DCN May 2016 - Page 31

design & facilities management Of course, with greater computing power comes higher energy consumption. But the computers themselves are not the only technology to consume more electrical power. It is also used to run the equipment designed to dissipate the increased heat generated by more sophisticated computers – namely, condensers, air handling units (AHUs), cooling towers, and so on. Indeed, one of the biggest energy users in a data centre is not the computing technology itself, but the means of keeping this equipment cool, which is essential to prevent downtime and ensure data centres run at their optimum. Furthermore, because cooling equipment is required to work harder as computers become ever more sophisticated, the risk of breakdown (and, therefore costly downtime) is that much greater. This is what makes maintenance so important. A measure of success A useful measure of the energy efficiency of a data centre is power usage effectiveness (PUE). This is the ratio of total amount of energy used by the data centre to the energy delivered to computing equipment. Heating, ventilation and air conditioning (HVAC) can be responsible for up to 45 per cent of the energy cost of a data centre and three per cent of the UK’s total electrical energy usage is thought to be attributable to data centres. Improving PUE focuses largely on the supporting cooling system. Cooling towers and air handling units draw in air from the outside that is potentially full of dust, leaves and pollen, all of which can clog system filters. Keeping filters clean and in good working order is a simple maintenance step that can offer big fuel bill savings and reduce the potential for equipment breakdown. Air intake screens stop airborne debris from entering a system in the first place, to ensure cooling is kept constant, risk of breakdown is reduced and maintenance requirements are cut. This can be achieved by external, pre-filtration media. It is a solution that can be applied at the specification stage, or retrospectively, to improve the operational efficiency of existing cooling equipment. Working with AMEY, ECEX conducted a controlled, long term field trial to accurately measure the energy saving benefits of using air intake screens. At Westminster City, AHUs were monitored initially without air intake screens and then with, and revealed a 4.9 per cent reduction in power consumed and a significant reduction in maintenance requirements. Maintenance The cost of a sound Planned Preventive Maintenance (PPM) programme is ridiculously low compared with the cost of unplanned downtime caused, for example, by having to deal with a catastrophic AHU breakdown or condenser failure (which can lead on to failure of the data centre itself). As well as preventing such disasters, effective maintenance also makes a significant contribution to the bottom line by ensuring that plant is energy efficient and therefore produces lower power bills and higher environmental performance. But, the most compelling argument in favour of a properly implemented maintenance strategy is that it guarantees reliability. And just about every indicator in a business – safety, environmental performance, morale, retention, customer service – improves if you establish reliability as a core value of your organisation. Broadly, maintenance is a five step cycle: 1. Determine where you are now with an audit. 2. Decide where you want to get to by setting performance targets. 3. Plan how to get there. 4. Implement the plan. 5. Continuous improvement demands that you return to step 1. Unfortunately, there is often a crushing sense of complacency over the way asset care is planned and organised. The good news is that there is much that can be done to improve how a data centre cooling system operates through simple maintenance steps. For example, there is technology to tackle high volumes of pollen and falling leaves, which can increase the strain on chillers, in particular, by clogging filters and restricting airflow. As well as reducing the possibility of cooling equipment failure, this also has an enormous impact on energy efficiency. A study in the US by Johnson Controls’ Institute of Building Efficiency, for example, found that when condenser flow rates are reduced by 20 per cent in mechanical and absorption chillers full load energy consumption is increased by three per c ent. The message is clear – investigate every opportunity to reduce the burden in cooling equipment. 31