Ethan E. Cruz

Challenges of data center thermal management

The need for more performance from computer equipment in data centers has driven the power consumed to levels that are straining thermal management in the centers. When the computer industry switched from bipolar to CMOS transistors in the early 1990s, low-power CMOS technology was expected to resolve all problems associated with power and heat. However, equipment power consumption with CMOS has been rising at a rapid rate during the past 10 years and has surpassed power consumption from equipment installed with the bipolar technologies 10 to 15 years ago. Data centers are being designed with 15-20-year life spans, and customers must know how to plan for the power and cooling within these data centers. This paper provides an overview of some of the ongoing work to operate within the thermal environment of a data center. Some of the factors that affect the environmental conditions of data-communication (datacom) equipment within a data center are described. Since high-density racks clustered within a data center are of most concern, measurements are presented along with the conditions necessary to meet the datacom equipment environmental requirements. A number of numerical modeling experiments have been performed in order to describe the governing thermo-fluid mechanisms, and an attempt is made to quantify these processes through performance metrics.

Overview of IBM zEnterprise 196 I/O subsystem with focus on new PCI express infrastructure

IBM zEnterprise® 196 introduces a new input/output (I/O) s5ubsystem, including a new I/O drawer that is largely based on a greatly expanded exploitation of industry-standard high-volume PCI Express® (PCIe®) links and switches. The System z® qualities of reliability, availability, and serviceability (RAS) are preserved and enhanced by combining the PCIe RAS capabilities with new System z capabilities. PCIe ports connecting the processor book to the I/O drawer are provided by a new IBM-designed PCIe fan-out card. This fan-out card and its firmware (Licensed Internal Code) support both traditional System z I/O and new I/O paradigms. In the new PCIe I/O drawer, PCIe switches provide fan-out and the well-established System z I/O failover function referred to as redundant I/O interconnect. This is the third generation of the I/O drawer/cage to be used in System z platforms. The PCIe I/O drawer design is extremely compact and provides enhanced I/O port granularity and density. It has been designed to provide performance extendibility for future I/O advancements. Traditional I/O such as FICONA, Fibre Channel Protocol, and Ethernet are provided with enhanced functionality and are packaged in this new PCIe I/O drawer. The advent of this new infrastructure opens up the possibility of attaching native PCIe adapters while allowing them to be controlled by system firmware or by the operating systems directly.

Raised Floor Computer Data Center: Effect on Rack Inlet Temperatures When High Powered Racks are Situated Amongst Lower Powered Racks

This paper focuses on the effect on inlet rack air temperatures when high-powered racks are situated amongst lower powered racks in a raised floor data center. Only the above floor (raised floor) flow and temperature distributions were analyzed for various flowrates exhausting from the perforated tiles and with one or two high powered racks placed at various locations amongst the lower powered racks. A Computational Fluid Dynamic (CFD) model was generated for the room with electronic equipment installed on a raised floor with particular focus on the effects on rack inlet temperatures of these high powered racks. Forty racks of data processing (DP) equipment were arranged in rows in a data center cooled by chilled air exhausting from perforated floor tiles. The chilled air was provided by four A/C units placed inside a room 12.1 m wide × 13.4 m long. Since the arrangement of the racks in the data center was symmetric only one-half of the data center was modeled. The numerical modeling was performed using a commercially available finite control volume computer code called Flotherm (Trademark of Flomerics, Inc.). The flow was modeled using the k-e turbulence model. Results are displayed to provide some guidance on the design and layout of a data center.Copyright

Comparison of Numerical Modeling to Experimental Data in a Small, Low Power Data Center Test Cell

