Alan McReynolds

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

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 centers overall energy usage is also growing. One key concern is that the amount of renewable energy necessary to satisfy a typical data centers 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.

Optimization and control of cooling microgrids for data centers

Reliable operation of todays data centers requires a tremendous amount of electricity to power both the IT equipment and the supporting cooling facilities. As much as half of total data center electricity consumption can be attributed to the cooling systems required to maintain the thermal status of IT equipment. In order to lower the electricity usage of the cooling system and hence reduce the data center environmental footprint, alternative cooling resources, such as water and air-side economizers, are being exploited to supplement or replace the traditional chilled water based cooling schemes. The various cooling resource options, together with the mechanisms to distribute and deliver the cooling resource to IT equipment racks, constitute a cooling microgrid. In this paper, we present a holistic perspective for the optimization and control of the data center cooling microgrid. The holistic approach optimizes the sourcing and distribution of cooling resources from the site portfolio in response to real-time weather changes and site demand. The cooling microgrid optimization and control framework has been implemented in a research data center; we estimate that the framework cuts the yearly cooling costs by 30%.

Data center cooling management and analysis - a model based approach

As the hub of information aggregation, processing, and dissemination, todays data centers consume significant amount of energy. The data center electricity consumption mainly comes from the IT equipment and the supporting cooling facility that manages the thermal status of the IT equipment. The traditional data center cooling facility usually consists of chilled water cooled computer room air conditioning (CRAC) units and chillers that provide chilled water to the CRAC units. Electricity used to power the cooling facility could take up to a half of the total data center electricity consumption, and is a major contributor to the data center total cost of ownership. While the data center industry has established the best practice to improve the cooling efficiency, the majority of it is rule of thumbs providing only qualitative guidance. In order to provide on demand cooling and achieve improved cooling efficiency, a model based description of the data center thermal environment is indispensable. In this paper, a computationally efficient multivariable model capturing the effects of CRAC units blower speed and supply air temperature (SAT) on rack inlet temperatures is introduced, and model identification and reduction procedures are discussed. Using the model developed, data center cooling system design and analysis such as thermal zone mapping, CRAC units load balancing, and hot spot detection are investigated.

Kratos: Automated Management of Cooling Capacity in Data Centers With Adaptive Vent Tiles

In data centers with raised floor architecture, the floor tiles are typically perforated, delivering the cold air from the plenum to the inlets of equipment located in racks. The environment of these data centers is dynamic in that the workload and power dissipation fluctuate considerably over both short-term and long-term time scales. As such, airflow requirements vary continuously. However, due to labor costs and lack of expertise, the tiles are adjusted infrequently, and many data centers are grossly over provisioned for airflow in general and/or lack sufficient airflow delivery in certain local areas. This wastes energy and reduces data center thermal capacity. We have previously introduced Kratos, an Adaptive Vent Tile (AVT) technology that addresses this problem by automatically adjusting mechanical louvers mounted to the tiles in response to the needs of nearby IT equipment. Our initial results were limited to a 3-tile test bed that allowed us to prove concept but did not provide for scalability. This paper extends the previous work by expanding the size of the test bed to 28 tiles and 29 racks located in multiple thermal zones. We present experimental modeling results on the MIMO (Multi-Input Multi-Output) system and provide insights on the external behavior of the system through CFD (Computational Fluid Dynamic) analysis. We develop an MPC (Model-based Predictive Control) controller to maintain the temperatures of racks below the thresholds through vent tile tuning. Experimental results show that the controller can maintain the temperature below the thresholds while reducing overall cooling air requirements.Copyright

Modeling and Control for Cooling Management of Data Centers With Hot Aisle Containment

