The Impact of UPS Design on Efficiency

Efficiency is a critical factor to consider when determining the optimal uninterruptible power system (UPS) for your environment. While efficiency can have a dramatic effect on operating costs, there are several dynamics that influence the level that a UPS will actually achieve. In our last blog, we explored how varying load capacities can cause the same UPS system to deliver significantly different levels of efficiency. Another influence is UPS design, where elements such as bypass mode and transformer type affect not only efficiency but also reliability.

Running on bypass
It is essential to look beyond the advertised efficiency rating of a UPS and instead, evaluate how a UPS’s load level will impact that number. The same can be said when it comes to a unit’s operation mode; be sure to distinguish if the advertised efficiency rating denotes a UPS in bypass mode or if it actually represents your preferred manner of operation. By operating in bypass mode — also known as energy-saving mode, high-efficiency mode, eco-mode or sleep mode — some UPS systems are able to achieve 99 percent efficiency.

The pros and cons of bypass systems can vary widely depending on the manufacturer, the model of the UPS, and even its compatibility with your own facility. It is also important to understand exactly how the unit achieves bypass operation. Some considerations are whether a static switch is utilized; if the inverters go off or idle; and the types of faults that might be passed to your critical load. Your UPS service provider is a great resource to ask when you are attempting to determine the possible risks and rewards of operating in bypass mode.

The presence of a transformer
A transformerless design is another way to improve efficiency and reduce operating costs. Unlike a transformer-based UPS, those with a transformer-free design can typically boost energy efficiency from 90 to 96 percent.

Another advantage of the latest transformerless designs is that their high operating efficiency extends over a much wider operating load curve, with the ability to achieve online operational efficiencies of 97.5 percent from full load down to 25 percent of load. In addition, transformerless UPSs are lighter weight and often have a smaller footprint, further reducing investment and operating costs.*

Above complements of Chris Diaz, Unified Power.

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