Search

• Developing a new water free-cooling system and its control schemes models. • Control performance quantification of free-cooling systems in three operating modes. • Evaluating energy performance and ecological benefit of economizers in worldwide climates. • Quantifying effect of space air temperature increase on energy efficiency. Water-side economizer (WSE) is an effective free-cooling solution aiming to enhance the natural cooling duration and in turn reduce the cooling-energy consumption of data centers. However, the system's performance is constrained by the limited understanding of its control mechanisms and the influence of local climatic conditions on its free-cooling capabilities. To overcome these limitations, a thermodynamic model of the WSE system with control strategies is provided and its adaptability performance in diverse worldwide locations is systematically evaluated. Modelica-based models of chiller plants and control strategies are firstly developed, and then the energy consumption and ecological benefit of the WSE system are investigated via large-scale simulations in worldwide climates. The performance indicators and application potential of the system are demonstrated through visualization maps. The analysis reveals significant energy savings potential of the WSE system, with the capacity to reduce annual cooling energy consumption of data centers by 4.4–33.7 % in hot to marine zones, and even by a remarkable 62.6 % in plateaus and cold zones. Furthermore, it is observed that every 1 °C increase in outdoor air temperature can reduce energy efficiency ratio by 1.3–8.7 % while simultaneously increase P U E by 0.3–1.0 %. The ecological benefit results revealed that the WSE system can effectively harness larger quantities of stable free-cooling resources in mixed and cool climate zones, exceeding its capabilities in hot and warm regions. These results offer valuable insights for the impact of climate on the energy and ecological benefits of WSE system for data center, which can be helpful to guide the design or retrofit of such cooling systems in specific locations, presenting an immense opportunity to maximize cooling-energy savings. [ABSTRACT FROM AUTHOR]

Since the onset of the 21st century, the number of data centers has been increasing continuously, and the energy consumption of these data centers has aroused people's attention. Many experiments have been conducted to reduce the energy consumption in data center cooling, and free cooling utilization based on the mechanically driven two-phase cooling loop (MTCL) system has been proven to be an effective solution for energy saving. This paper reviews the research on and developments in the practical application of the MTCL system for data center cooling in recent decades. It presents a detailed summary of the progress of research on the MTCL system in data centers. The aim is to provide an improved understanding of the system and promote the application of this system in data center energy saving. [ABSTRACT FROM AUTHOR]

The power consumption for cooling of data centers increases continuously contributed to the enlargement of heat dissipation demands. Waste heat recovery is regarded as a promising solution for energy conservation and carbon reduction. A compression-assisted absorption refrigeration-heating system aimed at waste heat utilization of liquid-cooling data center is proposed. The effects of heat sources, auxiliary compression process and split ratios on the proposed system performance are discussed, and the analysis of application that synchronously produces chilled water for liquid-cooling data center and hot water for domestic use is conducted. The compression process can provide effective compensation for the system performance that weakens the demands on the quality of cooling source and driving heat source. As the compression ratio raises from 1.067 to 2.0, the minimum generation temperature decreases from 52.0 °C to 27.2 °C. The system can completely satisfy the refrigeration need, of 4.29 kW for liquid-cooling data centers and provide additional thermal energy, of 1.37 kW for heating. A quantitative relationship between the flow split ratios and circulation ratios is found out that can be a wise presentation for the adjustment of the refrigeration and heating loads. This research results can provide theoretical basis and guidance for low-grade waste heat recovery in liquid-cooling data center based on the absorption heat pump technology. • A compression-assisted absorption refrigeration-heating system for waste heat recovery was constructed. • The compression process weakened the demands on the quality of driving heat source and cooling source. • A quantitative relationship between flow split ratios and circulation ratios was found out. • The system satisfied the refrigeration loads of data centers and provided heating effect. [ABSTRACT FROM AUTHOR]

Cooling of data centers requires a significant amount of energy, comparable to the energy consumption of the servers themselves. The current design of the centralized cooling systems for data centers is based on ideal IT loading conditions (i.e., 100 % loading). However, such conventional design often results in significant oversized cooling systems and leads to substantial energy waste, since most data centers operate at part load in their lifespan. To address this issue, this study proposes an optimal design for centralized cooling systems with multiple chillers under progressive loading. The optimization problem, aimed at minimizing life-cycle cost, is formulated adopting SLSQP (Sequential Least Squares Programming) algorithm. A cooling system model is developed using the manufacturer's performance data of cooling equipment. The optimal designs in different climate zones are identified according to energy performance under full-range loads and ambient temperatures. Furthermore, this study comprehensively analyzes and compares free cooling hours, cooling energy, and life-cycle cost of the optimized designs with conventional designs. The results show that the optimized cooling systems could operate more energy-efficiently, despite decreased free cooling hours (13–860). Significant cooling energy savings over the lifespan could be achieved, i.e., 4–22 %, corresponding to the PUE reductions of 0.02–0.11, depending on climate conditions and control strategies. [ABSTRACT FROM AUTHOR]

Data centers consume large amounts of electricity and water specifically for cooling purposes. Integrating free cooling technologies is an essential part of broad efforts to reduce data centers' energy, carbon, and water footprints. Adding a new technique to the existing portfolio of free cooling technologies for data centers, we present how all-day passive radiative cooling can reduce energy and water consumptions of data centers. All-day passive radiative cooling is a free cooling technique, in which sky-facing surfaces with high solar reflectivity and midinfrared emissivity spontaneously reject heat into the sky, without consuming electricity and evaporating water. Using custom-built physics-based models, we simulate three configurations that integrate all-day radiative free cooling into data centers. We show that data center cooling energy and water consumptions differ substantially depending on the integration configuration. Particularly, direct free cooling of data center return air gives the highest energy saving with an annual average of around 20.0% under the tropical climate of Singapore which hosts a large number of data centers, whereas free cooling of compressed refrigerant prior to the chiller condenser gives the highest water saving with an annual average of around 84.0%. These results offer multiple viable options for integrating radiative free cooling into data center cooling systems to simultaneously achieve water and energy savings. • Radiative free cooling is added to the existing portfolio of free cooling technologies for data centers. • Detailed physics-based models of a data center cooling system were built. • The effects of weather and operation conditions on the cooling system performance were investigated. • Direct free cooling of data hall return air yields the most energy saving with an annual average of around 20.0%. • Free cooling of compressed refrigerant of the chiller cycle gives the most water saving with an annual average of 84.0%. [ABSTRACT FROM AUTHOR]

The inefficient operation of cooling equipment is a significant impact factor to the high energy consumption of cooling system in data center. This study proposes an advanced model predictive control (MPC) strategy for a hybrid cooling with water storage system to improve energy efficiency and reduce the accumulation of cold storage losses. Mixed integer linear programming (MILP) in MPC strategy is used to optimize the operating parameters under free cooling, hybrid cooling, and mechanical cooling modes, further solving the problem of precise optimization for different modes. Taking Guangzhou city as an example, the equipment scheduling and the appropriate volume of cold water storage tank for MPC strategy are analyzed. The results indicate that, the emergency cold water storage tank 500 m3 only supports the efficient operation of cooling system under the maximum 60 % IT load rate, meanwhile, the optimal tank volume 1400 m3 could meet the 60–100 % IT load rate. Compared to Baseline strategy, the biggest reduction of annual energy consumption using MPC strategy would be attained by 12.19 % under free cooling mode, by 4.04 % under hybrid cooling mode, and by 22.15 % under mechanical cooling conditions at the 55 % IT load rate. Therefore, the MPC strategy proposed in this paper has important guiding significance for energy conservation and carbon reduction in global data centers. • A novel advanced MPC strategy and MILP solver is developed for hybrid cooling system of data center. • The energy consumption of MPC strategy decreases by 12.19 % under free cooling mode at 55 % IT load. • The relationship between the water tank volume and IT load rate under MPC strategy is studied. [ABSTRACT FROM AUTHOR]

