The best of both worlds

When it comes to optimising energy and water use in data centres, it is no longer a case of one or the other. Technologies such as adiabatic cooling can achieve both, while also helping to minimise maintenance costs. Yan Evans, director, Data Centre Solutions at FläktGroup UK, explains why operators should choose adiabatic cooling.


he volume of data collected and processed by companies is growing at an unprecedented rate. Data centres

are struggling to expand physically to cater for this growth, and instead face the challenge of increasing computer power in the same amount of space. This of course impacts on energy consumption – it is estimated that globally, data centres consume between 3-5% of the world’s power, which is equal to that of the aviation industry. And this is set to triple in the next decade alone. A study focused on Japan suggested that its data centres would consume its entire electricity supply by 2030 if growth continues at today’s rate. The rising cost of energy has undoubtedly been a huge driver for data centre efficiency, as has the effect of consumption on climate change. Operators are increasingly concerned about their carbon footprint and their impact on local power plants and water usage.

The energy used for just climate control and UPS systems alone can be around 40% of a data centre’s total energy consumption. With higher levels of micro processing power in the same space, efficient cooling systems can significantly cut carbon footprints and energy bills. However, whereas Power Usage Effectiveness (PUE) has become the main efficiency metric for operators, it has had some unintended consequences, including a staggering increase in the use of water. That is why, in recent years, there has been a new focus on Water Usage Effectiveness (WUE), a fairly new sustainability metric and natural extension of PUE.

Which cooling methods? A direct expansion (DX) air cooling system works well during colder months but draws much more

energy during hot weather. The latter requires a larger and more expensive infrastructure to support it, such as appropriately sized backup generators for the highest possible draw. Traditionally, evaporative coolers (cooling towers) have been viewed as more efficient than air cooling systems but they use high volumes of water and require regular maintenance which can be costly. A data centre can easily use many millions of gallons of water each year. Recently, new adiabatic technologies that use freely available natural phenomena to regulate temperature have become popular. The main advantage of adiabatic cooling is the ability to cool fluids to below dry ambient air temperature. In the UK we can experience up to 35°C air temperatures, but this method makes it possible to maintain 25°C fluid outlet temperatures all year round. It also uses up to 90% less annual water usage than other systems.

How does it work? Traditional systems use a water circuit as a go-between. However, the latest models use a plate heat exchanger (PHE) which has high dry efficiency. When outdoor air is cooler than the indoor air, heat transfer is just from air-to-air via a PHE and without the use of water. At very high outdoor air temperatures or when very low supply air temperatures are required, DX is fitted and in operation for a few hours per year. An issue arises when evaporation results in substantial water loss. Water is a resource that is becoming increasingly scarce and costly in some parts of the world – for instance, the state of California has 800 data centres and they consume enough water to fill 158,000 Olympic-sized swimming pools every year.

In light of this, and with the scale of these facilities increasing, data centre operators have started working with local municipalities and water utilities to reduce their impact on local water supplies.

The good news is that the principle of adiabatic cooling is now being harnessed to develop cooling units that can save the data centre industry millions of litres of water. Technologies are now available that use reverse osmosis water, allowing for the water to be reused in adiabatic cooling several times, dramatically reducing flush cycles from every hour to every few days. A system set up in this way allows data centres to efficiently cool their processors while using much less water than traditional cooling systems. This method also results in an improvement in water quality. Systems with reverse osmosis are not at risk from legionella, therefore eliminating the need for any circulation water treatment procedure and reducing replacement and maintenance costs in the process. As data centres have grown and adapted in

response to changing demands, cooling systems have done the same. Today’s data centres must balance the benefits of advanced, powerful technology against the cost of running such computing systems. Heat must be removed efficiently without adding significantly to the already high operational costs. Where once lowering power consumption could have a detrimental effect on water use, it’s now possible to have the best of both worlds. The rise of adiabatic evaporation and free cooling is showing that energy consumption can be curbed while simultaneously reducing water use. In turn, this means that data centres can continue to be profitable and meet their environmental objectives.

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