Finding Sustainable Solutions to Data Center Power and Water Use

Overview

StatePoint is an indirect evaporative chilled-water plant built around a membrane exchanger that keeps air and water separate. The paper proposes designing for typical annual conditions and accepting brief, allowed excursions in supply-air temperature (SAT). In 100% free-cooling applications the plant reaches pPUE 1.05-1.06 (1.025-1.03 excluding fan-coil wall energy), with annualised WUE below 0.1 L/kWh depending on climate. The manufacturer claims annual water and power reductions of up to 90% and 60% versus chiller/cooling-tower plants; the early development target was 20-30%.

The Frankfurt case is a 20 MW colocation with 12 StatePoint units at N+2, compared with hybrid fluid coolers and open cooling towers on annual pPUE/WUE versus SAT. Raising annual SAT from 23 to 29 C markedly improves pPUE and WUE. The peak design condition pairs ASHRAE N50 dry bulb 39.1 C with N20 wet bulb 23.9 C; letting SAT rise into the ASHRAE A1/A2 allowable range at that extreme greatly reduces trim-chiller capacity.

The peak numbers give a separate result for electrical sizing. At 100% IT load, the ASHRAE 50-year extreme and 1-2 units offline, peak pPUE is 1.23 for StatePoint, 1.28 for the hybrid cooler and 1.275 for the cooling tower, which is about 230 kW versus 275-280 kW of cooling power per 1,000 kW of IT. Peak hourly make-up water is about 41% below the hybrid cooler and 6% below the cooling tower. The paper also covers the membrane's water-quality and Legionella advantages and smaller on-site water storage. The comparisons come from the manufacturer's own case study.

Key points

1. In 100% free cooling, pPUE 1.05-1.06 (1.025-1.03 excluding fan-coil wall energy); annualised WUE <0.1 L/kWh depending on climate.
2. Manufacturer claim: up to 90% less annual water and 60% less power than chiller/tower plants; early target 20-30%.
3. Frankfurt: 20 MW colocation, 12 StatePoint units at N+2.
4. Raising annual SAT from 23 to 29 C markedly improves pPUE and WUE.
5. Peak condition: ASHRAE N50 dry bulb 39.1 C coincident with N20 wet bulb 23.9 C.
6. Peak pPUE: StatePoint 1.23, hybrid cooler 1.28, cooling tower 1.275 (~230 kW versus 275-280 kW per 1,000 kW IT).
7. Peak hourly make-up water ~41% below a hybrid cooler and ~6% below a cooling tower.

Using it in design

• Support peak pPUE (electrical sizing, with N-x units offline at ASHRAE N50/N20 extremes) separately from annual pPUE/WUE (energy) in the cooling plant model.
• Take allowable SAT excursion hours and ASHRAE A1/A2 limits as inputs; they drive trim-chiller sizing.
• Add an indirect evaporative chilled-water plant type to the catalog with a WUE curve versus SAT.
• Size make-up water and storage in the water module from peak instantaneous evaporation, not the annual average.

Who should read it

Design engineers and investment decision makers choosing cooling plant for water- and power-constrained sites.

Related standards

• ASHRAE TC 9.9 Thermal Guidelines
• ISO/IEC 30134-2
• ISO/IEC 30134-9

Publication details

Authors

Philip LePoudre; Pooya Navid

Publisher

Nortek Air Solutions

Year

2021

Document number

752F-0721

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