The data usage surge drives greater data center demand, amplifying global CO 2 emissions. Mitigating climate change necessitates reducing data center CO 2 emissions. Reusing waste heat from data centers offers a potential energy efficiency boost and environmental impact reduction. This study utilizes liquid cooling technology to raise waste heat temperature for building space heating and introduces the concept of 'data furnaces,' where data centers directly supply waste heat to heat buildings on-site, reducing district heating consumption and lowering CO 2 emissions. Efficiently designing a heat recovery heat exchanger system that accounts for both heat rejection and cooling sides of a liquid cooling system is crucial for achieving complete heat recovery without using heat pump, a commonly overlooked aspect in existing literature. To address this issue, we propose two heat exchanger schemes: connecting the building space heating network to the secondary side (Scheme 1) and the primary side (Scheme 2) of the cooling distribution unit. Implementing these innovations leads to the elimination of dependence on a heat pump, substantially cutting energy and CO 2 emissions. Using TRNSYS software, we develop, model, and compare waste heat recovery schemes to curb district heating consumption and CO 2 emissions. To demonstrate broad implications of the proposed approaches for energy efficiency and sustainability in the data centers and building space heating networks, a showcase study examines constant 25 kW waste heat from a direct-to-chip liquid-cooled rack in an office building with 285.7 MWh annual space heating demand. A novel waste heat recovery rate relationship graph is created to assist system design, uncovering an unexpected result in Scheme 2: waste heat recovery decreases as outdoor temperature falls. In contrast, Scheme 1 maintains a stable waste heat recovery rate around 25 kW, regardless of outdoor temperature fluctuations. As a result, Scheme 1 reuses 155.2 MWh of waste heat annually compared to 138 MWh for Scheme 2. Schemes 1 and 2 yield annual electricity savings of 2290.5 kWh and 905.2 kWh, respectively, for the cooling system. Both schemes achieve profitability within a year through a 25-year life cycle analysis (LCC) and substantially reduce CO 2 emissions, with Scheme 1 saving 291,996 kgCO 2 and Scheme 2 saving 258,192 kgCO 2. The study addresses critical gaps in existing literature by emphasizes LCC. The proposed heat exchanger designs represent pioneering solutions for optimizing waste heat recovery, particularly in challenging climates. New findings offer substantial benefits to both liquid-cooled and air-cooled facilities, making significant contributions to achieve carbon neutrality in data center operations. • Non-heat pump data center waste heat recovery for space heating is studied. • Two schemes, recovering from both sides of cooling distribution unit, are compared. • The two schemes achieve payback in under a year due to the elimination of heat pump. • Waste heat recovery on the secondary side outperforms that on the primary side. • Novel relationship graphs facilitate data center waste heat recovery system design. [ABSTRACT FROM AUTHOR]

To solve the problems of high energy consumed by the cooling system in the data center, this article puts forward a composite air conditioning system. The simulation platform for system operation performance is established, and the accuracy of the simulation platform is verified by experiments. The influence of operation parameters on system performance is analyzed by simulation. Finally, the optimal operation control parameters are determined. The results show that the system can adjust the condenser wind speed and the refrigerant pump operating frequency to meet the cooling requirements and solve the problem of low evaporation temperature in the heat pipe. The evaporative cooling effectively expands the working range of the heat pipe mode and raises the upper limit of outdoor temperature from 8 °C to 15 °C. In the vapor compression mode, when the ambient temperature is lower than 26 °C, the performance of the air-cooled mode is better than that of the evaporative-cooled mode. The condensation temperature can be ensured within a reasonable range by adjusting the condenser cooling wind speed and the compressor frequency. When the outdoor temperature is not less than 26 °C, the evaporative cooling can effectively improve the operation performance • A data center air conditioning system that can switch four operating modes is proposed. • The optimal operating parameters of the system at different ambient temperatures are obtained. • The variation of system performance with outdoor unit wind velocity is obtained. • The influence of refrigerant pump and compressor frequency on system performance is obtained. • The evaporative cooling effectively extends the operating temperature range of heat pipe mode. [ABSTRACT FROM AUTHOR]

A new type of ducted hot aisle containment system for racks cooling of data center has been proposed and put into practice gradually. However, the related academic research has not been carried out, especially for the improvement of cooling performance and influencing factors for the cooling system. In this paper, one experiment platform with 8 racks in 2 rows with multiple-heat-sources was established and tested under various working scenarios. In terms of improving the cooling performance, airtight treatment on the basis of ducted hot aisle containment system is better than itself and is also better than only collar, which is better than no collar. Besdides, doors closing is better than that doors opening, "V" diffuser is better than "T" diffuser, and "T" diffuser is better than no diffuser. Properly increasing installation ratio of blanking panels and air volume have also favorable impact. The experimental data and results in this paper will be of great significance to the design and application of ducted hot aisle containment system for racks cooling. [ABSTRACT FROM AUTHOR]

This is the first study of data center row-based cooling strategies under fault conditions. An optimal supply air temperature (SAT) for row-based cooling is proposed to ensure energy efficiency and operational reliability. The appropriate SAT for emergency operation is determined by evaluating how long the allowable IT equipment's inlet air temperature (IAT) can be maintained by only running the fan of the computer room air handling (CRAH) unit when the chilled water supply is interrupted. Three cases with SAT values of 20 °C, 22 °C, and 24 °C are evaluated in a numerical analysis, and the maintenance potential of the IAT is assessed by analyzing 600 s of transients from the time of cooling failure. In all cases, the IAT is almost the same as the SAT under normal cooling, but in cooling failure, the time to reach downtime beyond the allowable IAT is 246s in Case 1, 133s in Case 2, and 85s in Case 3. Response strategies to cooling failure include increasing uninterruptible power supply (UPS) capacity and applying a thermal buffer tank. The study concludes that it is reasonable to set the SAT of row-based cooling to 22 °C or lower and to install a thermal buffer tank in the chilled water system for effective downtime delay. These results are based on a rack power density of 7 kW/rack. • First study of row-based cooling strategies in data centers under fault conditions. • Proposed optimal supply air temperature for energy efficiency and operational reliability. • Evaluated appropriate SAT for emergency operation to maintain allowable IAT. • Analyzed maintenance potential of IAT in 3 cases with varying SAT values. • Response strategies to cooling failure include UPS capacity and thermal buffer tank. [ABSTRACT FROM AUTHOR]

As the demand for data centers rises, efficient cooling systems become increasingly vital to ensure uninterrupted operations and adaptability to IT service changes. The research focuses on quantitatively comparing the thermal performance and energy efficiency of cooling systems capable of handling high-density IT power. It aims to provide objective criteria for selecting suitable cooling solutions, including an assessment of three 150 kW-class IT and facility modules, a novel contribution not extensively explored in previous studies. The study evaluates room-based, row-based, and rack-based cooling options based on the configured ITE power density, ensuring that all three solutions meet ASHRAE's recommended IT operating environment through CFD analysis. The research reveals energy efficiency improvements, with PUE cooling decreasing from 1.33 for room-based cooling to 1.28 for rack-based cooling. These improvements are attributed to reduced fan power by CRAC/H type and decreased primary plant energy consumption by increasing COP through the supply chilled water temperature. The findings offer valuable insights for designing cooling solutions tailored to ITE power density and considering factors such as space requirements, thermal performance, energy efficiency, and cost for new hyperscale data centers. Overall, this research constitutes a significant academic contribution in the field of data center cooling solutions. • Efficient cooling systems to meet growing data center demand. • Comprehensive evaluation of room-based, row-based, and rack-based cooling options. • Quantitative comparison of thermal performance and energy efficiency in cooling solutions. • Compliance with ASHRAE's IT operating environment using CFD analysis. • Energy efficiency improvements, PUE cooling : 1.33 (room-based) to 1.28 (rack-based) [ABSTRACT FROM AUTHOR]

• The two sets of switch conditions and three working modes for the unit applied to data center was proposed. • The energy-saving ratio of the unit in the actual data center for the whole year in China was simulated by DeST. • The energy consumption characteristics and its influencing factors of the unit were investigated. To reduce the power consumption of the cooling system in the data center effectively, a prototype of the integrated cooling unit with rotary booster and compressor was developed, and the operating characteristics were tested comprehensively according to its cooling requirements throughout the year. A data center model reflecting the characteristics of energy consumption and environmental requirements was established, the energy consumption characteristics and influencing factors of the model data center when the integrated unit was used to meet its yearly cooling requirements in the typical climate zones in China were simulated by DeST software based on the measured characteristics of the integrated cooling unit. The results showed that compared with the traditional computer room air conditioner, the energy-saving ratio of the integrated system can be as high as 39.55% for the whole year, and the energy-saving effect is remarkable. The energy-saving potential of the integrated unit becomes more significant while the heat transfer coefficient of the envelope structure becomes larger, and the load rate of IT equipment and the annually-averaged ambient temperature lower. [ABSTRACT FROM AUTHOR]

