WHAT’S HOT datacentre alliance
Data Centre Engineering: hot topic or just blowing hot and cold!
By Dr. Jon Summers, University of Leeds
Engineering has many iconic disciplines, for example aerospace engineering – the sight of an aircraft in the sky is an everyday occurrence, but what is data centre engineering? In fact,
currently over 30% of the world’s population directly use data centres, much greater than those who fly. These data centres are the fabric of our digital society, they store and process vast quantities of digital information. The ever expanding number of users and their digital demands are creating a growth in this sector that is now unparalleled. Data centres have always been able to meet the demands of their customers, however more recently the power requirements of new data centres (upwards of more than 50MW), usually located in urban areas, cannot not always be met by the utility power companies.
The reason why data centres consume so much energy is because they contain large data halls which have hundreds of 2m high racks aligned in rows that are each stacked full of servers and network devices, all of which store, process and propagate digital information, processes that generate heat. It is then necessary to blow cool air (typically at 1000+ litres per second per rack) through all of the IT hardware to remove this heat. The management of the air is traditionally done by computer room air conditioning (CRAC) units. Fans, air conditioning and air handling units all consume energy on top of the energy that is used by the IT hardware.
The continued energy demand of the digital sector requires smarter, optimal, novel and overall sustainable approaches to cooling.
Cooling strategies within data centres are at the heart of a new research strand for iETSI. This area of research combines both experimental testing and computational fluid dynamics (CFD) to inform improved cooling strategies, whether it is simply reducing the mixing of hot and cold air within the data hall or analysing row/rack arrangements that enable proximity cooling, which is where the cooling technology is located closer to the heat sources.
The Leeds University High Performance Computing facility uses a novel proximity cooling technology provided by Airedale International that relies on liquid loop heat exchangers that are housed in the rear door of the server racks. The photograph below pictures fan assisted rear door heat exchangers, which are currently being assessed for their energy cost savings. The water passing through the back doors is cooled by rooftop chillers (see picture to the right) that can use free cooling in Leeds for a large proportion of the year.
Inefficiencies in energy use in data centres can stem from the mixing of the cold air intended for the servers with their hot exhaust air. CFD analysis can be used to assess the level of hot and cold air mixing as well as situations where hot air is transported in front of the inlet of the servers. The CFD result in the picture below demonstrates the most common arrangements of racks, which is where they are aligned in rows of hot and cold air. In this situation cold air is vented through the floor in the cold aisle, passes through the servers into the hot aisle where the hot air rises
to the ceiling and is carried back to the CRAC unit. There are many modifications to this layout, one that is currently being applied is called aisle containment, where either the hot or the cold aisle is completely enclosed.
Commercial data centres and those that are used in the financial sector have contractual obligations to deliver a continuous service. This is achieved by creating both a significant level of redundancy and resiliency.
It is unbelievable the lengths to which data centre providers go to in order to achieve the required levels of redundancy and resilience, maintaining both telecommunication and power connectivity. Uninterruptable power supplies (UPS) and backup generators are used, and they themselves are required to have a level of redundancy.
Data centre design and construction engineers have to consider the issues of being energy efficient, while at the same time maintaining a level of redundancy and resilience that is fit for purpose. The industry is growing pockets of best practice in the build and operation of data centres, but this is not as widespread as it could be. With the continued squeezes on energy utilisation in the industry, standards and regulations are now arising.
The research team in iETSI have joined forces with the data centre industry and helped to setup the not for profit organisation called the Data Centre Alliance (www.
datacentrealliance.org) to galvanise the growing best practice and influence the emerging European and global standards.
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www.dcseurope.info I March 2012
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