By Ed Spears
By Ed Spears
September 15, 2017 — A well-built power protection solution with highly efficient uninterruptible power system (UPS) hardware helps keep business applications available, power costs manageable and important data safe. By becoming familiar with the basics of a UPS and how to choose the right one, facilities operators and IT staff can ensure mission-critical systems always have the clean, reliable electricity they need to drive long-term success.
Choosing the right UPS
A UPS is the central component of any well-designed power protection architecture. So, how do you choose the right one to fit your specific application? There are some key areas to consider that can help guide you in selecting the right UPS and accessories.
The first consideration is whether you should get a single-conversion, double-conversion or multi-mode UPS. The answer depends largely on the importance of energy efficiency to your organization relative to protection.
Single-conversion UPSs are more efficient than double-conversion devices, but offer less protection. That makes them a good fit for loads with a higher tolerance for power anomalies, or where the incoming power is more stable. More specifically, standby UPSs are generally the best option for smaller applications, like desktop and point-of-sale solutions. Line-interactive UPSs are typically preferable for smaller server, storage and network applications located in facilities with access to relatively trouble-free AC utility power.
Double-conversion UPSs, which provide the highest levels of isolation from the utility AC source, are less efficient but are usually the standard choice for protecting mission-critical systems. They are also the most preferred topology in electrically poor environments, such as industrial applications and areas where severe weather is common.
While they may be more expensive than either single- or double-conversion systems, multi-mode UPSs are the best choice for companies looking to achieve an optimal blend of both efficiency and protection.
A UPS’s power rating is the amount of load—in volt-amperes (VA) or watts (W)—that it is designed to support. UPSs are available with ratings as low as 300 VA and as high as 5,000,000 VA (and even higher). Use this basic procedure to approximate the UPS rating your organization requires:
• List all the equipment your UPS will protect.
• From the list, determine how many volts and amps each device draws.
• For each device, multiply volts by amps to arrive at a VA figure.
• Add all the VA figures together and you have a decent approximation. Note: it is good practice to multiply that sum by 1.2 to accommodate for growth.
The UPS you buy should have a rating equal to or greater than the final number you arrived at, unless you have more precise load data for the equipment you are protecting. Here are a few additional considerations to keep in mind:
• When deploying a centralized power protection architecture, you typically deploy larger kVA UPSs than you would deploy using a distributed power protection scheme.
• When your UPS is supporting motors, variable-speed drives, medical imaging devices or laser printers, add more VA capacity to your requirements to account for the high power inrush that occurs when those devices start-up. Your UPS vendor can assist in applying the proper UPS and rating for these types of applications.
• Companies that anticipate rapid near- or medium-term growth should use a multiple higher than 1.2 when building in room for growth in the procedure above. Organizations that expect to upgrade server hardware soon should also accommodate for more growth, as newer servers tend to have higher power requirements than older models.
Organizations can utilize a variety of deployment options, technologies and services to increase the reliability of their power protection solution. The most effective techniques revolve around redundant deployment architectures, whereby UPSs are deployed in redundant groups to increase availability by ensuring critical loads remain protected should one or more UPS fail.
There are three main kinds of redundant UPS architectures:
• Zone: In a zone architecture, one or more UPS provide dedicated support for a specific set of data centre resources. That way, should a UPS fail during a power outage, the impact is limited to the zone that device supports.
• Serial: In a serial architecture, multiple UPSs are connected end to end such that, should any one UPS in the string fail, the others can compensate automatically.
• Parallel: Parallel and dual-bus architectures use multiple, independent parallel-connected UPSs to achieve increased redundancy. Should any UPS fail completely, the other systems can keep protected IT equipment loads operational.
UPSs come in a range of form factors that fit into two master categories: rack-mounted and freestanding. The largest UPSs aren’t available in rack-mounted form factors, so companies with substantial power requirements will use freestanding devices. For companies with more modest needs, deciding between rack-mounted and freestanding is largely a matter of data centre design philosophy.
Some organizations use rack-mounted UPSs in an effort to consolidate as much hardware as possible in their enclosures. Others prefer to maximize the amount of rack space available for servers by using freestanding UPSs. From a technical and financial standpoint, neither approach is inherently superior to the other.
Battery runtimes and maintenance
A typical UPS battery provides five to 15 minutes of backup power. Organizations that need more can use supplemental external battery modules or cabinets to add as much as several hours of emergency runtime at full load.
The battery is one of the most important parts of a UPS platform, which typically serves as the energy storage system. Most power protection solutions get their emergency standby power from either sealed batteries (a.k.a. valve-regulated lead acid [VRLA] batteries) or flooded batteries (a.k.a. vented lead acid [VLA] batteries).
Sealed batteries tend to be less expensive, but also wear out sooner. Flooded batteries generally require specialized installation and maintenance. New on the scene are lithium-ion batteries, which save floor space and weight, while offering a longer service life. They can also be instrumental in pioneering UPS applications like grid sharing and peak shaving, which were not viable with older technologies. Deciding which kind of battery is right for you basically comes down to whether you’re willing to pay more upfront for batteries that you won’t have to replace as often.
Many UPS systems continually float-charge the battery, which has a tendency to degrade the battery’s internal chemical composition over time, reducing battery service life. While large banks of flooded electrolyte batteries for high-power (>500kVA) UPS systems need to have the battery float charged, most non-spillable VRLA batteries used in today’s lower kVA UPSs can benefit from a charging technique where the charger turns off periodically and “rests”. This technique could help increase battery service life by as much as 50% with a three-stage charging process.
Tying it together with advanced power monitoring
Next-generation power monitoring services deliver comprehensive asset management capabilities. These solutions provide the capability to track data about a UPS, which includes details such as battery date code, model and type, firmware version, service history, capacitors, and so on.
This kind of information can be extremely useful. When an administrator can track data like battery date codes and service history, they can provide efficient planning and analysis. For example, they may see that a battery is five years old. That means it may be reaching the end of its useful life, and so will need to be replaced soon. The same principles apply for other consumable components in the UPS like fans and capacitors.
Whether it’s a data centre, healthcare or other environment where uptime is critical, power protection is an important consideration for today’s facilities. Choosing the right UPS and accessories will help you avoid downtime disasters. With the deployment of a strategic UPS platform backed by advanced power monitoring software, you can rest easy knowing that systems are up and running, and critical data is protected.
Ed Spears is a product marketing manager in Eaton’s Critical Power Solutions Division in Raleigh, N.C. A 37-year veteran of the power systems industry, Ed has experience in UPS systems testing, sales, applications engineering and training—as well as working in power-quality engineering and marketing for telecom, data centre, cable television and broadband public networks.
* This article also appears in the September issue of Electrical Business Magazine.