1 siemens.com/datacenters Distributed Redundancy in data center applications How power supply configurations increase reliability and optimize investment and operational cost White aper November 214 The Information Communication and Technology sector is moving at a rapid pace. It transforms our life vision and generates an increasing demand for centralized processing power and stored information. s a consequence, Data Center facilities grow in both number and size. Over two-thirds of global electricity production is based on the consumption of fossil fuels. Therefore, as major and increasing energy consumers, Data Centers are inextricably linked with global energy challenges and climate change. Generally, the optimal efficiency point (or 'sweet spot') of critical power distribution components occurs at the rated power capacity. However, as a result of redundancy requirements, critical power systems in Data Centers are operated below their rated capacity. Depending on the conceptual design and especially in dual cord server configurations, the critical power system can operate well below % during normal operation. Needless to say that this not an optimal situation from neither the efficiency nor the investment point of view. The conceptual design of the critical power path itself is a major contributor to the maximum operational load of the system during normal operation. The Distributed Redundancy concept is one of the designs that is implemented to increase normal load without sacrificing availability and reliability. It therefore has a positive effect on both investment and operational cost. This white paper elaborates on the design implications of the Distributed Redundant power distribution concept for dual cord server applications. Written by David Meulenbroeks Siemens Center of Competence Data Centers, The Netherlands. Siemens G 214. ll rights reserved 1
2 White paper Distributed Redundancy in data center applications November 214 Contents 3 Distributed Redundancy: the basics 3 Distributed Redundancy over two supply systems 4 Distributed Redundancy over three supply modules 5 Distributed Redundancy over four supply modules 6 General characteristics 7 Impact of Distributed Redundancy on data center facilities 8 cronyms and variables Siemens G 214. ll rights reserved 2
3 White paper Distributed Redundancy in data center applications November 214 Distributed Redundancy: the basics Distributed Redundancy over two supply systems Distributed Redundancy in its simplest form is probably the best known design concept for critical power supply systems in data centers. It is also referred to as the True - design. Figure 1 gives a simplified overview of this design. It shows normal operation as well as the power balance shift in case of a -side main supply fault. The figure presents the two main electrical operational modes for a data center: Normal operation and Emergency operation Normal Operation Emergency Operation Figure 1 Distributed Redundancy over two supply systems (True - design) In this example, the total ICT load [ICT] is presented as the mathematical sum of 6 individual loads of 1 ; the black figures in the picture. These loads are dual cord and it is assumed that the load is equally distributed over both cords, or - ; the green values in the picture. In the Distributed Redundancy nomenclature, the True - design as shown in figure 1 is defined as Distributed Redundancy over two supply systems. With these two supply systems, the 6 loads are combined in a single Group [LG], as there is only one combination of supply feeders: -. In this example the load of this load group equals 6. In normal operation, this configuration results in a cumulated load per ower Supply Module (or ) of 6 3. When in emergency operation - with - off line as shown in figure 1 - the load shifts to the -side supply. The cumulated load for - in that operational mode is therefore equal to the total ICT load [ICT], or 6 6. In this example, the design is characterized by the following Distributed Redundancy parameters: Total ICT load [ICT] 6 Normal load per [norm(2)] 3 Emergency load per [max(2)] 6 Installed base [inst(2)] 1.2 The index "2" in the variables [E.g. max(2)] indicates to Distributed Redundancy over two supply systems. 1 Neither the unit (W, kw or kv) nor the absolute value of the figures mentioned has significance in this example as the relation between the figures of the different configurations are relevant, not their absolute value. Siemens G 214. ll rights reserved 3
4 White paper Distributed Redundancy in data center applications November 214 When considering the ICT-load exclusively (thus excluding power requirements for cooling or other auxiliary systems), the nominal power rating of the is to be equal or larger than the Emergency load on each : max(2). In the example above, max(2) equals ICT and is 6. From these results, the following general relations can be derived. These are exemplary for Distributed Redundancy over two supply systems. The normal load relative to the emergency load per is: Normal load per norm ( 2 ) 3 % Emergency per ( ) 6 max 2 The installed base 2 inst relative to ICT equals: Total installed base inst( 2 ) 12 TotalICT load 6 ICT 2% Distributed Redundancy over three supply modules When an additional ower Supply Module is introduced in the design of figure 1, and the load is equally distributed over all three of the 's, the configuration of figure 2 is obtained. Following the nomenclature introduced above, this design is referred to as Distributed Redundancy over three supply systems. gain, for this example, the ICT load [ICT] equals 6. The loads are distributed over all combinations of 's. This results in a total of 3 Groups [LG] -, -C and -C each with a normal load of C 3 3 C Normal Operation Emergency Operation Figure 2 Distributed Redundancy over three supply systems nalogous as described for Distributed Redundancy over two supply systems previously, in this example Distributed Redundancy over three supply systems is characterized by the following parameters: Total ICT load [ICT] 6 Normal load per [norm(3)] 2 Emergency load per [max(3)] 3 Installed base [inst(3)] 9 2 The installed base inst(n) refers to the nominal output of the. This excludes any redundancy inside the as for example N+1 configured modular US systems. Siemens G 214. ll rights reserved 4
