The Green Grid recently announced public availability of a white paper that touches on a subject that is near and dear to us at Schneider Electric: energy efficiency with respect to UPSs.
The paper, titled “Evaluation of Eco Mode in Uninterruptible Power Supply Systems,” provides an extensive look at how using eco mode can improve data center efficiency and overall Power Usage Effectiveness (PUE) – saving significant sums of money in the process. Schneider Electric, of course, is on the forefront of energy efficient UPSs, having been the first company to achieve Energy Star qualification for a UPS.
The white paper, previously available only to Green Grid members, explains in great detail how best to employ eco mode and some of the key considerations. Chief among those considerations are understanding the quality of the power you’re getting from the local utility and the ride-through requirements of your IT power supplies, meaning the length of time that the IT equipment can continue to function during a complete loss of power.
The power supply units (PSUs) of IT equipment (ITE) are designed to store a small amount of electricity in capacitors, providing ride-through time in the event of a power failure. We’re only talking milliseconds here, however, typically 10 ms to 50 ms.
Here’s why ride-through time is important to eco-mode operation, according to the white paper:
As stated above, every PSU will have a different supported ride-through time. Prior to implementation, it is imperative to know the ride-through capabilities of every ITE PSU that will be powered by the UPS and to know the transfer time of the UPS operating in Eco Mode. For example, if an Eco Mode UPS has a transfer time of greater than 10 ms, and it is paired with IT equipment that has ride-through capabilities of only 10 ms, the UPS may not be able to support the IT equipment. Therefore, Eco Mode is not a solution that should be implemented in that data center.
With respect to utility power quality, the issue is whether power is within the voltage tolerance of the ITE power supplies and the UPS eco mode voltage settings. Again quoting from the white paper:
When the utility power quality is outside the voltage tolerance, the UPS will transition to a more protective mode (VFI or VI) and the efficiency could be lower than expected. Understanding the quality of the utility power is important for deploying UPS Eco Mode in such a way that the data center will realize the expected energy efficiency improvements.
When the stars align, however, those energy efficiency improvements can provide significant savings, and the paper goes into some detail on how to estimate what they might be. While warning that results will vary depending on various factors, The Green Grid provides an estimate of savings as a function of IT load, in kW or MW). The savings ranged from less than $100,000/year savings for 1 megawatt (MW) IT load to almost $500,000 per year for 5 MW load in a legacy data center. The paper details the assumptions behind those estimates.
It also gives a long-term view of how those savings add up over the typical 10-year operating life of a UPS, using a net present value calculation. The savings range from more than $20,000 for a 100kW IT load to almost $1.2 million for a 5MW IT load.
Figures like that should grab the attention of any data center operator. Check out The Green Grid white paper for all the details. While you’re at it you may also want to read a white paper APC by Schneider Electric published a while back on the same topic, no. 157, “Eco-mode: Benefits and Risks of Energy-saving Modes of UPS Operation.”