Ensuring smooth hand-off in eco-mode


28 July 2016
Pankaj Sharma of Schneider Electric

“Eco-mode” technology, or energy-saving operating technology for uninterruptible power supplies (UPS), represents a potential way to save energy in data centres, hospitals, and other critical power applications.

Most UPSs provide “clean” power in the event of a power failure or disruption via a double power conversion process. They take in AC power from the main power source, rectify it to DC to perform filtering and charge the UPS battery, and then convert the power back to AC. Through this process, the power output is always conditioned, meaning it is isolated from any power disruption be it spikes, brownouts or harmonic distortions in the main power source.

With eco-mode enabled on the UPS, data centre operators can expect savings in the order of 2 to 4 per cent in total energy. These savings in energy however, come at the expense of reliability. It takes a few milliseconds to transfer from eco-mode to the double-conversion mode. This can be enough to negatively impact the load in data centres, hospitals and manufacturing plants.

The use of traditional eco-mode therefore entails risks – like the hand-off of a baton in a relay race. Each hand-off is a little different, and on very rare occasions it may present a problem. For this reason, eco-mode is recommended only where there are minimal handoffs, that is, where power quality is excellent.

Let us take the example of a hospital. Let’s say you have a UPS protecting an MRI machine running on eco-mode. The large motor drives for the chillers, fans, and pumps in the hospital cause harmonic voltage on the mains. Because an MRI machine is delicate and requires good, clean power, any kind of sag or distortion may cause problems in its operation..

Things to consider when implementing eco-mode

There are several points that data centre operators need to consider before implementing eco-mode.

First, it is extremely important to match the switch-over time for an eco-mode UPS to the power supply ride-through or static switch time. Not all eco-mode may be initially tuned to meet this time requirement or able to meet it. Data centre operators should analyse the power distribution within their data centres and consult their UPS manufacturers for information prior to implementing eco-mode. All equipment must be tuned to work well together.

Second, UPS eco-mode operation requires an acceptable level of utility power quality. It must be within the voltage tolerance of all equipment to keep the UPS operating in the most efficient range possible. We recommend users to follow the three steps below:

  • Voltage immunity curves should be updated to help all designers and operators by accounting for the shorter ride-through times now implemented in many servers.
  • Users should identify their critical business types and the characteristics of their loads to determine the best implementation mode for their business.
  • Periodic, in-depth power quality studies should be conducted so that the results can be studied by possible eco-mode users.
  • UPS manufacturers will need to continue to identify and implement advances in eco-mode technology that can help close any gaps in current systems that prevent utilisation of eco-mode.  

The good news for all data centre operators who are looking to leverage UPS eco-mode operations to improve energy efficiency and reap cost savings is that there are constant improvements to the technology promising energy savings without compromising energy reliability. Schneider Electric’s ECOnversion, for instance, features a power inverter that runs constantly to perform whatever conditioning may be necessary to the main power source, such as harmonic compensation and power factor correction, and also constantly charges the UPS battery.

With such improvements in the technology, reliability and energy efficiency in the UPS world need no longer be mutually exclusive.

* Pankaj Sharma is vice president for IT Business at Schneider Electric Asia Pacific and Japan.