Emerson Network Power became a member of the small group of vendors whose Uninterruptible Power Supply (UPS) products were certified as more energy efficient than the norm under the US federal environmental regulators’ new program.

The US Environmental Protection Agency (EPA) issued Energy Star certification to Emerson’s Liebert APM UPS for data centers, the company announced earlier this week. The EPA’s Energy Star program has existed for years, but the agency only added the UPS category earlier this year.

Other vendors with certified UPS products are Schneider Electric (the first company to achieve the UPS certification), General Electric Company, Huawei Technologies and CyberPower Systems.

Emerson’s product – one of its many UPS systems – is an online UPS that does not use a transformer. Its capacity scales in a modular fashion, meaning users can increase or decrease capacity in 15kW increments by adding or taking away FlexPower assemblies.

The modular feature can be used to scale either capacity or redundancy of the back-up power system. A single cabinet can go up to 45kW (configured for redundancy) or 90kW.

Charles O’Donnell, VP of power engineering at Emerson, said, “We recognize that there are applications for transformer-free UPS systems in today’s data center.”

Transformer-free UPS systems are usually more energy efficient and take up less space, according to an Emerson white paper on the subject, but the trade-off, when compared to transformer-based ones, is they are not as robust and have more components (the modules). This means they need to be services more frequently.

Emerson recommends 200kW as a capacity threshold below which transformer-free UPS makes sense. Below this capacity space, weight and cost advantages generally “outweigh the robustness and higher capacity capabilities of transformer-based systems,” the paper read.

Major high-capacity mission-critical data centers need transformer-based UPS systems.

Emerson said it planned to put more of its UPS products through the Energy Star certification process in the future. Schneider has more than 20 UPS systems certified, GE has five, while CyberPower and Huawei each have one, according to a list available on the EPA’s website.