Green Grid: Eco Mode Offers UPS Savings, With Caveats

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This chart from The Green Grid outlines the potential energy efficiency gains from using an "eco mode" UPS configuration (Source: The Green Grid).

The energy-saving UPS configuration known as "eco mode" has become a viable option to help increase energy efficiency and save costs in the data center, according to The Green Grid, which offers some caveats and tips on implemention.

The Green Grid, a global consortium focused on improving energy efficiency in data centers, has released a white paper that takes a deep dive into Eco Mode in Uninterruptible Power Supply Systems (UPS). Eco mode boosts UPS efficiency and PUE when properly designed and deployed, and is identified as one of the energy savings recommendations in The Green Grid Data Center Maturity Model (DCMM). The white paper looks at deployment considerations and makes recommendations, discussing energy efficiency gains and economic benefits.

The need for energy efficiency is becoming more prevalent. There are many options to incrementally improve power system efficiency. UPSes can have several modes of operation, including eco mode, which is typically the highest mode of efficiency. Not all eco mode designs are the same, and the differences can matter, according to The Green Grid.

Switch-Over Timing is Crucial

There are several points that data center operators need to consider prior to implementation and several things that need to happen before it’s more widely used. Data center operators should analyze the power distribution within their data centers. It's also extremely important to match the switch-over time for an eco mode UPS to the power supply ride-through or static switch time. Utility power needs to be a certain level of quality for eco mode to be considered.

There’s a variety things that need to happen prior to wider implementation. Before many data centers will be able to move from Level 1 UPS Eco Mode implementation to Level 3 implementation in The Green Grid’s Data Center Maturity Model, the report says the following will need to take place:

Prior to implementing eco mode, everything needs to be tuned properly, and the whitepaper tells you what factors need consideration. How does it effect transfer times? Fault tolerance performance?

The savings and efficiencies from eco mode are highlighted in a variety of metrics. The Green Grid examined the impact on power usage effectiveness (PUE) of UPS eco mode efficiency relative to UPS double conversion efficiency with three types of data centers split by efficiency as measured by PUE:

Energy Efficiency Gains Outlined

There are all sorts of figures and graphs showing the overall efficiencies in all three data center examples when using Eco Mode. PUE gets better and the economic benefit from energy savings can also be estimated. Energy savings ranged from less than $100,000/year savings for 1 megawatt (MW) IT load to almost $500,000 per year for 5 MW load in a legacy data center, based on the operating assumptions listed in the report.

UPS inefficiencies generate heat in the data center, which is removed by the data center’s cooling system. That heat removal is accounted for with the PUE cooling contribution. Here's an excerpt:

There is a close conceptual relationship between UPS Eco Mode operation and the well-known “free cooling” operation that allows data centers to reduce energy consumption in their cooling systems when the outside ambient air temperature and humidity are within acceptable levels. As with external weather conditions, data center operators can make the most of available high-quality utility power to improve efficiency.  In this case, rather than free cooling, it is “free power quality” that data centers can take advantage of, available when the UPS Eco Mode uses external utility power that is already in highquality condition. Similar to free cooling, where the chiller is not used or is turned off when not needed, the UPS Eco Mode turns off the UPS rectifiers/inverters when the availability of “free power quality” makes them unnecessary.”

The bottom line: Eco mode boosts UPS efficiency from the usual high end of about 92% to 96% for the three data center PUE examples to as high as 98% to 99%.As part of its ENERGY STAR program, the EPA provides a 25% efficiency allowance to the manufacturer for the UPS Eco Mode capability.

Get the white paper here