• System-scale performance assessment is done for a two-phase immersion cooling system. • The best COP and PUE trends are found at the highest server power rate. • Exergy efficiency varies between 8.0 and 18.9% at various operation loads. • Exergy costs are found 3.25 times as higher than the energy costs. The liquid-cooling data center (DC) systems have been becoming important for the rapidly developing high-performance processors since the traditional air-cooled DC systems cannot efficiently manage them due to high heat dissipation rates. Two-phase liquid-immersion cooling is one of the promising direct liquid-cooled DC systems, but its system-scale thermal management performance has not been investigated in detail yet. This study performs the system-scale thermal management of a two-phase liquid-immersion cooling DC system under six different real-time and dynamic operation loads in the range of 3.43-9.17 kW to see the thermodynamic and thermoeconomic performances. The system includes the DC server tank, circulation pump, and dry tower. Results show that the best coefficient of performance (COP) and power usage effectiveness (PUE) values are seen at the highest operation load with 6.67 and 1.15 while the minimum COP and the highest PUE are seen at the lowest operation load with 2.5 and 1.4, respectively. In the component-based assessments, the dry tower is found as the most dominant component according to the exergy destruction ratio analysis, energy costing, and carbon-related costs. The exergy efficiency varies between 8.0% and 18.9% for different operation loads, and the operating temperatures have a crucial impact on the exergetic performances. The thermoeconomic analysis deduces that the levelized product cost is roundly 1.14 S$ · h-1 which means the exergy-related terms (e.g. destruction and loss) increase the costing trends 3.25 times as high compared to the traditional energy-based economic calculations. [ABSTRACT FROM AUTHOR]

• An innovative dew point cooling system was designed, constructed, installed and real live tested in live data centre. • The system can provide continuously stable cooling air and maintain the required temperature and humidity in data centre. • The average COP of 29.7 was achieved during the testing period. • 90 % energy saving can be achieved for data centre cooling. • Suitability, stability and reliability of the system used in data centre environment were proved. This paper presents the development and application of a super performance dew point cooling technology for data centres. The novel super performance dew point cooler showed considerably improved energy saving and carbon reduction for data centre cooling. The innovations of this technology are built upon a series of technological breakthroughs including, a novel hybrid flat/corrugated heat and mass exchanging sheets, an innovative highly water absorptive and diffusive wet-material for the sheets which enable an intermittent water supply with well-tuned water pressure and flow rate, and the optimised fan configurations. Following a list of fundamental research including theoretical, numerical and lab experimental testing of a small scale prototype system, a specialist 100 kW rated data centre dew point cooling system was dedicated designed, constructed, installed and real life tested in an operational live data centre environment, i.e., Maritime Data Centre at Hull (UK) to investigate its dynamic performance, suitability and stability for application in operational data centre environment conditions. During the testing period, the system showed its reliability and capability to remove a tremendous amount of heat dissipated from the IT equipment and maintain an adequate space temperature in the operational live data centre. The dynamic data collection and analysis during the continuous testing and monitoring period showed the average COP of 29.7 with the maximum COP of 48.3. Compared to the existing traditional vapor compression air conditioning system in the data centre, the energy saving using the super performance dew point cooling system is around 90 %. The work presented in this paper include detailed innovation aspects of the technology and the system operation, as well as the established bridging knowledges, methodology and technical procedure for bringing this new technology into real life operation which involve in data centre survey, optimum design and modularization of the specialist cooling system for data centre application, proven system installation, operating method and cooling air management for data centre as well as the assurance of the continuous sufficient cooling supply to the data centre. [ABSTRACT FROM AUTHOR]

Recent increases in the global demand for IT services have increased the power consumption, total ownership costs and environmental footprint of data centers. Recent efforts to reduce these effects have focused on either their cooling systems, or their power systems. In this paper, we have developed an integrated approach to minimize the total power demand of data centers, whilst their reliance on power imported from the grid is minimized. First, the power demand of data center has been reduced utilizing various air-side economizer-based cooling systems. Since the effectiveness of economizers significantly depends on the local weather conditions, 42 stations in major cities across the world have been considered. A more than 80% reduction in total cooling power consumption is achieved by using the most appropriate air-side economizer at each location. Second, the reliance of data centers on power imported from the grid is minimized utilizing on-site hybrid renewable power generation and energy storage. The on-site renewable power generation and capacity factors have been calculated for 1 MW wind and solar renewable power plants to identify the location with the highest renewable power generation capability. The optimal size of a hybrid renewable power plant, and associated battery energy storage system, is also determined for each data center using linear programming to minimize total levelized costs. Finally, the optimal location for constructing and operating the most energy efficient, cost-effective and sustainable data center has been identified by calculating its level of independence from the power grid. It is found that the level of grid independence increases as we move away from the equator, for example more than 50% grid independence can be achieved at Regina station located in Canada. [ABSTRACT FROM AUTHOR]

• Cooling water operation parameters under different heat sink were optimized. • Fitting correlation on affordable extreme atmospheric temperature is given. • The B-type system can achieve significant energy savings compared to the A-type system. • The B-type can meet the year-round cooling demand via a cooling tower cold source. • Optimal water flow rate fluctuation clearly responds to different atmospheric conditions. Data center, as a special building form, has attracted much attention because of its increasing energy consumption. In order to reduce the energy consumption of data center caused by cooling system, research on the water-cooled heat sinks used to cool chips has become increasingly important with the steep increase in the heat flux density of data centers. To explore the effect of different water-cooled heat sinks on cooling system performance, a server water-cooled system for the server cabinet was built, and the chip heat dissipation performance, optimal thermal management, and system energy consumption were simulated by equipping a cooling tower and two types of fin-type water-cooled heat sinks (A-type and B-type). By comparing the effects of A- and B-type heat sinks on the server water-cooled system performance, the optimal water working condition was obtained under different atmospheric conditions by minimizing the system power consumption to guarantee that the chip temperature is no higher than 70 °C. It was found that the optimal cooling water flow rate fluctuates in a large range under different atmospheric conditions. A server water-cooled system equipped with B-type can achieve significant energy savings compared to those from A-type system when the atmospheric relative humidity and temperature are high. Considering a case study from Tianjin, China, it is shown that the month-averaged power usage effectiveness in June is 1.2 for A-type and 1.14 for B-type systems. [ABSTRACT FROM AUTHOR]

• The finned tube heat exchangers with ultra-low temperature surfaces, a novel passive cooling system, directly cool down the data center. • The effect of ultra-low temperature surfaces on the temperature distribution in the room is analyzed through experiments. • The TSD value evaluates the degree of temperature stratification. As artificial intelligence has been leaping forward, data centers (DCs) are only capable of meeting to the daily needs of people through uninterrupted operations. A power outage or cooling system failure can result in high temperatures, trigger data center shutdowns, and even damage IT equipment. In terms of several special DCs, a prolonged cooling system interruption may lead to catastrophic and incalculable consequences. Accordingly, a novel passive cooling system was proposed in this study to address the long-term interruption of air conditioning systems. Liquid nitrogen (LN 2) was driven by the pressure of the cryogenic liquid container and flowed into finned tube heat exchangers (FTHEs) in the DC. LN 2 , i.e., a refrigerant, can absorb heat through vaporization and give FTHEs ultra-low temperature surfaces to drop the indoor temperature. The effects of refrigerant flow rate, temperature, and extreme indoor initial temperature on the indoor temperature distribution were examined. As indicated by the results, increasing the flow rate and decreasing the refrigerant temperature increased the room cooling rate while exacerbating the degree of temperature stratification (TSD). Compared with 35 kg/h, the cooling effect was enhanced by 1.5 times for a flow rate of 50 kg/h, whereas the TSD value near FTHEs was nearly 14 °C/m, approximately twice as high as that of 35 kg/h. Slightly raising the initial ambient temperature led to the rise of the cooling effect, whereas this method slightly affected the temperature stratification. This study provides a novel idea for solving long-term DC cooling system failure while laying a basis for the effect of ultra-low temperature surfaces on ambient temperature distribution. [ABSTRACT FROM AUTHOR]

