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From rack count to kVA, from kVA to an N+1 plant. Tier III and Tier IV configurations, fuel runtime, 10-second load acceptance, and the 250–625 kVA sets that carry the load.
Size the PlantData centre generator sizing fails in one of two directions: undersized because someone sized the IT load and forgot cooling, or oversized because someone added 100% margin on top of a number that already had margin in it. The honest sequence is racks → IT kW → total facility kW at PUE → kVA at 0.8 PF → generator count.
| Racks | IT load @ 10 kW/rack | Facility load @ PUE 1.4 | kVA required | Minimum configuration |
|---|---|---|---|---|
| 10 | 100 kW | 140 kW | 175 kVA | 1 × 250 kVA |
| 20 | 200 kW | 280 kW | 350 kVA | 1 × 375 kVA |
| 30 | 300 kW | 420 kW | 525 kVA | 1 × 625 kVA |
| 35 | 350 kW | 490 kW | 613 kVA | 1 × 625 kVA (92% loaded, no headroom) |
| 50 | 500 kW | 700 kW | 875 kVA | 2 × 625 kVA parallel |
| 70 | 700 kW | 980 kW | 1225 kVA | 2 × 625 kVA parallel (98% loaded) |
| 100 | 1000 kW | 1400 kW | 1750 kVA | 3 × 625 kVA parallel |
Two assumptions sit behind that table and both need checking against the real project. 10 kW per rack is a conventional enterprise or colocation density — GPU and AI halls run 30–100 kW per rack, which multiplies everything above by three to ten. PUE 1.4 is a typical air-cooled figure; a modern liquid-cooled hall may reach 1.2, an older one may sit at 1.8. Substitute both before quoting a plant size.
| Tier | Design intent | Generator topology | What it means on site |
|---|---|---|---|
| Tier II | Redundant capacity components | N+1 | One spare set. Maintenance requires a shutdown of the redundant path only. |
| Tier III | Concurrently maintainable | N+1 | Any component can be serviced while the load runs. The plant needs a maintenance path that never crosses the live bus. |
| Tier IV | Fault tolerant | 2N (or 2N+1) | Any single failure, including a failure during maintenance, does not drop load. Two independent plants, two independent fuel paths. |
The generator is only one line in the Tier audit. Concurrent maintainability also depends on the fuel system, the transfer switches, the cooling loop and the electrical distribution — a 2N generator plant feeding a single ATS is still not Tier IV. Design the whole chain, not just the machines.
Parallel capability is decided at the quote stage, not after delivery. Retrofitting a DSE7320 set to DSE8610 means a new controller, new load-sharing wiring and a re-commissioning visit — specify it up front.
| Set | Full-load consumption | Runtime on 1,000 L | Runtime on 5,000 L |
|---|---|---|---|
| 250 kVA / 200 kW | 46.0 L/h | 21.7 h | 108 h |
| 375 kVA / 300 kW | 67.2 L/h | 14.9 h | 74 h |
| 500 kVA / 400 kW | 88.6 L/h | 11.3 h | 56 h |
| 625 kVA / 500 kW | 109.6 L/h | 9.1 h | 46 h |
Most data centre specifications call for 12–48 hours of on-site fuel, and the number that matters is not the tank on the baseframe — it is the bulk tank plus the guaranteed refuelling contract. A 625 kVA set at full load empties a 1,000 L tank in about nine hours, so a 12-hour runtime requirement means either a 1,400 L tank or a documented delivery SLA. Add fuel polishing: diesel stored for months grows bacteria and water, and dirty fuel is the most common cause of a generator failing to start.
A data centre generator is judged on two numbers: how fast it accepts load, and how much block load it can take in one step. The first is a control and starting-system question; the second is an alternator and engine question, and it is where undersized plants fail their commissioning test.
