《Eco模式UPS节能运行模式的收益和风险.pdf》由会员分享，可在线阅读，更多相关《Eco模式UPS节能运行模式的收益和风险.pdf（13页珍藏版）》请在taowenge.com淘文阁网|工程机械CAD图纸|机械工程制图|CAD装配图下载|SolidWorks_CaTia_CAD_UG_PROE_设计图分享下载上搜索。
1、 Eco-mode:Benefits and Risks of Energy-saving Modes of UPS Operation by Neil Rasmussen Introduction 2Eco-modes described2Efficiency improvements5Loss of protection 7Reliability impacts 9Effect on operations10Conclusion 12Resources 13 Click on a section to jump to it Contents Revision 1 White Paper 1
2、57 Many newer UPS systems have an energy-saving operating mode known as“eco-mode”or by some other descriptor.Nevertheless,surveys show that virtually no data centers actually use this mode,because of the known or anticipated side-effects.Unfortunately,the marketing materials for these operating mode
3、s do not adequately explain the cost/benefit tradeoffs.This paper shows that eco-mode provides a reduction of approximately 2%in data center energy consumption and explains the various limitations and concerns that arise from eco-mode use.Situations where these operating modes are recommended and co
4、ntra-indicated are also described.Executive summary white papers are now part of the Schneider Electric white paper libraryproduced by Schneider Electric s Data Center Science Center Data Center Science Center DCSCSchneider-E Eco-mode:Benefits and Risks of Energy-saving Modes of UPS Operation Schnei
5、der Electric Data Center Science Center White Paper 157 Rev 1 2 The growing financial and environmental costs associated with the energy use of data centers has given rise to an appropriate drive to improve the efficiency of data center power and cooling systems.Efficiency improvements reductions in
6、 PUE can be accomplished at a number of levels in the data center:Overall system architecture Scalable,right-sized system design Better efficiency of individual devices Operational decisions Eco-mode is a benefit/risk decision here This paper will focus on a particular technique for improving the op
7、erating efficiency of a double-conversion UPS by operating it in eco-mode,traditionally called“bypass”.Eco-mode is a method of operating the UPS at reduced power protection in order to obtain improved electrical efficiency and save energy,and is marketed by vendors under a variety of names(see box,l
8、eft).This paper will address the following subjects What is eco-mode,and how does it work?What efficiency gains are possible and expected?Loss of protection and reliability associated with eco-mode Operational considerations Eco-mode will save energy,although the amount saved is surprisingly small.I
9、n addition,the energy saved comes at a significant cost in electrical protection and reliability.Some data center operators will decide the energy savings are worth the risks and problems,but many will not.Much of the marketing literature associated with UPS eco-mode is vague and describes it as a r
10、evolutionary new technology with little or no downside risks.This is misleading,because this mode of operation has been around for decades and,in fact,is the basic mode of operation used in offline UPS where it is called“standby”or“line interactive”mode1.All large double-conversion online UPSs are e
11、quipped with a“static bypass”path,which provides multiple features including acting as a source of redundancy for the UPS power inverter.This is shown schematically in Figure 1.1 See White Paper 1,The Different Types of UPS Systems Introduction Eco-modes described Eco-mode has many names Technical n
12、ames Bypass Vendor names ESS Energy Saving System SEM Super Eco-Mode VFD Voltage and Frequency Dependent Maximum energy saving mode Eco-mode:Benefits and Risks of Energy-saving Modes of UPS Operation Schneider Electric Data Center Science Center White Paper 157 Rev 1 3 There are two main paths that
13、can supply the load,the online(double conversion)path and the bypass path.Note that the load is connected to the raw2,unconditioned mains power when the bypass is active.The following table shows when each path is used in both online and eco-mode operation:Online mode Eco-mode Comment Normal operati
14、on Rectifier/Inverter Bypass Eco-mode exposes the load to raw mains During a power Disturbance Inverter Inverter Online mode requires no path change during power disturbances During a fault condition Bypass Bypass Extremely rare event Note that in online operation the UPS uses the bypass path only w
15、hen there is a fault.In the life of the UPS,this is an infrequent event and may actually never happen.Therefore,in online mode the critical load is not subject to power disturbances,even during a mains power problem.In eco-mode,any mains power abnormality causes the UPS to switch power paths between
16、 bypass and inverter.2 The term“raw mains”in this context means power that has the same voltage,waveform,frequency,grounding system,and impedance as the mains.Note the mains itself may have some parallel protection such as surge suppression.In some cases a transformer is added to the bypass path,whi
17、ch changes the ground system and impedance,but not the waveform or frequency.A UPS may also have output capacitors present between the voltage phases or between phase and ground;such capacitors do provide some filtering of high frequency noise,but do not correct frequency,voltage,or waveform;in fact
18、 they can actually make voltage distortions worse by adding resonances like those seen in the later Figure 2.RECTIFIERBATTERYINVERTERSTATIC BYPASSSWITCHDCACDCACFigure 1 Simplified schematic diagram of power flow of a UPS Bypass path Online path Table 1 Power path used by a UPS showing differ-ences o
