Cool running data at NTU

13th May 2013


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An innovative cooling system is helping to cut data centre energy consumption at Nottingham Trent University. the environmentalist finds out how

Nottingham Trent University (NTU) is one of the most sustainable universities in the country. In 2011, it was ranked top out of 142 universities in the people and planet green league, published in the Guardian. Last year, the university was ranked in the top five.

The initiatives for which NTU is consistently placed so highly include avant-garde elements such as a sedum roof, an “intelligent lift” system, which minimises the distance the lifts travel, and windows that open and close automatically depending on the internal temperature. It has also installed mainstream energy-saving measures such as voltage optimisation and insulation.

Environment manager Grant Anderson reports that the key to this strong environmental performance is a fierce commitment to sustainability on the part of the university and a determination to treat environment issues with the same priority as its other core operations.

NTU’s green agenda is ambitious. It plans to halve its carbon footprint by 2020 against a 2005 baseline, and one of the main areas of activity is to reduce the energy impact of the university’s data centres.

The university’s strategy to improve the energy efficiency of its computing network and enhance data resilience is multipronged. It includes replacing the traditional air-conditioning system at one of its data centres with an evaporative cooling system powered by renewable energy. As a result of the project, NTU is on target to achieve an 89% saving in annual energy consumption by the data centre at its Clifton campus

Considering the options

The impetus in 2010 to reduce the environment impact of NTU’s data operations came partly as a result of seizing the opportunity when it presented itself. The expansion and remodelling of the Clifton campus – the second-largest of the university’s three campuses – meant that it was necessary to enlarge and move its data centre. Although not representing a huge proportion of the NTU’s annual £5 million utilities bill, at around £200,000 the energy consumption of the data centre was still significant.

Before the data centre’s refurbishment, cooling for the IT hardware was provided by a 150kW air-conditioning system split over several locations. The servers had been housed in a number of different rooms, which had bumped up their energy requirements. Relocating them to a single, purpose-built site immediately improved the energy efficiency of the computing system.

In investigating the options for improving the data centre’s environmental performance, the NTU was forced to rule out significantly reducing the cooling requirements for the servers because IT equipment needed to be upgraded and additional hardware installed. Although the temperature at which the equipment needs to be kept has been raised slightly (to 24°C), the estates team knew that this change alone would not have sufficient impact to realise NTU’s sustainability aims for the project.

The university also investigated sourcing a more energy-efficient air-conditioning system, but found nothing suitable on the market.

Evaporative cooling

The team then turned to the possibility of installing an evaporative or “adiabatic” cooling system that could maximise the use of “free cooling” for much of the year. This kind of system can maintain a relatively stable temperature and humidity level in the server room irrespective of external conditions. To meet the 150kW cooling requirements of the data centre, NTU needed to install five evaporative cooling cubes – each measuring 1m3 and having a 35kW cooling capacity.

The system works because the temperature of dry air drops significantly when water evaporates into it. The cubes take in hot, dry air and, following the evaporation of the water circulating in the system, pump out cool air. Scott Brooks, senior energy and sustainability engineer at NTU, describes the process as a large volume of air being passed over filters in the cubes that act as giant, wet sponges.

The result is a large output of cool air. It was estimated that the system would require about 22,847kWh of electricity annually, taking into account the free cooling that it would benefit from in the winter when the required energy input would be reduced as a result of the lower external temperature. This compares with the 219,342kWh of electricity used each year by the university’s previous cooling process.

Using an evaporative system to cool a data centre is an innovative choice and the fact that the university struggled to find more than a couple of suppliers for the cubes was proof of the new ground that it was breaking. Because such a system had not been tried and tested in many similar situations, NTU needed to research it thoroughly before opting for installation. Concerns that had to be addressed included the noise level of the system, the risk of legionella developing if the system reached a certain temperature and its ability to cope with the cooling requirements of the data centre.

The university resolved all of these issues before embarking on the project, with its engineers visiting sites with similar systems to assess noise levels, and the implementation of strict control and monitoring procedures to negate the possibility of legionella.

Building the infrastructure to house the data centre and its new evaporative cooling system took several months. The system needs large 60x60cm ducts to pass around the large volume of air necessary to cool the room, and the floor needed to be raised to accommodate them. The work was completed in June 2011 and the system has performed as expected and with few teething problems.

The only issues that have arisen relate to control of the system. For example, the estates team realised early on that the dampers – the grills that open and close on the cubes – need to be fully closed if the fire alarm is activated to ensure the gas suppression system can operate properly.

According to Brooks, the system has proved that it can function consistently and effectively even on days when the temperature and humidity outside are high.

