Technologies Behind NEC's High Temperature Ambient Server

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Technologies Behind NEC’s High Temperature Ambient Server Environment • NEC IT platform Testing Center with 200 to 300 servers, storage devices, and network devices installed. • Eight air conditioners under operation • Total power of approximately 150 kW Issues • It is difficult to separate cool and warm air because there is no underfloor cooling system. The environment used for verification is a space designed to assess ICT equipment before shipment and therefore does not have any underfloor cooling system. It was therefore difficult to control the cool and warm air. • Frequent unit displacement and fluctuation of operating rate Multiple ICT devices are tested at the same time in the testing center and the device configuration is frequently changed according to the type of test. It is therefore difficult to keep the temperature constant, leaving no choice but to set the cooling system to a low temperature to avoid the generation of hot spots. Investigation After performing measurement across the whole floor, it was found that there were many low temperature areas where the indoor temperature was 23°C or less. Analysis As a result of performing heat analysis using an analysis tool, it was determined that five air conditioners could cover the current amount of heat generation. Three of the eight operating air conditioners were therefore stopped and the optimal temperature (25°C to 30°C) was successfully achieved at the air inlets of the ICT equipment.* 3 Measures We determined the positions of the three operating air conditioners that had to be stopped by using heat analysis. We also implemented measures to optimize the airflow of exhaust heat by using a capping method and adjusted the airflow direction of the cooling system for some racks to realize airflow control in which hot spots would not be generated even if those three air conditioners were stopped. Results We succeeded in reducing the cooling system power consumption from the current 24 kW to 15 kW (a reduction of 37%) without generating hot spots. This will lead to savings of approximately 1.1 million yen in annual power charges* 4 . As described above, it was demonstrated that the power consumption can be significantly reduced by raising the cooling system temperature. It is particularly difficult to maintain the supply of power to the cooling system when Development of NEC proprietary cooling technology using thermosiphon cooling Reduction in the amount of airflow required to cool down ICT equipment Because the layout of the ICT equipment in a data center is often very complicated, it is difficult to evenly feed in cool air. In general, this problem has been solved by installing fans in the ICT equipment itself to cool it directly by generating a large amount of airflow. If the CPUs and other components of the ICT equipment are more efficiently cooled down, it will require less fan airflow, and thus result in less power consumption. Based on this concept, NEC has developed a technology to cool down ICT equipment using a “thermosiphon cooling” method. With thermosiphon cooling, the heat is absorbed when the refrigerant changes from a liquid to a gas (evaporates). Applying this thermosiphon cooling technology to cool down the server reduces the fan airflow in the ICT equipment, cutting power consumption by 60% or more. This is estimated to result in a reduction in total cooling power, including that of the cooling system, of 20% or more. The amount of airflow from the cooling system can be reduced by cooling down the ICT equipment with a small amount of airflow. Amount of airflow in the ICT equipment100 Elimination of hot spots Measures to reduce the amount of airflow Amount of airflow in the ICT equipment70 Reducing the large amount of airflow for this rack eliminates hot spots. (It is not necessary to reduce the amount of airflow for all the racks.) It was verified that the power for the fan for a 1U server was reduced by 60% or more by adopting the thermosiphon cooling Thermosiphon cooling Features of thermosiphon cooling technology In the thermosiphon cooling method, refrigerant liquid is heated by the CPU or other heat generator and evaporates, generating a gas-liquid two-phase flow, which consists of liquid and gas. When vapor is generated in the heat receiving section, the liquid level drops in the heat receiving section, generating a level difference from the liquid in the heat emitting section. The gas-liquid two-phase flow, consisting of liquid and gas, is efficiently transferred to the heat emitting section due to gas-liquid equilibrium. Gas-liquid equilibrium is a characteristic in which the vaporization speed becomes equal to the devolatilization speed. This