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Improving heat transfer efficiency in data centres

Improving heat transfer efficiency in data centres

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Gemma Reeves, Business Unit Manager specialising in Data Centers for EMEA at Alfa Laval UK, discusses the need for more efficient heat transfer within data centre cooling systems, and how heat exchangers can act as an enabler of green IT.

According to data centre specialists, it has been said that the world’s 9 million data centres’ CO2 emissions were equal to that of global air travel in 2019, and this only continues to rise. The last two years have seen a significant drop in air travel due to COVID-19 but the global lockdowns have prompted an explosion of video conferencing and remote working, leading to some referring to digital infrastructure as ‘the fourth utility’.

What many people don’t know is that at present, 40% of an average data centre’s energy usage is used solely for cooling. Developing more efficient heat transfer systems and looking at not just the cooling, but the reclamation of the waste heat will be paramount to achieving net zero targets by 2050. There is a desire in the industry to become greener, however, many data centres are currently far too reliant on mechanical cooling techniques which are simply not a sustainable option for the future. Cue the heat exchanger.

The role of the heat exchanger

There are many possible applications for heat exchangers in a data centre. At the heart of the data centre is the server room, a pristine white space processing millions of megabytes of data every hour. Such sensitive electronic pieces of equipment need protecting at all costs from the dirty exteriors that surround them, and heat exchangers fulfil that exact role as a protective shield, while enabling accurate control of temperature.

There are many common applications for a heat exchanger include a cooling tower interchanger, providing free cooling utilising localised water sources such as the sea or a river, a free cooling interface with dry or adiabatic air coolers, or some of the newer applications in the industry drive to a greener future including liquid immersion cooling and waste heat recovery. We will go on to discuss some of these in more detail.

Heat exchangers come in many forms such as gasketed and copper brazed, and are ideally suited to data centres and their demanding performance targets to achieve reductions in power and water usage. It is crucial to specify the right heat exchanger for the job, involving the heat exchanger manufacturer early in the design process will ensure a design that delivers the right performance over the whole life cycle.

An invaluable indicator of a heat exchanger’s performance is whether it is certified by the industry-trusted Air-Conditioning, Heating and Refrigeration Institute (AHRI). This independent organisation develops standards and certification programmes to ensure that the unit supplied will perform as specified.

Reducing reliance on mechanical cooling

While mechanical cooling has certainly served a purpose over the years, it is fundamentally based on using energy to cool a system, often using fossil fuels or electricity to achieve this. These days, it is naturally viewed as an energy drain that should be operated as little as possible.

One alternative option is to use free cooling when the outside air temperature allows, and as a result minimise the use of a chiller. In the average data centre, chillers represent one of the highest consumers of utility electricity which often results in high operating costs as well as significant environmental concerns due to the increased carbon footprint. Cooling towers, which are widely used to dissipate heat from data centres, can also be used in free cooling mode to bypass the chiller and thus help solve these challenges.

However, open cooling towers can also be a major source of fouling in data centre cooling systems, leading to reduced thermal efficiency, laborious maintenance and risk of equipment failure, in turn leading to increased operational costs. Installing a gasketed heat exchanger as an intermediate is one smart way to both enable free cooling and minimise the risk of fouling, without sacrificing the cooling performance of the system.

Another option is to recover as much heat as possible since most of the electrical energy used in a data centre will be transferred to heat. This ‘waste heat’ can be used for numerous applications, only the designer’s imagination will set the limits. This concept has been proven in a Danish data centre where Alfa Laval equipment assisted in recovering waste heat from servers and used it to supply heat to a district heating network. This example saved 100,000 MW in energy – or in other words, enough energy to power New York City for nine days.

A sustainable future in immersion cooling?

Machine Learning and high-computing applications, such as Blockchain technology, use high-density processors. This higher heat density necessitates more efficient cooling strategies. In many cases, it is no longer enough to simply blow air over the equipment anymore, so the next best option is to use a liquid. The core advantage of liquid cooling over air cooling is that liquid can absorb heat more efficiently – up to thousands of times more efficiently if we look at water.

This is where immersion cooling comes in – the current buzzword of the data centre cooling space. This is done by submerging the servers or other components into a liquid that is thermally conductive, but not electrically conductive. This is known as a dielectric coolant.

Today, there are a couple of different types of immersion cooling options available, single phase and two-phase, both of which from initial results appear to typically provide significant reductions in cooling energy usage by 35% to 75%.

Overall sustainability savings associated with this methodology remain to be evaluated, however, all things considered, the power density now required by servers is increasing and air-cooled systems can no longer cope – hence the need for more efficient liquid-cooled solutions.

Explore more about heat exchanger potential

As you can see, there are multiple opportunities available which could benefit from the use of heat exchange technology to improve efficiency within a data centre, both in current systems and the innovations of the future. Here we have only touched the tip of the iceberg in terms of realising the heat exchanger’s full potential in data centre energy optimisation.

For those wanting to learn more, there is a dedicated knowledge hub on our website for this sector which I encourage professionals to take advantage of.

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