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Characterizing Data Center Cooling System Water Stress in the United States (2022 ASHRAE Annual Conference paper)

ASHRAE · Li Chen, Aaron P. Wemhoff

Li Chen and Aaron P. Wemhoff propose Water Scarcity Usage Effectiveness (WSUE), which weights on-site cooling water and the water embedded in purchased electricity by the scarcity of the basins they come from. It shows strong location dependence and that dry design is not always better.

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Overview

The paper was presented at the ASHRAE 2022 Annual Conference; its authors are Li Chen and Aaron P. Wemhoff. The accepted manuscript is openly available through NSF PAR (10341797). The proposed metric is intended to support siting and cooling-system selection.

WSUE combines a scarcity-weighted on-site WUE term with a scarcity-weighted source (electricity) term multiplied by PUE. WUE_source = EWIF x PUE + WUE, where EWIF is the energy water intensity factor of the supplying grid. The authors use balancing-authority-level electricity and water-transfer data for the contiguous US.

The modelling covers three cooling systems, each for a 400 kW IT load: CRAH with chillers and cooling towers, DX CRAC units, and pure evaporative cooling. The CRAC model has 100 kW per unit, 20 C supply air, 2.0 m3/s indoor and 4.0 m3/s outdoor airflow, and COP varying with condensing temperature. Several climates are examined.

The main finding is that WSUE depends strongly on location, and that depending on the grid's water footprint a water-intensive cooling solution can yield a lower WSUE than one with little or no on-site water use. As a limit, the model rests on 400 kW examples and US data.

Key points

  1. WSUE combines a scarcity-weighted on-site WUE term with a scarcity-weighted source (electricity) term multiplied by PUE.
  2. WUE_source = EWIF x PUE + WUE, where EWIF is the energy water intensity factor of the supplying grid.
  3. Three modelled systems: CRAH with chillers and cooling towers, DX CRAC units, and pure evaporative cooling, each for a 400 kW IT load.
  4. CRAC model: 100 kW per unit, 20 C supply air, 2.0 m3/s indoor and 4.0 m3/s outdoor airflow, COP varying with condensing temperature.
  5. A water-intensive cooling solution can yield a lower WSUE than one with little or no on-site water use, depending on the grid.
  6. The metric is intended to support siting and cooling-system selection.
  7. The accepted manuscript is open on NSF PAR.

Using it in design

  • In site comparison, compute both site WUE and source (grid) water using a regional EWIF, and optionally a scarcity-weighted index.
  • Do not steer users to dry cooling everywhere on the basis of site WUE alone.
  • Compare evaporative and dry designs together with the grid's water footprint.

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Who should read it

Designers and analysts evaluating water sustainability in site selection and cooling-system comparison.

Related standards

  • ISO/IEC 30134-9 (WUE)
  • The Green Grid WUE

Publication details

Authors
Li Chen; Aaron P. Wemhoff
Publisher
ASHRAE
Year
2022
Document number
ASHRAE Annual Conference papers 2022; NSF PAR 10341797
Event
ASHRAE 2022 Annual Conference
Document language
English
Source type
Standard
Access
Free to read
Licence
Copyright retained; citation only — the publisher’s terms apply to the original document

Citation

Li Chen; Aaron P. Wemhoff (2022). Characterizing Data Center Cooling System Water Stress in the United States (2022 ASHRAE Annual Conference paper). ASHRAE. ASHRAE Annual Conference papers 2022; NSF PAR 10341797. ASHRAE 2022 Annual Conference. https://par.nsf.gov/biblio/10341797

WaterSustainabilityPerformance metricsSite planning

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