method is applicable even to 1U servers with a design optimized for the best airflow because a pump or other external driving force is not required to circulate the refrigerant. As the thermosiphon cooling method transfers heat using latent heat* 5 , there is almost no difference in temperature between the liquid and the gas. The gas-liquid two-phase flow technology. T he total power required for cooling, including that of the cooling system, could be reduced by 20% or more. Server fan Power consumed by fan airflow Power consumed by refrigerator 55 54 30 Reduction by 60% 15 21 5 Current Cooling using less air Features of technology – 1 Heat receiving section Heat emitting section Heat receiving section Heat emitting section Vapor Vapor + liquid Liquid Heat generator Liquid Radiation fin Because there is a fin flow channel, generated air bubbles include surrounding liquid and become a gas-liquid two-phase flow when rising due to buoyancy. When vapor starts to occur, the liquid in the heat receiving section drops, generating a level difference and refrigerant circulates to achieve a gas-liquid equilibrium. (The vaporization speed is equal to the condensation speed.) goes from the heat receiving section to the heat emitting section and simply condenses the refrigerant vapor. Therefore, the power consumed by the fan in the heat emitting section can be reduced compared with the air-cooling method, in which a large amount of airflow is supplied to the radiator for cooling, and the water-cooling method, in which the rise in the refrigerant temperature is large. Assuming that this thermosiphon cooling technology will be applied to 1U servers, NEC has adopted a structure whereby the heat receiving section can be connected to a radiator through the tube for heat transfer. Separate installation of the heat generator and radiator in this way enables a high implementation density and flexible component layout. The thermosiphon cooling module is the outcome of the “The Research and Development Project for Green Network/System Technology,” a Japanese government project in which NEC is involved* 6 . This module is currently being researched with the goal of practical application. Features of technology - 2 An air duct structure is used to cool down all the ICT equipment by using airflow management technology. Heat emitting section (flow line graph) Condensation part Condensation part equipped with a guide vane that concentrates airflow onto the memory. Vapor Chipset Heat receiving section (flow line graph) Chipset Heat receiving section Cylinder-type vaporization part, which sends airflow to the chipset Operating temperature Temperature rise CPU Rated temperature Fan powerW Temperature rise Thermosiphon Air cooling (21W) 6 Without air duct Parts other than CPU Liquid level Reduction of 60% or more Thermosiphon 6 With air duct Air cooling (21W) *5 Latent heat indicates that the temperature remains the same even if the state changes. For example, water evaporates and becomes vapor at 100°C and ice melts and becomes water at 0°C. *6 This project is being run by the New Energy and Industrial Technology Development Organization (NEDO), an Incorporated Administrative Agency of Japan. OFF ON © 2012 NEC Corporation The NEC logo is a registered trademark or a trademark of NEC Corporation in Japan and other countries. 6
using a UPS or other device in the case of a power outage, in which the indoor temperature rises as time passes. The adoption of HTA servers and storage devices allows operation under such an environment. Before 4.2 Free cooling After *3 The optimal temperature at the air inlet is set to be between 25°C and 30°C, taking into account the cases in which the cooling system stops due to a power outage or other factor, causing the temperature to rise. *4 Calculated based on an electricity fee of 14 Japanese yen/kWh. What is free cooling?* 7 The free cooling method uses outdoor air rather than a chiller in cold seasons when the outdoor air temperature is sufficiently low. In summer when the outdoor air temperature is high, cool air is constantly supplied because the refrigerating machine operates like a normal cooling system. The cooling environment can be stably maintained and the power consumption kept low by controlling the operation of the refrigerating machine. Usually, the cooling system compresses and devolatilizes refrigerant by using a refrigerating machine and volatilizes it by using a heat exchanger to absorb the surrounding heat and cool down the air. This kind of cooling system consumes a large amount of power, because it operates a refrigerating machine throughout the year. If HTA servers or storage devices are implemented in a free cooling environment, outdoor air can be used for a longer period of time, shortening the operating