Holistic Study of Thermal Management in Direct Liquid Cooled Data Centres: from the Chip to the Environment

The IT (Information Technology) infrastructure power consumption constitutes a large portion of global electricity consumption and a large proportion of this energy is to maintain an acceptable thermal environment for the IT equipment. Therefore, it is important to understand and improve the thermal and energy management of data centres for lower cost and higher sustainability. Toward this goal, Direct Contact Liquid Cooled (DCLC) servers, where liquid loop heat exchangers are attached to the CPU, were proposed to study the use of chiller-less energy efficient data centre. Thirty Sun Fire V20z servers in a data centre rack have their CPUs water cooled with the remaining components air cooled, together with a rear door heat exchanger to capture this air heat flow. The heat generated by the servers is ultimately transferred to the environment using an Air Handling Unit (AHU). The AHU was fitted with a water spray system to increase the heat transfer capacity. The designed DCLC system was tested and characterised in terms of power consumption and thermal performance. The design successfully provided stable inlet coolant temperature (±1℃) to the IT despite the variation in the IT workload and environmental conditions. Activating the spray reduced the thermal resistance of the AHU heat exchanger (HE) by 50%. However, the power consumption and pressure drop across the HE was increased. The flow distribution and the coolant pumping configurations of centralised (where the coolant is pumped by two central pumps connected in series) and distributed (where small pumps inside the servers are activated) was investigated. The EPANET software was used to analyse the flow and showed that the servers in the top of the rack receive a higher flow rate (by approximately 30%) than the servers in the bottom of the rack. This resulted in a variation in the CPU temperatures of different servers. Optimisation analysis proposed increasing the manifolds size to improve the flow rate and reduce the flow maldistribution. In the distributed pumping case, the CPUs temperature showed to be 2℃ higher compared with the central pumping case for the high IT workload. The rack inlet temperature was tested in the range of the ASHRAE W4 envelope in terms of CPU temperatures, power consumption and computational efficiency. Increasing the coolant inlet temperature resulted in high energy saving in the AHU, while the rack energy consumption increases marginally in idle operation and considerably more in high IT workloads. This results in an improvement in the energy effectiveness of 17% but a deterioration in the computational efficiency of 4%. Finally, a parallel study was carried out to investigate the droplet evaporation over heated surfaces which ultimately be used in studying sprays in the AHU or in direct on chip cooling via evaporation. A novel experimental design was proposed to track the lifetime of any droplet size that span the surface tension to gravitydominated regimes. A theoretical model was also proposed to predict the droplet lifetime based on the initial contact angle, contact radius and the receding contact angle. The model predicted the droplet evaporation over hydrophobic surfaces with good accuracy of an error less than 4% while under estimated the evaporation with hydrophilic surfaces

Advanced Concepts for Renewable Energy Supply of Data Centres

The rapid increase of cloud computing, high performance computing (HPC) and the vast growth in Internet and Social Media use have aroused the interest in energy consumption and the carbon footprint of Data Centres. Data Centres primarily contain electronic equipment used for data processing (servers), data storage (storage equipment), and communications (network equipment). Collectively, this equipment processes, stores, and transmits digital information and is known as information technology (IT) equipment. Advanced Concepts for Renewable Energy Supply of Data Centres introduces a number of technical solutions for the supply of power and cooling energy into Data Centres with enhanced utilisation of renewable energy sources in order to achieve low energy Data Centres. Because of the high energy density nature of these unique infrastructures, it is essential to implement energy efficiency measures and reduce consumption before introducing any renewable energy source. A holistic approach is used with the objective of integrating many technical solutions such as management of the IT (Information Technology) load, efficient electrical supply to the IT systems, Low-Ex air-conditioning systems, interaction with district heating and cooling networks, re-use of heat, free cooling (air, seawater, groundwater), optimal use of heat and cold storage, electrical storage and integration in smart grids. This book is therefore a catalogue of advanced technical concepts that could be integrated into Data Centres portfolio in order to increase the overall efficiency and the share of renewable energies in power and cooling supply. Based on dynamic energy models implemented in TRNSYS some concepts are deeply evaluated through yearly simulations. The results of the simulation are illustrated with Sankey charts, where the energy flows per year within the subsystems of each concept for a selected scenario are shown, and graphs showing the results of parametric analysis. A set of environmental metrics (as the non-renewable primary energy) and financial metrics (CAPEX and OPEX) as well of energy efficiency metrics like the well-known PUE, are described and used to evaluate the different technical concepts

