How Much Water Storage Does a Data Centre Really Need? A Complete UK Sizing Methodology
Data Centre Water Tank Sizing - UK Sizing Methodology (Tier II–IV)
Why sizing matters
Right sized storage prevents thermal escalation, satisfies insurer and regulator expectations, and reduces OPEX by enabling off peak replenishment and stable water chemistry. Our “Water Storage as a Pillar of Resilience for CNI Data Centres” Guide provides tier based autonomy norms and a practical calculation method. Here’s a summary:
The core inputs for Data Centre Water Tank Sizing
1. Cooling load (MW) and hours of operation.
2. Water use rate by cooling technology (approx. ranges):
- Evaporative towers: 1.2–1.8 L/kWh of cooling.
- Hybrid/adiabatic: 0.6–1.0 L/kWh.
- Closed loop water chillers: 0.2–0.5 L/kWh (makeup/blowdown).
(Assumes ~8,760h/yr; see guide’s comparison table.)
3. Redundancy model: Tier III (N+1) vs Tier IV (2N / 2N+1) with higher autonomy expectations.
4. Autonomy target:
- Tier III: 24–48h cooling water.
- Tier IV: 48–120h cooling water.
5. Fire reserve per BS EN 12845 (hazard class, discharge density, duration) with clearly dedicated volume in combined tanks.
6. Local risks: mains reliability, drought stress, tanker access; add 10–15% buffer.
Worked example (10MW Tier IV with evaporative cooling)
- Cooling load: ≈4 MW (illustrative, using PUE based split from the guide).
- Water consumption: 1.5 L/kWh × 4,000 kW × 24 h = 144 m³/day.
- Autonomy: 72 h → 432 m³ (cooling).
- Fire reserve: ~600 m³ (subject to hazard class/hydraulics under BS EN 12845).
- Total (before buffer): ~1,032 m³; add 10–15% as site specific buffer.
Quick reference (illustrative ranges)
- Tier III / 5MW: 700–1,140 m³ (cooling + fire reserve, 72h standard).
- Tier IV / 10MW: 1,140–1,850 m³ (as above).
- Tier IV / 20MW: 1,850–3,300 m³ (as above).
Use this as a screening estimate; final sizing must be engineered to your hazard class, makeup chemistry, ambient envelope, and redundancy model.
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Compliance essentials (UK)
- Backflow & contamination: Water Fittings Regulations; BS EN 1717 air gaps (AA/AB).
- Hygiene & testing: BS 8558 for hygienic storage/testing.
- Legionella management: HSE L8 risk assessment and monitoring cadence.
- Firewater: BS EN 12845 capacity/duration with insurerrecognised certification (LPCB/LPS) where required.
Design notes for engineers
- Segmented/compartmented GRP arrays enable phased builds and maintenance without losing capacity.
- BMS instrumentation: level (ultrasonic/radar), flow (electromagnetic), pH/conductivity/turbidity, leak detection; alarms at operational thresholds.
- Climate adaptation: review capacity every 3–5 years; consider 20–30% buffers and rainwater harvesting (potential 15–30% offset) where viable.
Q&A
Size for peak temperature demand, not average daily use; adiabatic draw spikes during heatwaves.
Yes, but clearly mark and protect the dedicated fire volume; insurers often expect LPCB aligned documentation.
It’s a strong target (24–48h typical). Consider ≥72h where mains reliability or tanker access is uncertain.
Every 3–5 years or after major plant/cooling changes; include climate stress scenarios.
Sources
- Ponemon Institute (2023). Cost of Data Center Outages. Traverse City, MI: Ponemon Institute LLC.
- UK Environment Agency. Water Resources Planning. Available at: https://www.gov.uk/government/organisations/environment-agency
- Health and Safety Executive. Legionnaires’ disease: The control of legionella bacteria in water systems (L8). HSE Books.
- British Standards Institution. BS 8558:2015 Guide to the design, installation, testing and maintenance of services supplying water for domestic use within buildings and their curtilages. London: BSI.
- Met Office. UK Climate Averages. Available at: https://www.metoffice.gov.uk
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