19、f Eco-mode Eco-mode:Benefits and Risks of Energy-saving Modes of UPS Operation Schneider Electric Data Center Science Center White Paper 157 Rev 1 4 In online mode,the UPS continuously regenerates the output voltage.In eco-mode the load is normally powered by the bypass path,allowing raw mains power
20、 to supply the load,and the UPS inverter is engaged only when the utility mains fails.In eco-mode the UPS inverter operates in a“standby”mode.In principle,this is a simple change in the control software of the UPS.However,the reality is considerably more complex as explained in the later sections of
21、 this paper.The benefit of eco-mode is that the efficiency of the bypass path is typically between 98.0%and 99%,compared to the base UPS efficiency of 94%to 97%.This means there is a pickup in UPS efficiency of between 2-5%in UPS efficiency when eco-mode is used.The cost of eco-mode is that the IT l
22、oad is exposed to raw utility mains power without the conditioning normally provided by the UPS.The UPS must continuously monitor the mains power and quickly switch to the UPS inverter when a problem is detected,before the problem can affect the critical load.This may sound simple,but actually is qu
23、ite complicated and entails a number of risks and has some potentially undesirable side-effects,as explained later in this paper.An example of an output voltage waveform of an actual UPS with eco-mode responding to a power failure is shown in Figure 2.Note that this vendor claims a detection and tra
24、nsfer time response of 1.2 milliseconds to a power failure performance that is clearly not attained in this example.Different vendors implement eco-mode differently.There are variations in the way the system operates the standby inverter.There are variations in the way the mode is enabled,where it w
25、ill revert to normal UPS mode under various conditions.Some vendors claim to have special patented ways to control their transfer switch.But they all have the same basic concept of exposing the IT load to unconditioned power and transfer events in return for a gain of a small percentage gain in effi
26、ciency.It is important to note that most UPS systems offering eco-mode do not require its use.This is a mode that can be enabled by the customer.In fact,when APC first offered eco-mode in the 1990s on larger UPS systems,we found that no customers actually used the feature.Nevertheless,the recent dri
27、ve to reduce data center energy use has renewed the interest in eco-mode for UPS systems.Figure 2 Output voltage wave-form of a 275 kVA UPS in eco-mode responding to a power failure Upper waveform is output voltage,lower waveform is output current Eco-mode:Benefits and Risks of Energy-saving Modes o
28、f UPS Operation Schneider Electric Data Center Science Center White Paper 157 Rev 1 5 The UPS system is one of many contributors to the overall inefficiencies(electrical“losses”)of the data center,and its typical contribution to the data centers PUE is shown in Figure 3.Note that the vertical axis o
29、f the graph begins at 0.8 not at zero to show detail.The IT load always contributes exactly 1.0 to a PUE value.The contribution of the UPS to the PUE is in two parts:the energy used by the UPS itself at around 9%,and the energy used to cool the heat produced by the UPS at approximately 5%.The PUE co
30、ntribution of the UPS electrical losses is equal to the UPS loss expressed in a percent of the IT load.The PUE contribution of the UPS cooling load is equal to the UPS loss divided by the marginal Coefficient of Performance3(COP)for the cooling plant.To illustrate how these UPS-caused losses contrib
31、ute to a typical PUE value,these losses are the topmost two segments of the bar in Figure 3.The above figure represents the installed base of data centers,with a typical PUE of 1.93.However,the installed base is comprised of older equipment that does not represent the current generation of devices u
32、sed in data centers.Using current-generation equipment in a higher density data center design we achieve a better PUE as shown in Figure 4.3 The marginal COP is the incremental cooling capacity in watts created per incremental watt of power needed by the cooling plant.Typical values range from 2-6 a
33、nd are typically much better(larger)than the overall cooling plant COP,which is reduced by the presence of fixed loads such as fans and pumps.Efficiency improvements Figure 3 PUE of a typical data center,showing how energy consumption of UPS and other systems contribute to the total PUE 0.801.001.20
34、1.401.601.802.00typicaldesignUPScoolingUPSallotherpowerallothercoolinglightingITloadEco-mode:Benefits and Risks of Energy-saving Modes of UPS Operation Schneider Electric Data Center Science Center White Paper 157 Rev 1 6 Note that a new data center with a PUE of 1.54 is significantly better than th
35、e installed base value of 1.93.In fact,the energy bill for a given IT load is directly proportional to the PUE,so we can say that a current generation data center will typically have a 20%reduction in energy use for the same IT load,when compared with the typical installed base.We can now add a thir
36、d entry to the chart to show the PUE improvement of using eco-mode,as shown in Figure 5.When eco-mode is engaged,the UPS loss drops from 4%to 1.5%(corresponding to an efficiency improvement from 96%to 98.5%),but the PUE only falls from 1.54 to 1.50.This represents a savings of total energy use of 2.
