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Building Operating Management

Comparing Uninterruptible Power Supply (UPS) Energy Storage Options



Four UPS energy storage options have advantages and disadvantages. Here's how to know what's right for your mission-critical environment.


In data centers and mission-critical facilities, the uninterruptible power supply (UPS) is an essential failsafe device. If power goes down, the UPS provides brief ride-through time during the automatic switchover to auxiliary power. But during that 10-12 second switchover, the UPS needs to deliver a high amount of power to the facility to keep it operational. To handle that switchover, the UPS needs a reliable stored energy power source: If the UPS fails, power goes out in the facility, resulting in costly downtime. 

Facility managers should be familiar with four types of UPS energy storage systems: lead-acid batteries, lithium-ion batteries, nickel-zinc batteries, and flywheels (a.k.a., rotary systems). All have advantages and disadvantages; by taking a close look at their characteristics, facility managers can decide which they should consider using in a mission-critical environment.

A Few Technical Terms

It’s important for facility managers to understand a few basic technical terms to compare the performance of batteries and flywheels.

• Cycle Life: The number of times a battery can be discharged to 50 percent power and recharged to 100 percent power before it dies. For example, a battery with a cycle life of 300 can be discharged and recharged 300 times.

• Discharge Rate: The rate at which a battery or flywheel discharges its entire power load. The faster the discharge rate, the more capable the device is of delivering large amounts of power to the UPS. For example, a battery with a two-minute discharge rate can deliver power faster than a battery with a 10-minute discharge rate.

Thermal Runaway: A dangerous condition that may occur if a battery is overcharged, charged too quickly, or operated in very high temperature environments. If the heat generated by the battery is not properly dissipated (released), the chemical reaction in a battery cell exceeds its ability to disperse that heat, resulting in a battery explosion. Different batteries have higher or lower susceptibility to thermal runaway, based on their design and/or chemistry.

• Battery Management System: A monitoring platform that provides facility engineers with real-time battery status and performance data. All lithium batteries come with a built-in battery management system, but a battery management system is optional for lead-acid and nickel-zinc batteries.


posted on 11/7/2018

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