Developed by The Uptime Institute, the Tier Classification and Performance Standard defines four levels of availability for a complete site, ranging from the basic Tier l to Tier lV, which describes the highest possible data processing availability.
Kenny Green, technical services manager at our business partner UPSL, recently had a look at the four classification tiers for data centres and explained the impact they have on UPS power.
The following table shows the key parameters for the standard’s four tiers. The system is based on two variants of two design techniques – dual cording and redundancy. Dual cording refers to IT equipment that has two independent power inputs. Redundancy brings the same type of resilience to failure at a system level, using the ‘N+1’ technique.
The most important point of achieving a tier classification is the availability. But as you can see on the following table by UPSL, availability comes at a cost, in terms of both capital and operating expenditure: It shows the relative capital costs of different Tiers, using the Tier l figures as a base reference.
The question remains what the impact of modern UPS technology is on Tier Classification. UPSL’s Kenny Green about that:
“Tier lV requirements were recently reduced by The Uptime Institute from the double-redundant 2(N+1) to 2N, where each system is fully redundant for the other. This raised the UPS module load by several percentage points. Transformerless technology, due to its size and weight saving, has brought much greater efficiency at all loads, designed to achieve over 95%, even at 50% loading. It also allows UPSs to be configured incrementally and right sized to their load. Additionally, many modern systems offer Eco-mode options which enable efficiencies of around 98% even at 10% load. Even users with reservations about subjecting their load entirely to eco-mode may accept using it with one of their two power buses.”
For more information about Tier Classification see this Uptime Institute White Paper (“Tier Classifications Define Site Infrastructure Performance”)