Ensuring that all the critical components like CPU's receive sufficient amount of flow as per their requirement is an vital importance in implementing air cooling for IT equipments. In addition to that the overall system resistance varies with the component location within the chassis. In this study, parametric improvement in chassis ducting system is made to counteract the effects of thermal shadowing in a open compute air cooled server in which a CPU thermally shadows the other. Commercially available computational fluid dynamics codes have permitted simulation of server models to predict efficiency of the servers with every changes made in the design and input variables. Initially this study discusses about the methodology that outlines experimental procedures and tests employed for generating data for calibration of a detailed server model generated using a commercially available CFD tool. The resulting experimentally-calibrated computational fluid dynamics model of the server is used to parametrize and improve the duct design and the location with the view of estimating the effect of airflow bypass on fan power consumption and CPU die temperatures. Improvements achieved are experimentally tested by prototyping the improved chassis using acrylic sheets and reported with reduced flow rates, flow speeds, fan power consumption and fan acoustic noise levels. Further, the study is extrapolated for evaluating the savings in total pumping power and flow rates in the layout of a traditional data center and highly-efficient data center working on air side economization. Savings in amount of water consumed by the layout and savings in number of computer room air conditioning(CRAC) units are also evaluated.
Due to the doubling of processing power ever so often, designing an efficient thermal management system for database centers is becoming more and more difficult. Two studies have been done, one on air cooling using bigger rack level fans and another in liquid cooling minimizing the size of flow control devices. Fans are one of the most inefficient and power hungry devices used in an air cooled database center. Study has been done to improve the air cooling efficiency using larger rack level fans on 2OU open compute server. Simulations have been done using commercial computational fluid dynamic (CFD) software and power consumption of this rack level fan configuration has been compared with the baseline server level fans. Fan failure scenario is also studied by failing one fans and observing the flow through the servers using CFD. An innovative concept of liquid flow controlling device is introduced for liquid cooling applications. These mini flow control devices (MFCD) use thermostatic bimetallic effect. This mode of flow control is cost effective, scalable, and easy to control by passing current directly through the strip. The advantages and applications of this flow control devices are great. This flow control device is designed and analyzed using theoretical formulas for passive flow control in Dynamic liquid cooling plate. Structural and flow interaction is also simulated by using computational flow dynamics. Six 120mm Rack level fans are advisable for this open compute rack configuration, only if the servers are performing less than 70% of utilization above which we steadily loses the increased in efficiency. Initial cost of 6 fans costs approximately less than half of 30 server level fans. Designed MFCDS can be successfully used in efficient cooling of multi core processors.
Heating and cooling losses from forced-air ducts can result in high energy costs, lead to thermal comfort problems, and -- in some extreme situations -- result in serious health and safety concerns. Reducing air leakage and conductive losses from ducts can be a straight-forward way to reduce energy use and improve comfort in homes. This book discusses the basics of air distribution and duct design; strategies to seal and insulate ducts in existing homes; accurate heating and cooling load calculations and HVAC equipment sizing.
The objective of this study is to improve and optimize the cooling efficiency of liquid and air cooling from server to room level while applying best practices in the industry. The effect of increased air and coolant temperature has been explored through a literature survey and studies are conducted from device level to room level for air and liquid cooling. Three major aspects are considered. A closed-form air cooling solution is proposed for high-powered racks in a modular data center equipped with in-row coolers. Direct-to-chip liquid cooling technology is extensively studied at the server level for raised air and coolant inlet temperature for determining thermal performance and reliability of IT equipment. A cost analysis for liquid cooling has been conducted with a TCO model for the performance improvement and holistic evaluation of a data center with air and liquid cooling.The first part consists of a room-level numerical study conducted with high powered racks in a modular data center with regular low-powered racks. Typical modular data centers are cooled by perimeter or outdoor cooling units. A comparative analysis is performed for a typical small-sized non-raised facility to investigate the efficacy and limitations of in-row coolers in thermal management of IT equipment with variation in rack heat load and containment. Several other aspects like a parametric study of variable opening areas of duct between racks and in-row coolers, the variation of operating flow rate, and failure scenarios are also studied to find proper flow distribution, uniformity of outlet temperature, and predict better performance, energy savings and reliability. The results are presented for general guidance for flexible and quick installation and safe operation of in-row coolers to improve thermal efficiency. The Second Part consists of a server-level numerical and experimental study with raised inlet air and coolant temperature for a hybrid cooled server. A detailed numerical study of an enterprise 1U hybrid cooled server is performed to predict the effect of raised inlet air temperature on the component temperatures following the limits of ASHARE air cooling classes. Then, an experimental study is performed in an environmental chamber with high inlet air temperatures. Results for both studies are compared. Previously warm water cooling or increased coolant inlet temperature has been experimentally tested on the respective server. Thus, the effect of both air and liquid coolant temperature has been presented and scaled up to a data center level with help of industry-standard tools for 1D flow network analysis to address the cooling efficiency improvement. The third part consists of a cost analysis of a data center with air and liquid cooling using an established TCO model. The ASHRAE cooling classes for air and liquid cooling are used based on the experimental findings. Also, the effect of cooling efficiency improvements at component and server level and increased inlet conditions are used to compare with a baseline model with air cooling.
