The efficiency trade off

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Want to improve the efficiency of your UPS system without having to sacrifice on availability? Giovanni Zanei, senior director, global large power offering at Vertiv, discusses how you can improve the efficiency of your UPS – without having to rely on ECO Mode.

 

In our always on and connected world, there is an increasing expectation that online services – from Netflix to business email – will just work.

One way to ensure that consistent uptime and availability is through the use UPS technology. UPS systems provide clean power to electronic devices such as computer networks and servers, building management and security systems. UPS also protects against power outages which could potentially lead to a halt in operations, a loss of information, productivity and profit for businesses.

According to Vertiv’s recently released Data Centre 2025 report, in terms of protecting the availability of data centre services, AC UPS systems continued to be the strategy of choice for survey participants, growing from 30% in 2014 to 47% in 2019. 

 

However, while UPS provide resiliency, they also come with an energy cost. Given that most organisations are also focused on improving energy efficiency, and lowering carbon emissions, controlling energy costs, and thus the energy efficiency, is an increasing priority. 

The energy efficiency of a UPS is the ratio between the power entering the UPS and the power exiting the UPS to supply the load. Whenever current passes through the internal components of a UPS, a certain amount of energy is dissipated as heat, which results in energy losses. 

Additional energy is also consumed when air conditioning systems operate to sustain the ideal environmental temperature of the installation. Whilst a certain amount of energy loss is inevitable, it is evident that the reduction of UPS power consumption and the consequent increase of its efficiency will significantly contribute to lowering excess energy waste, maximising the overall running cost-saving of the energy bill.

The savings generated by increased UPS efficiency extrapolated over 24 hours a day, 365 days a year over a five-year period, would not only exceed the purchase price of a UPS but also actively contribute to reducing CO2 and other global warming emissions, ensuring the lowest environmental impact of the chosen power protection solution. 

Double-conversion mode

Nowadays, the most common UPS mode of operation used for supplying secure power to data centres is double conversion mode, which ensures a Voltage and Frequency Independent (VFI) type of operation by providing the highest level of power quality to the load at all times. 

At the same time, as there are two stages of power conversion, this is also the mode of operation that consumes the largest amount of energy. Even when considering a double conversion UPS, there are significant differences in terms of double conversion efficiency: legacy UPS may operate with 93% efficiency when operating in double conversion mode, while the highest efficiency present-day UPS can achieve levels approaching 97%. 

Pros and cons of eco-mode UPS 

To further increase efficiency, most UPS manufacturers have introduced high energy efficiency modes of operation, such as ECO mode. However, most of these modes still serve as marketing hype rather than a concrete way of improving the data centre efficiency.

One would not expect the reliability of a UPS to be affected while operating in ECO Mode. In fact, in ECO mode, some of the internal components present inside the inverter and rectifier are less stressed, so the reliability of a UPS may actually increase. 

On the other hand, since there is no power conditioning performed by the UPS during this mode of operation, there may be a decrease in power quality supplied to the load, thus affecting the load power availability.

It seems that the increased efficiency with ECO mode comes with drawbacks to load availability. So, is it possible to find the right balance? 

Minimising the trade-off between availability and energy efficiency 

Recently, new efficiency improvements have been introduced to the market. And these modes are finally contributing to reduce data centre PUEs to the minimum possible, while still maintaining the highest levels of availability. 

One interesting feature comes from a combination of two deep-rooted innovations: 

●      Capability for the inverter to work as an active filter (VI mode), hence compensating on the reactive power of the load

●      Capability for the inverter to instantaneously assume the load and maintain the output voltage within the IEC 62040 Class 1 specification 1.

Hence the UPS can transfer safely from high efficiency mode (easily reaching 99% efficiency) to inverter mode with a 0-millisecond transfer (e.g. in the order of microseconds in worst case scenarios after a mains short circuit failure), thus providing complete load power protection under any input power outage condition. This is the same output performance and power quality offered in standard double conversion UPS but with 60% reduced losses. 

How does it work? 

The combination of these two technologies creates a Dynamic Online mode which offers an operating efficiency up to 99% without sacrificing availability to the load.  

Dynamic Online mode is the latest high efficiency mode of operation offered by Vertiv with Liebert Trinergy Cube and Liebert EXL S1, developed with the understanding that many of our customers do not want to trade-off any level of reliability for incremental gains in efficiency. A UPS with Dynamic Online mode offers an operating efficiency up to 99% without sacrificing reliability.

By analysing the mains quality and adjusting the mode accordingly, the superior availability of a double conversion mode can be combined with the excellent energy cost savings of a high efficiency mode for a reduced total cost of ownership. 

How businesses around the world are using this mode to improve the way they work 

Analysing data received from customers already taking advantage of this Dynamic Online mode, if you compare the cost of energy dissipated by a transformer free 1 MW UPS and the same UPS using this mode, the saving on the energy bill can surpass $15,000 per year. That’s equivalent to the energy required to drive 28 times around the equator using an electric car. 

And just as electric cars offer a more sustainable approach for transport, new UPS technologies are helping to manage the trade-off between availability and efficiency in the IT world.

Finding the right balance ultimately depends on the specifics of the business and the applications being supported, but suppliers of UPS equipment will continue to innovate in order to give customers as much choice as possible in how they choose to balance efficiency and availability.