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COOLING
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By Brendan Leonard , Managing Director , STULZ UK
Figure 1 - Direct free cooling www . stulz . co . uk
How cooling can create efficiency and have a positive impact on data centre optimisation
Figure 2 - Indirect free cooling with air / air plate heat exchanger
Data centre cooling is a continually evolving science due to the amount of equipment variations possible and the number of options in terms of facility design and operation . There ’ s now a plethora of cooling methodologies , from hot aisle to cold aisle , row containment , rack containment and water cooling but one of the most effective – both in terms of cost and application – is free cooling .
Power ranger Data centres consume almost as much energy for noncomputing resources as they do in powering their servers . That ’ s why Power Usage Effectiveness ( PUE ) has become such a prevalent industry metric – the closer it is to 1.0 then the better the facility is doing in managing its use of non-computing energy – and free cooling can help lower this figure .
So what do we mean by the term free cooling ? Gartner defines it as ‘ any technique used to reduce the energy consumed by cooling systems , or the time that the cooling units run by using the outside temperature of air or water to cool the data centre or other facilities ’. Free cooling helps save energy , and for most of the time UK ambient air temperature is actually colder than that required in the data centre – so a simple ventilation system can maintain compliant conditions .
Figure 3 - Indirect free cooling with heat exchanger thermal wheel
Temperature gauge Before looking at free cooling in greater depth , it ’ s worth noting that there are various measurable temperatures present in a data centre including supply air , return air , room air , cold aisle , and server inlet and exit temperatures . Server inlet temperature and server exit temperature are well known to have a significant effect on the efficiency of any cooling system and the higher the former , the more efficient a cooling system can become .
Just as importantly , attitudes towards data centre temperatures have changed drastically over the last 20 years or so . Previously , the computer room air conditioner ( CRAC ) return air temperature was the main control parameter and was set to 22-24 ° C . This resulted in unnecessarily low supply air temperatures in a range of 12 ° C . Today , the best practice is very different . In a modern data centre , supply air temperature is the main control parameter and it is typically set between 18 ° C and 27 ° C , as recommended by ASHRAE TC9.9 . This has resulted in return air temperatures to the cooling equipment of 25-40 ° C . Although the concept behind free cooling is relatively straightforward , there are a number of ways to go about achieving it .
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