37、3%4.In this analysis,it is assumed that the data center is operating at 50%load using modern UPS systems.The result is that,as a rule:4 Total energy use savings of 2.3%was computed from the PUE values of 1.536 and 1.500 derived from the losses in the bar charts.Figure 4 Typical PUE of data centers,s
38、howing im-provement of PUE of current designs compared with installed base Figure 5 Typical PUE of data centers,showing im-provement of PUE of current designs compared with installed base 0.801.001.201.401.601.802.00typicaldesignnewdesignUPScoolingUPSallotherpowerallothercoolinglightingITload0.801.0
39、01.201.401.601.802.00typicaldesignnewdesignEcomodeUPScoolingUPSallotherpowerallothercoolinglightingITloadEco-mode:Benefits and Risks of Energy-saving Modes of UPS Operation Schneider Electric Data Center Science Center White Paper 157 Rev 1 7 The energy savings associated with the use of UPS eco-mod
40、e is approximately 2.3%,corresponding to an energy savings of about US$15,000 per year for a 1 MW rated data center at 50%load with an electric rate of$0.10/kWh.The actual energy saved will depend on the specific equipment and architecture chosen,the loading of a particular data center,and the local
41、 cost of electricity,but the above is a reasonable estimate of the savings that applies to a typical situation.It is interesting to see that,in general,the percent savings in total energy for a data center will be slightly less than the percent UPS efficiency improvement.Many discussions of eco-mode
42、 suggest that the total energy savings will be much more than the UPS efficiency improvement5,but these analyses have made incorrect assumptions about how UPS losses contribute to the PUE,and how UPS losses contribute to air conditioner energy use.While 2.3%is not a major efficiency pickup,it is val
43、uable.Unfortunately,there are conse-quences associated with operation in eco-mode,which must be fully comprehended in the decision to use this mode and gain its efficiency improvement.These considerations are:Loss of electrical protection Reliability impacts Operations issues These factors frequentl
44、y cause operators to decide against using eco-mode,and will be discussed in the following sections.A key function of a UPS system has historically been to regenerate“clean”electrical power without the variations of voltage,variations of frequency,or transients that are present on raw utility mains p
45、ower the central concept being that such variations would interfere with the operation of sensitive IT systems.However,remarkable improvements have occurred in the characteristics of IT equipment,such that virtually all equipment sold today is immune to mains frequency variations and designed to acc
46、ommodate any variations of mains voltage within a specified operating range.It is a fact that IT equipment today,in order to run reliably,requires less power conditioning than in prior decades.In the case of the modern personal computer,it will operate reliably if it can be assured that mains voltag
47、e does not drop more than 20%for more than about 8 milliseconds,and that damaging surge voltages are filtered.In principle,this can be achieved by a standbytype desktop UPS,which is essentially a UPS permanently running in eco-mode.Naturally,this suggests that an entire data center might be run in s
48、uch a standby or eco-mode.However,the load in a data center is not like a large personal computer.The UPS load in a data center is a complex system of circuits including many different types of IT equipment and transfor-mers,possibly including other complex devices such as static switch PDUs,fans,an
49、d pumps.5 Example of incorrect analysis quoted in“Raising UPS Efficiency with Eco-mode”,UPSonN:“The gain in Eco-mode is quite tempting.In average about 3.5%power saving is gained,just considering UPS efficiency.Taking in account also cooling requirements,close to 9%of output power can be spared.”In
50、fact,a 3.5%power savings in UPS efficiency will only translate to about a 3.2%savings in total energy.Loss of protection Eco-mode:Benefits and Risks of Energy-saving Modes of UPS Operation Schneider Electric Data Center Science Center White Paper 157 Rev 1 8 While a personal computer can be well cha