Recently, the rapid development of data centers has led to an increased requirement of cooling systems, resulting in high energy consumption. A two-phase thermosyphon loop (TPTL) system effectively utilizes a natural cold source and reduces energy consumption in data centers. In this study, an experiment was conducted to compare the heat transfer performance of CO 2 TPTL with the commonly used R134a and R410A TPTLs. Under their respective optimal filling ratios, CO 2 TPTL exhibited the lowest required driving temperature difference, which was 3 °C lower than that of R410A TPTL and 5 °C lower than that of R134a TPTL. The energy-saving effect of CO 2 TPTL was analyzed based on a typical data center case and the climate parameters of different cities in China. In Beijing, the annual average PUE (power usage effectiveness) of the data center using conventional centralized cooling systems, R134a TPTL, R410A TPTL, and CO 2 TPTL was 1.43, 1.36, 1.34, and 1.32, respectively. The calculation for other cities showed that the energy saving ratios of the CO 2 TPTL system in Kunming were the highest. They were 58.6%, 40.7%, and 30.4% higher compared with those of conventional centralized cooling system, R134a TPTL, and R410A TPTL, respectively. • Thermal performance of CO 2 , R134a and R410A TPTLs was compared by experiment. • PUE and CLF of the data center using different cooling systems were calculated. • CO 2 TPTL cooling system had the best energy-saving effect. • Energy consumption of the cooling systems in different cities was analyzed. [ABSTRACT FROM AUTHOR]

Conventional air-conditioners in data centers generally have the problems of high energy consumption and poor cooling effect. In this paper, a composite cooling system with pump-driven heat pipe and vapor compression operation modes is proposed to solve the above problems. The system adopts pump supply liquid technology and rack-level terminals. The cooling effect, energy efficiency, and annual performance of the system are analyzed in this paper. In terms of energy efficiency, the coefficient of performance in vapor compression mode is 6.6–3.8 (outside temperature is 15–35 °C); the coefficient of performance in heat pipe mode is 15.8–9.7 (outside temperature is −15–15 °C). In terms of the cooling effect, the novel system performs well for temperature control accuracy, and the on-demand supply cooling of each rack can be realized. In terms of the annual performance of the typical city, the annual average coefficient of performance of the novel system in vapor compression mode increases by 8.5% compared with the system adopting direct expansion technology. The power usage effectiveness of the data center that adopts the novel cooling system can reach 1.23 which satisfies the current standard. • A rack-level data center cooling system adopting pump supply liquid technology is presented. • The cooling effect and energy efficiency performance are analyzed through experimental study. • The on-demand supply cooling of each rack can be realized. • The power usage effectiveness of the data center adopting the novel cooling system can reach 1.23 in the typical city. [ABSTRACT FROM AUTHOR]

• Pump-driven/buoyancy-driven single-phase immersion cooling systems are studied. • Pump-driven SPIC systems reduce average temperature and PUE by 55.5 and 11.6%. • Natural convection enhances heat transfer while inducing temperature stratification. • Low inlet temperature and appropriate flow rate are suggested for applications. Improving power usage effectiveness (PUE) in data centers becomes a key challenge for carbon neutrality and carbon peaking strategies. In this context, this paper investigates the single-phase immersion cooling (SPIC) system that promises to improve PUE. Three-dimensional mathematical models of pump-driven and buoyancy-driven immersion cooling tanks are established and numerically solved. The thermal characteristics, flow resistance, and energy consumption levels of immersion cooling tanks in three operating modes are investigated. Moreover, the roles of volume flow rate, inlet temperature, and device power in immersion cooling characteristics are analyzed. The results indicate that the heat dissipation of buoyancy-driven SPIC systems is less effective than pump-driven ones. Compared to buoyancy-driven SPIC systems, the average temperature of immersion coolants and PUE in pump-driven SPIC systems reduces by 55.5 and 11.6%, respectively. Interestingly, although natural convection in mixed convection operation enhances convective disturbance, it induces temperature stratification that weakens temperature homogeneity. Increases in inlet temperature and device power both worsen the immersion cooling performance. However, increasing inlet temperature improves temperature uniformity and reduces flow resistance losses, while increasing device power has the opposite effect. Besides, the increased flow rate enhances the convective heat transport and temperature uniformity but increases the flow resistance loss. [ABSTRACT FROM AUTHOR]

Immersion cooling technologies have become an emerging cooling method for data center cooling. The studies available in open literature dealt with immersion cooling performance of data servers using mineral oil, EC-100, and Opticool 872552, but the studies focusing on the performance of FC-40 dielectric fluid is not available. Therefore, this study aimed to develop a single-phase liquid immersion cooling system using FC-40 dielectric fluid for a 1U (44.45 mm height) data server. The present study experimentally investigated the influence of different design and operating parameters, including the inlet/outlet port configuration (T and Z configurations), the bypass effect, the flowrate (1–3 LPM), the heating load (200–600 W), the inlet fluid temperature (15–35 °C), the presence of suction fan with various arrangements, and different heat sink bases (solid base, vapor chamber and heat pipe base). The results showed that the T-configuration could provide a 12.6% and 0.5–2.8 °C reduction in thermal resistance and case temperature compared to the Z -configuration, respectively. Furthermore, the heat sink with heat pipe and vapor chamber base offered a minimum case temperature of 56.7 °C and 55.2 °C against the 60 °C experienced in the heat sink with flat plate base, respectively. [ABSTRACT FROM AUTHOR]

It is important to cool data centers for improving IT equipment reliability through indoor temperature control. The air conditioning energy consumption is almost 38% of the total energy consumption. Free cooling in cool days is a promising technology for energy conservation. A pump-driven loop heat pipe (PLHP) system for free cooling was developed and installed in a data center project, which has a high energy efficiency ratio (EER) compared to air conditioners. The running performance of the PLHP system in the case project was tested and studied. The fitting rule of EER and outdoor temperature was obtained. The hourly energy savings and payback periods of the PLHP system for different cities of different climate regions in China were analyzed basing on the fitting formula compared to air conditioners. A national distribution map was developed to show the annual energy saving ratio in China. Results show that the PLHP system provides remarkable energy savings and the indoor temperature is remained at 18°C to 25°C. About 74.2% of Chinese cities lie in regions suitable for applications, and the annual energy saving ratio is over 30%. The average payback period for most cities in China is about 3.9 years. [ABSTRACT FROM AUTHOR]

The increasing energy consumption of data centers has become a global concern. Over 30% of the total energy use in a data center is consumed by the cooling system and it is necessary to reduce this consumption by efficient cooling techniques. Free cooling is an alternative method, which means utilizing natural cold source when the outdoor temperature is lower than the indoor temperature to achieve energy-saving. Thermosyphon and its integrated system have distinct advantages over other free cooling methods and have great application potential. In this paper, the states of the art are reviewed and overviews are presented for thermosyphon and its integrated system, respectively. The features of existing designs are compared and shortcomings of current studies are concluded. This paper will be helpful for researchers in this field and promote the application of this new free cooling method. [ABSTRACT FROM AUTHOR]

The data centre air conditioning system has a huge energy consumption and has the characteristic of requiring year-round cooling. Cooling tower cooling technology can realize free cooling and reduce the operating time and energy consumption of the refrigeration host. In this paper, through the engineering examples, it discusses the cooling tower with free cooling of the air conditioning system combined with conventional refrigeration way design points. It analyses the way to realize the operation and transformation of conventional refrigeration mode, free cooling mode, partial free cooling mode and other operation modes through automatic control system. [ABSTRACT FROM AUTHOR]

In recent years with the concept of Internet of things, cloud computing and mobile Internet, the large data center construction presents the fast growth the tendency in China, the air conditioning system energy consumption is too high, the problem is urgently needs to solve. Based on data center operation features of air conditioning system, in combination with the practical situation of engineering, free cooling mode was applied to air conditioning system, air conditioning energy consumption decreased significantly. [ABSTRACT FROM AUTHOR]

