For this issue, we're putting the focus on UPS efficiency, and how with UPS efficiency ratings, what you see is not always what you get. Find out how to accurately calculate a UPS's utility cost analysis to determine which UPS model fits best with your operations.
As electricity prices continue to surge, guaranteeing UPS efficiency has become an imperative for data center managers. Many decision makers base their decisions on which UPS to acquire based on UPS units' efficiency ratings. However, while these ratings remain an important factor for cost analysis, side-by-side comparisons often do not take into consideration the potential capacity effects on efficiency that can mask the net efficiency of a UPS system. For a more accurate picture of UPS efficiency, therefore, we offer you an easy-to-follow formula for utility cost analysis.
How to Develop a Basic Utility Cost Model
Step 1: Identify the expected Loaded Capacity of the UPS.
Step 2: Identify the Output Efficiency at the Loaded Capacity.
Step 3: Determine your electricity cost.
Step 4: Calculate the real power in kilowatts of the UPS by taking the kVA
rating and multiplying it by the unit’s power factor.
Step 5: Calculate using the standard formula:
(Cost Per kWh x Annual Operating Hours) x (UPS Real Power x Load Utilized)
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UPS Efficiency at Load Utilized
Based on information gathered through the first four steps, a basic efficiency analysis
example would look like this:
- Loaded Capacity: 40%
- Output Efficiency at the Loaded Capacity: 92%
- Electricity Cost: 10 cents per kilowatt hour
- The 750 kVA UPS has a power factor of .9 and thus a real power rating of 675 kW (750 x .9)
- 8760 operating hours in a year (24 hours x 365 days)
For this specific example, the operating cost calculation would be:
(10 cents x 8760 hours) x (675 kW x 40% capacity)
----------------------------------------------------------------------------- = $257,086 in utility operating costs for one year
(92% efficiency)
It's important to note that in the quest to maximize the efficiency of your UPS, you might compromise key features like availability and reliability. The following factors are examples of this scenario:
- Utilizing bypass mode
- Utilizing capacitors instead of breakers
- Momentary duty static switch instead of continuous duty
- Elimination of the isolation transformers from the UPS
In summary, a thorough understanding of how partial-load configurations impact a UPS system’s performance and efficiency is essential to achieving an accurate utility cost model. However, utility costs are only a single component of a Total Cost of Ownership analysis. Any cost analysis must include maintenance, reliability, monitoring and, especially, the impact of UPS design on IT system availability.
It also is critical to understand how a UPS is able to achieve its efficiency rating and what the impact is on availability. The high-efficiency UPS might not be the most fault-tolerant and might not be the best option for extremely critical environments. By asking some questions and doing the math, you can find the UPS that is ideal for your specific operations.