Data centre cooling
12 January 2010
For many years, raised floors have been the preferred option as a method of climate control in data centres. However, they have a number of disadvantages. If, for example, the height is reduced or swirl mixing occurs, predicted performance can no longer be guaranteed.
In order for a cooling system to perform at its optiumum it is essential that the air intake and outlet openings to all the servers blow into defined cold and warm aisles, and that a suffient body of cold air is available, which cannot mix with any warm exhaust air before it is consumed. This resulted in new rack technology such as hot aisle containment (HAC), cold aisle containment (CAC) and high density cooling. However this brought with it confusion over which was the best technology to deploy.
Hot aisle and cold aisle containment fundamentally do the same thing - they create a barrier which is made up of roof panels and end of aisle doors to encapsulate the aisle. Both systems increase the overall delta T of the computer room air conditioning (CRAC) or in line coolers (CRACS that mount in between racks). The delta T is the difference between the hot air going into the CRAC and the cold air going out of the CRAC.
The higher the delta T the better, in fact a typical CRAC system with a 5 degree delta could be rated at 50Kw, increase the delta T to 15 degrees then the same CRAC systems can then provide 110kW of cooling. This is one of the reasons why aisle containment systems raise the capacity of the rack, but also offer the ability to throttle the CRAC back if required to save energy.
So what are the advantages and disadvantages between hot and cold aisle containment? Quite simply cold aisle containment is an easy retrofit and can use existing CRAC systems. With hot aisle containment there is a need to install cooling systems between the racks making it harder to retrofit. It also takes up more space. However, both systems provide a more even spread of cooled air across the whole height of the rack, providing a reduced risk of any hot spots occurring.
As many organisations seek to host their hardware and applications in purpose built facilities rather than investing in the high cost themselves, Data Centres have become an integral part of today’s business environment. Node4 owns and operates Data Centres throughout the UK which conform to the highest service levels within the commercial data marketplace. The company chose to equip its latest new Data Centre, in Wakefield, with Rittal TS 8 racks and to maximise cooling to utilise the Rittal Cold Aisle Containment System.
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