Diesel Generator Sizing for Philippine Data Rooms: kVA, Load Factor, and Runtime
A generator that is too small trips under load during a typhoon. A generator that is too large suffers wet stacking — a condition where running at very low load (below 30% of rated capacity) causes unburned diesel to accumulate in the exhaust system, leading to increased maintenance costs, carbon buildup, and eventual failure.
The correct generator size for a Philippine data room or server room balances safety margin against the wet stacking risk — and accounts for the specific power factor of IT equipment loads, which is different from the power factor of motors and general office loads.
The Sizing Methodology
Step 1: Calculate Total Connected Load in kW
Sum the real power consumption of all loads the generator must supply:
| Load | Power Draw |
|---|---|
| UPS input power (kW, not kVA) | Varies by UPS and load |
| Air conditioning (server room cooling) | kW from nameplate |
| Lighting (if on generator circuit) | kW |
| Security systems (CCTV, access control) | kW |
| Any other critical loads | kW |
Important: Use the UPS input kW, not the UPS kVA rating. If your UPS is a 10 kVA unit at 80% load (8 kW output) with 92% efficiency, the UPS input power is 8 ÷ 0.92 = 8.7 kW. This is what the generator must supply.
Step 2: Apply the Load Factor
The generator should not run at 100% of rated capacity — this leaves no margin for load fluctuations and starting surges. Recommended operating range: 60–80% of rated capacity for continuous operation.
Formula: Required generator kW = Total load kW ÷ Load factor (0.70 is a common target)
Example: Total load = 12 kW. At 70% load factor: Required generator kW = 12 ÷ 0.70 = 17.1 kW minimum
Step 3: Convert kW to kVA
Generators are rated in kVA (apparent power). The conversion depends on the power factor (PF) of the connected loads:
kVA = kW ÷ Power Factor
Power factor of typical server room loads: IT equipment (servers, switches, UPS) typically presents a power factor of 0.85–0.95 to the generator. Modern UPS units with active PFC (power factor correction) on the input present near-unity (0.95–1.0) power factor to the generator — a significant improvement over older UPS technology.
Example (continuing): 17.1 kW at PF 0.90: Required kVA = 17.1 ÷ 0.90 = 19 kVA minimum
Standard generator sizes: round up to the next available standard size. In the Philippine market, common sizes are 15, 20, 25, 30, 40, 50, 60 kVA. For this example: 20 kVA generator.
Step 4: Verify the Wet Stacking Risk
At the expected load, verify the generator will operate above 30% of its rated capacity:
At 12 kW actual load on a 20 kVA / 18 kW generator: Load percentage = 12 ÷ 18 = 67% — within the optimal 60–80% range. No wet stacking risk.
If actual load were only 5 kW (28% of rated capacity), wet stacking risk would be present. In this case, either select a smaller generator or plan for regular load bank testing to burn off accumulated carbon.
Fuel Consumption and Tank Sizing
Diesel Consumption Rate
Diesel generators consume approximately 0.25–0.35 litres per kWh at rated load. The exact figure depends on the generator model, load percentage, and ambient temperature.
At 70% load (most efficient operating zone): approximately 0.28 L/kWh
Example: 20 kVA generator producing 14 kW at 70% load, running for 24 hours: Fuel consumption = 14 kW × 24 hours × 0.28 L/kWh = 94 litres
Day Tank Sizing for Philippine Deployments
Typhoon preparedness requirement: For Philippine data rooms in typhoon corridors, plan for 72-hour minimum runtime without refuelling. After major typhoons, fuel delivery logistics can be disrupted for 48–96 hours.
72-hour tank for 20 kVA generator at 70% load: Fuel needed = 14 kW × 72 hours × 0.28 L/kWh = 282 litres minimum
Standard day tanks: 200L, 500L, 1,000L. For typhoon preparedness, specify a 500L day tank (provides buffer above the 72-hour requirement).
For generators in permanent installations (not portable), a main fuel tank connected to the day tank via a fuel transfer system allows longer runtime without manual refuelling.
See our typhoons and data centre power guide for the full typhoon preparedness framework including fuel management procedures.
Generator and UPS Integration
The generator must integrate with the UPS system via an Automatic Transfer Switch (ATS). The ATS sequence:
- Grid fails → UPS switches to battery (zero transfer time for online double-conversion)
- ATS detects grid failure → sends start signal to generator
- Generator starts and stabilises to rated frequency and voltage (10–30 seconds)
- ATS transfers building load from grid to generator
- UPS detects generator power on input → switches from battery to generator
- UPS battery recharges from generator
Generator compatibility with UPS: Online double-conversion UPS units accept generator power cleanly — the rectifier handles frequency and voltage variation from generators that are still stabilising after startup. Line-interactive and standby UPS units may have compatibility issues with some generators. Always specify online double-conversion UPS for generator-integrated Philippine data rooms.
See our generator + UPS integration guide for the wiring architecture.
Philippine Generator Maintenance Requirements
Engine Exercise Protocol
Generators that are only started for emergencies frequently fail to start when needed. The correct maintenance protocol:
- Monthly: Run under load for minimum 30 minutes (not unloaded — use a load bank or connect to actual building load)
- Quarterly: Full load test at 75–100% rated capacity for 2 hours
- Annually: Oil change, coolant check, fuel filter replacement, belt inspection, battery check (starter battery), load bank test
Tropical Climate Considerations
Philippine tropical conditions accelerate generator component degradation:
- Fuel degradation: Diesel stored in tanks degrades after 12–18 months. Rotate fuel, use a fuel stabiliser, and drain/replace fuel if the generator has not run for over 12 months.
- Corrosion: Salt air in coastal locations accelerates corrosion on electrical connections and alternator windings. Inspect and treat with anti-corrosion compound annually.
- Cooling system: Higher ambient temperatures stress the cooling system. Check coolant level and condition every 6 months.
Summary: Generator Specification for Common Philippine Data Room Sizes
| Data Room Size | Typical IT Load | Generator Size | Day Tank (72h) |
|---|---|---|---|
| Small server room (2–4 servers) | 3–5 kW | 10 kVA | 200L |
| Medium server room (5–15 servers) | 8–15 kW | 20–30 kVA | 500L |
| Large data room (15–30 servers) | 20–40 kW | 50–60 kVA | 1,000L |
Related reading: Generator + UPS integration guide · Typhoons and data centre power · UPS for Philippine data centres · UPS runtime calculation
For Philippine data rooms specifying generator systems — sizing, ATS integration, and commissioning — get in touch.
Talk to our Power Systems team →