A cooling plant by using lake water source was proposed to cool the space in data centers. It combines free cooling technology and variable capacity technology to remove heat and reduce energy consumption effectively. In this paper, firstly, the control strategies for this cooling plant were proposed. Then, a detailed annual energy consumption model with considering the effect of the dynamic heat dissipation characteristics of servers, lake water temperature, outdoor weather conditions, and cooling plant thermal performance, will be established to evaluate the performance and energy efficiency of this cooling plant under different load factors. The results show the mode 1 and mode 2 of this cooling plant are 67.6% and 32.4% of the year’s running time, respectively. The average EER of the cooling plant under different load factor ranges from 16.8~49.3, and the average PUE value ranges from 1.11 to 1.15 under different load factors, which demonstrates this cooling plant poses higher energy efficiency than the conventional cooling plant for the data centers. [ABSTRACT FROM AUTHOR]

Cooling system consumes more than 35% of total electricity in most data centers. The provided cooling normally exceeds the actual demand of IT equipment in order to assure the safe operation, resulting in a low energy efficiency. In this paper, a novel method based on demand response was proposed to precisely control the cooling supply, and the energy saving potential was assessed systematically. Compared to the reference case, in which the cooling demand is determined by assuming all of servers are in the running status, when the cooling demand was determined based on the measured dynamic IT load at room level, row level, rack level and server level, it can be reduced by 7.9%, 14.2%, 15.6% and 17.9% respectively for the random selected 48 h. In addition, IT load shifting also has a big potential to save energy, as it can make the cooling system working at a higher energy efficiency, which varies with loads. Two cases were studied: even distribution of IT load and optimized IT load shifting. Compared to the best case that determines the cooling demand according to the IT load at server level, they can further reduce the electricity consumption of cooling systems by 0.9%, and 1.2%. [ABSTRACT FROM AUTHOR]

Cooling systems in information technology (IT) equipment account for the greatest share of direct energy consumption in data centers. Conventional air-cooling schemes are thermally inefficient and energy intensive as they require large temperature difference between heat source and cooling medium. To overcome the aforementioned drawbacks of air-cooling, a "chillerless" novel spraying architecture which has the capability of performing high heat flux cooling, is highly scalable and easily adaptable by modern data centers is proposed in this paper. To demonstrate the scalability and performance of this new cooling scheme, a full-scale spray cooled rack system which has the capacity of housing up to 12 server units is developed. The dynamic performance of the spray cooled rack system under variable ambient temperature is studied. It is found that the ambient temperature strongly affects the spray cooling performances and the chamber pressure stability. A grey box model of the system is established. The newly developed model has successfully predicted the temperature variation on both the water side and spray cooling side with reasonable accuracy. Our model sets the foundation for predictive control of the chamber pressure and workload management of the spray cooling scheme for application in large-scale data centers. • A chillerless spray cooled 24U server rack system is established for data center cooling. • Dynamic thermal performances have been investigated. • Weather affects pressure stabilization and spray cooling performance. • A theoretical capacitance resistance model is established. • The model accurately predicts the system thermal responses. [ABSTRACT FROM AUTHOR]

This research examined the application of fan-assisted cooling within open and contained raised-floor data centers with the intention of assessing the effectiveness of the system’s cooling method. A computational fluid dynamics (CFD) approach that incorporated both airflow and thermal analysis was employed to examine the detailed effectiveness of fan-assisted air-cooling in a data center that exhibited the behavior of under-cabinet leakage. The CFD technique was also used to assess the impact that three distinct aspects had on the performance of the fan-assisted air-cooling system: cold aisle containment, straightened air flow and fan-to-tile distance. In addition, the mixed-level Taguchi statistical approach was applied to understand how variations in these parameters directly and interactively modified the heat transfer in the surroundings of the inlets of the server racks. The results of the research reveal that fan-assisted perforations, taking the combination of the key factors (the main and interact effects) into account, would represent a viable means through which the cooling systems employed in both open and closed aisle data centers can be enhanced. The well-constructed CFD-based Taguchi methodology might yield a good level of validity for use in substantial and timely optimization procedures to further improve the cooling effectiveness and efficiencies of data centers. [ABSTRACT FROM AUTHOR]

Advancements in information technology have led to an increasing demand for data centers (DCs), and the energy consumption of DCs has gained attention worldwide. Many researchers have attempted to develop efficient DC cooling systems to reduce the energy required for cooling DCs, however, there are limitations in identifying the effect of such systems from the economic perspective. Subsequently, project owners find it difficult to decide whether to apply these systems to their particular DCs. The present research aims to analyze the economic performance of seven cooling strategies developed by the combinations of widely used DC cooling systems. The economic performance of each strategy is estimated by the life cycle cost analysis technique, and the analysis results show that Strategy 5 (A2_M: air-side economizer and supplementary cooling by a mechanical system) yields economic benefits of 26.84% in comparison to the conventional cooling system. The proposed research methodology and obtained results are expected to aid project owners in making effective decisions regarding the selection of an appropriate cooling strategy from an economic perspective. [ABSTRACT FROM AUTHOR]

The development of emerging technologies such as Internet of things, blockchain, and artificial intelligence put forward higher requirements for the computing power of edge data center servers, which is mainly restricted by cooling technology. To improve the heat dissipation performance and the deployment flexibility of the edge data center, the concept of integrated indirect liquid cooling system for the edge data center server was introduced, and two samples were investigated through the tests. Firstly, the factors affecting the system performance were studied by experiment and numerical simulation. Then, the heat transfer performance, the flow characteristic, and the system's stability were analyzed. Finally, the temperature control ability of the air cooling and liquid cooling server was compared and analyzed by numerical simulation method. The results show that increasing the flow rate improves the heat dissipation performance when the surface temperature and thermal resistance of the chip reduce. But the further increase in flow rate slows down this trend. The heat dissipation performance of the system also reduces with the increase in coolant temperature. Two sets of the cooling systems, which are respectively arranged inside and outside the server, have similar flow characteristics, but the feasibility of the external system server is higher, which is verified by the numerical simulation method. [ABSTRACT FROM AUTHOR]

This study presents a prototype of an independent modular air containment (MAC) system that overcomes the limitations of the existing room-based cooling and applies a row-based cooling system for a high-density data center that can meet the requirements of energy efficiency. Furthermore, to improve the cooling efficiency and safety, we developed a novel in-row cooling package with multiple heat-transfer media (a sequential water-to-refrigerant-to-air heat exchange system). While complying with the standard test method, the objective cooling performance and PUE are derived through in-situ measurement in connection with the actual operation of a reference data center, and the energy saving contribution is analyzed. As observed from the result of the experimental measurement for the MAC with the novel in-row cooling package, the thermal balance is maintained between the water to refrigerant primary cycle and the refrigerant to air secondary cycle, and the air temperature in the cold aisle converges to 23 °C, satisfying the ASHRAE thermal guidelines. The energy influence of the in-row cooling package is extremely low with average 0.019 pPUE. For a reference data center, the analyzed energy efficiency can be improved from baseline PUE 1.563 to PUE 1.361 through 43.5% reduction in the cooling system. • Independent modular air containment (MAC) with row-based cooling developed. • MAC prototype overcomes the limitations of the existing data center cooling. • MAC prototype meets the requirements for IT environment and energy efficiency. • Cooling performance, energy efficiency, and safety are improved. [ABSTRACT FROM AUTHOR]