In traditional raised-floor data center design with hot aisle and cold aisle separation, the cooling efficiency suffers from recirculation resulting from the mixing of cool air from the Computer Room Air Conditioning (CRAC) units and the hot exhaust air exiting from the back of the server racks. To minimize recirculation and hence increase cooling efficiency, hot aisle containment has been employed in an increasing number of data centers. Based on the underlying heat transfer principles, we present in this paper a dynamic model for cooling management in both open and contained environment, and propose decentralized model predictive controllers (MPC) for control of the CRAC units. One approach to partition a data center into overlapping CRAC zones of influence is discussed. Within each zone, the CRAC unit blower speed and supply air temperature are adjusted by a MPC controller to regulate the rack inlet temperatures, while minimizing the cooling power consumption. The proposed decentralized cooling control approach is validated in a production data center with hot aisles contained by plastic strips. Experimental results demonstrate both its stability and ability to reject various disturbances.Copyright

Real time asset tracking in the data center

The importance and difficultly of asset tracking make it worthy of attention. We focus on data centers consisting of vertical racks where each rack may accommodate a variety of equipment. We describe an asset tracking system which automatically detects and identifies equipment within rack; has “pinpoint” accuracy, i.e., location resolution equals asset size; relays this information to possibly several management back-ends; includes a back-end application that maintains a location history for all equipment; and uses a visualization tool to display both the current state and the history of deployment.The solution features a flexible architecture that simplifies the connection with both existing and future asset management applications. The architecture supports simple configuration, load balancing, and redundancy. Care has been taken to use widely recognized standards wherever possible.

Integrated management of cooling resources in air-cooled data centers

To accommodate the dynamic environment within raised floor data centers, cooling capacity is tuned during operation through zonal control means, e.g., active management of air conditioning resources. However, due to the spatial variance of cooling efficiency and time-varying cooling demand within zones, zonal adjustments alone are not able to maximize the thermal capacity of data centers. Without making local adjustments to the physical structure, such as altering vent tile openings, a data center can suffer significant reduction in thermal capacity and cooling efficiency, and such that facility lifespan. In this paper, we present active cooling technologies using both local and zonal actuators that improve overall cooling efficiency. Experimental evaluation in a data center shows that the integrated controller can adapt to changes to the system under control, significantly improve the controllability of the temperatures and reduce the energy consumption of the cooling facility.

Invisible light: Using infrared for video conference relighting

Desktop video conferencing often suffers from bad lighting, which may be caused by harsh shadowing, saturated regions, etc. The primary reason for this is the lack of control over lighting in the users environment. A hardware-based solution to this problem would be to place lights near the video camera, but these would be distracting to the user. We use a set of infrared lights placed around the computer monitor to gather a sequence of frames which is used to infer surface normals of the scene. These are used in combination with a visible spectrum image to create an improved relighting result.

Optimization of Outside Air Cooling in Data Centers

Airside economizers in data centers introducing outside air directly in cold aisles or at CRAC level have been considered recently to reduce overall energy to cool IT equipment. However, such designs limit the operational envelope of free cooling based on the required supply air temperature to the IT equipment. More studies are required to optimize airside economizer layouts to increase the operation time and hence, increase the energy savings. This paper presents a case study of different outside air delivery configurations including outside air introduced in cold aisles, in plenum close to CRAC units’ supply side, at return side of CRAC units and in hot aisles. The temperature and flow fields are studied numerically and are compared to each other. Mixing of the cooler outside air with the hot air is studied to determine optimal local distribution of the outside air in a non-homogeneous data center to maximize natural cooling. The paper also quantifies the annual average performance of the outside air infrastructure to include the effects of the seasonal variations in the ambient temperature.Copyright

Smart edge server: beyond a wireless access point

Wireless access at cafes, airports, homes and businesses have proliferated all over the globe with several different Wireless Internet Service Providers. Similarly, digital media has created a paradigm shift in media processing resulting in a complete change in media usage models, revamped existing businesses and has introduced new industry players. We believe there is a tremendous opportunity for application and system services at the intersection of the above two domains for exploiting the wireless connectivity to provide ease of use in handling media. In this paper, we propose a feature-rich, secure wireless service delivery framework over enhanced public access points (called Smart Edge Servers), which provides the right platform for deployment of specialized services to the mobile users. The Smart Edge Server provides secure wireless access to the clients, has sophisticated media handling and storage capabilities and uses advanced techniques to manage resources available to it, such as bandwidth, power and the type of connectivity. A prototype implementation of our Smart Edge Server has been built that implements all the features discussed above.