Understanding high-efficiency mode UPSs

Power efficiency is hardly a new concern among data centre operators, but today’s constrained budgets and corporate sustainability initiatives have combined to make energy usage minimisation more critical than ever.

For colocation service providers, cloud computing vendors and other operators of multitenant data centres, there is another incentive to decrease energy use: low margins and intense pricing pressures that make cutting costs a competitive necessity.

Companies looking to save money and shrink their environmental impact can dramatically improve power efficiency by deploying high-efficiency mode uninterruptible power supplies (UPSs). As the name implies, under normal conditions a high-efficiency mode UPS operates in a highly efficient energy-saver mode. If power conditions fall outside predetermined limits, however, the UPS automatically and immediately switches to double-conversion mode. Later, when power quality returns to acceptable levels, the UPS automatically transitions back into energy saver mode.

In older high-efficiency mode UPSs, transition times between energy-saver and double-conversion modes were sometimes lengthy enough to jeopardise data centre reliability. These days, UPS products are more sophisticated, capable of completing transfers in two milliseconds or less. As a result, deploying the latest high-efficiency mode UPSs empowers companies to decrease power consumption without weakening reliability.

Calculating high-efficiency mode UPS ROI

The newest double-conversion UPSs are often more than 93% efficient when fully loaded, but may deliver as little as 86 to 89% efficiency at the lighter loads commonly encountered in data centres. High-efficiency mode UPSs, by contrast, are up to 99% efficient when running in energy-saver mode and they maintain high efficiency even at light loads. As the table shows, this small difference quickly adds up to significant savings.

While prices on high-efficiency mode UPSs vary widely, the potential for substantial savings should deliver 100% return on investment within two to three years in most cases.

Possible utility incentives for energy-efficient power systems in the data centre would reduce the capital cost of the UPS and improve the ROI payback period.

Capabilities to look for in a high-efficiency mode UPS

In addition to a transition time of less than two milliseconds between energy-saver and double-conversion modes, and high-efficiency regardless of load, the major capabilities that will help to deliver a higher ROI include:

Robust surge suppression: Some data centre managers question the ability of high-efficiency mode UPSs to suppress the kind of extreme power surges produced by lightning strikes. In truth, well-designed high-efficiency mode UPSs feature the same input and output capacitors that double-conversion models use and are therefore every bit as effective at limiting the impact of voltage spikes.

Efficient electromechanical component utilisation: Well-made high-efficiency mode UPSs utilise electromechanical components in a manner that increases their reliability. For example, they extend the lifespan of their fans by switching them on only during heat-intensive processes such as charging batteries.

Similarly, when operating in energy-saver mode, advanced high-efficiency mode UPSs leave critical mechanical components like contactors in a closed state. This results in two important reliability advantages. First, contactors experience significantly less electrical and thermal stress when closed, so they’re less likely to malfunction. Second, a contactor that’s already closed is incapable of failing to close during abnormal power conditions, so it’s guaranteed to perform as intended when needed most.

Ability to correct load harmonics when in high-efficiency mode: The UPS should be able to utilise its power conversion circuitry to cancel undesirable load harmonics that could appear on the UPS input while operating in high-efficiency mode. This harmonic mitigation prohibits voltage distortion being reflected onto the site electrical system. This may be more desirable in large systems, although it will reduce efficiency slightly.

Fault discrimination: The high-efficiency mode UPS should be capable of supporting the IT load if a fault occurs. Faults upstream of the UPS require a different reaction to those downstream and if the UPS cannot discriminate between these, it may drop the load. Therefore, the UPS must detect the location of the fault and react appropriately to protect the IT load under any fault scenario.

Secure remote operation: It is important for the high-efficiency mode UPS to be capable of automatically switching between double-conversion and high-efficiency modes, even when operators are not present. If power conditions degrade overnight or during the weekend, for example, the UPS will be able to switch to double-conversion mode on its own and switch back again unassisted when power quality improves.

Remote access capabilities: The most advanced high-efficiency mode UPSs come with secure remote access capabilities that allow operators to change modes manually over the internet.

With any new data centre purchase, operators need to know that their funds will result in a quick and significant payback. They also need to know that this rapid ROI won’t come at the expense of lower reliability. As the calculations above show, a properly equipped high-efficiency mode UPS pays for itself in as little as two years without reducing availability. As an additional benefit, it also produces substantial environmental benefits.

As a result, organisations eager to cut costs while preserving uptime should carefully consider replacing legacy double-conversion UPS hardware with more modern and efficient high-efficiency mode devices.

Image credit: ©iStockphoto.com/Oleksiy Mark