Data Center Site InfrastructureTier Standard: Topology
This Section will cover the Following
Commentary for Application of the Tier Standard– TopologyOutcome-Based TierStandardImpact of Ambient DesignConditionsTier FunctionalityProgressionFractional or Incremental Tier Classification
Outcome-Based Tier Standard
The definitions usedare necessaryand intentionally very broad to allow innovationand clientmanufactureinachieving the desired level of site infrastructure performance oruptime.Theoperational outcomes that define the four Tiers are very straightforward.Many designs that pass a checklist approach will fail an operational performance requirements approach.
Tier I sites experience 2 separate 12-hour, site-wide shutdowns per year for maintenance or repair work. In addition, Tier I sites experience 1.2 equipment or distribution failures on average each year.The annual impact of maintenance and unplanned outages is 28.8 hours per year, or 99.67 percent availability.
Tier II sites (On Average) schedule 3 maintenance over a 2-year period and have 1 unplanned outage each year.The redundant components of Tier II topology provide some maintenance opportunity leading to just 1 site-wide shutdown each year.Theannual impact of maintenance and unplanned outages is 22 hours per year, or 99.75 percent availability.
Tier III topology is Concurrently Maintainable, so annual maintenance shutdowns are not required, but needs aggressive maintenance program improving overall equipmentperformance.Unplannedfailures are up to 4-hours event every 2.5 years, or 1.6 hours on an annual basis. Tier III sites demonstrate 99.98 percent availability
Tier IV provides robust, Fault Tolerant siteinfrastructureUnplannedfailures are up to 4-hours event in a 5-year operating period, or 0.8 hours on an annual basis.TierIV sites consistently demonstrate 99.99 percent availability.Availability calculations do not determine the Tier Classification.e.g.A site with a measured infrastructure availability of 99.90 percent
Impact of Ambient DesignConditions
The effective capacity of most cooling and power generating equipment is impacted by the actual ambient conditions in which it operates. These components typically require more energy to operate and provide less useable capacity so the ambient air temperatures rise.Mostconventional facilities selects design values applicable to most but not all anticipated hours of operation of that facility.This is not appropriate for data centers that are expected to operate on a 24 X Forever basis.
Impact of Ambient Design Conditions Cont..
Another concern arises when selecting heat rejection systems. Many manufactures provide product based on 95°F (35 C) ambient outside conditions. These components will be at best when operating in up to 95°F (35 C) outside air.Thesecomponent capacities must be adjusted downward to provide the required capacity when temperatures exceed 95°F.
Tier I and Tier II solutions are typically solutions to short-term requirements, they are usually tactical solutions, driven by first-cost and time-to-market more than life-cycle cost and uptime (or availability) requirements.Long-term viability found more often in Tier III and Tier IV site infrastructure.Strategic site infrastructure solutions enable the owner to make strategic business decisions concerning growth and technology, unconstrained by current site infrastructure topology.
Tier I solutions acknowledge the owner’s desire for dedicated site infrastructure to support IT systems.TierI infrastructure provides an improved environment over an ordinary office setting and includes: a dedicated space for IT systems; a UPS to filter power spikes, sags, and momentary outages; dedicated cooling equipment not shut down at the end of normal office hours; and an engine generator to protect IT functions from extended power outages.
Tier II solutions include redundant critical power and cooling capacity components to increase the margin of safety incase of infrastructure equipment failures.Theredundant components are typically extra UPS modules, chillers, heat rejection equipment, pumps, cooling units, and engine generators.A malfunction or normal maintenance will result in loss of a capacity component.
Tier III site infrastructure has Concurrent Maintenance.ConcurrentMaintenance means that each and every capacity or distribution component can be maintained on a planned basis without impact to the IT environment.Maintenanceallows the equipment and distribution paths to be returned to like new condition on a frequent and regularbasis, Thus, the system will reliably and predictably perform as originally intended.
Moreover, each and every system or component that supports IT operations must be able to be taken offline for scheduled maintenance without impact to the IT environment.Thisconcept extends to important subsystems such as control systems for the mechanical plant, start systems for engine generators, EPO (Emergency Power Off System) controls, power sources for cooling equipment and pumps, isolation valves, and others.
Tier IV site infrastructure builds on Tier III, adding the concept of Fault Tolerance to the site infrastructure topology.FaultTolerance extends to each and every system or component that supports IT operations.Tier IV considers that any one of these systems or components may fail or experience an unscheduled outage at any time.
However, the site must be designed and operated to tolerate the cumulative impact of every site infrastructure component, system, and distribution path disrupted by the failure.E.g.the failure of a single switchboard will affect every subpanel and equipment component deriving power from the switchboard. A Tier IV facility will tolerate these cumulative impacts without affecting the operation of the computer room.
Fractional or Incremental Tier Classification
The four Tier Classifications address topology, or configuration of a site rather than a list of components to achieve a desired operational outcome.Forexample, the same number of chillers and UPS modules can be arranged on single power and cooling distribution paths resulting in a Tier II solution (Redundant Components), or on two distribution paths that may result in a Tier III solution (Concurrently Maintainable).
Fractional or Incremental Tier ClassificationCont…
Selecting the appropriate topology solution based on the IT availability requirements, and the substantial financial consequences for downtime, provides the best foundation for investment in data center facilities.Fractional or incremental descriptions for site infrastructure are not appropriate and are misleading.(Tier III +, Enhanced Tier III, or TierIV-lite)Including a criteria or an attribute of a higher Tier Classification in the design does not increase the overall Tier Classification
Fractional or Incremental Tier ClassificationCont…
1)A site that has an extra (redundant) UPS module but needs all the installed cooling units running to keep the computer room temperature within limits does not meet the redundancy requirements for Tier II.2)A switchboard that cannot be shut down without affecting more than the redundant number of secondary chilled water pumps (reducing the available capacity to less than N) is not Concurrently Maintainable and will not be Certified as Tier III.3)Including a UPS system patterned after a Tier IV system within a site having a Tier II power distribution backbone yields a Tier II Certification.
The most significant deviations from the Tier Standard found in most sites can be summarized as inconsistent solutions.Asite will have a robust, Fault Tolerant electrical system patterned after a Tier IV solution, but utilize a Tier II mechanical system that cannot be maintained without interrupting computer room operations. This results in an overall Tier II site rating.The mechanical system fails Concurrent Maintenance because of inadequate coordination between the number and location of isolation valves in the chilled water distribution path.
If more than the redundant number of chillers, towers, or pumpsare de-energizedfor electrical maintenance, computer-room cooling is impacted.Electrical systems often fail to achieve Tier III or Tier IV criteria due to design choices made in the UPS and the critical power distribution path.Topologiesthat include static transfer switches in the critical power path for single-corded IT devices will likely fail both the Fault Tolerance criteria and the Concurrent Maintenance criteria.Consistent application of standards is necessary to have an integrated solution for a specific data center.
Non-Compliance Trends Cont..
An investment in one segment must be met with a similar investment in each of the other segments if any of the elements in the combined solution are to have the desired effect on IT availability. A well-executed data center master plan or strategy should consistently resolve the entire spectrum of IT and facility requirements.