Brandon Rubenstein

Hybrid cooled data center using above ambient liquid cooling

Customers who operate large data centers are looking for new ways to reduce their energy consumption and improve the ability to support higher compute density. An approach to liquid cooling that uses warm water instead of chilled water to cool system components and eliminate or greatly reduce the need for chillers in the data center is described in this paper. This change would have the dual effect of reducing the energy consumption of the cooling infrastructure by as much as 50% while increasing supported power densities (relative to air cooled solutions). In this paper is a description of the hybrid data center concept. An analytical model is constructed of both the hybrid data center and a baseline data center using heat transfer fundamental calculations and equipment data sheets. Variations in environmental conditions and the percentage of heat removed with liquid are investigated. The overall energy savings for these variations and the estimated cost savings are reported.

From Chip to Cooling Tower Data Center Modeling: Influence of Air-Stream Containment on Operating Efficiency

In the drive to enhance data center energy efficiency, much attention has been placed on the prospect of airflow containment in hot-aisle cold-aisle raised floor arrangements. Such containment prevents airflow recirculation, eliminating the mixing effects of the hot and cold air streams that can cause an undesirable temperature rise at the inlet of the equipment racks. The intuitive assessment of the industry has been that the elimination of such mixing effects increases the energy efficiency of the data center cooling system by enabling delivery of air at higher inlet temperatures, thus reducing the amount of infrastructure cooling required. This paper employs an end-to-end modeling approach to analyze the effect of air stream containment in the computer room and its impact on the holistic system efficiency. Dimensionless heat index parameters are employed to characterize the effects of containment, recirculation and mixing within the computer room environment. The extent of recirculation is shown to primarily influence the operation of the rack and CRAC level cooling systems, with the chiller systems also impacted. The overall effect on the complete cooling system performance and data center efficiency requires balancing of these effects. Through this model analysis, it is shown that containment may negatively impact overall energy efficiency in some circumstances, and that recirculation may actually be beneficial to overall energy efficiency under certain system dependent operating thresholds.Copyright

Influence of Experimental Uncertainty on Prediction of Holistic Multi-Scale Data Center Energy Efficiency

As the energy footprint of data centers continues to increase, models that allow for “what-if” simulations of different data center design and management paradigms will be important. Prior work by the authors has described a multi-scale energy efficiency model that allows for evaluating the coefficient of performance of the data center ensemble (COPGrand ), and demonstrated the utility of such a model for purposes of choosing operational set-points and evaluating design trade-offs. However, experimental validation of these models poses a challenge because of the complexity involved with tailoring such a model for implementation to legacy data centers, with shared infrastructure and limited control over IT workload. Further, test facilities with dummy heat loads or artificial racks in lieu of IT equipment generally have limited utility in validating end-to-end models owing to the inability of such loads to mimic phenomena such as fan scalability, etc. In this work, we describe the experimental analysis conducted in a special test chamber and data center facility. The chamber, focusing on system level effects, is loaded with an actual IT rack, and a compressor delivers chilled air to the chamber at a preset temperature. By varying the load in the IT rack as well as the air delivery parameters — such as flow rate, supply temperature, etc. — a setup which simulates the system level of a data center is created. Experimental tests within a live data center facility are also conducted where the operating conditions of the cooling infrastructure are monitored — such as fluid temperatures, flow rates, etc. — and can be analyzed to determine effects such as air flow recirculation, heat exchanger performance, etc. Using the experimental data a multi-scale model configuration emulating the data center can be defined. We compare the results from such experimental analysis to a multi-scale energy efficiency model of the data center, and discuss the accuracies as well as inaccuracies within such a model. Difficulties encountered in the experimental work are discussed. The paper concludes by discussing areas for improvement in such modeling and experimental evaluation. Further validation of the complete multi-scale data center energy model is planned.© 2011 ASME

Cable management arm airflow impedance study

A heavily loaded cable management arm at the rear of a server system can have the visual appearance of presenting a significant obstruction to airflow. Tests were carried out to evaluate the level of airflow impedance presented by a fully cabled arm in a relatively low profile server system. This investigation reveals that airflow pressure drop due to the presence of the cable management arm is less than 2% of the overall system impedance at typical operating conditions. This level of impedance would cause a nearly imperceptible temperature rise within the system.