In today's technology-driven world, data centers play a crucial role in supporting a variety of industries, including e-commerce, finance, healthcare, and communications. As the backbone of digital infrastructure, data centers require reliable, uninterrupted power to avoid costly downtime and protect valuable data. One key aspect of ensuring this uninterrupted power is through Uninterruptible Power Supply (UPS) systems. Despite its crucial role, the efficiency of UPS systems is often overlooked, even though it has a significant impact on both operational costs and sustainability.

This blog will explore what UPS efficiency is, how it is calculated, and what factors influence it in the context of data centers.

What is UPS Efficiency?

In the context of UPS systems, efficiency refers to the ratio of energy delivered to the load compared to the energy absorbed by the UPS from the mains grid or battery system. In technical terms, efficiency measures how effectively the UPS system utilizes absorbed energy to power and protect the load. The higher the efficiency, the less energy is wasted during conversion, leading to lower energy costs and reduced heat generation.

This metric is essential for data centers operating 24/7 with high energy demands. Even a small increase in efficiency can generate substantial cost savings over time, particularly at scale. Improving efficiency also aligns with sustainability objectives and carbon footprint reduction.

Over the past 40 years, advancements in power electronics have driven significant improvements in UPS efficiency, reflected in modern system designs capable of meeting rising data center demands.

How is UPS Efficiency Calculated?

UPS efficiency is calculated as the ratio between output power and input power, typically expressed as a percentage. The calculation depends on whether the system is operating on mains power or battery power.

• On Mains Power: Some input energy is temporarily used to charge batteries, but this is usually excluded from efficiency calculations. In modern UPS systems, battery charging energy is minimal and has negligible impact.
• On Battery Power: All energy is drawn from batteries, and efficiency is calculated based on how much energy is delivered to the load versus absorbed from the batteries.

Efficiency values are measured using high-precision watt meters connected to UPS input and output. Manufacturers typically provide efficiency data for both operating modes in technical documentation.

The efficiency is calculated as:

“Output Power” is the actual power delivered to the load, while “Input Power” is the power drawn from the utility or battery system.

Factors Influencing UPS Efficiency

Several factors affect UPS efficiency:

• Load Level and Type: UPS systems operate most efficiently at higher load levels. Underutilization reduces efficiency due to idle losses.
• Power Factor: A power factor close to unity improves efficiency by minimizing reactive power.
• Ambient Temperature: High temperatures increase thermal stress and cooling requirements, reducing efficiency.
• Component Aging: Aging capacitors, fans, and batteries degrade performance over time, requiring maintenance and replacement.

Comparing UPS Topologies for Efficiency

Different UPS topologies deliver different efficiency levels depending on internal architecture and operating modes. Higher efficiency often correlates with reduced protection and power conditioning.

Off-Line (VFD)

• On Mains Run: Very high efficiency, but no voltage or frequency protection.
• On Battery Run: Efficiency equals the ratio between inverter output and battery input.

Line-Interactive (VI)

• On Mains Run: Voltage regulation via AVR; high efficiency with limited disturbance filtering.
• On Battery Run: Similar to off-line operation with inverter supply.

On-Line Double Conversion (VFI)

• On Mains Run: Rectifier and inverter operate continuously; efficiency depends on both converters.
• On Battery Run: Efficiency depends on DC/AC conversion performance.
• On Bypass Run: Efficiency depends on bypass circuit performance, especially the static switch.

This topology offers the highest level of load protection but lower efficiency due to continuous power conversion.

In some scenarios, efficiency can be increased using ECO Mode, where the UPS operates on bypass when input power is stable and switches back to on-line mode if voltage or frequency deviates.

For critical IT applications, especially three-phase systems, on-line double conversion remains the preferred topology due to its superior power quality and continuity.

Image 2: Comparison of UPS Topologies

Conclusion

Understanding UPS efficiency is critical for optimizing energy use, reducing operating costs, and ensuring reliable power delivery in data centers. As UPS technologies evolve, efficiency continues to improve while maintaining robust protection against power disturbances.

In the next part of this blog series, we will explore advanced technologies driving UPS efficiency and the practical benefits for data center operators.

Need help identifying the best UPS solution? Contact Legrand for an online demo or consultation here.