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What Is ECO Mode On A UPS System?

Also known as ‘Active Standby’ or ‘Economy’, ECO mode is the most energy-efficient UPS operating mode. Capable of exceptional efficiency up to 99%, ECO mode sees the bypass line (raw mains supply) power the load, with the inverter powered but remaining off as long as the mains supply remains in tolerance. 

It is similar to the basic operating mode of an Offline or Line Interactive UPS, where the inverter is on standby and ready to switch on if there’s a power problem or the incoming supply goes outside a pre-set voltage and frequency tolerance. 

When there’s an issue with the mains, the load experiences a fractional break in supply (perhaps up to 15ms), while the UPS system’s automatic bypass switches back to the inverter. 

This short break in continuous power is the main drawback to using ECO mode, particularly for mission-critical facilities with sensitive equipment, such as data centres, where even a fractional break in continuous power can cause chaos.

Another disadvantage of ECO mode is the lack of power conditioning provided by true double-conversion online UPS mode.


How Much More Efficient Is ECO Mode Compared To Online UPS?

The main benefit of ECO mode is the increased efficiency of the bypass line, which typically runs at 98-99% compared to standard online UPS efficiency of 93-97%.

That difference of anywhere between 2-6% has the potential to deliver significant savings. Consider a large-scale facility, where even a 1% improvement in efficiency could equate to tens or even hundreds of thousands of pounds a year in lower energy costs.

ECO mode is only recommended on sites where the utility supply is relatively stable and the load generates low harmonics so isn’t sensitive to any mains interference.


What Is Active ECO Mode? 

In recent years, some UPS systems (such as Riello UPS’s NextEnergy range) now offer an operating mode called Active ECO Mode, sometimes referred to as Advanced ECO.  

Just like in standard ECO mode, the bypass line (mains supply) powers the load. But with Active ECO, the inverter remains on at all times and runs in parallel with the input without actually carrying the load.  

This means that power transfer is far quicker in the event of a mains failure, ensuring higher availability than true Economy mode. And even though the inverter isn’t processing the load, it does absorb harmonic currents and provide power filtering in a similar way to online UPS.

Obviously, powering the inverter all the time in Active ECO does require more energy than standard ECO mode. The trade-off for this is that efficiency in Active ECO is between 0.5-1% lower than normal ECO mode. But efficiency is still considerably higher than online UPS mode, so it offers something of a happy medium.

In the event of a mains failure, the inverter takes over far quicker in Active ECO mode, meaning it offers higher availability than the standard ECO mode.  

Obviously, the operating efficiency when using Active ECO is slightly less (around 1%) than it is with pure ECO, but this is still considerably better than online, so offers users something of a happy medium. 


When To Use ECO Or Active ECO Modes

Mission-critical sites such as data centres are reluctant to use these energy-saving operating modes, with the trade-off in resilience and power quality putting operators off.

While it may not be practical to have a UPS running in energy-saving modes all of the time, it might be practical to use when a site’s most critical loads are inactive, such as overnight or out of hours.

Parallel UPS systems offer an opportunity too. In such an example, one UPS would run in online mode as the ‘master’, with the remaining units operating in ECO mode until the condition of the mains supply changes and they’re required to actively support the load. 


Learn more about ECO mode and other UPS operating modes such as Smart Active by watching our fun and fact-filled ‘UPS Basics’ video: 



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