to meet code and operational requirements. Standalone and integrated system sensors can further optimize energy efficiency, providing a “lights out” facility. Some locales have requirements for daylighting. Despite its many advantages, security and climate control concerns may make the introduction of natural light undesirable.

At least as important is ensuring consistent and adequate white space illumination, both to ensure a safe working environment but also to improve productivity (as much as 9% in some studies). Data centers often have many overhead elements. These require careful coordination during construction to minimize and eliminate shadows at the work plane, both in the data hall and in back of house support spaces.