How UPS Eco-modes Save Energy and Reduce Data Center Emissions

Data centers are invariably focused on 100% availability, which comes down to reliability of power and various mechanical and electrical components throughout the facility. But energy efficiency is a major priority as well, even for data centers that don’t call themselves “green” or “sustainable”.

With electricity providing a bulk of the operating expense, any gains in efficiency can go a long way towards minimizing OpEx. Many data center efficiency measures focus on containment, cooling, and other measures within the white space, but critical power infrastructure can be a good target for efficiency gains as well.

Major UPS manufacturers often include an “ecomode,” or in the case of our Cheyenne data center, Eaton’s Energy Saver System (ESS). These modes can lead to efficiency gains of several percentage points, which sounds low, but in practice can lead to thousands of dollars of savings and carbon emission reductions in the hundreds or thousands of pounds.

Load Sharing and Typical UPS Efficiency

In an N+1 or greater facility, there are multiple Uninterruptible Power Supplies to cover a single maximum IT load. They are all powered on, so while a single one of the UPS could take on 100% of the load, the majority of facilities will share the load between them, often about 40-50% between each. This places less stress on each UPS and extends its lifespan while reducing the overall risk of failure.

At a 40% load level, a modern UPS can operate at around 95% efficiency. But where does that 5% of the electricity go? Typically the UPS will be running in double conversion mode. The incoming electricity from the utility provider is converted from AC to DC by the rectifier, which sends a charge to the batteries and passes on the current to the inverter. The inverter then converts electricity from DC back to AC for the IT load to use.

This helps keep any sudden changes in the electrical load from the utility, like sudden spikes or sags, from reaching the IT load, while also maintaining the battery levels. It also reduces the switching time from utility feed to battery power should there be a power outage, as the utility feed does not go directly to the IT load.

The switches within the rectifier and inverter lead to additional resistance, which leads to the generation of heat and a loss of energy from the electrical current. That can reduce the efficiency of the double conversion UPS by 5% on average.

How much energy can 5% be?

An efficiency rating of 95% seems pretty good, especially for the increased reliability a double conversion UPS offers. For our 5MW of power in Cheyenne, however, that adds up to over 2,500,000 kWh of electricity a year (at maximum load). Meanwhile, the additional heat generated by the switches also adds to the overall heat within the UPS and/or battery rooms in the data center, which require their own cooling systems – an additional expense.

According to the EPA, that lost electricity is equivalent to driving an average vehicle 4,560,163 miles, burning 2,035,604 pounds of coal, or providing electricity to 279 homes for a year. In other words, that measly 5% adds up to a very significant amount of energy in a midsize data center.

By operating our UPS in Energy Saver System mode, the efficiency rate is closer to 99%, allowing us to reduce our carbon footprint at maximum 5 MW load by approximately 1,800 metric tons (again according to EPA equivalencies). At this maximum load, we would also be saving between $125,000 and $250,000 per month.