Climate protection needs energy efficient data centers - Stulz GmbH

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The requirements for the individual components of a doubleconversion UPS depend to a great extent on the applicationconditions and operational security demands. Theinput power factor should be about 1 to avoid generatorcompatibility issues. This can be achieved through powerfactor correction at the UPS input or by the applicationof so-called IGBTs (Insulated-Gate Bipolar Transistors) inthe UPS rectifier. Possible efficiency losses through powerfactor correction are compensated for by reduced systemperturbations from the IGBT switch. These can affect theinput environment.Thanks to developments in power electronics, it is nowpossible to operate the IGBT inverter without an outputtransformer. This does not impair the quality of theoutput voltage. Apart from avoiding losses in the invertertransformer, it also dispenses with the need for eitherthe galvanic isolation of the battery voltage from theconnected load or the use of a transformer in the outputnetwork configuration. It is therefore eminently advisableto involve specialists at the early stages of consulting andplanning.• 6.4 Redundancy: security and efficiency6.4.1 The conflicting goals of redundancyand energy efficiencyEnergy management has to allow for the required levelsof equipment reliability as well as technical constraints.Whereas the schematic illustration in Fig. 12 supplies noinformation on redundancy in the power supply channels,increasing numbers of organisations are engaged inclassifying power infrastructure according to availabilityrequirements. The best known example of this is probablythe American Uptime Institute’s “Tier Classification”system.Fig. 13 shows a Tier IV configuration calculated to deliver99.99 percent availability.MV Main DistributionMV Main DistributionG G G GCoolingTowerCoolingTowerLV Main DistributionLV Main DistributionChillerUPS UPS STSUPS UPSPDU PDU PDUChillerIT ComponentsULKGSTSULKGULKGIT ComponentsULKGIT ComponentsComputer RoomFig. 13: Infrastructure conforming to Uptime Institute’s Tier IV Classification 1628
Energy Efficiency in the Data CenterSimilar classification systems are offered by IEEE (AvailabilityClasses, Class V is the equivalent of 99.999 percent)and the Harvard Research Group (AEC = AvailabilityEnvironment Classification). A clear, concise data centerperspective on this subject is provided in two BITKOMpublications 17 : a guide and a planning matrix bothentitled “Reliable Data Centers”, which include designsuggestions for the individual installation components.It is also important to strike the right balance betweensecurity and efficiency when developing redundancyconcepts.The typical efficiency curve for UPS systems (Fig. 14)shows low efficiency under low load conditions and thebest efficiency levels at full load. The main reason for thisis that losses occur even when the system is in standbymode and these occur consistently over the entire loadrange. Proportional losses occur as the load increases.The initial ascent of the efficiency curve should be assteep as possible and then flatten out to a plateau. SomeUPS systems operate most efficiently at loads of between50 and 80 percent.Efficiency [%]97%96%95%94%93%92%91%0 20 40 60 80 100Load [%]Low Mains (380 V)Nom. Mains (400V)High Mains (415 V)Fig. 14: Typical UPS efficiency curve (Low mains: 380 V, Nom. mains: 400 V,High mains: 415 V)When UPS systems are operating in continuous operationmode, it is recommended that they are run at a maximum80 per cent load, to provide reserve capacity for suddenload variations and instant expansion.6.4.2 The different UPS configurationconcepts in comparisonSingle module configurationRightsizing is always a critical factor in single module systems,as they are configured to meet future load requirements.They are often oversized for fear that performancelimits will be met too soon. But this leads to underutilizationand unnecessary losses (see efficiency curve of theselected UPS).Dual module parallel system for N+1 redundancy(also 1+1)This is a configuration for individual unit loads of betweenapprox. 20 kVA /kW and 250 kVA /kW, as it offersbetter availability than single module systems. As withthe single module set-up, this system configuration is alsosized to allow for future maximum loads, but with theadded constriction that each module must stay below50% load if the redundancy concept is to be properlyimplemented.Multiple UPS modules operating in parallel for N+1redundancyThis set-up is for individual unit loads of between about20 kVA/kW and 1000 kVA/kW, as it offers better scalabilitythan dual module parallel systems. In this systemconfiguration, an external maintenance bypass switch,sized to meet the desired maximum load and with thecorresponding number of UPS connections, makes itpossible to connect the required number of UPS modulesto meet the momentary load and redundancy level. Whenload demands increase, one or more UPS modules can beadded without compromising normal operations.This ensures better utilization rates than with 1+1 configurationand the UPS systems can be operated with fewerenergy losses.Modular UPS systems with power modules inparallel mode for N+1 redundancyThis set-up has capacity ratings of between about 10 kVA/kW and 200 kVA/kW per individual module and thusoffers better scalability than two or more UPS systemsin parallel operation. The system framework of modular29
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