UPS Efficiency Part 3: ECO-Mode and the 3-Button Suit Coat Rule

3 Button Coat Rule

For today’s professionals, business casual is the norm. But on occasion, I find myself having to wear a suit/sport coat for important meetings. I often found myself wondering which buttons I should on the front, until I discovered the “Sometimes, Always, Never” rule. Since most suit/sport coats have 3 buttons, the rule states you should “sometimes” button the top button, “always” button the middle button, and “never” button the bottom one. What does this have to do with UPS Efficiency? Read on to find out.

In the previous portion of this series, we covered why UPS Efficiency is important. In this part, we will review one of the common UPS efficiency features that is hitting the market: Eco Mode. Is this feature able to deliver the efficiency clients require without sacrificing reliability? Like the suit coat rule, the answer is “Sometimes. Always. Never.”

Before we discuss “Sometimes, Always, Never,” let’s briefly define what Eco Mode really is.
EcoMode is essentially UPS operation in “off-line” or “line-interactive” mode, where raw, unconditioned, utility power is passed through to the critical load. The incoming utility power is continuously monitored for out of specification parameters. Should the incoming power fall out of specification or totally lost, the UPS switches to inverter operation very quickly (usually less than a quarter cycle of the 60-cycle sine wave).
One of the concerns with Eco Mode operation is the passing of quick voltage transients present in the utility power to the switched mode power supplies within the critical data processing equipment. Although the switched mode power supplies may shield the data processing circuitry from these transients, the switched mode power supplies will themselves experience degraded reliability due to the accumulated effects of successive voltage transients. The net effect is slow to manifest itself.
Now that you’ve had your blitz overview on Eco Mode, now let’s discuss when you should use it.

Sometimes use Eco Mode…When you need a combination of Reliability and Efficiency. Several critical factors must first be met. “Operating in Eco Mode can improve efficiency and thus conserve energy. In order to deploy Eco Mode without compromising performance and reliability, one must have some knowledge of UPS technology and performance, critical power system configuration, IT power supply ride-through, and utility grid reliability.” – The Green Grid White Paper #48 (emphasis ours) Basically, unless you already have reliable power (and if so – why have a UPS?) or have a highly reliable and redundant data center design, you probably don’t want to use Eco Mode on a continual basis.

Always use Eco Mode…if High UPS Efficiency is the top priority. This is pretty much the only instance you should operate in Eco Mode since the trade-off if lower UPS reliability/performance during power events.

Never use Eco Mode…If you demand the highest reliability and protection from power events. There are simply better options – albeit less efficiency – than a UPS running in Eco Mode.


Figure 2 through Figure 6 represent various possible modes of the double conversion UPS. Red represents the power flow path. Blue indicates load power is not flowing. Yellow implies power is available.

If you have questions how to optimize the operating modes available in your current or in a new UPS, please contact us for a follow-up to discuss an assessment.

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Dale Klein

Dale Klein is the president and owner of Parallel Technologies. He has more than two decades of experience in technology and business leadership. He transformed Parallel Technologies from a cabling services company into a high-growth technology company by helping clients with their reliable data center and intelligent building strategies.