Heat pipe, a high efficient, cost effective and reliable device, is considered one of the most promising passive technologies for cooling data centres. Aiming to provide comprehensive information and focused perspective on heat pipe system for cooling data centres, the literature reviewed in this review is obtained from the Web of Science by searching the topic "heat pipe" and "data centre" conducted on Sep. 1, 2019 for the decade from 2009 to 2018. In this paper, a comprehensive review on heat pipes for use in data centre cooling systems will be carried out, starting from the working principle, heat transfer analysis and applications. The review works will be analysed in terms of the system research methodology, energy performance evaluation, and IT tasks. From the system research methodology, the heat pipe structure, simulation and testing analyses were conducted. From the energy performance evaluation, the energy consumption, energy recovery and energy saving analyses were studied. From the IT tasks, the avoidance of hot spots and thermal management in the data centres were analysed. The opportunities for further works are revealed including: developing new and efficient data centre cooling systems employing advanced technology; optimising the heat pipe structure for the data centre cooling systems; testing the data centre cooling systems under actual conditions; and evaluating the economic feasibility and market potential of the data centre cooling systems. This review provides the guidelines for the development of data centre cooling system based on the heat pipe. • The heat pipe systems for cooling data centres are summarized from the research methodology, energy performance evaluation, and IT tasks. • Opportunities of data center cooling system based on the heat pipe are emphasized. • The evaluation of economic feasibility and market potential of the data centre cooling systems based heat pipe is needed. • Further tests of the data centre cooling systems in real environment should be carried out. [ABSTRACT FROM AUTHOR]

Data centers require a set of uninterruptible cooling systems to operate. For uninterruptible cooling, latent thermal energy storage (TES) systems offer an alternative solution in the event of a power outage. In this study, a novel integrated cooling system comprising a loop thermosyphon and latent TES is proposed for emergency cooling. A water-cooled loop thermosyphon was used to absorb the heat dissipated from the servers. In addition, a multi-tube TES unit containing the paraffin RT11HC with a phase transition temperature of 10–12 °C was designed as a supplementary cold storage system. To evaluate the thermal characteristics of the emergency cooling system, an experiment was conducted by shutting down the chiller. The results showed that the integrated system could maintain the servers operational for approximately 6 min. Moreover, parametric analysis was performed to extend the emergency cooling time to 15 min. The analysis showed that as the thermal conductivity of the phase change material (PCM) increased to 2 W/(m·°C), the cooling capacity met the emergency cooling demand within 15 min. The proposed cooling system can act as a reference for the optimal design of emergency cooling systems in data centers. • The cooling system integrated a loop thermosyphon and a latent heat storage unit. • The novel system could reduce the risk of servers overheating under emergency. • Effects of PCM thermal properties on the thermal performance were analyzed. • Increasing PCM thermal conductivity could obviously prolong emergency cooling time. [ABSTRACT FROM AUTHOR]

• A thermodynamically-rigorous model enables reliable PUE and WUE estimations. • A PUE variance of 62% is quantified, depending on technology, efficiency, climate. • A WUE variance of 100% is quantified, depending on technology, efficiency, climate. • Best-practice values and their determinants are quantified. • Results enable more reliable DC direct and indirect water footprint estimation. The water use of data centers (DCs) is becoming an increasingly important consideration for sustainability analysts, but has been difficult to quantify due to lack of reported data by DC operators. This work develops thermodynamically-compatible water use effectiveness (WUE) and power usage effectiveness (PUE) ranges needed for direct and indirect water use analysis for 10 different DC archetypes in 15 U.S. climate zones, using a hybrid physical-statistical approach that is validated with real-world data. The ranges further capture variabilities between best and poor DC efficiency practices, showing that PUE and WUE values can have relative difference as much as 62% and 100% respectively, depending on cooling technologies, efficiencies, and locations. PUE results indicate significant climate effects, whereas WUE results indicate the strongest climate effects for airside economizers with either adiabatic or water-cooled chiller systems. Collectively, the results underscore the importance of considering technology, efficiency, and climate effects when estimating PUE and WUE for direct and indirect DC water use analysis. Results also identify variables leading to best-achievable PUE and WUE values by climate zone and cooling system type—including operational set points, use of free cooling, and cooling tower equipment and operational factors—which can support DC water- and energy-efficiency policy initiatives. [ABSTRACT FROM AUTHOR]

• Two DCs located in a hot-arid climate with distinctive cooling systems are compared. • A novel method is presented for water-energy usage trade-off in DCs. • Synergistic water and energy conservation approaches are presented. Although energy and water are intertwined, the analysis of energy consumption in data centers (DCs) has largely ignored water needs. In this study, we utilize established DC efficiency metrics, power usage effectiveness (PUE) and water usage effectiveness (WUE), to analyze the water and energy use in two colocation DCs (DC1 and DC2) located in the greater Phoenix area. These DCs use distinct cooling systems: DC1 uses air-cooled chillers and DC2 uses both water-cooled chillers and evaporative cooling. We also present a method for analyzing the water-energy tradeoff in DCs as a useful tool for DC designers and managers to evaluate different cooling systems. The results highlight that although DC1's average PUE is nearly 13% higher compared to DC2's average PUE, its source WUE is 66% lower than DC2. In addition, DC1's PUE is more affected by seasonal changes (variation of dry-bulb temperature) , while DC2's WUE has a larger seasonal variation. Our cooling system analysis indicates that hybrid evaporative cooling has the least power consumption, while air-cooled chillers have the most water use. Utilizing free cooling and evaporative cooling when outside air condition permits (∼40% per year), results in substantial power and water savings in Phoenix DCs. [ABSTRACT FROM AUTHOR]

This paper addresses the technical and economic issues associated with waste heat recovery in data centers through the use of absorption cooling machines. The theoretical possibility of utilizing the heat dissipated by a server, or a number of servers, to power an absorption system, which in turn produces cooling for other servers in the data center, is investigated. For this purpose, a steady-state thermodynamic model is developed to perform energy balance and exergy analyses for a novel configuration of an on-chip two-phase cooling system and an absorption refrigeration system. This combination is created by replacing the condenser in the on-chip cooling circuit with the generator of an absorption refrigeration cycle. The performance of the developed model in simulating both LiBr–water and water–ammonia absorption cooling systems is examined through verification of the model results against the reference data available in the literature. The verification indicates the superiority of LiBr–water absorption system for data center/server operating conditions. Therefore, a LiBr–water absorption refrigeration system is modeled in the novel combined heat recovery system. For these systems it is shown that the traditional definition for the coefficient of performance (COP) is not appropriate to evaluate the performance and, in its place, introduce a new figure of merit. Through a sensitivity analysis, the effects of server waste heat quality, server coolant type, solution peak concentration, solution heat exchanger effectiveness, evaporator temperature, and operating pressures on the performance of the novel system are investigated. Finally, using the thermodynamic model and cost information provided by the absorption refrigeration industry, an economic analysis is carried out to calculate the payback period when this technology is used for data center waste heat recovery. [ABSTRACT FROM AUTHOR]

• A green and sustainable method for packing servers is investigated. • Cooling principles on cooling efficiency and packing capacity are constructed. • The problem is formulated as bin-packing models via segmenting and gridding. • Mathematical analyses and solution strategies help to pack servers efficiently. An Underwater Data Center (UDC) is an underwater vessel full of computing servers and designed with a cooling system using cold water in the ocean. A UDC vessel is composed of cabinets for computing servers, and the cabinets are finally packed into racks that facilitate the installments of the computing servers. We formulate the problem of packing cabinets into the vessel by considering the water volume required for server cooling and the placement of the cabinets of servers. Due to different patterns of racks, a set of mixed-integer linear programs were developed, and they were solved by methods with several stages. As demonstrated by experiments, the proposed models and strategies effectively solve the simulated instances generated by considering the cooling principles. The cabinets with more considerable differences in their width and height are better than single-sized cabinets because the smaller cabinets make the packing process more flexible. Moreover, multi-sized cabinet packing is significantly better than single-sized cabinet packing. Additionally, it is not always appropriate to use racks with large capacities. However, racks with multiple capacities may improve the space and energy utilization degrees when the size and the designed heat power consumption of the data center are fixed. [ABSTRACT FROM AUTHOR]

