A Review on efficient thermal management of air- and liquid-cooled data centers: From chip to the cooling system

The exergy method of energy systems analysis

Water, energy, and food are lifelines for modern societies. The continuously rising world population, growing desires for higher living standards, and inextricable links among the three sectors make the water-energy-food (WEF) nexus a vibrant research pursuit. For the integrated delivery of WEF systems, quantifying WEF connections helps understand synergies and trade-offs across the water, energy, and food sectors, and thus is a critical initial step toward integrated WEF nexus modeling and management. However, current WEF interconnection quantifications encounter methodological hurdles. Also, existing calculation results are scattered across a wide collection of studies in multiple disciplines, which increases data collection and interpretation difficulties. To advance robust WEF nexus quantifications and further contribute to integrated WEF systems modeling and management, this study: (i) summarizes the estimate results to date on WEF interconnections; (ii) analyzes methodological and practical challenges associated with WEF interconnection calculations; and (iii) points out opportunities for enabling robust WEF nexus quantifications in the future.

https://www.mdpi.com/1996-1073/9/2/65/pdf

Quantifying the Water-Energy-Food Nexus: Current Status and Trends

«Environmental sustainability: universal, and non-negotiable»

Reduction of resource consumption in data centers is becoming a growing concern for data center designers, operators and users. Accordingly, interest in the use of renewable energy to provide some portion of a data center's overall energy usage is also growing. One key concern is that the amount of renewable energy necessary to satisfy a typical data center's power consumption can lead to prohibitively high capital costs for the power generation and delivery infrastructure, particularly if on-site renewables are used. In this paper, we introduce a method to operate a data center with renewable energy that minimizes dependence on grid power while minimizing capital cost. We achieve this by integrating data center demand with the availability of resource supplies during operation. We discuss results from the deployment of our method in a production data center.

/pdf/towards-the-design-and-operation-of-net-zero-energy-data-5c4zguvmiv.pdf

Towards the design and operation of net-zero energy data centers

This paper summarizes recent explorations of the use of lifetime exergy consumption as a thermodynamically based metric for sustainability of information technologies. Other proposed thermodynamic metrics are described and compared with life cycle exergy consumption. The pros and cons of different metrics are discussed, and the advantages of life cycle exergy as a metric for information technologies are described. A lifetime exergy consumption model designed specifically for data center server analysis is presented as an example of how this type of metric can be used for information technologies. Database needs to facilitate this type of analysis are described. The operation of the lifetime exergy consumption model is demonstrated for case studies examining the effects of varying some of the data center design parameters. The use of this type of life cycle exergy consumption analysis for other information technologies is also discussed and assessed.

Lifetime exergy consumption as a sustainability metric for information technologies

Computational and Experimental Validation of a Vortex-Superposition-Based Buoyancy Approximation for the COMPACT Code in Data Centers

This paper summarizes the comparison of predictions by a compact model of air flow and transport in data centers to temperature measurements of an operational data center. The simplified model and code package, referred to as COMPACT (Compact Model of Potential Flow and Convective Transport), is intended as an alternative to the use of time-intensive full CFD thermofluidic models as a first-order design tool, as well as a potential improvement to plant-based controllers. COMPACT is based on potential flow and combined with an application of convective energy equations, using sparse matrix solvers to seek flow and temperature solutions. Full-room solutions can be generated in 15 seconds on a commercially available laptop, and an accompanying graphical user interface has also been developed to allow quick configuration of data center designs and analysis of flow and temperature results. Experiments for validation of the model were conducted at the HP Labs data center in Palo Alto, CA, which is in a traditional configuration consisting of inlet floor tiles feeding cold air between two rows of multiple server racks. Subsequently, air exits either through ceiling tiles or direct room-return to CRAC units located on the side of the room. Temperatures were recorded at multiple points along entering and exiting flow faces within the room, as well as at various points in cold and hot aisles, and are presented and compared to model predictions to assess their accuracy. Areas of greater and lesser accuracy are analyzed and presented, in addition to conclusions as to the strengths and weaknesses of the model. For some cases, the average predicted temperature along in-flowing rack faces was within one degree of the average measured temperature. However, the differences in temperature are not evenly distributed. The most pronounced variations between the model and room measurements were located in areas above server racks where recirculation was shown to most likely occur. In these areas, the predicted temperature was higher than experimental values; this can likely be attributed to the absence of buoyancy effects in the simplified potential flow model. Adaptations of the model and its configuration standards for more accurate temperature distributions are proposed, as well as investigations into the effect on temperature comparisons to idealized model output by unaccounted heat sources or flow phenomena.Copyright © 2010 by ASME