A multipronged approach

At the outset of the project, NTU decided to reduce carbon emissions on three fronts. As well as introducing the evaporative cooling system, the information systems department introduced “server virtualisation” software to maximise the efficiency of the university’s servers. This change has resulted in a considerable reduction in energy demand because if one server is functioning at or below a certain capacity, its operations can be switched to another server with spare capacity.

“The servers consume a high proportion of energy even when functioning at a low level so focusing the demand on as few servers as possible can really heighten the energy efficiency of the data centre,” Brooks explains.

Virtualisation can significantly reduce the number of servers needed in a data centre and, therefore, have a dramatic positive impact on electricity consumption.

The final piece of the data centre’s sustainability jigsaw is renewable energy. Brooks explains that NTU enhanced its cooling system by connecting it to a 10kW photovoltaic (PV) system to minimise demand from the mains supply during periods of high usage.

The array of 45 PV panels was installed on the roof of the building where the data centre is located. The panels are wired directly into the electrical panel that provides power to the cooling system, so it can tap into the renewable energy source whenever possible. The PV system provides more than one-third of the cooling system’s energy needs and in 2012 it saved seven tonnes of carbon.

Return on investment

It cost £72,000 to install the evaporative cooling system and build the necessary infrastructure. It was funded by the university’s ongoing loan for sustainability projects from Salix Finance and the Higher Education Funding Council for England’s “revolving green fund”, which provides finance to higher education institutions to reduce their carbon emissions. Eligibility for funding under these arrangements requires projects to meet a strict five-year payback period for the loan. Payback for the cooling system is forecast at less than four and a half years.

This relatively short payback period is achievable because of the energy efficiency of the cooling system. Compared with the traditional air-conditioning units it replaced, the new system saves more than 195,000kWh in electricity a year, which equates to around 106 tonnes fewer carbon emissions. Annual cost savings are estimated to be £16,500. The 174kW evaporative cooling system costs £1,900 in electricity consumption compared with £18,400 for the 150kW air-conditioning system.

Because the payback time on the PV system is longer – between nine and 10 years – this element of the project was not eligible for funding through the university’s revolving green fund loan. The £40,000 cost of buying and fitting the university’s first PV array was met internally.

The estates team is so pleased with the performance of the evaporative cooling system and its positive effect on the data centre’s environmental impact, that it has investigated the possibility of installing a similar system at another university site. However, with large ducts and other specific infrastructure necessary, there are few locations where such a system can be installed. NTU has been able to rollout PV more easily, with panels installed across its three campuses.

Learning points

As far as Anderson and Brooks are aware, no other establishments were using the same combination of technologies – evaporative cooling, server virtualisation and PV – when NTU’s system came online. “It is the combination of these three technologies and how they work together in a data centre that makes the project unique and innovative,” says Anderson. The number of suppliers of evaporative cooling systems is now growing, however.

Aside from the technologies selected for the initiative, a large part of the success of the project is due to the close collaboration between the estates team and the information systems department. “The information systems team was very open to considering less traditional solutions,” says Brooks.

His advice to other organisations considering refurbishing a data centre is to investigate the potential and not be too risk averse. “Don’t be discouraged by the possible risks, such as legionella in this case, as there could be very little basis for them if properly researched – and you may find that the environmental benefits and financial return-on-investment far outweigh the perceived risks and actual cost.”

Data centre GAMES

Emissions from data centres worldwide are around half the volume produced by the global aviation industry and more than the total emissions of the Netherlands, according to the European Commission. Recent research funded by the commission aims to make the facilities that store data remotely more energy efficient.

The project, called GAMES (green active management of energy in IT service centres), has developed methodologies, software tools and services, and metrics to investigate and measure the energy consumption of IT infrastructure in a more detailed way than was previously possible, all the way down to server level. It helped cut energy consumption by more than 20% at the two data centres where it was tested, the commission reported in March 2013.

The data centres at Pont Saint Martin in Italy and Stuttgart in Germany were already relatively energy efficient. At the Italian site, which is used mainly for hosting services, the technology improved its PUE – power-usage effectiveness, the ratio of the total power used by the facility, divided by the power delivered to its IT equipment. An ideal PUE would be 1, while the average is about 1.83 to 1.92.

At Pont Saint Martin the project saw the data centre’s PUE improve from 1.35 to 1.25, a considerable energy saving. Similar improvements were recorded at the Stuttgart site – a high performance computing centre operated by the local university – despite the different technology and applications of the centre.

“For data centres to become more efficient, it is essential to know how energy is being consumed. Our focus was therefore to develop effective monitoring solutions that allow performance and processes to be adapted in real time,” says Dr Massimo Bertoncini, from Engineering Ingegneria Informatica in Italy, who coordinated a team of researchers.

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