Uninterruptible Power Supplies; A Data Center Efficiency 0 California Energy Commission's Public Interest Energy Research Program Technical Brief A1. ºu.” S.J PER Buildings Program Research Powers the Future º - www.energy.ca.gov/research The Problem Data centers depend on uninterruptible power supplies (UPSs) for continuity of service in the event of a power outage. These systems were believed to consume a large amount of energy in both standby and active modes, yet until now that energy use has not been accurately characterized. Also, UPSs vary widely in efficiency but data on efficiencies of existing products have not been compiled and there has been no uniform labeling requirement to encourage the use of more efficient UPSs. The Solution A detailed study characterized the efficiencies of various types of UPSs under a variety of operating conditions, proposed an ef- ficiency label for UPSs, and estimated the current energy use of the existing stock of UPSs and the potential savings if effic standards were in place. Features and Benefits By characterizing current UPS efficiencies and estimating their savings potential, the study provides results that could help to develop a market for more energy-efficient UPSs. Current efficiencies. Measurements of efficiency were taken under controlled factory conditions and in the field for a number of dif- ferent types of UPS. Efficiencies varied widely, even among units of the same type (Table 1). All types tend to be more efficient at full load than at partload—an important observation because UPSs in a data center environment typically operate at or below 50 percent of their rated active power output. This is primarily because they are often part of a redundant system in which they share the load with another UPS but must be sized to carry the full load. The measured efficiency of a given UPS also decreases by 1 to 2 per- cent when meeting nonlinear loads such as the switch mode power supplies used in low-end servers. The most efficient configurations were flywheel and delta-conversion designs. The UPS types found to be most relevant for data centers include: In Delta conversion, which is a proprietary topology that uses a special transformer configuration to interface between the load and utility power, with a “delta” inverter in the trans- former secondary to regulate input current and power. | Double conversion, also called “online,” is the most com- mon configuration because it is capable of completely isolat- ing sensitive IT loads from unconditioned utility power. In Line-interactive, which allows the load to be powered from the line until a disturbance is detected, at which time the load is disconnected from the line and fed from an energy storage device—batteries, capacitors, or flywheels. This ap- proach can be quite efficient because under normal condi- tions, the load is directly connected to the source. Proposed efficiency labels. The wide range in UPS efficiency suggests an opportunity to encourage higher-efficiency designs through product labeling and standards. To promote UPS en- ergy efficiency, the researchers designed a product label that lists efficiency in different modes of operation, estimates the annual energy consumption, and shows where a product falls in relation to the highest available efficiencies (Figure 1). The bel design is based on a proposed European label, which ould help to harmonize international efforts to promote 'PS efficiency. Energy use and savings potential. Researchers estimate that the data center/IT sector uses roughly 7.1 billion kilowatt- hours (kWh) of electricity per year. In California, home to about 15 percent of the nation's data center floor space, data center UPSs consume about 1 billion kWh of electricity— about 0.41 percent of the state's electricity use. The introduction of efficiency standards would result in consid- erable savings—nationwide, about 2.8 terawatt-hours (TWh) per /~ Table 1: UPS efficiency varies with type and load N The efficiency of UPSs varies widely even for units of the same type. Full-load efficien- cies are higher than part-load efficiencies. Efficiency UPS type at 25% load at 50% load at 75% load at 100% load Delta conversion 93-94 96-97 97 97 Double conversion 81–83 85-94 86-95 86–96 Line interactive NA 97–98 98 98 Standby NA NA NA NA Average of all units 86 - 89 90 90 Notes: NA = not available, UPS = uninterruptible power supply. \ A straight average was used in the table, _/ 2- Figure 1: Proposed UPS efficiency label N California Codes and Standards g=co An energy-efficiency label Such as the One shown here would enable buyers to # * consider energy efficiency as one of their criteria for buying an unintemptible Currently, there are no standards for UPS in California. #F" power supply UPS system. The label's designed to be similartoone proposed by However, this research may be used to guide future standard- <=N- the Swiss Federal Office of Energy. setting efforts or the adoption of a voluntary label approach. :=-5 - - 9 G- Uninterruptible Power Supply What's Next $EQN Energy Efficiency Label :=& This work inspired a demonstration of the benefits of elimi- #=- Manufacturer XYZ Company - - - g Brand xyz Brand nating some of the typical data center power-conversion 5=CO model | xyz Mºdel steps. The demonstration showed how direct current (DC) | Nominal Power wºrkva xxxi xxx power could be effectively used in data centers. Both this Mudu uſ Operation =[º]. ----- UPS study and the DC power demonstration have raised Conversion Efficiency Categories' awareness of the opportunity to improve power distribution | > (A efficiency. Organizations such as Green Grid, an associa- |Bºº B - - - - - == tion of IT professionals seeking to raise the energy efficiency |EFFET KD of data centers (www.thegreengrid.org), are examining the LConversion Efficient, 29.0% TEX - ibili - f - h - - - - OSS1D111tles for Dutting theSe measures 1ntO Dract1CC. [conversion Efficiency -88% FX p p g p |Conversion Efficiency «58% GX | Energyrosses whives" --- Collaborators ----------------------, :::...…. | E The organizations involved in this project include Lawrence ºr:-------- - Berkeley National Laboratory and its subcontractors, EPRI \ _/ Solutions, and Ecos Consulting. For More Information year with a mandatory program and 0.71 TWh/year with 25 percent compliance in a voluntary program. In California, cor- responding savings would be 0.42 TWh/year and 0.11 TWh/ year. Even more savings would result if UPSs installed in small offices, industrial facilities, hospitals, and units smaller than 5 kilovolt-amps (kVA) were included in the analysis. For more information, please contact the California Energy Commission researcher listed below. A Microsoft Excel calculator for estimating savings from more efficient UPSs and other measures is available at http://hightech.lbl.gov/server-ps-tool.html. More PIER Technical Briefs can be found at www.energy.ca.gov/research/techbriefs.html. COntacts California Energy Commission, Paul Roggensack, proggens@energy.state.ca.us, 916–654-6560 Accounting for reduced facility cooling needs would almost double the savings potential. Less cooling would be required because less waste heat is generated from the conversion and storage equipment. Up-front savings are also possible from reduced capital investment in equipment and reduced real- estate investment from smaller equipment footprints. Applications - The data and analysis apply to the data center/IT market, which accounts for about two-thirds of installed UPS units in the U.S. The analysis also excludes units smaller than 5 kVA. Lawrence Berkeley National Laboratory, Bill Tschudi, wftschudi albl.gov, 510-495-2417 Electric Power Research Institute, Brian Fortenbery, bfortenberyQepri.com, 865-218–8012 About PIER º º This project was conducted by the California Energy Commission's Public Interest Energy Research (PER) Program. # G r PIER supports public interest energy research and development that helps improve the quality of life in California ** by bringing environmentally safe, affordable, and reliable energy services and products to the marketplace. *Research Powers the Fºrture" Arnold Sch G F informati / h CEC-500-2008-065-FS rnold Schwarzenegger, Governor or more information see www.energy.ca.gov/researc September 2008 California Energy Commission Chairman: Jackalyne Pfannenstiel Vice Chair: James D. Boyd Commissioners: Arthur H. Rosenfeld, Jeffrey Byron, Karen Douglas