Demonstration of a High-Efficiency Evaporative Cooler for Improved Energy Efficiency in DoD Data Centers
Dr. Thomas Butcher | Brookhaven National
Objectives of the Demonstration
The objective of this project was aimed at reducing energy use for data center cooling. The objectives of the demonstration were to show that: the evaporative cooling system can be integrated with an existing mechanical chiller cooling system; the system can meet the cooling demand of the data center for nearly 100% of the year; and the energy savings and water use targets can be met.
The technology planned for this demonstration involved hybrid evaporative cooling. Water was cooled in outdoor exchangers that operated either in a wet or dry mode (hybrid) to maximize energy savings and minimize water consumption. The planned demonstration site was a data center in Port Hueneme, California. In the pre-existing situation at this site, water was cooled with conventional mechanical chillers circulated through indoor air handler units. In the planned demonstration, the cooling load was transferred to the lower energy, hybrid evaporative cooler with the existing mechanical chillers remaining as backup. The indoor air handler units were not changed. Two different fluid cooler technologies were candidates for use in this project. An analysis of both was completed using an hourly annual analysis. Several different options for integration at the site were evaluated including the addition of thermal storage and integration with direct-to-chip cooling.The project involves installation of the PFC system at a DoD data center in Port Hueneme, California, followed by careful monitoring and analysis to evaluate actual reduction in energy use, impact on data center temperature distribution, validation of predicted weather impacts on performance, and potential areas for improvement.
An analysis was done of the expected energy performance of the two evaporative cooler concepts evaluated in this project and energy savings relative to the baseline mechanical chiller. An analysis of the annual hours for which the hybrid evaporative cooler concept can run in a dry mode and the annual hours for which the hybrid evaporative cooler concept will not be able to meet the cooling load of the data center was also completed. Annual electrical energy savings from 51 to 79% were projected. At this site the number of annual hours for which the evaporative coolers could not nominally meet the data center cooling load ranged from 2 to 111, depending on technology used.
To achieve energy savings as high as 75% with this technology, the data center temperature must be increased from traditional levels. This project documents the challenges and solutions associated with this. A key factor in performance is the temperature of the circulating water and this, in turn, is affected by the heat transfer characteristics of the indoor air handlers. The analysis showed that, at the Port Hueneme site, this approach could be used to completely displace the existing mechanical chillers. An extension of this analysis to other climate zones around the US showed that the evaporative chillers may not be able to completely displace the mechanical chillers everywhere, but in many cases can still provide substantial reductions in the data-center energy use.
After completion of a detailed installation design and specifications, the decision was made not to proceed with the actual installation due to the manufacturer withdrawing from the project and other reasons such as cost relative to alternative technologies, water quality in specific target market areas, and the relatively large footprint of their unit.
Points of Contact
Dr. Thomas Butcher
Brookhaven National Laboratory
Energy and Water
SERDP and ESTCP