Liquid cooling for the cloud

The Coronavirus pandemic has resulted in a worldwide increase in homeworking. This has lead to even greater reliance on cloud computing as more data gets lodged somewhere in the stratosphere. Or so many of us believe. But actually of course, the data is stored in massive, energy-intensive data centres, all over the world.

In July Knight Frank, the global property adviser, released findings from its Data Centre Report 2021* that show the data centre market has experienced significant growth this year.

The report, published in partnership with DC Byte, the leading data centre research and analytics platform, shows EMEA (Europe, Middle East and Africa) markets have seen take-up rise by 4 percent, to 120MW with a 10 percent increase in new supply overall, totalling more than 180MW.  In APAC (Asia Pacific) total supply increased by just under 200MW, reflecting a similar pace to 2020 take up – recorded at just over 800MW – making total supply 5800MW across the region.

In EMEA, the core markets of Amsterdam, Frankfurt, London, Paris and Dublin continued their momentum. But the overall trend is towards expansion beyond these markets with Africa poised to become a significant region, highlighted by the level of supply coming online in South Africa and Kenya. Istanbul and Warsaw are also noted in the report as key “edge” markets to watch.

Whether this expansion of data centres across the world is a good or bad thing is a moot point as it will continue to happen. It is therefore crucial to find ways to minimise the massive amounts of energy and water that they use and to benefit from the surplus energy that they create.

Energy efficient cooling is critical to building more sustainable data centre operations, given that cooling costs can account for more than half of a data centre’s total annual operating cost. There are a number of ways that such cooling can be deployed.

Free cooling involves lowering the air temperature in a data centre by utilising naturally cool water instead of mechanical refrigeration. The ambient outdoor air at many latitudes and elevations can be considerably cooler during certain seasons and times of the day than the air that is warned by data centre equipment. By filtering and humidifying cooler outdoor air and converting it through a heat exchanger for use inside into the data centre, it is possible to reduce or eliminate the use of mechanical cooling for the majority of operating hours, particularly in drier and cooler climates.

As an alternative, cold water sourced from a local river, lake or even the ocean can be processed through a heat exchanger into a data centre and used to achieve the same result. Systems that use this approach are often called water-side economizers, which can either be used to cool the ambient room air or they can directly cool IT equipment cabinets using rear-door heat exchangers or other systems.

Mechanical cooling is only needed when the outdoor air temperature becomes too high for free cooling systems and consequently, the working life of installed refrigeration systems can be significantly extended. The Logarithmic Mean Temperature Difference (LMTD, the temperature approach between the cold side and the warm side), can be as low as 1K.  Even with a larger heat transfer area of the heat exchanger it can still work, but if the ambient goes lower than that, the chiller will take over. A further cooling technology, particularly for dealing with sudden increases in temperature, is an ice storage cooling system.

Two of the most common applications of mechanical cooling are absorption cooling, working on the principle of vapor absorption, and chillers, which provide a continuous flow of coolant to the cold side of a process water system at a desired temperature of about 20°C. A chiller uses a vapor compression mechanical refrigeration system that connects to the process water system through an plate heat exchanger, better known as an evaporator.

Looking ahead, liquid cooling of servers is the most energy-efficient way to drive the data centre industry forward. This allows optimum energy use in the technology suite, so that more power drives the applications on the servers, rather than the cooling systems. Smaller ‘edge’ data centre facilities (2MW or less in power capacity) that cache content locally in order to offload processing of data and services from central cloud servers, particularly benefit from liquid cooling technology over air cooling techniques.

How can excess heat from data centres be utilised and not just wasted? Surplus heat, for example heat from servers or indeed other machines or industrial processes, can be sourced for various heating applications. For example, data centre excess heat obtained from cooling can be recovered using our SWEP BPHE and supplied directly to a district energy network. As waste heat is an unwanted by-product from another application it therefore has a very low carbon footprint. Given the expansion of data centres across Europe, there is considerable potential for this type of heat recycling, though there is still some way to go to balance the potential costs with the likely environmental benefit.

The rise of the data centre is likely to continue for some years to come. While much of the heat they produce is currently wasted, the applications discussed can play a key role in the future provision of affordable, sustainable and low carbon heat and in turn helping to decarbonize the planet.

For more information, visit SWEP data Centre cooling landing page.