| Parameter | Typical requirement | What we specify |
|---|---|---|
| Time to accept load | 10 s (NFPA 110 Type 10) | DSE7320 MKII / DSE8610 with jacket heater and battery charger as standard |
| Single-step block load | 60–70% of rating | Alternator sized for the block load, not just the continuous rating — confirm at quote stage |
| Voltage transient | ±15% recovery in 1.5 s | Leroy Somer or Stamford alternators with PMG excitation |
| Parallel control | Load sharing, kW and kVAR | DSE8610 with load-sharing line and synchronising panel |
| Remote monitoring | Modbus / SNMP to BMS | Modbus RTU over RS-485 standard, TCP gateway optional |
| Model | Prime | Standby | Engine options | FOB band |
|---|---|---|---|---|
| JJP-M200GF | 250 kVA / 200 kW | 275 kVA / 220 kW | Weichai, Cummins, Perkins, Volvo, Yuchai | US$14,000–20,000 |
| JJP-M300GF | 375 kVA / 300 kW | 413 kVA / 330 kW | Weichai, SDEC, Perkins, Volvo, Yuchai | US$20,000–28,000 |
| JJP-M400GF | 500 kVA / 400 kW | 550 kVA / 440 kW | Weichai, Cummins QSK19, Perkins, Volvo, SDEC | US$28,000–38,000 |
| JJP-M500GF | 625 kVA / 500 kW | 688 kVA / 550 kW | Weichai, Cummins QSK19, Perkins, Volvo | US$38,000–52,000 |
Above 625 kVA per set, the plant is built from parallel units rather than one larger machine — that is how N+1 and 2N are achieved anyway. For a hall needing 1,750 kVA, three 625 kVA sets in parallel is a better commercial and operational answer than one 2,000 kVA unit, because a spare module is a stock item and a maintenance outage only costs one third of the capacity.
The generator is roughly half the plant cost. Budget the whole chain or the number will be wrong by the time the commissioning engineer arrives.
| Line item | Typical share | Notes |
|---|---|---|
| Generator sets (FOB China) | 45–55% | US$14,000–52,000 per set depending on rating and engine brand |
| Sound-attenuated canopy | +8–12% | Residential grade needed if the hall is near a boundary |
| Synchronising / paralleling panel | 8–12% | Required for N+1 and 2N; not optional above one set |
| ATS and switchgear | 10–15% | Two ATS for 2N, one for N+1 |
| Bulk fuel tank and pipework | 6–10% | 12–48 h runtime, plus polishing and leak detection |
| Foundation, exhaust, cabling | 8–12% | Plinth rated 1.5× wet weight, remote radiator if indoor |
| Freight and commissioning | 5–10% | 2.5–3 t per canopied set, fuel tank drained for shipping |
Individual sets in a data centre plant typically run 250 kVA to 2,500 kVA. Our range covers 250–625 kVA per set, and larger halls are built from parallel units rather than single machines — which is how N+1 and 2N redundancy is achieved anyway.
Racks × kW per rack = IT load. Multiply by PUE for facility load. Divide by 0.8 for kVA. Then add the redundancy topology: N+1 means one extra set, 2N means a second complete plant. Do not size from the UPS rating alone — cooling and losses sit outside it.
N+1 is N sets carrying the load plus one spare on a shared bus — the Tier III default. 2N is two complete independent plants each capable of the full load — the Tier IV default. 2N roughly doubles generator, fuel and maintenance cost.
Concurrent maintainability: any set must be serviceable while the load runs. In practice that means N+1 with a maintenance path that never crosses the live bus, plus independent fuel and control paths. A single ATS downstream still breaks Tier III even with a perfect generator plant.
Most specifications call for 12–48 hours at full load. A 625 kVA set burns 109.6 L/h, so 12 hours is about 1,400 L. The baseframe tank is never enough — bulk storage plus a guaranteed refuelling contract is what satisfies the audit.
NFPA 110 Type 10 requires load acceptance within 10 seconds. That depends on jacket water heaters, a healthy battery bank and a charger, not on the engine size. Specify all three and test them monthly, not annually.
Diesel dominates because fuel can be stored on site and the set starts cold and unassisted. Gas sets need a reliable pipeline, which is the failure mode they are meant to protect against. Gas is worth considering only where the pipeline has a separate supply path.
65–75 dB(A) at 7 m for a canopied set. Urban data centres near a boundary usually need the low end plus acoustic treatment on the hall itself — check the local limit before specifying the canopy grade.
Yes — DSE8610 controllers with load-sharing line, synchronising panel, and Modbus to BMS. Tell us the topology (N+1, 2N or block redundant) and the number of sets, and the panel is specified with the machines rather than retrofitted later.
We will come back with the kVA, the set count, the fuel runtime and the paralleling configuration — priced as a plant, not as loose machines.
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