Climate- and technology-specific PUE and WUE estimations for U.S. data centers using a hybrid statistical and thermodynamics-based approach

Abstract

The water use of data centers (DCs) is becoming an increasingly important consideration for sustainability analysts, but has been difficult to quantify due to lack of reported data by DC operators. This work develops thermodynamically-compatible water use effectiveness (WUE) and power usage effectiveness (PUE) ranges needed for direct and indirect water use analysis for 10 different DC archetypes in 15 U.S. climate zones, using a hybrid physical-statistical approach that is validated with real-world data. The ranges further capture variabilities between best and poor DC efficiency practices, showing that PUE and WUE values can have relative difference as much as 62% and 100% respectively, depending on cooling technologies, efficiencies, and locations. PUE results indicate significant climate effects, whereas WUE results indicate the strongest climate effects for airside economizers with either adiabatic or water-cooled chiller systems. Collectively, the results underscore the importance of considering technology, efficiency, and climate effects when estimating PUE and WUE for direct and indirect DC water use analysis. Results also identify variables leading to best-achievable PUE and WUE values by climate zone and cooling system type—including operational set points, use of free cooling, and cooling tower equipment and operational factors—which can support DC water- and energy-efficiency policy initiatives.