With government and private-sector pressure to reduce data center operating costs and related energy usage, manufacturers of uninterruptible power supply (UPS) systems have made design improvements to improve operating efficiencies.
Data center industry organizations such as The Green Grid Association1 strongly recommend the use of new multimode UPS system technologies that allow for operating efficiencies in the 98 to 99 percent range in lieu of older, legacy single-mode UPS systems that operate in the 93 to 95 percent range. Currently, about 50 percent of large UPS system manufacturers employ multimode technology with fast transfer logic. This type of UPS will most likely grow significantly in the next five years.
What is a Multimode UPS System?
Multimode UPS systems offer data center operators the ability to select between two operating modes: double-conversion mode, which provides premium power protection, and multimode or “ecomode,” which provides premium operating efficiency. When the user selects multimode as the default operating mode to achieve 98 to 99 percent efficiency, the UPS system will automatically transfer to premium protection mode in less than two milliseconds (ms) if a power anomaly is detected on the UPS input. In the U.S., power anomalies that are harmful to information technology (IT) critical loads typically represent only three percent of total annual operating hours, so switching between operating modes will most likely be minimal throughout the year.
Double-conversion mode is the classic power-protection mode that has served in large UPS systems for decades, but its Achilles’ heel has always been mediocre operating efficiency in the 93 to 95 percent range. Users today are demanding better UPS operating efficiency and a lower total cost of ownership (TCO) without sacrificing adequate power protection. That is what multimode UPSs are all about.
A study by Frost & Sullivan2 revealed that energy consumption for a 50,000-square-foot data center could be reduced by $3.1 million over 10 years simply by using multimode UPS systems and operating in multimode for the majority of the time. These savings come from decreased energy usage by the UPS system and decreased load on the heating, ventilation and air conditioning (HVAC) systems used to overcome the UPS system’s heat rejection. With a continued rise in utility costs, energy savings from multimode UPSs will only become larger over time.
TCO Plus Other Multimode Benefits
Multimode UPSs offer other advantages in addition to TCO and lower energy usage. This technology provides a level of “smart” input-power monitoring in which the UPS will record the number and frequency of input-power anomalies that cause transfers from multimode to double-conversion mode. Excessive or frequent power anomalies will “lock out” the UPS from multimode for a period of time, allowing the utility power some time to stabilize. Thus, multimode UPS systems make smart, real-time logic decisions about when to use multimode or double-conversion mode to maximize protection of the critical load without sacrificing operating efficiency.
A second benefit of multimode UPS systems is extended parts life. During multimode operation, many UPS module components operate at low current and in low thermal ranges, thus allowing for life extension. Other components, such as fans, don’t operate at all. Manufacturers of multimode UPSs expect many components to have a minimum life extension of one to two years.
A third benefit of multimode UPS systems is output-fault mitigation. Any UPS output short circuit or large overload will quickly be handled by upstream overcurrrent protection without any internal transfers of operating modes in the UPS system. These UPS output faults will be put directly on the source impedance of the utility in lieu of the “softer” UPS inverter source.
Some manufacturers, such as GE’s Critical Power business, have designed additional unique features into their multimode systems, which GE calls eBoost technology. These features include the use of a line reactor in the ecomode power path that provides a level of power conditioning while in this high-efficiency mode; specifically, it mitigates high-frequency “surge” events and lower-frequency “ring waves” so that transfers to double-conversion mode will be minimized. This reactor design also allows a cable length differential of up to +/- 25 percent for the cabling of multiple UPS modules to a parallel output bus. This cable length differential also provides enhanced flexibility in floor-layout design. Some other UPS manufacturers must keep the cable length differential to +/- 10 percent or risk UPS power derating or improper parallel UPS operation.
The reduction in operating expense (opex) from multimode UPS systems, coupled with the additional advantages noted above, provide many compelling reasons for data center users to employ this UPS technology for the foreseeable future. Multimode UPS technology should also be considered for other mission-critical and/or critical-process applications, especially for large power applications 225kVA and above, where energy consumption is a key concern.
Note: The figures cited in this article unless otherwise noted, are based on industry-standard information or data collected by GE in the deployment of critical power systems. The results cited in this article are not a guarantee of performance or specific results, and individual results may vary based on specifications and operating conditions.
(1) Green Grid Association, Evaluation of Eco Mode for UPS Systems, The Green Grid Forum, 2012
(2) Frost & Sullivan, Analysis of the Global Data Center Uninterruptible Power Supplies Market, Dec. 19, 2013
About the Author
Raymond Prince is Commercial Segment Leader, Americas, Uninterruptible Power Supply (UPS) Systems, for GE’s Critical Power business.