How Chilled Water Systems Meet Data Center Availability and Sustainability Goals

Overview

Cooling accounts for roughly 25-35% of data-centre energy in many facilities. The paper uses TEWI as its yardstick: direct refrigerant-leak emissions plus indirect electricity emissions. The formula is GWP x leakage rate x years, plus GWP x charge x (1 - recovery factor), plus years x annual energy x grid CO2 factor. For scroll chillers, R410A (GWP 1924) gives way to R454B (466), R32 (677) or R290; for screw and centrifugal chillers, R134a (1300) to R513A (573) or R1234ze (below 1).

Efficiency steps are shown in sequence: typical white space now runs at 24-25°C server inlet with 36-37°C return air, with chilled water raised from 10-15°C to 15-18°C or higher; then come free-cooling chillers, plant-level control, inverter compressors, adiabatic pads, heat recovery and thermal storage. The simulation basis is, per 5 MW hall, 5 (N+1) chillers of 1250 kW and 28 (N+1) CRAHs of 185 kW, at 80% load (12 MW total).

The results make each step concrete. Ashburn pPUE goes from a 10/15°C baseline of 1.217 to 1.128 with 20/28°C water and free-cooling chillers, 1.117 with plant control, 1.106 with inverter compressors and low-GWP refrigerant and 1.094 with adiabatic, while WUE rises from 0 to 0.277 L/kWh. In Tokyo the baseline of 1.235 falls to 1.108 with adiabatic (WUE 0.253 L/kWh). The paper also notes that 2-5 MW halls are moving to non-raised floors, where standard perimeter CRAHs can create high-velocity air and negative pressure at the first rack row.

Key points

1. Cooling accounts for roughly 25-35% of data-centre energy in many facilities.
2. TEWI = GWP x leakage rate x years + GWP x charge x (1 - recovery factor) + years x annual energy x grid CO2 factor.
3. Refrigerant swaps: R410A (GWP 1924) to R454B (466), R32 (677) or R290 for scroll chillers; R134a (1300) to R513A (573) or R1234ze (<1) for screw/centrifugal.
4. Typical white space now runs at 24-25°C server inlet with 36-37°C return air; chilled water is raised from 10-15°C to 15-18°C or higher.
5. Simulation basis per 5 MW hall: 5 (N+1) chillers of 1250 kW and 28 (N+1) CRAHs of 185 kW at 80% load (12 MW total).
6. Ashburn pPUE: baseline 10/15°C 1.217; 20/28°C water with free-cooling chillers 1.128; plant control 1.117; inverter compressor + low-GWP 1.106; adiabatic 1.094 (WUE 0 to 0.277 L/kWh).
7. Tokyo equivalent: 1.235 baseline down to 1.108 with adiabatic (WUE 0.253 L/kWh).
8. 2-5 MW halls are moving to non-raised floor; standard perimeter CRAHs can create high-velocity air and negative pressure at the first rack row.

Using it in design

• Add a TEWI calculation to cooling options (refrigerant GWP, charge kg, leak rate, life years, grid emission factor).
• Give the chiller catalogue refrigerant, GWP (AR5), free-cooling capability, adiabatic option and compressor type, and flag high-GWP refrigerants against F-gas and Kigali phase-down.
• Report pPUE and WUE together so adiabatic gains are never shown without their water cost.
• Warn on non-raised-floor halls with standard perimeter CRAHs near the first row.

Who should read it

Mechanical designers evaluating chilled-water plant architecture, refrigerant choice and adiabatic options.

Related standards

• ASHRAE TC 9.9 Thermal Guidelines
• EU F-gas Regulation
• ISO/IEC 30134-9 (WUE)
• ISO/IEC 30134-2 (PUE)

Publication details

Authors

Vertiv

Publisher

Vertiv

Year

2024

Document number

SL-18066

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation