Most facilities keep their UPS in double-conversion mode by default because it delivers the cleanest, most predictable power. Eco-mode (sometimes called “high-efficiency” or “economy” mode on Liebert systems) changes that operating philosophy. It routes utility power directly to the load during normal conditions and uses the inverter as a standby filter that takes over when quality drifts out of tolerance. The reward is higher efficiency and a lower electricity bill; the risk is that transfers back to the inverter are not strictly zero-time, and more of the utility’s imperfections can reach the load.
In this blog, we will discuss how eco-mode works on Liebert UPS, the real efficiency trade-offs, when to use it, when to avoid it, how to tune settings, and what typical B2B sites can expect in practice.
What does eco-mode really do on a Liebert UPS
Under normal utility conditions, the UPS synchronises the inverter and bypass, keeps the inverter in a ready state, and feeds the load through the conditioned bypass path, which results in significantly lower losses than full double-conversion. If voltage, frequency, or waveform quality exceeds the set thresholds, the UPS transfers to the inverter to “re-isolate” the load.
Once the source stabilises for a defined dwell time, the system returns to eco-mode. Two details matter for planners: transfer behaviour (measured in milliseconds, not zero) and source quality (eco-mode assumes a reasonably clean, stable upstream). Understanding both helps determine whether the efficiency gain fits the site’s operational risk profile.
The efficiency vs. exposure trade-off
Why teams consider eco-mode
Lower operating cost: Efficiency gains can be material over the year for medium to large loads.
Lower heat in the UPS room: Reduced losses mean less heat rejection and, often, slightly lower HVAC run time for the electrical room.
Sustainability optics: Small reductions at scale support energy-intensity targets.
What you accept in return
Non-zero transfer time: Sensitive or latency-intolerant devices might notice a few milliseconds.
More of the grid’s “character” reaches the load: Minor sags, notches, or higher THD can pass through compared with strict double-conversion filtering.
Upstream dependency: Performance leans on utility stability and the quality of any upstream generator, ATS, or PFC equipment.
The decision is not philosophical; it is a site-by-site business case that weighs electricity savings against the cost of even brief disturbances.
When eco-mode makes sense
Eco-mode tends to be a good fit when the source is stable and the load is moderately tolerant.
Office and commercial campuses with reliable utility supply and IT loads that use modern power supplies.
Data halls with N+1 or higher redundancy where a subset of rows can run eco-mode while at least one path remains in online double-conversion.
Edge rooms with strong utility and good grounding, where short transfers are acceptable and energy savings matter to the business case.
Sites with meaningful tariff spreads and demand charges, where every incremental efficiency point contributes to Opex control.
When to avoid or limit eco-mode
Use online double-conversion as your default when the incoming power is unstable or “noisy.” This includes feeders that dip in voltage, show notches from heavy VFDs, or have high distortion on the line. Skip eco-mode if you run on generators often, because many gensets vary more in voltage and frequency, which can cause frequent transfers or let generator imperfections reach the load.
Also avoid eco-mode for very sensitive equipment, such as medical imaging, older PLCs, or any device that has struggled with short power events or imperfect waveforms. It is not suitable where strict SLAs allow no interruptions and even a few milliseconds could trigger an incident or penalty. If you are unsure, test on a non-critical section first, monitor the results, and roll out more widely only after the data looks solid.
Tuning eco-mode on Liebert: settings that matter
The “should we” question is followed by “how do we set it up.” Typical parameters to review with your integrator:
Input qualification window: Voltage and frequency tolerances that must be met to enter or stay in eco-mode. Tighten if nuisance transfers occur.
Transfer logic and dwell times: Define how long the source must be stable before re-entering eco-mode, and how quickly to exit on excursions.
Synchronisation and slew limits: Ensure stable sync between the inverter and bypass to keep transfers smooth.
Overload and short-circuit behaviour: Verify how the UPS responds under eco-mode if a downstream fault happens.
