As good as this may sound, hardly any data centres choose to use ups eco mode. Because this mode doesn’t offer the same level of protection as a true on-line uninterruptible power supply.

Also known as ‘economy’, UPS ECO mode is a special UPS operating mode offering enhanced energy efficiency. Capable of delivering efficiency up to 99%, ECO mode sees the bypass line (raw mains supply) power the load.

What is ECO mode on ups?
ECO mode is very similar to the basic mode of operation used in an offline UPS where it is called “standby” or “line interactive” mode. In these traditionally smaller, single-phase UPSs, the inverter/rectifier circuits are “offline” standing by, ready to switch on if the power fails or a problem is detected.
Similarly with an On Line UPS operating in eco-mode, the bypass path powers the load normally, allowing raw mains power to supply the load, and engage the UPS inverter only when the utility mains fails. In normal eco mode operation, therefore, essentially raw mains power expose to the load.
Rather than true online mode, where the UPS continuously regenerates the output voltage through the inverter, in eco-mode the UPS inverter operates in a “standby” mode. In principle, this is a simple change in the control software of the UPS. However, the reality is considerably more complex.

Benefits of ECO Mode

The benefit of eco-mode is that the efficiency of the bypass path is typically between 98.0% and 99%. This means there is a pickup in UPS efficiency of between 2-5% when using eco-mode.
That difference of anywhere between 2-6% has the potential to deliver significant savings.

Risks of ECO Mode
Eco-mode cannot predict the future. It must respond to a problem that already exists and then switch to the inverter. This means that a mains power problem can get through the UPS to the critical load until the following four things
happen:
 Detect power problem
 The UPS determines whether and how to respond
 Energize UPS inverter
 Actuate the static bypass switch
In practice, these events may take from 1 to 16 milliseconds, during which the critical load due to the power problem.
The loss of power for even a few milliseconds on a circuit feeding a PDU equipped with a static switch will cause a state change on that switch. This can lead to an undesirable state change of the overall power system, including overloads and dropped loads.

What is active ECO mode?
In recent years, some UPS systems 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 Mode
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.

Should I use ECO mode?
It is useful therefore to consider that UPS efficiency is based on how much of the original incoming power is needed to operate the UPS. For example, an older uninterruptible power supply with a 94% efficiency rating will transfer 94% of the original input power to the load and connected systems, whilst the remaining 6% will be “wasted” running the UPS and usually emitted as heat.
This extra heat will usually then also have to be dealt with, further increasing facility cooling costs.
On balance, most data centres and other mission-critical sites are understandably reluctant to operate their UPS systems in eco-mode, as the trade-off in resilience and power quality is not worth the potential energy saving. Instead they prefer to select more modern equipment that has higher energy efficiency when operating in the most protective continuous online
mode. Only where utility supply is relatively stable, the load generates low harmonics (so isn’t sensitive to mains interference) and where supported equipment can easily handle a fractional break will operators look more favourably on operating in eco-mode.