Experimental Validation of the COMPACT Code in Data Centers

The growing environmental footprint of data centers suggests the need for comprehensive models that enable designers and operators to optimize deployment configurations. In this paper, we discuss an exergy-based approach to the environmental design of one component of a data center, the computer room air conditioning (CRAC) unit. Previous work has examined the lifetime exergy consumption of the server technology portion of a data center. In this work we construct a lifetime exergy model for a direct expansion CRAC unit which when combined with the computer server model provides a more complete picture of the environmental impact of a data center. The lifetime model includes the material and energy consumption of the raw materials, transportation, manufacturing processes, operation and disposal. The application of the model is then explored under a variety of design configurations and utilization scenarios. Key parameters that affect the environmental footprint of the CRAC unit (as predicted by the lifetime exergy model) are identified. Case studies are performed to illustrate how variations in these key parameters can lead to significant differences in the lifetime exergy consumption of the CRAC unit. The paper concludes by recommending strategies to reduce the lifetime exergy consumption.© 2009 ASME

Exergy-Based Environmental Design of a Computer Room Air Conditioning Unit

The prediction of flow and temperature in data center operation is of particular importance in creating better capacity utilization and lower capital costs. However, it is often a time- and computing-intensive task, and would be well served by more expeditious modeling methods than full Computational Fluid Dynamic (CFD) thermofluidic models. A software package named COMPACT (Compact Model of Potential Flow and Convective Transport) was developed to provide one such alternative. Recent versions of COMPACT take under 10 seconds on a commercially available laptop to characterize a 550 square foot data center; the same room modeled with a CFD solver took 8 hours. Having the ability to create velocity and temperature predictions orders of magnitude faster than conventional CFD allow a variety of data center applications for the model, such as use as a first-order design tool, a potential improvement to plant-based controllers, a tool for system-wide assessment of life-cycle efficiency, and as an initial guess for complex CFD solvers. COMPACT applies convective energy transport equations to a computed potential flow field to approximate a flow and temperature field. The results from this model were compared to experimental measurements taken from a data center at Hewlett-Packard Laboratories in Palo Alto, CA. The presence of high localized temperatures in the model led to the conclusion that recirculation and buoyancy were contributing excessively to error in the model. A novel approach was proposed to account for these effects: a non-iterative (to preserve computational resources) method of vortex superposition, in which hot locations in the original model are analyzed and a corrective flow field consisting of Rankine vortices is superimposed on the solution. An updated model using this approach was tested with further experimental measurements taken from the data center at HP Labs, and identical inputs were used to compare COMPACT to commercially available CFD. These newer results showed a marked decrease in mean deviation of the model from measured temperatures, as well as elimination of the highly localized temperatures which afflicted the original COMPACT results. The vortex superposition model was also “tuned”, with vortex strength optimized for multiple test cases at varying levels of recirculation. In addition, the model-generated velocity and temperature fields were used to locate and quantify the destruction of exergy resulting from the mixing of warmer and cooler air in the room; these results are used as a measure of system efficiency.

David J. Lettieri

Papers

Lifetime exergy consumption as a sustainability metric for information technologies

Computational and Experimental Validation of a Vortex-Superposition-Based Buoyancy Approximation for the COMPACT Code in Data Centers

Experimental Validation of the COMPACT Code in Data Centers

Exergy-Based Environmental Design of a Computer Room Air Conditioning Unit

Evaluation of a vortex model of buoyancy-driven recirculation in potential flow analysis of data center performance