How is ups efficiency calculated?

Orson Zhong

2 years ago

UPS efficiency is a big deal. The more efficient your UPS, the cheaper it is to run. As energy costs continue to increase, we’ve seen that businesses and organisations across multiple sectors are now looking for ways to increase their energy efficiency and subsequently reduce their energy bills. One of the ways to do this is by investing in an efficient uninterruptible power supply (UPS). Here, we’re going to discuss all things relating to UPS efficiency so that you can make an informed decision about the solution that’s right for you.

FIg. #1 UPS efficiency curve (Efficiency vs Load)

ups efficiency curve — FIg. #1 UPS efficiency curve (Efficiency vs Load)

What is UPS efficiency?

The efficiency of an uninterruptible power supply is based on how much of the original incoming power is needed to operate the UPS.

As an example, a UPS that scores 90% for efficiency will use 90% of the original input for powering the load and the connecting systems. Then, the remaining 10% of energy will simply go to waste whilst running the UPS.

For a UPS, higher efficiency equates to lower losses of electrical energy in terms of heat output; low-efficiency UPS systems often require more air conditioning to help keep the surrounding temperatures safe.

When comparing UPS systems and calculating the efficiency of uninterruptible power supply, there are two things you need to keep in mind:

UPS systems have different efficiency rates
the efficiency differs, depending on the load level

The energy efficiency of a UPS system is influenced significantly by its design. On paper, double-conversion systems should be less efficient than single-conversion systems, for example. However, manufacturers now produce UPS systems with a variety of modes that can deliver higher efficiency rates than ever before.

You will also find that energy efficiency increases when using a larger UPS. This is simply because the support power required to power the control electronics and other components is a much smaller proportion of the UPS’s total capacity.

In general, the efficiency of uninterruptible power supply has improved significantly over recent years. Thanks to a series of technological advances, principally the development of transformerless UPS systems.

The difference in operating efficiency between transformer-free UPS and transformer-based UPS designs can be as much as 5-6%. Although this divergence is less for the latest transformer-based models. Transformerless UPS have a flatter efficiency curve too. It can achieve high efficiency (>95%) at 25% load all the way through to full load.

How does ECO operating mode impact the efficiency?

Running the UPS in its dedicated energy-saving mode, commonly known as ECO mode, can boost efficiency to 98-99%. It achieves this by in effect operating as a line-interactive UPS, so the load is powered by the bypass line with the inverter inactive but ready to take over if there’s mains supply failure or fluctuation.

But while efficiency improves running in ECO mode, it can affect reliability and so should only be used sparingly. An appropriate example would be overnight or out of hours when critical loads are inactive.

Smart active operating mode can also help enhance the efficiency of uninterrupted power supply. With this functionality, the UPS automatically decides whether to run in full online mode or ECO mode depending on the stability of the incoming mains supply.

In ECO mode, UPS systems can be up to 99% efficient. The downside is that it can affect reliability, so we advise you only use it during periods where critical business activities aren’t taking place or critical loads to your data center aren’t required.

How to calculate UPS efficiency

UPS efficiency is measurable and can be expressed as a ratio or percentage. You can measure it by using the following formula:

UPS Efficiency = UPS Output / UPS Input * 100%

Output (or work output) is the total amount of useful work completed without accounting for any waste and spoilage. If you want to express efficiency as a percentage, simply by multiplying the ratio by 100.

Efficiency measures any performance that uses minimal inputs to get the maximum number of outputs. Put simply, you’re efficient if you get more by using less.
FAST FACT

Manufacturers provide detailed information on the energy efficiency of their UPS systems under varying load conditions. You’ll see this displayed as an efficiency curve.

Energy efficiency is about saving money. If you’re handy with a calculator and have access to the figures you need, you can use this equation to calculate the annual running costs of operating your UPS at different efficiency levels.

(UPS kW Rating x Load % ) / UPS Efficiency) – (UPS kW Rating x Load % ) x (24×365) x kWh Price

To run the calculation, you’ll need to know how much you’re paying for your energy (kWh price) and the efficiency levels for load profiles. You should be able to find this information on your UPS manufacturers website.

Why is efficiency important to ups?

It’s all about money.

The more efficient a UPS is, the cheaper it will be to run. Many of the UPS installations are designed to be in place for over ten years, during which you can make significant savings (or experience high extra costs).

It’s not just about power consumption saving. Low-efficiency UPS systems produce more heat, which needs to be cooled by an air conditioning system. The more efficient your UPS, the lower your air conditioning costs, and your utility power bill.

Modern UPS systems are highly efficient, delivering real-life performance that was unheard of even ten years ago. In the past, UPS performance levels rarely achieved 90%, and certainly not the 95%+ efficiency that operators can expect today.

New technologies used in UPS transformer-based systems and innovations such as ‘transformerless’ UPS systems are pushing the boundaries of what’s possible, and customers are benefitting.