DCN August 2016 - Page 23

cooling Inside the building, existing services, cabling or pipework can cause airflow to be less than optimal and therefore the capacity and efficiency of the cooling system is reduced. The pitfalls of current cooling strategies The increase in power costs and the recent Climate Change Agreement for data centres is leading operators to reduce their overall site power usage effectiveness (PUE), and this is pushing operators towards certain types of solutions – usually adiabatic systems. While PUE is the current measure of choice, it’s not perfect and it may well be replaced in the future by a different metric, one that may take more account of water usage or the effects of higher supply temperatures. Some companies have also rushed into solutions that are based purely on electrical running costs, to then discover that it is lacking in other technical areas, such as environmental control. Some data centres are now using pure fresh air systems to cool data centre space. While this may be very simple and cheap to run, this brings many complications when it comes to air contamination from outside, fire protection and humidity control. Data centres have been taken offline due to external fires closing the cooling systems down, for example. Of course, having a back up direct expansion (DX) or chilled water system mitigates the risk, but it does complicate the solution. The current trend is towards indirect adiabatic coolers, which seem to provide a good compromise on running costs vs. environmental control, yet the sheer physical size of these units does not make them the solution for every problem. There may always be a use for more traditional chilled water systems – or DX systems – even on new builds. What’s the right approach? It’s clear that when it comes to choosing and deploying data centre cooling solutions, there’s a number of issues at play. Operators need to decide what is most important and where they are comfortable making a compromise, if necessary. One vital element to take into account is current rack densities and ascertaining a best guess projection of what will be required in the future. A big challenge for colocation providers in particular is the unknown load distribution from customers, who are deploying higher and higher rack densities. It is important to know what a solution can and can’t cope with, therefore having plenty of capacity in the system will help cope with such scenarios. The quality of the data centre environment and its maintainability should also be acknowledged as more significant than low running costs. Once a cooling system is deployed, the environment needs to be managed to ensure the most effective performance. That means an appropriate amount of airflow around the racks, good aisle containment, tidy cabling, blanking panels and a clear floor void, if used for air delivery. Running at <50 per cent in normal operation puts less strain on components and reduces faults, therefore the data centre environment is more stable during maintenance or other events. Data centres are technologically complex and it is critical now more than ever to ensure the right operating environment. If the temperature inside the data centre rises to excessive levels, Cooling at the Node4 Northampton facility Earlier this year, Node4 invested £2m to expand its Northampton data centre, and the upgrade saw the facility built around an innovative cooling system. When choosing its cooling solution we started by selecting the type of cooling technology to deploy. Selecting the right solution meant evaluating several critical factors: the quality of components and controls, the support/maintenance provided and upfront running costs. Node4 puts in a lot of cooling capacity in its data centres (N+N on its main sites) to cope with maintenance events or faults, but also to ensure that equipment runs efficiently. At the Northampton data centre, Node4 has a number of systems in place, reflecting the best solution available at the time of install. The facility has a free cooling chilled water system, which uses traditional CRAC units and an even more efficient ‘cool wall’ system by Rittal/Weiss, consisting of giant cooling coils and decoupled fans. Node4 also uses cold aisle containment in its data halls, however in its new 400 rack hall it uses hot aisle containment and an indirect adiabatic cooling system based on Emerson EFCs. The solutions are as efficient as they can be without compromising on the quality of the environment. As such, the cool wall system gives typical PUEs of 1.3, while the EFC system will be as low as 1.1. This will still deliver air in the low 20s using a DX boost on the hottest days. considerable damage could be caused. By understanding customer requirements, future demands and the physical data centre itself, operators can create the optimal temperature environment that balances cooling with costs, efficiency and control. 23