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| TABLE 1: Uptime Institute definitions of tier levels | ||||
| Tier I | Tier II | Tier III | TierIV | |
| Number of delivery paths | Only 1 | Only 1 | 1 Active, 1 Passive | 2 Active |
| Redundancy | N | N+1 | N+1 | S+S or 2(N+1) |
| Compartmentalisation | No | No | No | Yes |
| Concurrently maintainable | No | No | Yes | Yes |
| Fault tolerance to worst event | None | None | None | Yes |
| TABLE 2: The tier attributes of the sites from which the actual availability numbers were drawn | ||||
| Tier I | Tier II | Tier II | Tier IV | |
| Building type | Tenant | Tenant | Stand-alone | Stand-alone |
| Staffing | None | 1 Shift | 1 + Shifts | %2224 by Forever%22 |
| Useable for critical load | 100% N | 100% N | 90% N | 90% N |
| initial gross watts per square foot (W/ft²) (typical) | 20-30 | 40-50 | 40-60 | 50-80 |
| Ultimate gross W/ft² (typical) | 20-30 | 40-50 | 100-150 ¹ ² ³ | 150+ ¹ ² |
| Uninterruptible cooling | None | None | Maybe | Yes |
| Support space to raised-floor ratio | 20% | 30% | 80-90%² | 100+% |
| Raised-floor height (typical) | 12%22 | 18%22 | 30-35%22² | 30-36%22² |
| Floor loading ibs/ft² (typical) | 85 | 100 | 150 | 150 |
| Utility voltage (typical) | 208,480 | 208, 480 | 12-15 kV² | 12-15 kV² |
| Single points-of failure | Many + human error | Many + human errors | Some + human error | None + human error |
| Annual site-caused IT downtime (actuals) | 28.8 hours | 22.0 hours | 1.6 hours | 0.4 hours |
| Site availablity | 99.671% | 99.749% | 99.982% | 100.00% |
| Months to implement | 3 | 3-6 | 15-20 | 15-20 |
| Year first deployed | 1965 | 1970 | 1985 | 1995 |
| Construction cost (:30%)¹²³ | ||||
| Raised floor | $220/ft² | $220/ft² | $220/ft² | $220/ft² |
| Useable UPS output | $10,000/kW | $11,000/kW | $20,000/kW | $22,000/kW |
| ³ 100 W/ft² maximum for air-cooling over large areas, water or alternate cooling methods greater than 100 W/ft² (added costs excluded). | ||||
| ² Greater W/ft² densities require greater support space (100% at 100 W/ft² and up to 2 or more times at greater densities), higher raised floor, and if required over large areas, medium voltage service entrance. | ||||
| ¹ Excludes large architectural, engineering, and commissioning fees; permits and other fees; interest; and abnormal civil costs. These can be several million dollars. Assumes minimum of 15,000 ft² of raised floor. Architecturally plain one-story building, with power backbone sized to achieve ultimate capacity with installation of additional components or systems. Make adjustments for NYC, Chicago, and other high cost areas. | ||||
| TABLE 3: Comparison of Various UPS Systems | |||||
| Specification | 6 Pulse Series Online | 12 Pulse Series Online | Parallel Online | Hybrid Rotary | Diesel Rotary UPS |
| Typical Operating Efficiency | 94% | 94% | 96% | 90 - 95% | 90 - 96% |
| Input Power Factor | 0.8 | 0.85 | 0.99 | 0.98 | 0.99 |
| Output Voltage Regulation | Yes | Yes | Yes | Yes | Yes |
| Input Power Factor Correction | No | No | Yes | Yes | Yes |
| Energy Store | Battery | Battery or DC Flywheel | Battery | Battery or DC Flywheel | AC Flywheel |
| Output Fault Current Without Mains Available | Up to 2.2 x In | Up to 2.2 x In | Up to 2.2 x In | 14 x In | 10 - 12 x In |
| Range of sizes to Largest Unit Size | 0 – 800 kVA | 0 – 800 kVA | 500 kVA | 180 -1100 kVA | 2 MVA |
| Actual useful size allowing for derating for leading Power Factor | 640 KVA | 640 KVA | 400 KVA | 1100 KVA | 2 MVA |
| Indicative cost of UPS Only (£/kVA) | £180 - £200 | £180 - £200 | £180 - £200 | £245 - £265 | N/A |
| Indicative Cost of UPS if derated to allow for leading power factors (£/kVA) | £225 -£250 | £225 -£250 | £225 -£250 | £245 - £265 | N/A |
| Indicative cost of UPS in £/kVA on N+1 basis at most optimum module size | TBC | TBC | TBC | TBC | TBC |
| Indicative cost of UPS and Standby Generation (£/kVA) | £405 -£435 | £405 -£435 | £405 -£435 | £440 - £470 | £450 -£480 |
| Indicative cost of UPS and Standby Generation if UPS derated to allow for leading power factors (£/kva) | £450 -£485 | £450 -£485 | £450 - £485 | £440 - £470 | £450 -£480 |
| Indicative Space Requirement of UPS and standby generation (m²/kVA) | 0.06 -0.07 | 0.06 -0.07 | 0.06 -0.07 | 0.06 - 0.07 | 0.04 -0.05 |