Evaluation of Energy and Airflow Performance of Data Centers with Centralized Thermosiphon

The need of fast and uninterrupted online services and applications in our daily life leads to rapid expansion in both quantity and capacity of data centers to handle these huge amounts of digital information. However, the energy use associated with hundreds of information technology (IT) equipment running 24/7 in data centers creates a huge burden to the global economy and environment. Globally, electricity consumption of data centers accounts for about 238 billion kWh per year which is corresponding to about 1.3% of total global electricity consumption. In a typical data center, about 30-50% of its total energy is dedicated to remove the heat from running the IT equipment all year round. Conventional cooling energy saving strategy is to utilize outdoor air directly to cool the IT equipment when outdoor temperature is lower, which known as direct airside free cooling. However, the main concerns about this approach is the breakdown of IT equipment due to poor outdoor air quality. This could be a limiting factor in certain locations for using the direct free cooling system. Therefore, an indirect free cooling approach is more interested to be used under poor outdoor air environments. In this thesis, an indirect airside free cooling based on thermosiphon loop is proposed and investigated to reduce energy consumption and improve the IT equipment reliability in a novel vertical data center (VDC) which is designed by Vert.com Inc. An energy model was established to evaluate the energy performance of this new proposed design in different selected cities across North America. The energy results show that approximately 41% to 59% of an annual overall HVAC energy are saved with the thermosiphon free cooling system depending on the local climate conditions in comparison to the data center without any free cooling implementations. Analysis of indoor airflow distribution was also conducted in this VDC project because it can help to optimize different design options and enhance cooling efficiency. Unlike other typical data centers that are designed horizontally and occupied a large footprint like warehouses, the proposed data center in this study is designed vertically like a tower with a compact rectangular form. In this thesis, two proposed locations of the indoor thermosiphon heat exchangers were compared and analyzed through CFD simulation. The simulation results indicate that there are many turbulent flows developed inside the building, especially at 90° bends, which can affect the air distribution uniformity and cooling performance through the heat exchanger

Best Environmental Management Practice in the Telecommunications and ICT Services sector: Learning from front runners

The steady growth over the past decades of the Telecommunications and ICT Services sector, and its uninterrupted progress with the constant provision of renewed and ever-faster services as well as new applications, has transformed many aspects of our society and lives but has also spurred the development of ever more power- and resource-hungry systems, contributing to the sector’s ever-growing environmental footprint. On the basis of an in-depth analysis of the actions implemented by environmental front runners and of existing EU and industry initiatives addressing the environmental performance of the sector, this report describes a set of best practices with high potential for larger uptake. These are called Best Environmental Management Practices (BEMPs). The BEMPs, identified in close cooperation with a technical working group comprising experts from the sector, cover improvement of environmental performance across all significant environmental aspects (energy consumption, resource consumption, etc.) at the different life cycle stages (planning and design, installation, operation, end-of-life management, etc.) and for different ICT assets (software, data centres, etc.). Besides actions aimed at reducing the environmental impact of Telecommunications and ICT Services operations (with a special focus on data centres and telecommunications networks), the report also identifies best practices in the ICT sector that contribute towards reducing the environmental impact of other sectors of the economy ("greening by ICT" measures). The report gives a wide range of information (environmental benefits, economics, indicators, benchmarks, references, etc.) for each of the proposed best practices in order to be a source of inspiration and guidance for any company in the sector wishing to improve its environmental performance. In addition, it will be the technical basis for a Sectoral Reference Document on Best Environmental Management Practice for the Telecommunications and ICT Services sector, to be produced by the European Commission according to Article 46 of Regulation (EC) No 1221/2009 (EMAS Regulation).JRC.B.5-Circular Economy and Industrial Leadershi