The growing cloud computing infrastructures increase the demand for energy-intensive machines, such as high-performance servers and the associated cooling system. That brings challenges to the energy management of the concerned modern buildings such as the data centers. Transient Thermal System Modeling (TTSM) is an essential solution to illustrate the instant thermal variation inside the buildings based on heat transformation prediction. TTSM can help plan, organize and optimize corresponding settings to improve energy efficiency. The adoption of row-based and rack-based structures as a cooling solution has recently emerged, especially boosted by its high efficiency. In contrast, few studies have concerned the related TTSM. In this study, we propose two frameworks exclusively targeting the TTSM of data centers that adopted row-based or rack-based cooling systems. A model-driven framework (MDF) and a data-driven framework (DDF) are developed, respectively. The MDF is expressed by Ordinary Differential Equations (ODEs), it is built based on the lumped-capacitance method under several pre-declared assumptions as a general TTSM solution to related structures. The DDF is developed as an extension of the Long-Short-Term-Memory (LSTM) method to realize multivariate I/O (MIMO) predictions, which is commonly demanded in Industrial Internet of Things (IIoT) applications. Both frameworks are evaluated experimentally on a physical cluster equipped with a high-level IIoT sensor measurement system. The guide for parameter-tuning of the model is also provided in the experiment part for use case analysing. The validation results show that both frameworks can build reliable TTSM in terms of real-time temperature predictions. Moreover, a comprehensive comparison study is conducted with valuable application suggestions based on experimental discoveries. [ABSTRACT FROM AUTHOR]

Loop thermosyphon system is an efficient cooling system for energy saving in data center. It is necessary to investigate the performance of the loop thermosyphon system filled with alternative refrigerants to prompt its application. In this paper, a R32 loop thermosyphon system is experimentally investigated in an enthalpy difference laboratory for its performance. R22 and R134a are also used for comparison. The results show that the optimal filling ratio of R22, R134a and R32 is the same (37.3%). At the optimal filling ratio, the flow stability of R32 is obviously better than those of R22 and R134a. When cold water temperatures are 10–22 °C, the cooling capacity of R32 is 5.4–15.6% higher than those of R22 and R134a. After controlling extractor fans, the energy efficiency ratio of R32 is 4.9–206.6% higher than those of R22 and R134a. Moreover, the free cooling potentials of the three refrigerants in five typical climate cities across China are analyzed and compared. Compared with R22 and R134a, R32 has 3.6–11.0% and 18.5–26.7% higher free cooling percentages and annual energy efficiency ratio, respectively; and its annual average partial power usage effectiveness is 0.0012–0.0017 lower than that of other two refrigerants. [ABSTRACT FROM AUTHOR]

This elaboration presents the configuration of the cooling system of the POLCOM Data Center which utilizes commercially available components, proposes steering strategy and analyzes their functionality. The designed architecture of cooling and dedicated control system is presented to demonstrate the novelty and customization with respect to the demanding outdoor temperatures existing in the climate of the Małopolska Province. The cooling system control and operation is illustrated by a comprehensive analysis of compressor and freecooling modes. The discussion on embedded functionality of chillers is undertaken. According to features and limitations of the complex solution, the cooling system reached the annual average coefficient of performance of 8.63 in 2015 (increase of 110% compared to the year 2014), operating 65% of the time during the year in compressor mode and 35% in freecooling mode. This coefficient in compressor mode amounted to 4.39 while in freecooling mode totaled 16.50. It was proved that in the real case under consideration they generated losses in electricity consumption amounting to 557MWh per year. The real-time experimental data collected from the commercial Data Center installation are used to present a unique operation of a such complex system. • Custom controller incensed efficiency and performance of cooling system. • The freecooling mode is more energy-efficient compared to the compressor mode. • In freecooling mode, a single chiller works more effectively than two simultaneously. • The operating modes strongly correlates with external temperatures distribution. • Embedded controllers limits freecooling operating time and results in energy losses. [ABSTRACT FROM AUTHOR]

• A novel spray cooled rack is developed for data center cooling in the tropics. • This new cooling system eliminates the need for high energy consuming chiller. • Microprocessor temperature of spray cooled scheme is lower than air cooled scheme. • Characterized system thermal performance over a wide range of operating parameters. • Spray cooled rack system contributes to significant energy savings. A lab-scale spray cooled rack system with a server and simulated heaters, operating with near-ambient temperature coolant of approximately 30 °C, was developed for data center cooling application. This system has significant energy saving potential as it eliminates the need for a chiller unit, which is usually necessary in conventional air-cooling schemes. The system was designed to dissipate a maximum heat load of 5.6 kW. Despite its higher operating temperature, our investigation shows that the spray cooled system leads to better cooling performance of the microprocessors as compared to conventional air-cooling scheme. A durability study for more than 40 h of cumulative intermittent operation showed no degradation in system performance when operated at high chamber temperature conditions (>35 ℃). The thermal performance of the spray cooled system and the effects of parameters such as spray nozzle flow rate, condenser fan power, condenser flow rate and heat loads were systematically characterized. It is found that the thermal performance of the simulated heaters is mainly affected by the spray nozzle flow rate, while the condenser fan power and condenser cooling water flow rate strongly affect the condensation rate and are, therefore, critical parameters for spray chamber pressure control. In summary, this work demonstrates the possibility of employing the newly developed spray cooled system for the thermal management of high-performance servers of data centers in tropical climates and identified key operating parameters that are useful for the design, operation and implementation of this system. [ABSTRACT FROM AUTHOR]

• In-situ sensor correction method based on Bayesian inference and autoencoder. • Impacts of the system model accuracy on the correction performance. • A series of case studies were designed to fully demonstrate the performance. • Result shows that deviation rates of sensor measurements are decreased to 7.67%. The quality of measurements from working sensors has a considerable influence on the system operation and energy usage in data center cooling systems. However, due to the malfunction, aging, and installation positions, it is very common phenomenon that the measurements are far away from their true values. Virtual sensor correction is a promising solution to correct erroneous measurements. This study proposed a novel sensor correction method for data center cooling systems using the Bayesian Inference coupling with autoencoder (AE) to eliminate the sensor errors. The correction performance of the proposed method was comprehensively investigated under a series of single/multiple sensor error scenarios in a typical computer room air handler (CRAH) unit. Furthermore, the impact of the system model accuracy on the correction performance was also quantified. The results show the excellent correction accuracies of the proposed method in the data center cooling systems: following correction, the sensor deviation rates are decreased to 7.67% and 3.00% for the single and multiple simultaneous sensor error scenarios, respectively. Additionally, the sensor correction error increases to 18% when the deviation rate of the heat transfer coefficient is set to 10%. [ABSTRACT FROM AUTHOR]

• A PEMFC-driven CCP system with heat pipe for data center applications is proposed. • New operation strategies for power and cooling supplies in a CCP system are proposed. • Performances of two PEMFC-driven CCP systems with multiple cooling are compared. • Effect of heat pipe on the power and cooling supplies in the CCP system was studied. With the dramatic development of data centers, the energy management system in data center applications has become significantly important in recent years. A proton exchange membrane fuel cell (PEMFC)-driven combined cooling and power (CCP) system with multiple cooling devices was proposed in this paper to fully utilize a natural cold source. Another CCP system without natural cold source utilization was also proposed for comparison. Power and cooling were supplied to these systems with new operational strategies. Based on the proposed model, the operational performance of the two CCP systems was analyzed for a sample data center. The seasonal and annual power supplied, cooling supplies, matching degrees, energy consumption for removing cooling loads, and system efficiencies in the two proposed CCP systems are discussed and analyzed in detail. Results indicate that by using the designed operational strategies, the power and cooling supplies almost matched perfectly with the requirements of the sample data center. The annual energy efficiencies can reach 86.53% and 85.02% for the two proposed CCP systems. [ABSTRACT FROM AUTHOR]

• We develop a joint energy efficiency optimization scheme to coordinately optimize the energy of servers and cooling systems. • l An online task scheduling algorithm is developed using marginal cost evaluation. • l We design a resource management strategy integrated workload prediction technique. • l We develop a task migration strategy with marginal cost evaluation and prediction results. • l We validate the designed optimization scheme though experiments based on real traces. With the widespread development of cloud computing, the dramatic increase in the number and size of data centers (DCs) has resulted in substantial energy consumption and serious environmental problems. This creates a challenge for the further development of DCs. It is imperative to improve the overall energy efficiency of DCs. According to the statistics, servers and cooling systems are the main energy-consuming components of DCs. Recently, several energy-efficient strategies have been developed to address these problems. However, most of these works only consider the energy optimization of servers or cooling systems separately. Therefore, a Jo int E nergy E fficiency Optimization S cheme (JEES) is proposed in this paper, where the energy consumed by servers and the cooling system is jointly considered, and coordinately optimized. JEES includes a dynamic online task scheduling algorithm based on marginal cost evaluation, a resource management strategy that integrates the workload prediction technique to manage resources, and a task migration method using marginal cost evaluation. By using the proposed techniques, the total energy consumption of DCs can be reduced. Extensive experiments have been conducted based on real-world workload traces, and the results demonstrate that compared with other techniques, the proposed scheme effectively improves the overall resource utilization and reduces the total energy consumption of DCs. [ABSTRACT FROM AUTHOR]