As the performance of Information Technology (IT) equipment continues to rise, so do the power dissipated and overall power density. Air cooling this increasing power has proved a significant challenge even at the data center level. In order to combat this challenge, Computational Fluid Dynamics and Heat Transfer (CFD/HT) models have been employed as the dominant technique for the design and optimization of both new and existing data centers. This study is a continuation of earlier comparisons of CFD/HT models to experimentally measured temperature and flow fields in a small data center test cell. It compares previously unpublished experimentally collected data for the 11 kW dissipation cases using three different layouts of perforated tiles to a CFD/HT model using eight turbulence models and a laminar flow model. Insight into the location of the deviation between the different turbulence models and experimental data are discussed, along with the computational effort involved in running the CFD/HT models. It was found that the laminar flow model and the Spalart-Allamaras turbulence model produced the smallest deviations from experimental data, but the former required only one twentieth of the computational effort of the latter.Copyright

Cluster of High Powered Racks Within a Raised Floor Computer Data Center: Effect of Perforated Tile Flow Distribution on Rack Inlet Air Temperatures

This paper focuses on the effect on inlet rack air temperatures as a result of maldistribution of airflows exiting the perforated tiles located adjacent to the fronts of the racks. The flow distribution exiting the perforated tiles was generated from a computational fluid dynamics (CFD) tool called Tileflow (Trademark of Innovative Research, Inc.). Both raised floor heights and perforated tile free area were varied in order to explore the effect on rack inlet temperatures. The flow distribution exiting the perforated tiles was used as boundary conditions to the above floor CFD model. A CFD model was generated for the room with electronic equipment installed on a raised floor. Fourty racks of data processing (DP) equipment were arranged in rows in a data center cooled by chilled air exhausting from perforated floor tiles. The chilled air was provided by four A/C units placed inside a room 12.1 m wide × 13.4 m long. Since the arrangement of the racks in the data center was symmetric only one-half of the data center was modeled. The numerical modeling for above the raised floor was performed using a commercially available finite control volume computer code called Flotherm (Trademark of Flomerics, Inc.). The flow was modeled using the k-e turbulence model. Results are displayed to provide some guidance on the design and layout of a data center.© 2003 ASME

Modeling blower flow characteristics and comparing to measurements

Thermal management for high performance electronic systems such as servers and I/O boxes has become increasingly challenging due to the ever growing demand for higher computing performance and packaging density. Proper modeling, design and characterization of the cooling system have become critical to the overall system performance, reliability and energy consumption. Air moving devices such as blowers (centrifugal fans) are key components of the air-cooled electronic systems. This paper focuses on the flow characteristics of blowers and the impact on the system air flow distribution. To capture the flow characteristics, different levels of numerical modeling methodology are considered using a commercially available tool. It is demonstrated that a simple compact model, typically used in system level models, is not sufficient to resolve the air flow distribution near the exhaust. A more detailed model which includes the actual geometry of the blower blades resolves the body forces using MRF and predicts the flow distribution with better agreement with measurement data. Comparing the different modeling methodologies for systems of different impedance characteristics, a general guideline is subsequently proposed.

Raised Floor Computer Data Center: Effect of Rack Inlet Temperatures When Rack Flowrates Are Reduced

This paper focuses on the effect on inlet rack air temperatures when rack flowrates are reduced. Reduced flowrates for the same heat loads results in higher air temperature differences across the rack and thereby higher air temperatures exiting the rack. The effect of the higher rack exhaust temperatures on the inlet rack air temperatures is the focus of this investigation. Only the above floor (raised floor) flow and temperature distributions were analyzed for a range of rack flowrates and with various flowrates exhausting from the perforated tiles. A Computational Fluid Dynamic (CFD) model was generated for the room with electronic equipment installed on a raised floor with particular focus on the effects on rack inlet temperatures of these high powered racks. Fourty racks of data processing (DP) equipment were arranged in rows in a data center cooled by chilled air exhausting from perforated floor tiles. The chilled air was provided by four A/C units placed inside a room 12.1 m wide × 13.4 m long. Since the arrangement of the racks in the data center was symmetric only one-half of the data center was modeled. The numerical modeling was performed using a commercially available finite control volume computer code called Flotherm (Trademark of Flomerics, Inc.). The flow was modeled using the k-e turbulence model. Results are displayed to provide some guidance on the design and layout of a data center.Copyright