Harmonic limits: If upstream THD is high, consider filtering or stick with double-conversion.
Coordination with generators: Many sites disable eco-mode during generator operation and re-enable it when the utility returns.
Visibility: Integrate alarms and mode changes into DCIM/BMS so operations can see transfers, counts, and reasons in real time.
Well-chosen thresholds reduce chatter, minimise exposure, and preserve the efficiency win.
Use-case snapshots: what different sites actually do
Colocation and cloud rooms: The Common approach is split-mode operation. One UPS path remains in online double-conversion, the other in eco-mode. This balances efficiency with a clean power reference and gives operations a rollback path.
BFSI branch networks: For branches on strong urban feeders, eco-mode often runs during business hours, with a policy to revert to online mode if power-quality alarms exceed a set count per week.
Manufacturing with heavy drives: If the plant bus shows voltage dips when large motors start, most facilities stay in online mode for the UPS feeding control systems, while less sensitive office IT may use eco-mode.
Hospitals and diagnostics: Life-safety and critical clinical loads remain in online mode. Non-clinical areas (admin IT) may use eco-mode after a power-quality study confirms stability.
These patterns show a consistent theme: selective adoption based on source quality, redundancy, and load sensitivity.
Quick decision guide
Use this simple table during design reviews. It is not a substitute for a site study, but it helps frame the conversation.
| Criterion | Prefer Online (Double-Conversion) | Consider Eco-Mode |
|---|---|---|
| Source quality | Fluctuating voltage, high THD, frequent sags | Clean utility, stable frequency/voltage |
| Load sensitivity | Legacy PLCs, medical imaging, tight SLAs | Modern IT with tolerant PSUs, non-critical office IT |
| Generator usage | Frequent or extended generator runs | Generator only in rare emergencies |
| Redundancy | Single path to critical load | Dual path with at least one online at all times |
| Opex pressure | Energy cost secondary | Energy savings prioritized with monitoring |
| Policy and reporting | Zero-event mandate | Some tolerance for brief transfers, with visibility |
Conclusion: turn efficiency into policy, not a gamble
Eco-mode is neither a silver bullet nor a risk to be categorically avoided. It is a policy choice that should be driven by measured source quality, load tolerance, and redundancy. Where the utility is stable and the load is modern and moderately tolerant, eco-mode on Liebert UPS can trim operating cost without compromising reliability. Where the source is noisy or the Service Level Agreements are unforgiving, keep online double-conversion as the default and pursue savings elsewhere in the power chain.
We at Meghjit Power Solutions help enterprises assess power quality, set eco-mode policies on Liebert UPS fleets, and integrate alarms with DCIM or BMS so operations teams stay fully informed. From feasibility checks and pilot tuning to rollout and training, our team aligns economics with uptime. Recognised by Vertiv as an Emerging 1-Phase Contribution Partner in 2024, Meghjit Power Solutions brings trusted implementation across India. If the goal is to capture efficiency without surprises, our team at Meghjit Power Solutions can structure the path from assessment to deployment.
Frequently Asked Questions
1. Will eco-mode affect my SLAs or sensitive equipment?
Eco-mode introduces a transfer that is in milliseconds rather than zero time. Most modern IT power supplies tolerate this, but legacy PLCs, medical imaging, or ultra-sensitive systems might not. Review load tolerance and run a monitored pilot before adopting eco-mode on critical paths.
2. Should eco-mode be enabled during generator operation?
Usually no. Many sites disable eco-mode whenever the load is on generator power because gensets can have wider voltage and frequency swings. A simple policy is to re-enable eco-mode only after stable utility returns and the UPS confirms source quality.
3. How do we know if eco-mode is working for us?
Track a few metrics in your DCIM or BMS: number of transfers, reasons for transfer, time in eco-mode vs online mode, room temperature impact, and estimated energy saved. If transfer counts are low and savings are consistent without alarms from sensitive loads, the policy is working.