period of the refrigerating machine. This results in a reduction in annual power consumption. Structure of a normal air conditioner system Cooling tower Cooling tower Heat exchanger Heat exchanger Measure to reduce exhaust heat Semicylinder-type capping (rack image from oblique bird’s eye view) Refrigerating machine (compressor) Stopped these three air conditioners Air conditioner (indoor) Structure of a free cooling system (operating environment when outdoor air temperature is low) The refrigerating machine operates like a normal air conditioner systems when the temperature of the outdoor air is high. Cooling Used TempertureC Refrigerating machine (compressor) Air conditioner (indoor) The refrigerating machine is bypassed. 4.3 Direct free air cooling What is direct free air cooling?* 8 In conventional cooling methods, a cooling system is used to cool air in the whole server room to indirectly cool down the ICT equipment. This leads to a large amount of energy consumption. In contrast, the direct free air cooling method takes cold outdoor air into the server room and blows it onto the ICT equipment to dissipate internal heat and let the remaining exhaust heat escape directly outside. This method directly cools down devices, dramatically improving the power efficiency. This results in a significant reduction in facility costs associated with the cooling system and other equipment. Effects of direct free air cooling 1. Reduction in PUE* 9 The PUE (Power Usage Effectiveness) index indicates the energy efficiency of a data center. This is the ratio of the power consumed by the ICT equipment to the power consumed by the whole data center. When the power consumed by the whole data center is close to power consumed by the ICT equipment (that is, the PUE is close to 1.0), the energy efficiency is high. The PUE is approximately 1.9*10 when using a conventional cooling method in which a cooling system is used. This means that the cooling system and other equipment account for almost half of the total power consumption. With the direct free air cooling method, power consumption by equipment is dramatically reduced and the PUE drops to between 1.1 and 1.2*11 indicating improved efficiency. Conventional cooling method : PUE of approx. 1.9 Direct free air cooling method : PUE of 1.1 to 1.2 2. Reduction in power consumption The direct free air cooling method significantly reduces cooling system power consumption. The total power consumed by the data center is reduced by 54% (calculated assuming the use of 50 servers with a power consumption of 200 Wh). 3. Reduction in equipment-related costs Average equipment-related costs in a data center are between four to six million yen per rack when using a conventional cooling method. In contrast, when using the direct free air cooling method, the cost of installing one rack is approximately two million yen because a large cooling system and cooling system installation space are not required. This means a cost reduction of 50% or more (if the building is renovated). Conventional method Approx. 23,000 Wh Reduction of 54% Direct free air cooling Approx. 10,500 Wh Significant reduction in cooling system power consumption —Cooling system using the free cooling method— A hybrid-type cooling system for data centers equipped with a normal refrigerating machine and a refrigerant pump is an example of this kind of cooling system. This solution is useful even in environments in which it is difficult to directly take in outdoor air. Because the refrigerant pump circulates refrigerant and performs direct free air cooling without using the refrigerating machine in cold seasons when the outdoor air temperature is low, cooling system power consumption can be reduced throughout the year. Conventional method Approx. four to six million yen/rack Reduction of 50% Direct free air cooling Approx. two million yen/rack Significant reduction in cooling system costs *7 Select the optimal air conditioning method for free cooling considering the regional climate and geographical conditions. *8 Select the optimal air conditioning method for direct free air cooling considering the regional climate and geographical conditions. *9 PUE = Total power consumption in the data center divided by power consumption by IT devices *10 Quoted by “Consideration on New Data center Power Saving Indicator in Japan, DPPE, in International Conferences” (Green IT Promotion Council, February 28, 2011). *11 Calculated in a data center in Japan © 2012 NEC Corporation The NEC logo is a registered trademark or a trademark of NEC Corporation in Japan and other countries. 7
Page 1 and 2: White Paper Technologies Behind NEC
Page 3 and 4: 2.1 Server cooling technologies Sy
Page 5: 3.1 Direct free air cooling verific

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