Dynamically Controlled Long Duration Operation of a Highly Energy Efficient Chiller-Less Data Center Test Facility

Data center energy consumption makes up a significant and rapidly growing portion of the national energy use. A large fraction of this energy consumption, in the range of 25%–40%, is used by the data center cooling infrastructure, particularly by the computer room air handlers (CRAH) and by the chiller plant. A joint US Department of Energy and IBM effort investigated the use of warm water server cooling and water side economization to help improve energy efficiency in a volume server by minimizing the use of CRAH and chiller hours with the goal of reducing the ratio of cooling energy to IT energy from the conventional value of approximately 50% to less than 10%. Previous work focusing on system characterization and one day runs found significant energy savings as compared to a traditional chiller based data center. In the work reported in this paper we discuss the development and implementation of a dynamic control approach followed by details and results from a 60+ day run of the data center test facility starting May 11^th, 2012. Results from this long term study found the average cooling energy consumption to be 3.5% of the IT energy, which is consistent with previous short one day runs. The implemented control scheme was also able to reliably control the water temperature to within 0.5°C of the set-point under most conditions and could react and stabilize to a new set-point in 30 minutes. The work presented demonstrates the high energy efficiency of a warm water cooled, water-side economized, chiller-less data center over a long sustained period of time and highlights the benefits of energy aware control to help limit cooling energy.