5 White paper Distributed Redundancy in data center applications November 214 The general relations for Distributed Redundancy over three supply systems are therefore: The normal load relative to the emergency load per : Normal load per Emergency per norm max ( 3 ) ( ) % 3 Installed base relative to ICT: Total installed base inst( 3 ) 9 TotalICT load 6 ICT 1% Distributed Redundancy over four supply modules When the three design of figure 2 is expanded with an additional module, the four configuration of figure 3 is obtained: Distributed Redundancy over four supply systems. The example is based on a total ICT load ICT of 6. nd again, the loads are distributed over all combinations of 's: -, -C, -D, -C, -D and C-D. This results in a total of 6 Groups with a load of each C D C D Normal Operation Emergency Operation Figure 3 Distributed Redundancy over four supply systems In this example Distributed Redundancy over four supply systems is characterized by the following parameters: Total ICT load [ICT] 6 Normal load per [norm(4)] 1 Emergency load per [max(4)] 2 Total installed base [inst(4)] 8 Siemens G 214. ll rights reserved 5
6 White paper Distributed Redundancy in data center applications November 214 The generic relations for Distributed Redundancy over four supply systems become: Normal load relative to the emergency load per : Normal load per Emergency per norm max ( 4 ) ( ) % 2 Installed base relative to ICT: Total installed base inst( 4 ) 8 133% TotalICT load 6 ICT General characteristics Theoretically, the Distributed Redundancy principle can be expanded infinitely by adding ower Supply Modules. s a result, both norm( )/max( ) and inst( )/ICT will approach %. In the limit situation - an infinite number of 's - the normal load of the will equal the emergency load. lso, the installed base will equal the total ICT load. From an installed base and efficiency point of view, this limit situation might look like ideal. However tempting, this limit obviously represents a hypothetical configuration. With the increasing number of ower Supply Modules, the number of Groups will also become infinite as it equals the sum (#-1). ut besides being infinite in number, these Groups will have a maximum load value max(lg ) that approaches. Furthermore, the distribution system is going to be infinite as well. Not a very useful configuration. Table 1 summarizes the main characteristics of the Distributed Redundancy principle with an increasing number of ower Supply Modules. Number of supplies Table 1 Main characteristics of Distributed Redundancy with increasing number of 's Number of Groups Ratio of normal and emergency load on supply Ratio of installed base and load Ratio of load group load and emergency load on supply # [n] # LG norm(n)/max(n) inst(n)/ict max(lgn)/ max(n) 2 1 % 2 % % % 1 % 67 % % 133 % % % 125 % 4 % % 12 % 33 % % 117 % 28 % % 114 % 25 % From this table we can conclude that - depending on the application - the optimum configuration for Distributed Redundancy is somewhere between 4 and 6 ower Supply Modules: elow 4 Modules there is relatively much to be gained by adding a as the ratio norm()/max() significantly increases and the number of Groups remains manageable. bove 6 Modules the ratio norm()/max() flattens and the number of Groups becomes impractical to handle. Siemens G 214. ll rights reserved 6
7 White paper Distributed Redundancy in data center applications November 214 Impact of Distributed Redundancy on data center facilities When selecting optimal power architecture for a facility, data center managers have to consider different factors and understand the impact of each one on their facility. When designing the electrical power distribution configuration, the data center designers need to consider both initial and future load demands. s a result, many data centers are operating at significantly less than percent of design load much of the time. Considering the right power distribution load balancing design before a facility is constructed, is a good way to move to cost efficient data center without compromising on reliability. When correctly implemented and maintained, the Distributed Redundancy principles meet with the reliability criteria. It can be applied to the power distribution level of redundancy requested for the data center (N, N+1, 2N, 2(N+1); etc.). Distributed Redundancy can definitely provide both flexibility on power capacity and cost control optimization without losing data center reliability. Siemens G 214. ll rights reserved 7
8 White paper Distributed Redundancy in data center applications November 214 cronyms and variables ICT LG ICT inst max norm US Information and Communication Technology Group ower Supply Module Sum of critical load Installed power: sum of total installed ower Supply Modules in emergency operation mode in normal operation mode Uninterruptible ower Supply Siemens G uilding Technologies Division International Headquarters Gubelstrasse Zug Switzerland Tel Siemens G Energy Management Division Freyeslebenstrasse Erlangen Germany ll rights reserved. ll trademarks used are owned by Siemens or their respective owners. Siemens G 214 Siemens G 214. ll rights reserved 8
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