Theoretical and Empirical Energy Impacts of Economization in Data Centers

Abstract

Data center energy consumption can be divided into three broad categories: Information Technology (IT), Electrical, and Mechanical. An efficient data center uses the least amount of non-IT energy, which is typically divided between the mechanical and electrical systems. Mechanical systems generally contribute a large portion of the non-IT energy use by providing cooling from compressor-based equipment [1,2] and because of this, strategies to reduce compressor energy consumption can lead to significant mechanical system energy savings. The most efficient way to reduce compressor energy is through elimination or significant reduction in annual runtime. This is possible with the use of integrated airside or waterside economizers. This paper demonstrates the impacts of economization in data centers through data collected from four operating facilities over the course of implementing various economizer improvement projects. System architectures include water-cooled centrifugal chiller plant with waterside economization, direct expansion air handling units (AHU) with airside economization, air-cooled centrifugal chillers with integrated waterside economization, and direct expansion computer room air conditioners (CRAC) with evaporative cooling and waterside economization. A systematic and methodical comparison of the baseline and post-conditions is discussed, comparing expected to observed economizer operating conditions. The comparison of multiple real-world scenarios revealed a range of variances in expected operation of economizer sequences to actual observations, indicating a need for close monitoring of system performance by data center operators to fully realize economizer benefits within facilities.