Edge Suite Marketed as Tier III Equivalent
A colocation provider is converting a 90 m2 former storage room into an eight-rack edge suite. The room has a 4.1 m ceiling, 600 mm raised floor, one 1.2 m double door, and no adjacent electrical room. Each rack is planned for 7 kW, with dual-corded servers. The design team proposes two 250 kVA UPS modules in the same room, one 200 kVA transformer, N+1 100 kW chilled-water CRAHs, and a single chilled-water branch with no isolation valves. The sales team wants to market the suite as 'Tier III equivalent' because the UPS and cooling are redundant. The building has a single utility service and a single 500 kVA generator serving the whole site. The landlord will not allow structural penetration or a second door. The customer requires concurrent maintainability for all critical systems and a maintenance window of no more than four hours per year. The project is two weeks from design freeze.
1. Can the proposed design honestly be marketed as 'Tier III equivalent'? Assess the topology against the customer's concurrent-maintainability requirement and identify the three most serious gaps.
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Not honestly, unless the contract defines 'Tier III equivalent' narrowly and the customer accepts the exclusions. The proposal has component redundancy, but the customer's stated requirement is concurrent maintainability: every critical path must be maintainable without taking the IT load down and without relying on a short annual window. The three most serious gaps are: (1) a single utility service and a single generator create a site-level single point of failure; the UPS can ride through a short outage, but generator maintenance or failure cannot be made concurrent. (2) A single 200 kVA transformer and a single chilled-water branch with no isolation valves mean replacing or repairing the transformer or a branch cannot be done while the suite remains energized and cooled. (3) Both UPS modules in the same room without a maintenance bypass or separate fire compartment make UPS maintenance dependent on the other module and on room-level events. The single door and lack of an electrical room also constrain maintenance access and fire separation. Marketing language should not outrun the topology; either redefine the claim or price the missing scope.
2. Recommend a revised minimum design that preserves the eight-rack footprint, and explain what you would defer or reject.
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Preserve eight racks by using a true 2N or concurrent-maintainable power train: two UPS modules each rated for the full 56 kW critical load plus design margin, fed from separate upstream breakers or panels, with external maintenance bypass and physically separated or fire-rated compartments. Cooling should be N+1 CRAH with dual power feeds, a ring or dual-header chilled-water distribution with isolation valves, and controls that tolerate one CRAH or one branch isolation. If the building's single utility and generator cannot be changed, the site cannot meet full concurrent maintainability for utility loss; that must be contracted as a reduced scope. I would reject the single transformer, the shared UPS room without bypass, and the unvalved single chilled-water branch. I would defer nonessential architectural finishes, not electrical separation. If the landlord truly forbids a second door or any separation, reduce the marketed tier and document the constraint rather than pretending the design meets the customer's requirement.
3. The customer refuses to pay for a second utility feed but still wants a contractual availability commitment. How should you document the residual risk and what operational mitigations would you require?
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Document the residual risk in a design decision record: single utility feed, single generator, single transformer, and any shared room are known single points of failure. The availability commitment should define what counts as downtime, exclude events outside the provider's control only to the extent enforceable, and state the actual ride-through: UPS runtime, generator start and transfer time, and fuel autonomy. Require operational mitigations: monthly generator exercise with load, annual full-load bank test, UPS battery monitoring and impedance tests, spare breaker and CRAH components, documented isolation procedures, 24/7 monitoring with escalation, and an annual failover and maintenance drill. Set a capacity threshold that triggers review. If the customer still wants a Tier III-like SLA, obtain written risk acceptance from an authorized owner and price the risk; do not let sales language substitute for engineering.