[Display omitted] • New hot aisle containment using a vortex flow. • Reduce the supply heat index (SHI) to 0.11 compared with the conventional layout with no containment. • 4.3% lower normalized server temperature than full hot aisle containment by relieving high backpressure. Poor airflow management attributed to hot air recirculation and cold air by-pass adds massive thermal inefficiencies to air-cooled data center's cooling system. The containment system usually was adopted to mitigate such drawbacks by isolating the space using a physical partition wall, such as hot aisle containment. Although the recirculation and by-pass can be effectively suppressed, the consequent high backpressure built up in the containment reducing the server air flowrate and possibly increasing the server temperature beyond the acceptable limit. This study presents a new enclosure mechanism for air-cooled data center using a vortex flow as an alternative to the conventional hot aisle containment to reduce the hot recirculation and, at the same time to retain the server air flowrate. The experiments conducted in a half-scale test cell (2-times smaller than a typical data center hall in length scale) examined vortex containment's effectiveness. The experiment results revealed that the average Supply Heat Index (SHI) in vortex hot aisle containment could be reduced to 0.11. Although vortex hot aisle containment did not enclose all hot recirculation compared to the full containment deployed in the benchmark layout, the relieved backpressure (the high pressure in the hot aisle) retains the rack flowrate by 42% (2.1 m/s in the vortex hot aisle containment with a diameter 1.2 m (VFL1200) layout compared to 1.2 m/s in full containment) and results in a 4.3% lower normalized server temperature (1.03 in VFL1200 layout compared to 1.076 in full containment CL). In the end, the validated CFD model provides more insights on vortex containment characteristics, such as the vortex strength and pressure distribution. [ABSTRACT FROM AUTHOR]

With the development of big data and cloud computing technologies, data centers have grown rapidly worldwide. Although the commonly used data center cooling system (computer room air conditioning system, CRAC) is safe and reliable, it has a high energy consumption. Loop thermosyphon consumes less energy than the CRAC system and can be used in data center cooling system. This review presents the operating principles of the loop thermosyphon and its application in a data center cooling system. First, this review introduces the types of heat pipes and the operating principles of the loop thermosyphon. Second, the application of the loop thermosyphon in the room-, rack- and on-chip-level cooling of data center is reviewed. Finally, a combined compressor and loop thermosyphon system is introduced, which can be used to cool telecommunications base station. As the system can use cold ambient air directly as heat sink, it is more energy-efficient in comparison with using air conditioning alone as the cooling method. After reviewed and compared recent articles, we have indicated the imperfect points in recent researches and the future's development trend based on the results of researches and our experience. We think the points of this review is useful to the industrial applications. • The operation principle of the loop thermosyphon and the flow boiling heat transfer mechanism have been reviewed. • The application of the loop thermosyphon in data center cooling has been introduced, and it has better energy saving effect. • A combined compressor and loop thermosyphon systems by different researchers has been introduced and compared. • Choosing better coolants, using cold ambient air and on-chip level cooling will become the future development trend. [ABSTRACT FROM AUTHOR]

Data center is a fundamental infrastructure of computers and networking equipment to collect, store, process, and distribute huge amounts of data for a variety of applications such as Cyber–Physical–Social Systems, business enterprises and social networking. As the demands of remote data services keep increasing, both the workload of the data center and its power consumption are rapidly rising. An indispensable part of a data center is the cooling system which provides a suitable operation environment, and accounts for around 30% of the power consumption of the data center. Therefore, optimized energy management of data center's cooling system is a highly profitable research area. Generally, a cooling system is made up of a mechanical refrigeration sub-system and a terminal cooling sub-system. Heat generated during operation of the data center will be absorbed by the latter one, and transferred into the outdoor environment via the former one. Depending on the cooling principle, current cooling solutions can be classified into air-cooling, liquid-cooling or free cooling technology. Although air-cooling is widely used in most existing data centers, the other two solutions have attracted more interests due to their excellent cooling effectiveness and higher energy efficiencies. Among the different cooling equipment, the chillers and fans are the major power consumers of the entire cooling system. Therefore, modeling of their power consumption is important for energy management of the cooling system, which can be classified into mechanism-based methods and data-driven methods. Based on the aforementioned models, optimization strategies for the operation management of cooling equipment are proposed to reduce the power consumption of the cooling system, which mainly includes the model predictive control-based methods and reinforcement learning-based methods. This paper is an overview of the data center's cooling system, which mainly includes the mainstream cooling solutions, the power consumption modeling methods and the optimization control strategies. In addition, several current challenges and future work in the data center's cooling system are described. [ABSTRACT FROM AUTHOR]

The failure of cooling systems in data centers (DCs) leads to higher indoor temperatures, causing crucial electronic devices to fail, and produces a significant economic loss. To circumvent this issue, fault detection and diagnosis (FDD) algorithms and associated control strategies can be applied to detect, diagnose, and isolate faults. Existing methods that apply FDD to DC cooling systems are designed to successfully overcome individually occurring faults but have difficulty in handling simultaneous faults. These methods either require expensive measurements or those made over a wide range of conditions to develop training models, which can be time-consuming and costly. We develop a rapid and accurate, single and multiple FDD strategy for a DC with a row-based cooling system using data-driven fault classifiers informed by a gray-box temperature prediction model. The gray-box model provides thermal maps of the DC airspace for single as well as a few simultaneous failure conditions, which are used as inputs for two different data-driven classifiers, CNN and RNN, to rapidly predict multiple simultaneous failures. The model is validated with testing data from an experimental DC. Also, the effect of adding Gaussian white noise to training data is discussed and observed that even with low noisy environment, the FDD strategy can diagnose multiple faults with accuracy as high as 100% while requiring relatively few simultaneous fault training data samples. Finally, the different classifiers are compared in terms of accuracy, confusion matrix, precision, recall and F1-score. • A methodology to detect faults in data center (DC) cooling systems is presented. • Temperature maps are obtained from the gray-box model to train fault classifiers. • Convolutional and recurrent neural network-based fault diagnosis are compared. • OCSVM and NARX fault detection algorithms are assessed for an application. • The recurrent neural network exhibits superior performance for fault diagnosis. [ABSTRACT FROM AUTHOR]

Modular air containment (MAC) prototype was developed for optimal row-based cooling system for high-density data centers. The main purpose of this study is to evaluate the thermal performance and compare the cooling provisioning of different configurations of row-based cooling system to find the optimum placement of in-row CRAC units. Techno-optimal estimations were performed considering different in-row CRAC placements and aisle layouts. A matrix combination was analyzed based on total 2592 cases that can be implemented. By the whole optimization process of in-row cooler placement, we can achieve the best solution with the statically balanced cooling provisioning with a margin of error of 0.2%. The cooled air from in-row CRAC units was supplied with almost no heat loss in the air distribution paths to each server. Numerical simulations confirmed that the cold-hot-cold (C–H–C) aisle layout can improve the minimum 9% of heat balance for the provisioned CRACs compared to the hot-cold-hot (H–C–H) aisle layout. Temperature distributions, air streamlines and net cooling usages showed that the C–H–C aisle layout has better thermal performance and cooling provisioning especially for the row-based cooling. The C–H–C aisle layout is more proper than the H–C–H aisle layout for achieving the desired cooling efficiency. • A modular air containment (MAC) was developed and numerically investigated by CFD. • Techno-optimal estimations were performed considering CRAC and aisle layouts. • We investigated with the aid of 2592 different in-row CRAC placement combinations. • Thermal performance and cooling provisioning was evaluated for cooling efficiency. • New independent row-based cooling provides high standards of cooling performance. [ABSTRACT FROM AUTHOR]