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How variable frequency drives and motors create energy-efficient cooling for data centres

09 Jun 2020

Data centres use enormous amounts of energy, especially in cooling the IT equipment housed within their walls.  However, investing in variable frequency drives (VFDs) and energy efficient motors in cooling systems can make a massive contribution to keeping energy consumption under control. We asked ABB Group's Global Product Marketing Manager, Maria Fedorovicheva, to explain how.   

Why look for efficiency gains in data centre cooling processes?

As an integral element of modern computing infrastructures, data centres already use around one percent of the world’s total energy production. Cooling systems, which play a critical role in ensuring the reliability and availability of the facility around the clock, typically consume up to 40% of all the energy used by the data center. The other large user is the IT equipment itself. Based on these figures, it is clear that the fans, pumps, and compressors – which form the heart of data center cooling systems – should be one of the first places to look for efficiency gains. 

Are there any regulatory parameters to control energy usage in data centres?

One of the most common metrics for energy efficiency has been devised by the industry consortium, Green Grid. This is the power usage effectiveness (PUE) - the ratio defined as the total power entering the data centre divided by the power used by its IT equipment. In an ideal world, a data centre would have a PUE of 1.

According to a study performed by the Uptime Institute, the PUE levels of data centres have been decreasing over the years, from around 2.6 in 2006 to 1.7 in 2019, although the recent trend, since 2013, is flat. To help drive PUE down further, it is necessary to take actions to increase the efficiency of data centres during their operating life as well as implementing cutting edge technologies in new projects. One solution that can help in decreasing PUE substantially is to adopt VFDs and energy-efficient motors for the cooling systems.

Why VFDs specifically? 

VFDs have proved to be a highly effective energy-saving solution for cooling. Drives enable the speed of electric motors used in cooling applications to be controlled precisely, so that they produce the required flow at any time, resulting in energy savings of up to 35%. This is in contrast to running the motor at full speed and controlling the output by throttling and damping. The relationship between motor speed and energy consumption means that even just a moderate reduction in speed can result in a very significant improvement in energy efficiency.

While data centre cooling systems are sized to handle peak loads under the most adverse conditions – from summer heat to component failures – they seldom, if ever, operate at their design loads. Instead, they operate mostly in a lightly loaded state. VFDs provide the flexibility to enable the cooling system to match the varying load profile so that high system efficiency can be maintained even at partial loads. 

Does motor technology matter as well?

Absolutely. Different motor technologies show a different performance depending on the load. At 25% load the efficiency difference between motor technologies can easily be over 10%. It therefore makes sense to choose a motor based on its performance in the range where it will be operating most of the time. And in most cases, that range is not the nominal load, but well below it. 

Are there any other considerations regarding cooling process efficiency?

In fact, the whole system efficiency matters – we can install highly efficient motors to run applications like pumps, fans or compressor with the minimum possible losses and use drives to match the motor speed to demand so that we save energy. But if, say, the design of a fan causes it to create massive aerodynamic losses, the whole system efficiency or wire-to-air efficiency may suffer. That means when considering energy efficiency in data projects, it makes sense to go beyond looking at each element on a component by component basis to evaluate the efficiency of the entire cooling system. 

As the server density of data centres continues to increase then so will their heat loads. Future-proofing data centre cooling systems means that they must be specified with the scalability to meet future needs. By scalability, we mean that they can be adjusted to suit changing loads, such as when a facility is expanded in size. Again, VFDs developed specifically for heating, ventilation and air conditioning (HVAC) applications as well as motors with high-efficiency characteristics- not only at nominal speed but also at part loads - offer an important benefit, as they are designed with flexibility and scalability built-in.