Colocation data centers, perhaps more than most businesses, are on a constant journey towards peak operational efficiency. More often than not, data centers measure and adjust the mechanical side of their facility, such as cooling, to increase efficiency, while passing over the electrical distribution side. They replace their UPS batteries every few years and move on. However, given the latest advancements in energy storage and electrical distribution infrastructure, data centers can be doing a lot more with their electrical components to conserve space, reduce costs, and decrease waste. There are plenty of claims out there that insist traditional static battery UPS systems are the only way to go, but these claims are simply not true.

More reliable, cost-effective, and efficient approaches to data center electrical distribution design are actually utilizing the most recent models of diesel rotary uninterruptible power supplies (DRUPS). These newer models are simplified, more reliable, require less maintenance, and have a longer life-cycle, making them superior to battery UPS and flywheel systems. Below you will find a discussion of the more widely-used traditional battery UPS systems and the newer DRUPS systems that continue to supplant them in modern data center designs.



The purpose of any UPS system is to provide short-term backup power for brief outages, to guard the load against power events like spikes and sags, and to supply the data center with clean, steady power. The UPS should be able to supply power in the event of a utility power failure, and give the facility time to switch to its own or another form of backup power generation if the outage continues.

Static UPS takes AC power from the utility, stores some of that energy in batteries, and transfers the rest to the connected equipment after conditioning it. To function, most static UPS systems need the following components: batteries to provide an unbroken source of power, a rectifier/charger to charge the battery and give input to the inverter when utility power is available, an inverter to provide power to the load throughout normal operation, a static switch to transfer the load between inverter and utility power automatically and seamlessly, a manual switch to bypass the static switch for maintenance, input and output isolation transformers and filters to provide isolation and disturbance attenuation, as well as monitors, sensors, and control circuits. The batteries also require a thorough ventilation, spill, and containment systems due to their operation and toxic and corrosive nature.

Flywheel UPS systems consist of the same components and functions similarly, except the batteries are replaced with flywheels. A flywheel is a mechanical wheel that rotates and stores kinetic energy through angular momentum. When an outage occurs, the flywheel’s kinetic energy is converted back to electrical energy to power the equipment, spinning slower and slower as more and more energy is used.

DRUPS systems are different. There are a few DRUPS manufacturers leading the market and their systems vary slightly, but arguably the most efficient concepts are mechanically coupled DRUPS alternator systems. Contained within a common frame power module, it conditions utility power and uses stored kinetic energy to support the load during the transition to power provided by the diesel engine while it starts up.

Mechanically coupled DRUPS utilizes one massive kinetic energy device per power module that rotates and stores kinetic energy constantly when the utility is available. With the diesel engine incorporated into the power module, a DRUPS system only needs about two seconds of stored power before the engine comes on line. If the engine doesn’t start for whatever reason, the system automatically closes the clutch and essentially jumpstarts the generator, providing added redundancy and ensuring power every time.

Although DRUPS and flywheels are often confused, they are not the same. Flywheels incorporated into a UPS system are only meant to replace batteries and are built with a low weight and spin at a high speed or RPM. Per one megawatt of power, a flywheel UPS often needs three or four small flywheels, whereas a DRUPS system needs only a single large kinetic energy device. Flywheel UPS (and battery UPS) also require extra components to convert its DC power back to AC to supply the load.  DRUPS power is already AC and primed for use within seconds.



In addition to pre-conditioned power and a redundant and highly-reliable generator start system, there are many advantages to DRUPS over traditional static UPS. The most effective DRUPS shift the weight of the kinetic device further from the shaft, which causes a slower rotation and RPM to accomplish the same amount of kinetic energy. This equates to lower temperatures and less stress on the bearings, extending their lifecycle to at least 10 years. The bearings are the only component of a DRUPS that needs regular replacement, whereas batteries in many cases must be replaced every three to five years, and UPS capacitors must be replaced approximately every seven years at significant costs for each. Greater replacement and maintenance costs aside, each replacement event at a data center has the potential to cause larger issues. Additionally, the compact design of DRUPS allows for fewer points of failure in comparison to a traditional UPS and associated switchgear design.

DRUPS systems’ modular deployment makes its physical footprint significantly smaller than static UPS systems. There have been a few white papers circulating on the internet that assert that there is no real difference, but what these documents have conveniently left out is all the extra infrastructure a static UPS requires to run. To give a real life example, a leading data center in the U.S. recently revealed plans to switch from their current traditional battery UPS to DRUPS for ongoing expansion. They calculated that they would be able to reduce the amount of their facility’s expansion MEP space by 7,500 sq ft. About 5,000 sq ft of that conserved space will be converted into IT equipment or colocation space, which will increase the amount of critical IT kW to its customers by 500 kW. They estimate that this will result in an average of $1,200,000 in increased revenue on an annual basis.



Although DRUPS systems have gained their most significant surge of popularity over the past eight years, they have actually been around for close to 30. You may be wondering why the data center industry in the U.S. has been slow to adopt DRUPS if it is a more cost effective, reliable, and efficient system. There are a few reasons for this. Large American corporations have traditionally manufactured static battery UPS systems, while small European companies have produced DRUPS. With fewer connections and clout in the U.S., these companies found it difficult to convince data center construction consultants and engineers to recommend DRUPS systems to the data center owners that hire them.



Over the past 15 years or so, DRUPS manufacturers have continued to refine their designs and reoriented their businesses around consumer experience. After a few very successful installations in the U.S., engineers have begun to recommend DRUPS for data center designs. Following the recommendations of consulting engineers and perhaps sensing a shift in the wind, a few top data centers across the U.S. have already announced their plans to deploy DRUPS in their facilities.

The data center market is ripe for a DRUPS movement, given the current trends that have been driving the industry towards simplicity, more efficient use of space, and lesser environmental impact. These trends have become the most apparent with the burgeoning popularity of modular data center approaches. As the Internet of Things pushes the industry towards edge computing, larger quantities of smaller data centers will be distributed in closer proximity to the enduser. Data center engineers and owners will need to seriously consider the best avenues to optimize square footage and increase efficiencies of their data centers. Now that DRUPS manufacturers have condensed the MEP side of the data center into a modular footprint, it follows that their adoption will continue to increase at an exponential rate to keep up with modern IT demands.

It is expected that once the U.S. market becomes more educated on the advantages of the DRUPS technology and its cost efficiency from ongoing total cost of ownership (TCO) reports, the DRUPS will become an ideal alternative to the traditional static UPS system. 

Costs vs. profits will be the deciding factor and ultimate supporter of the DRUPS movement. Based on the above comparisons, data centers that deploy DRUPS will spend less in TCO over the long run because they won’t have to use employee time and money on maintenance or replacement; they will have fewer, cheaper components to replace less frequently; and their critical systems will have fewer points of failure that could potentially result in costly outages. Not to mention, used batteries are toxic waste and having to recycle/dispose of them every few years has a negative impact on the environment. DRUPS will also conserve physical space, which the data center could then convert into more IT equipment space for endusers or revenue-generating colocation areas.

In the data center’s never-ending journey towards peak efficiency, it’s safe to say that the next step will be the simplistic, all-in-one, modular approach to MEP design, cost, and increased reliability with DRUPS.