Best Practices for Designing N+1 UPS Configuration

Editors note: Lifeline Data Centers uses N+N redundancy in construction of both power and cooling facilities. N+1 redundancy is less resilient. This post describes N+1 redundancy and its characteristics.

N+1 (or parallel) redundancy is one method used to ensure system availability in the event of component or power failures. In engineering terms, it is “the duplication of critical components or functions of a system with the intention of increasing reliability of the system, usually in the case of a backup or fail-safe.”

In data centers, it is the total number of necessary power equipment + 1 extra/ backup power supply to ensure uninterruptible power supplies. Some tips to design a reliable N+1 UPS configuration in data center include:

• Redundancy shouldn’t be for a single UPS in a data center. Data centers which use legacy systems may have to deploy static transfer switches (STS) in front of a single input load which transfer the load to a bypass source during power loss at UPS output. Whereas, modular systems have extra UPS modules that come in to action when any module fails.
• Use separate power branch circuit sources for each power supply to achieve redundancy in case of power loss at the source.
• It is ideal to have the same output current and voltage ratings for every power supply.  Undersized power supplies might lead to current sharing which defeats the purpose of an actual redundant system.
• To allow for proper setup, each individual power supply should have adjustable output voltage, and should be enabled to operate reliably under no load conditions.
• Use high power density UPS for data center blade servers as these servers have 4 times higher power requirement than normal servers.
• As opposed to the 75% usage of efficiency in normal UPS, N+1 redundant UPS is used only to 50% of its efficiency.  Generally, full load efficiency of any system is higher than its part load efficiency. Thus, improving part load efficiency is a challenging factor.
• If the UPS works on a wide range of input voltages, the UPS batteries can be avoided altogether. But when there is more battery usage, it wears out soon, requiring expensive replacements. Choose advanced battery management technologies that carefully control the battery charging.

Need more tips and suggestions on how to improve your data center uptime? Contact the experts at Lifeline Data Center today.

Alex Carroll

Managing Member at Lifeline Data Centers

Alex, co-owner, is responsible for all real estate, construction and mission critical facilities: hardened buildings, power systems, cooling systems, fire suppression, and environmentals. Alex also manages relationships with the telecommunications providers and has an extensive background in IT infrastructure support, database administration and software design and development. Alex architected Lifeline’s proprietary GRCA system and is hands-on every day in the data center.