DATA CENTRES EVAPORATIVE COOLING
W
hen it came to further enhancing the data resilience and security of Nottingham Trent
University’s computing network, it was identified that the storage requirements of the network based at the university’s Clifton Campus data centre needed to be improved. To facilitate the required network upgrades, however, it was also deemed necessary to carry out a number of improvements to the data centre and its supporting infrastructure. Prior to the refurbishment works, the
required cooling for the data centre room was provided using a 150 kW split system containing R407c refrigerant. As a result of planned works, engineers noted that it would be the ideal time to address the cooling system in the room, in order to assist in meeting Nottingham Trent University’s carbon reduction target of 48% by 2020, based on a 2005 baseline. As the cooling equipment in the
data centre was not sub-metered, it was necessary to estimate the energy used by the system, so that the team could look at possible options for cooling in the data centre, and, as such, the subsequent energy and carbon savings that could be achieved. The university employed a heating and
ventilation sub-contractor to assess the efficiency of the current cooling system and to estimate the energy consumption of the units over a period of a year. It was estimated that, due to the age of the system and the refrigerant used, the coefficient of performance (COP) of the system would be about 2.75. In order not to overestimate the energy consumption of the current system, and subsequently overestimate any potential savings, it was assumed that the system would operate at 50% of its potential output throughout the year, despite the fact that there was known to be a constant cooling requirement in the room
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of between 100 kW and 150 kW. From this, the annual energy consumption of the current system was estimated to be around 238,909 kWh. At the same time as the proposed upgrade works to the system were being assessed, the university was also in the process of installing a new cast resin transformer in order to reduce the onsite voltage and benefit from the energy savings associated with minimising overvoltage. This installation was forecast to reduce energy consumption by 8.19% and, to ensure continuity with all of the calculations, this potential saving was also taken into account when estimating the annual energy consumption of the current cooling system. Applying this additional 8.19% energy saving reduced the estimated total annual consumption of the current system to 219,342k Wh. With an annual energy consumption
base established, it was possible to assess the possible options available for the cooling of the room.
Free cooling First, the possibility of reducing the cooling requirements of the room was considered. However, because of the upgrades and additional IT equipment to be installed in the data centre, this was not possible. Second, the option of fitting more energy efficient air conditioning was looked into, but nothing could be found that would achieve the required degree of energy saving. Having considered these options, it was
October 2011 CIBSE Journal 45
The data centre’s new cooling system was estimated to be able to deliver energy savings of 89%
Taking into account the energy savings of the proposed new system, the project provided a simple payback time of less than 4.4 years
Scott Brooks
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