Tier certification: what an owner is actually buying

A Tier objective is a short description of a data center’s infrastructure that a lender, a tenant and an engineer can all read the same way. It states how the facility must behave when an element is taken out of service or fails. It does not guarantee an annual uptime, cover operations or prescribe a design.

What the four classifications commit a design to

Uptime Institute defines four progressively more resilient infrastructure classifications. Tier I provides basic capacity: a single path for power and cooling with no redundant components. Tier II adds redundant capacity components, the spare chiller or the spare UPS module, on that single path. Tier III addresses concurrent maintainability: every capacity component and every distribution path can be removed from service on a planned basis without the IT load being affected. Tier IV adds fault tolerance: a single unplanned failure anywhere in the infrastructure does not affect the load, within the standard’s defined requirements.

For an owner, the practical difference is in the maintenance calendar. A Tier II facility is maintained in a shutdown window that the business has to tolerate. A Tier III facility is maintained with the business running, because every element has a second path. A Tier IV facility survives the failure the maintenance team did not plan for. Each step adds cost, mostly in distribution, isolation points and plant space rather than in the headline equipment.

The familiar annual uptime percentages that used to accompany the Tiers should not be used to predict a facility’s performance. Uptime Institute removed its expected downtime references in 2009, because operations and other factors dominate real outcomes.

Three certifications, three different assessments

Tier Certification of Design Documents assesses the design: the single-line diagrams, the cooling schematics, the control narratives and the calculations, read path by path and state by state. It confirms that the design, if built as drawn, would meet the objective.

Tier Certification of Constructed Facility assesses the facility as built, and includes demonstrations of its behaviour performed on site under the assessor’s witness: taking each path out of service, failing the elements the objective requires, with the load supported throughout. It confirms that the built facility behaves as the certified design said it would.

Tier Certification of Operational Sustainability assesses the management, staffing, maintenance and operating practices that keep the performance over the facility’s life. One certification does not imply the others. Time is often lost between the first two, when a design certified on paper is built with substitutions, re-routed distribution and changed control sequences that nobody checked against the certified drawings.

Four decisions to settle in the brief

Each of the four questions below should have a written answer before design starts.

• What interruption can the business tolerate, and for which loads? A facility can hold different objectives for different halls, and a brief that says “Tier III” for everything may be paying for resilience on loads that do not need it.
• What must remain available during planned maintenance? Concurrent maintainability is a statement about every element: chillers, pumps, headers, transformers, switchboards, UPS, busway, controls. The brief should say so, because a design team will otherwise interpret it narrowly.
• Which phase and which installed capacity are being certified? Certification applies to a defined installation. A phased facility needs a phasing plan that keeps each phase certifiable with the previous one live.
• Who owns the design evidence, the change review and the demonstration planning? In procurement and construction, certification is put at risk when nobody owns the comparison between what was certified and what is being built.

Record the answers in the design basis. A redundancy label on an equipment schedule, such as N+1 beside the chillers, describes one group of plant. The behaviour of the complete facility is shown on the single-line diagram with its maintenance states marked.

Manage changes after the design is certified

During procurement and construction, every substitution, every value-engineering proposal and every change to a control sequence or a distribution route should be reassessed against the certified design. Its effect on isolation points and on the separation of paths is checked on the drawings the assessor will read.

Keep the drawings, the calculations, the operating narratives and the test evidence in agreement with each other, because the assessment compares them, and plan the constructed-facility demonstrations together with the integrated systems test, so that one set of witnessed results serves both the certifier and the client.

UBIK supports gap analysis, design coordination and certification readiness. Uptime Institute performs the assessment and awards its certification, and a consultant’s involvement is not a guarantee of an award.