Guidelines for Specifying Data Center Criticality / Tier Levels

Overview

The paper reviews three common classification systems: Uptime Institute Tiers, TIA-942 rating levels and Syska Criticality Levels. It concludes that all converge on four broad levels but lack the detail needed for a defensible specification. The four TIA-942 levels are based on Uptime's Tier Standard, while Syska defines ten levels that map onto four. The paper's aim is to replace vague Tier claims with measurable criteria, and to give teams that use different systems a common specification language.

The proposal is to use criticality C1-C4 to describe the business need, and to build a balanced design in which no subsystem is weaker than the target. Business characteristics and design effects are tabulated per level. C1 accepts UPS-only with at least 8 minutes of backup and tolerates outages of about 10 minutes. C2 adds generator backup and can sustain a 24-hour outage. C3 has redundant power and cooling, concurrent maintenance, 72-hour endurance, two utility paths and a 1-hour fire rating.

C4 provides 2N power and cooling, two independent utility paths, 96-hour endurance, a fire rating of at least 2 hours and 24/7 onsite staff. Fit-out cost estimates for power and cooling are $11.5/W for C1, $12.5/W for C2, $25/W for C3 and $28/W for C4, with core and shell at roughly $300/ft² ($2,880/m²). The paper stresses that criticality drives lifetime total cost of ownership, especially through the energy used by redundant systems. A limit is that the cost figures are estimates tied to a particular year and set of assumptions, so they need adjusting for local conditions. Even so, it offers a practical framework for giving owners and designers a shared vocabulary.

Key points

1. C1: UPS-only acceptable with at least 8 minutes of backup; tolerates about 10-minute outages; many single points of failure.
2. C2: generator backup; able to sustain a 24-hour outage; some power and cooling redundancy.
3. C3: redundant power and cooling, concurrent maintenance, 72-hour endurance, two utility paths (active/passive), 1-hour fire rating.
4. C4: 2N power and cooling, two independent utility paths, 96-hour endurance, at least 2-hour fire rating, 24/7 onsite staff.
5. Fit-out cost (power+cooling): C1 $11.5/W; C2 $12.5/W; C3 $25/W; C4 $28/W; core and shell about $300/ft² ($2,880/m²).
6. The four TIA-942 levels are based on Uptime's Tier Standard; Syska maps ten levels onto four.
7. No subsystem should be weaker than the target criticality (balanced design).

Using it in design

• Build a novice criticality wizard (C1-C4) and map defaults to it: fuel autonomy 0/24/72/96 h, utility feeds 1/1/2/2, fire rating 0/0/1/2 h.
• Map redundancy defaults to N / N+1 / N+1 concurrently maintainable / 2N.
• Show the $/W cost multipliers as editable estimate defaults.
• Enforce the balanced rule: overall rating equals the lowest subsystem rating.

Who should read it

Owners, consultants and design engineers choosing the target criticality level for a data centre.

Related standards

• Uptime Tier Standard: Topology
• TIA-942
• EN 50600-1
• BICSI 002

Publication details

Authors

Victor Avelar

Publisher

Schneider Electric

Year

2015

Document number

WP 122

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation