Which is Best? Centralized vs. Distributed UPS

Centralized UPS, Distributed UPSData centers of all sizes rely on a consistent power supply and therefore must employ some type of redundant power solution to ensure there is constant power for mission critical equipment.  Though redundant power solutions are commonplace, there are many different strategies that can be used to protect a data center from unplanned downtime. This means that a data center must determine which strategy is best for them based on a number of factors including data center size, risk tolerance, management capabilities, budget, risk tolerance, and more.  For the purposes of this discussion, we will be looking at two of the most common types of UPS systems: centralized and distributed. 

What is a Centralized UPS System?

A centralized UPS system consists of one large, often robust UPS system that is capable of supporting the full load necessary to maintain uptime. A centralized UPS system will often need a transformer because of their high voltage. Because of their size, centralized UPS systems tend to take up more physical space and be more costly up front which is why this type of backup power supply is more common in a large, enterprise-level application.

What is a Distributed UPS System?

A distributed UPS system has multiple smaller UPS systems that support various devices or equipment but do not support the entire load (and are not capable of doing so). They are often housed near critical equipment and then the power is distributed as needed.  These types of systems typically cost less than a large UPS system and can be scaled up or down as needed in the future. 

Advantages & Disadvantages of a Centralized UPS System

Centralized UPS systems do tend to cost more initially so if initial budget is an issue, it may not be an accessible option. However, there are a number of advantages to making the investment.  Centralized UPS systems streamline maintenance and repairs and reduce potential points of failure to one which is often advantageous. For large system applications, a centralized system is popular because it can support the entire anticipated load while keeping monitoring centralized for more effective management.  Larger UPS systems tend to have a longer service life and better energy efficiency which thereby lowers overall operating costs. It is also easier to monitor and manage the climate of one central UPS rather than a distributed network of UPS systems.

Though most data centers are trying to reduce their potential points of failure, there are drawbacks to only having a centralized UPS system to support your facility’s entire load.  First and foremost, if your UPS was chosen based on initial data center anticipated load predictions, those predictions may now be inaccurate depending on how your data center has scaled or changed equipment. Can your centralized UPS actually support your data center’s current full load? What about your full load n 6 months or 1 year? Data centers are scaling rapidly to meet demand and your centralized system may no longer actually support your needs. Additionally, as mentioned, centralized UPS systems have are more difficult and costly to install because they have a larger footprint and therefore take up more precious space in your facility – do you have that much space to spare or do you need it for other equipment?

Advantages & Disadvantages of a Distributed UPS System

Centralized UPS, Distributed UPSDistributed UPS systems have become very popular because they require a lower initial investment and are easily scalable should your needs change. Because distributed UPS systems are smaller, they take up less valuable space in your facility, and are easier to install and deploy.  These types of systems tend to be most popular in small or medium-size applications. It is undeniable that one of the biggest advantages of a distributed UPS is how easily scalable it is, particularly in today’s data center climate where scaling is rapid and sometimes unpredictable but Data Center Knowledge points out that there are some other key advantages, “By grouping small loads and placing critical battery reserves close to the physical computing equipment, decentralized systems reduce the potential single point of failure to a smaller portion of the facility, improving resiliency amid increasing demand without burdening the entire site. Instead of relying on numerous AC-to-DC conversions, distributed DC power architecture directly connects the AC utility source to the cabinet, where smaller, more power-dense batteries and rectifiers are housed directly inside along with the networking equipment. This approach helps reduce the number of power conversion steps required to step down utility power to the needs of the servers and routers, helping improve efficiency, reliability, and scalability.”

Because distributed systems have more components there is a higher likelihood that one component or an entire system could fail, necessitating more monitoring and maintenance to prevent unplanned downtime. Additionally, because there is more than one battery, more battery replacements will be necessary. And, because the batteries are distributed, you will need to appropriately cool your separate UPS systems to maximize UPS performance and battery lifespan.

Centralized AND Distributed – Should You Combine UPS Configurations?

If you are uncertain which type of UPS configuration is ideal for your facility, you may be best served designing a combined UPS system configuration. Schneider Electric discusses a great example of when combining configurations is optimal, “Consider a hospital, for example. It may use a centralized UPS to protect critical loads such as emergency lighting, largely because it’s simpler to connect all the lighting circuits to the same UPS. But it’s common practice for each surgical or MRI room to have its own, dedicated UPS because these areas are so critical. You wouldn’t want to risk all of them being without power in the case of a centralized UPS failure.” Centralized and distributed UPS strategies can absolutely be used simultaneously for a more robust, redundant backup power supply for your mission-critical applications. Your faulty can be backed up by a large, centralized UPS system and you can simultaneously add a layer of protection by employing a distributed system for a specific set of equipment. Every data center is unique and there is no one-size-fits-all approach so carefully consider your needs, budget, and facility when determining what UPS system configuration is best for your facility. 

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