As we pointed out in a recent article, “modular UPS lays the foundation for right-sizing. The infrastructure of a data centre can be correctly sized from the outset and can then grow over its lifetime as a function of increasing requirements. At the same time, a correctly sized 40 kW UPS working at a capacity of 90 % for example, renders a 94.5% efficiency, whereas an incorrectly-sized (i.e. over-dimensioned) UPS working at a capacity of 25 % will merely render an inferior efficiency of 91 %.”
A few days ago Schneider Electric released the revised version of a white paper titled “Making Large UPS Systems More Efficient” (pdf-Download). This highly recommended document discusses the common errors and misunderstandings in evaluating UPS efficiency, quantifies their cost implications and provides further details about the effects of right-sizing. Overall, the author concludes that right-sizing modular UPS reduces the total costs of the system by 40-50% in ten years. For more information have a look at the paper linked above.
By the way: If you are interested in details about your potential savings, the site High-Performance Buildings for High-Tech Industries offers an Excel-based calculator for download, that provides a first-order estimate of the magnitude of the energy savings based on improving the efficiency of any one or more of the elements (UPS, AC-DC and DC-DC power supply) involved in powering a rack of servers.