Continually increasing demand for information technology (IT) applications and services has provided sustained growth and interest in data centers. The large amounts of energy consumed by data center facilities have placed a significant emphasis on the energy efficiency of their overall operation. One area of particular importance is the cooling energy required. Heat generation within a data center starts at the server level, specifically within the microelectronic devices that process digital information. Convective heat transfer is the primary driver for the removal of heat from an individual server. As such, cooling efficiency at the server level will be dictated by the pumping power required to move a cooling fluid through the system. Many methods are available for removing heat from the server, either with air or liquids as the cooling medium. This work evaluates new, efficient approaches for removing that heat and the pertinent design considerations that must be taken into account for successful implementation. In general, smaller fans operate at lower efficiencies than larger fans of proportional linear dimensions. The applicability of replacing smaller, 60mm fans from within the chassis of web servers with an array of either 80mm or 120mm fans consolidated to the back of a rack is experimentally tested. Initial characterization of the selected fans showed the larger 80mm and 120mm fans operate at double peak total efficiency of the smaller 60mm fans. A stack of four servers was used in a laboratory setting to represent a rack of servers. When all four servers were stressed at uniform computational loadings, the 80mm fan array resulted in between 50.1% to 52.6% reduction in total rack fan power compared to the baseline 60mm fans. The 120mm fan array showed similar reduction in rack fan power of 47.6% to 54.0% over the baseline 60mm fan configuration. Since actual data centers rarely operate at uniform computational loading across servers in a rack, a worst case scenario test was conceived. In this test, the arrays of larger fans were controlled by a single server operating at peak computational workload while the other three in the rack remained idle. Despite significant overcooling in the three idle servers, the 80mm and 120mm fan configurations still showed 35.3% and 33.8% reduction in total rack fan power compared to the best possible operation of the 60mm fans. The findings in this study strongly suggest that a rack-level fan scheme in which servers share airflow is more efficient alternative to fans contained within the server. Air flow management is a critical tool to maintain efficient operation of a data center cooling scheme. Provisioning of airflow from CRAC units and containment systems often lead to changes in the static pressure at the inlet to server racks. Through experimental testing on an Air Flow Bench it is observer that static pressure at the inlet to servers has a significant influence on the thermal performance and fan cooling energy consumption within the server itself. Reduction in server fan power or component temperatures can be achieved by increasing the static pressure at the server inlet. Complementary design and control at the room level with this information at the server level can lead to reduction in overall system fan power and more energy efficient data center operation. Complete immersion of servers in dielectric mineral oil has recently become a promising technique for minimizing cooling energy consumption in data centers. However, a lack of sufficient published data and long term documentation of oil immersion cooling performance makes most data center operators hesitant to apply these approaches to their mission critical facilities. In this study, a single server was fully submerged horizontally in mineral oil. Experiments were conducted to observe the effects of varying the volumetric flow rate and oil inlet temperature on the thermal performance and power consumption of the server. Specifically, temperature measurements of the CPUs, motherboard components, and bulk fluid were recorded at steady state conditions. These results provide an initial bounding envelope of environmental conditions suitable for an oil immersion data center. Comparing the results from baseline tests performed with traditional air cooing, the technology shows a 34.4% reduction in the thermal resistance of the system. The cooling loop was able to achieve partial power usage effectiveness (pPUECooling) values as low as 1.03. This server-level study provides a preview of possible facility energy savings by utilizing high temperature, low flow rate oil for cooling. Following this, visual observations, microscopic measurements, and testing of mechanical properties were taken. Evaluation of the technology's impact on the mechanical reliability of components and operability of data centers is made.
Rising energy demands in data centers have constantly made thermal engineers to think and come up with innovative cooling solutions in data centers. It is of utmost importance to have control over the environmental impact of Data Centers. In 2011, the Open Compute Project was started which aimed at sharing energy efficient practices for data centers. The hardware and electrical specifications of the first open compute server -Freedom was shared on open compute project's website. It was a vanity free design and its components were custom designed. It was deployed in one of the data centers in Prineville, Oregon and within first few months of operation, considerable savings in every and cost were observed. Since then, many open compute servers have been introduced for applications like - compute, storage, etc. The open compute servers which were being introduced mainly had a 2 socket architecture. Yosemite Open compute server was introduced for serving heavy compute workloads. It provided significant improvement in performance per watt as compared to previous generations open compute servers. Yosemite Open Compute Server has a system on a chip architecture and has 4CPU's (1 CPU per sled). This study involves optimization of Yosemite Open Compute server to improve its cooling performance using. CFD tools are very useful for thermal modeling of these servers and predict their efficiency. A commercially available CFD tool has been used to do the thermal modeling of the server and its optimization has been done to improve the cooling performance of the server. The model of the improved design has been compared to the existing design to show the impact of air flow optimization on the cooling performance of the server. The air flow characteristics and utilization of the fans have been significantly improved in the improved design.
