Tuesday, August 25, 2015

Data Center Design Case Study

When the reliability demand is high and the data center has to work around pre-existing building constraints, there are significant design challenges.

With approximately 120,000 sq ft of white space divided into eight Tier III, 2 MW power data halls, the 20 MW data center meets a number of design challenges before construction even began.

The data center was originally the site of an old manufacturing facility. Coupled with the owner’s building requirements, this created a few challenges to the data center’s electrical distribution system design. Here’s a look at how Environmental Systems Design, working together with the other members of the building team, was able to solve them.

Challenge No. 1: The transformer

In an effort to maintain consistency across others data centers, the corporation likes to specify company-standard mechanical, electrical, plumbing (MEP), and fire protection equipment for all of its mission critical facilities. However, much of this equipment is designed for outdoor use, and because this particular facility has very limited outdoor space, significant adjustments had to be made for the transformer and switchgear equipment to work indoors.

For example, the heavy transformer couldn’t be placed on the raised floor designed for the data hall and electrical room space and wouldn’t be able to be removed from the building at the end of its useful life, as the 2500 kVA transformers each weigh approximately 16,000 lbs.

Instead, the facility was designed with the intent of moving in the transformer prior to the raised floor construction. Coordinating with the architect, saw cuts were designed into the pre-cast panels on the side of the building to make it easier for the contractor to remove/replace the exterior wall to get the transformer out for future installations or replacement.

Additionally, because the liquid-filled transformers specified are typically used outdoors, special design considerations were needed for the electrical room to contain the fluid in the event of a leak. A 4-in. metal dam was constructed along the perimeter of the room to contain the liquid, while perforated raised-floor tiles were installed around the transformer to facilitate the flow of liquid to under the floor.

Challenge No. 2: Uniform design

The owner wanted a repeatable, scalable design for each of the eight data halls to both create uniformity across the facility and provide the ability to build out data halls as needed over time. However, due to existing building conditions, including the different quantity and compact nature of the structural columns on the building’s first and second floors, an offsite modular construction design was eliminated.

Instead, the solution was to bring each component of the mechanical and electrical systems into the facility individually and build out the data halls one at a time as identically as possible.

Challenge No. 3: Medium-voltage equipment

Because the switchgear and transformers were located inside the building, medium-voltage (MV) feeders were routed throughout. The MV system itself was daisy-chained so it had to be installed and commissioned in its entirety when the first of the eight data halls were installed.

The active MV system presents a potential risk to workers during construction. Therefore, the MV feeders and conduit were routed through the ceiling of the first floor for safety, stubbing back up through the second floor slab and directly into the equipment. The feeders for the first floor equipment were routed similarly under the first floor slab. Because the eight data halls will be built out over time, this technique permits construction on the floor without subjecting workers to the active feeders.

Challenge No. 4: Switchgear and metering equipment

With very limited space for outdoor equipment, there wasn’t enough room for the utility’s 34.5 kV ground-level switchgear and metering. In addition, this equipment has not been fully vetted for the application and was seen as a risk by the owner. The only option was for the utility’s switchgear and metering to be pole mounted. This meant that the site’s 20 poles had to be spaced 20 ft from each other, taking up 400 ft of linear space on a site with little outdoor area.

The Reliability

Utility Service:

2N, or two separate utility sources/feeders, one general source and the second as backup. The switchgear is daisy-chained together, creating a connection from one switchgear to another down the line so that the power can feed into one switchgear, back out and into the other, rather than having multiple connections to the site.

Backup generators:

N+1 redundant swing generator. While each of the eight data halls has its own backup generator, another redundant swing generator for every two to three halls was designed as well, providing additional backup (a total of four swing generators in all). This provides an extra level of redundancy without the cost of providing an additional backup for each generator.

UPS system and distribution (2N):

Two sides to the electrical system were designed, where each side is a mirror of the other. The benefit of the 2N system topology allows for maintenance or a fault to occur on one of the sides, while still maintaining a completely active data center.

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