Indian Data Centre Cooling — CRAC vs CRAH vs Immersion + PUE Strategy
By MEPVAULT Editorial Team · MEP Consultant · HVAC / Data Centre · 11 May 2026
Reading time ~ 10 min · Originally published: 09 May 2026 · Last revised: 11 May 2026
For a 5 MW Mumbai hyperscale facility, traditional CRAC delivers PUE 1.7, CRAH-CHW 1.45, in-row + airside economiser 1.3, liquid immersion 1.08. The PUE delta from 1.3 to 1.08 saves ~10 GWh/yr per 5 MW but costs ₹20-30 Cr in capex premium — only justified for GPU/AI workloads. For mainstream commercial DC, the right target is PUE 1.3 via in-row containment + 14 °C CHW + airside economiser. Three architectural decisions that lock PUE for life.
Indian data centre cooling — the PUE arms race
Indian data centre capacity has expanded ~5× over 2020-2026, driven by hyperscale cloud, regulated payments infrastructure, and government cloud mandates. For a 1 MW IT load facility in Mumbai-Hyderabad-Chennai (the three big hubs), four cooling architectures compete: traditional CRAC (DX), CRAH (chilled-water), in-row + airside economiser, and liquid immersion. Each lands at a different annual PUE (Power Usage Effectiveness = total facility power / IT power).
Four architectures — by-the-numbers comparison
| Architecture | PUE annual | Capex (₹ Cr/MW IT) | Footprint (m²/MW) | Reliability | Best fit |
|---|---|---|---|---|---|
| CRAC (DX, perimeter) | 1.6-1.8 | 2.2-2.8 | 28-32 | High | Small DC ≤ 500 kW + edge |
| CRAH (chilled water, perimeter) | 1.4-1.5 | 3.0-4.0 | 38-45 | High | Mid + large DC; mainstream |
| In-row CRAH + airside economiser | 1.25-1.35 | 4.0-4.5 | 25-30 | High | Hyperscale + > 5 MW |
| Liquid immersion (2-phase) | 1.03-1.10 | 8-10 | 12-18 | Very high | HPC / AI / GPU cluster only |
| Direct-to-chip cold-plate | 1.10-1.15 | 7-9 | 20-25 | Very high | GPU + ML workloads |
Why PUE 1.3 is the right Indian commercial target — not 1.05
Liquid immersion delivers PUE 1.08 but costs ₹8-10 Cr/MW capex vs ₹3.5-4 Cr for CRAH + airside economiser. The PUE delta of 0.27 (1.3 vs 1.03) on a 5 MW facility saves ~10 GWh/year = ₹85 lakh annually at ₹8.5/kWh. The capex delta is ₹20-30 Cr for the immersion solution. Payback > 25 years on energy alone — only justified if the IT workload requires immersion (high density GPU/ML > 50 kW/rack) for technical reasons.
A 5 MW Mumbai hyperscale facility — design choice
| System | Capacity | Configuration | Capex (₹ Cr) | Annual energy (GWh) | PUE achieved |
|---|---|---|---|---|---|
| Chillers + cooling towers | 2 × 3,000 TR + 4 × 1,500 TR cooling tower | N+1 redundancy | 12 | 13.5 | — |
| CRAH units (in-row) | 30 × 60 kW + 12 × 100 kW | Hot-aisle/cold-aisle containment | 5 | 7.0 | — |
| Airside economiser (DOAS) | 5 × 30,000 m³/h economiser AHU | Outside-air pre-cool when ambient < 22 °C | 3 | Reduces above by 1.2 GWh | — |
| UPS + STS | 2 × 2.5 MVA UPS + STS | N+1 | 8 | 3.5 | — |
| Total | — | — | 28 + IT | 21.3 + 32 (IT) | 1.33 |
5 MW IT load × 8,760 hours = 43.8 GWh IT consumption. Plus 21.3 GWh facility = 65.1 GWh total. PUE = 65.1 / 43.8 = 1.49. After in-row containment + airside economiser optimisation, achieved PUE settles at 1.33 on annual basis (Mumbai climate gives ~28 % free-cool hours).
Three architectural decisions that lock PUE for the building life
- Cold-aisle / hot-aisle containment — solid roof + end-of-aisle doors. Without containment PUE drops by 0.10-0.15. Mandatory specification.
- Chilled water supply temperature — 14 °C (vs 7 °C traditional) for CRAH. Allows chiller to run higher COP + enables airside economiser more hours. Coordinate with rack inlet specification (recommended 27 °C max per ASHRAE TC 9.9 Allowable A1).
- Free-cooling sequence design — partial (waterside economiser) when ambient WB < 16 °C + full (airside economiser bypassing chiller) when ambient DB < 22 °C. The control sequence must be commissioned, not just installed.
References
- ASHRAE TC 9.9 Thermal Guidelines for Data Processing Environments (5th Edition), ASHRAE Atlanta 2021.
- ASHRAE Datacom Series — Best Practices for Data Center Energy Efficiency, ASHRAE 2022.
- AHRI Standard 1361:2021 — Performance Rating of Computer and Data Processing Room Air Conditioners.
- Uptime Institute Tier Classification System (Tier I-IV), Uptime Institute.
- TIA-942-C:2024 — Telecommunications Infrastructure Standard for Data Centers.
- ANSI/BICSI 002-2019 — Data Center Design and Implementation Best Practices.
- The Green Grid PUE Whitepaper (latest edition) — definition and measurement of PUE.
- Indian Data Centre Industry Report 2024 — KPMG India + NASSCOM cross-reference data.
// About the Authors
MEPVAULT Editorial Team — A team of practising MEP consultants based in India. ISHRAE-affiliated; FSAI-aligned.