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Data centres generate an awful lot of heat, so much so that without any cooling the heat generated by the servers would destroy the components within four minutes.
That’s why data centre cooling systems are so important and why there is so much innovation to deliver more effective cooling methods for a cheaper price. If you can image, for an electrically powered cooling system, every kilowatt of power used by severs must be matched by the cooling systems, which can lead to quite a large expenditure.
However, there has been a lot of research into different and more efficient methods of data centre cooling, and we’ll be looking at a few of the most promising and effective.
This is a tried and tested means of data centre cooling, and works to deliver the cold air to where it is needed most. While it is in itself not a method of cooling, it is a means of effectively & efficiently delivering cooling when combined with other methods.
After being brought in, the cold air is delivered into a plenum underneath the data centre floor and escapes upwards directly into the line of servers. The efficiency of this system is that you are not trying to keep the whole data centre cold, only the actual servers.
Fresh Air Cooling
This method of cooling has been around for a while, but it can be so effective when properly utilised that it definitely deserves a mention. The principle of fresh air data centre cooling, or “free cooling” as it is sometimes known, is simple. Air is supplied from outside the building directly to the servers without the use of any chiller or refrigerant. Of course, this method only works if the external ambient temperature is low enough to be used, somewhat limiting its availability. The term “free cooling” is also somewhat of a misnomer, as the fans used to circulate the air must still be powered.
It is a very viable method for data centre cooling in colder climates, such as Iceland, Finland, and parts of the US due to the lower average temperatures found there.
Kyoto Wheel Cooling
A rather unusual design, a Kyoto wheel works by manipulating air streams and utilising cold external air to cool itself, and the internal air in the data centre. In effect, it is a large rotating heatsink. The idea of the wheel is that it is split in two halves, a hot half and a cold half. Throughout a rotation, the cold half begins by sitting in line with the hot air return from a data centre, and because of its honeycomb matrix, it takes the heat out of the air before returning it to the data centre. On the other half of the wheel; which is now hot having absorbed the heat from the data centre, cold air from outside flows over the wheel, taking the heat out of it before being rejected back outside.
It is a very large and expensive data centre cooling system, but it is highly efficient, delivering a PUE of less than 1.25.
This has been used since the early 1980’s though drastically declined in popularity since the 90’s, it’s now making a comeback as a valid method for data centre cooling. It works by attaching the sealed unit directly to your servers, then pipes deliver cold water to it, which absorbs the heat before it is carried away. While it can be an efficient method of data centre cooling, it is only really useful in smaller data centres and individual servers, as each unit must be attached to each server.
Deep Water Source Cooling
This method of data centre cooling can be extremely efficient, but like the fresh air cooling, is restrictive in its deployment locations, and is also extremely expensive to install.
Deep water source cooling works by utilising a large body of water as a heatsink, negating the need for any refrigerant. Hot air is drawn from the data centre, and travels to a heat exchange facility, there it is cooled by water drawn from 50m below the water surface, before it is returned to the data centre, and the now hot water is returned to the lake, or sent elsewhere.
This method of server cooling is a rather unusual one, and involves submerging a server into a thermally conductive but not electrically conductive liquid. Using heat convection, the servers heat the liquid which circulates to the top of the tank and is cooled by evaporation. The cold liquid then sinks back to the bottom as new warm liquid rises. It is a useful method of data centre cooling for facilities of all sizes, however needs a very large footprint, as instead of normal vertical cabinets to hold your servers, they are horizontal baths with a large surface area to aid the cooling of the liquid.
Underwater Data Centre
The latest development courtesy of Microsoft’s “Project Natick”, it’s a method of data centre cooling based on Deep Water Source Cooling. A modular data centre is constructed and sealed to be made watertight, and the whole unit is submerged at the bottom of the sea. The walls of the data centre act as one large heat exchanger, absorbing the heat of the interior of the data centre, which is then cooled by the outside liquid.
Microsoft trialled this recently and found that after being left submerged for a year, there were no problems with the system. However, despite the advancement, its use will be limited until the development of undersea buildings, as the data centre is completely isolated and inaccessible, meaning that to make the slightest change to a rack will involve retrieving the whole data centre from the bottom of the ocean.
Of course, we only need data centre cooling because servers are designed to work at certain temperatures, and as a by-product of their work they generate a lot of heat. This is being dealt with by many manufacturers, developing servers that can run more efficiently and are able to work at higher temperatures which will mitigate the amount of cooling your data centre will need.
You can improve the efficiency of your own data centre quite easily however, simply by using purpose built servers. Whereas “plug & play” servers are designed to do a range of different tasks and must be able to cope with various demands, a purpose built server is designed only for your tasks, and can therefore lose all the unnecessary extras that would otherwise be draining power yet not being used.