Eco-mode : Benefits and Risks of Energy-saving Modes of UPS Operation

by Neil Rasmussen

Executive Summary

Many newer UPS systems have an energy-saving operating mode known as “eco-mode” or by some other descriptor. Nevertheless, surveys show that virtually no data centers actually use this mode, because of the known or anticipated side-effects. Unfortunately, the marketing materials for these operating modes do not adequately explain the cost / benefit tradeoffs.

This paper shows that eco-mode provides a reduction of approximately 2% in data center energy consumption and explains the various limitations and concerns that arise from eco-mode use. Situations where these operating modes are recommended and contraindicated are also described.

Conclusion

Eco-mode represents a potential way to save energy in data centers and other UPS applications. Data Center operators can expect to see savings on the order of 2-3% in total energy if eco-mode is enabled. Higher percent savings are possible if the data center is operated at very light electrical loads. The energy savings associated with eco-mode are getting smaller as newer generation UPS systems improve in efficiency.

The use of eco-mode entails risks. Eco-mode introduces a number of new modes of operation of the data center, and reduces power protection. Current IT equipment is much more resilient to power variations than the IT equipment of prior generations, suggesting that this equipment should operate reliably using eco-mode. However, complex data center systems comprised of a mix of IT equipment, transformers, transfer switches, and other possible non-IT loads are less predictable in their response to infrequent and unusual power
events, and their compatibility with eco-mode is less certain. These considerations have greatly limited the use of eco-mode in real data centers in the past, and are likely to continue to do so.

The operation of eco-mode is like the hand-off of a baton in a relay race. It is critical that it works correctly, each hand-off is a little different, and on rare occasions there may be a problem. For this reason, eco-mode should be used in situations where the number of handoffs are as few as possible, e.g. where power quality is excellent. As data center designs become more standardized, IT equipment continues to improve, and real world experience using eco-mode accumulates, predictability and confidence in ecomode will improve and its application may begin to expand, especially in data centers with lower availability requirements.

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