Determining wasted energy in the airside of a perimeter-cooled data center via direct computation of the Exergy Destruction

Abstract

To keep pace with the growing energy demand, legacy air-cooled data centers begun implementing energy efficiency strategies: Perfecting air flow management, enhancing cooling air delivery and collecting (re-using) waste heat. However, one may wonder: What is the magnitude of these energy savings? Is it worth the effort? The second law of Thermodynamics offers unique insights about energy wasteful practices by estimating the Exergy Destruction in a system. Exergy is equivalent to the “available energy”, hence the presence of inefficiencies “Destroys Exergy”. In this work, we numerically modeled the behavior of the airside in an existing data center laboratory (CEETHERM) using the commercial Finite Volume software 6SigmaDCXTM. The collected numerical data were used to post-process two Exergy Destruction approaches (Direct and Indirect method), whose behavior was tested against: (1) A simplified study case and (2) Actual data center flow. Both approaches worked well against the study case, although for case (2) the Indirect Method–which neglects turbulence effects–predicted zones of artificial negative Exergy Destruction. The Direct Method permitted associating large inefficiencies in the airflow to hot–cold airstream pre-mixing and important pressure drops in the raised floor. The airside Exergy Destruction encompassed a significant amount of the total irreversibilities in the system, suggesting that mitigating (or eliminating) it, can substantially improve energy saving efforts, especially in legacy data centers.