Data centers house a variety of compute, storage, network IT hardware where equipment reliability is of utmost importance. Heat generated by the IT equipment can substantially reduce its service life if Tj,max, maximum temperature that the microelectronic device tolerates to guarantee reliable operation, is exceeded. Hence, data center rooms are bound to maintain continuous conditioning of the cooling medium. This approach often results in over-provisioned cooling systems. In 2014, U.S. Data center electricity consumption is about 1.8% of the total electrical energy in the country. Hence, data center power and cooling have become significant issues facing the IT industry. The first part of the study focuses on air cooling of electronic equipment at room level. Data centers are predominantly cooled by perimeter computer air handling units that supply cold air to the raised floor plenum and the cold air helps in removing the heat generated by IT equipment. This method tends to be inadequate especially when the average power density per rack rises above 4 kW. As a solution to mitigate this problem, different rack and row based cooling solutions have been proposed and used. The primary focus of these cooling methods is to bring cooling closer to the heat source which is the IT rack thereby improving the heat dissipation process along with controlled air flow management in the data center room. Mostly known close-coupled cooling solutions include rear-door heat exchanger, in-row coolers, and over-head cooling. In this study, a new end-of-aisle close-coupled cooling solution for small data center cooling room has been proposed. As oppose to the existing designs, this design is distinctive in eliminating the risk of placing the liquid on top of IT racks along with achieving cooling energy efficiency. Three different configurations of the proposed designs are studied for its thermal performance using computational modeling. The second part of the study focuses on liquid cooling at rack level. Liquid cooling addresses the critical issues related to typical air cooling in servers because of its better heat transfer characteristics. Water-cooling at the device level can be an efficient solution since water has higher thermal capacitance when compared to traditional heat carrying medium i.e., air. The emerging practice in the data center industry is to maximize the use of economizer usage by reducing/eliminating the usage of chiller while taking advantage of outside ambient conditions to cool the data centers. Liquid cooled racks are generally designed with different configuration of pumping systems. Empirical study is conducted on a state-of-art liquid cooled electronic rack for high coolant inlet, commonly known as warm-water cooling in order to evaluate the cooling performance of distributed vs. centralized coolant pumping systems. Experimental set up is instrumented such that detailed analysis is employed to study component temperatures as well as cooling performance of the rack at elevated inlet conditions. The third part of the study focuses on the impact of high server inlet temperatures to static power at server level. In order to maximize the use of economizers, the IT hardware will be exposed to higher inlet temperatures which would lead to higher operating temperatures of the processors. The operating temperature of the CPU has direct influence on the static power due to subthreshold leakage which is known to reduce the performance of the processor. The current work serves as a firsthand investigation to study trade-off between IT performance and energy efficiency for elevated inlet temperature in air vs. liquid cooled servers. Air cooled IT along with the liquid cooled counter-parts are instrumented and extensively tested to simulate the high ambient conditions at the test bed data center.
This Guide & Workbook is intended to provide a working knowledge of heating and cooling duct systems, an understanding of the major issues concerning efficiency, comfort, health, safety; and practical tips on diagnostics, installation and repair of duct systems. This Guide & Workbook starts off with the basics and explains the operation of a duct system, the impacts of air leakage from ducts, and focuses on how technicians can make improvements that will result in:?Lowering of operating expenses; ?Improving occupant comfort; ?Protection of occupant health and safety; and?Improvements to building envelope durability.
The Global Energy Assessment (GEA) brings together over 300 international researchers to provide an independent, scientifically based, integrated and policy-relevant analysis of current and emerging energy issues and options. It has been peer-reviewed anonymously by an additional 200 international experts. The GEA assesses the major global challenges for sustainable development and their linkages to energy; the technologies and resources available for providing energy services; future energy systems that address the major challenges; and the policies and other measures that are needed to realize transformational change toward sustainable energy futures. The GEA goes beyond existing studies on energy issues by presenting a comprehensive and integrated analysis of energy challenges, opportunities and strategies, for developing, industrialized and emerging economies. This volume is an invaluable resource for energy specialists and technologists in all sectors (academia, industry and government) as well as policymakers, development economists and practitioners in international organizations and national governments.
Occupational exposure to heat can result in injuries, disease, reduced productivity, and death. To address this hazard, the National Institute for Occupational Safety and Health (NIOSH) has evaluated the scientific data on heat stress and hot environments and has updated the Criteria for a Recommended Standard: Occupational Exposure to Hot Environments [NIOSH 1986a]. This updated guidance includes information about physiological changes that result from heat stress, and relevant studies such as those on caffeine use, evidence to redefine heat stroke, and more. Related products: Weather & Climate collection is available here: https://bookstore.gpo.gov/catalog/weather-climate Emergency Management & First Responders can be found here: https://bookstore.gpo.gov/catalog/emergency-management-first-responders Fire Management collection is available here: https://bookstore.gpo.gov/catalog/fire-management
