DATA CENTRES EVAPORATIVE COOLING
Hot dry air
Figure 1: This diagram shows the principle of evaporative cooling – latent heat is removed from the hot dry air as a result of the evaporation process of the water circulating in the system, which in turn results in a cool air output
Cool air
decided to look at installing a form of ‘free cooling’ to the data centre room. After investigating a number of alternatives, it was felt that an evaporative cooling system would be the most suitable form of cooling for the data centre’s requirements, as this solution appeared to be able to maintain a relatively stable internal environment in terms of temperature and humidity, regardless of the external conditions. In order to achieve the required 150 kW
Owing to the success of this project, Nottingham Trent University is currently investigating a number of other locations where this type of system could possibly be installed
cooling requirements of the data centre, five evaporative cooling cubes were needed, each with an equivalent cooling capacity of 35 kW and a COP of 2.4. The principle behind the cooling solution
is shown in Figure 1: heat is removed from the hot, dry air as a result of the evaporation process of the water circulating in the system, which in turn results in a cool air output. The evaporative cooling system proposed for the data centre also had the potential to benefit from free cooling during periods of the year when the external dry-bulb temperature was below that of the required internal temperature. With a target internal temperature of
24C, and a constant load throughout the year, it was estimated that the electricity requirements of the system would be 22,847 kWh, as the evaporative cooling
46 CIBSE Journal October 2011
system would benefit from free cooling during the winter, and would be able to regulate the required energy input into the system according to the external temperature and humidity levels. Compared with the energy requirements
of the cooling system it was to replace, the forecast energy saving that could be achieved by the evaporative cooling system was up to 89%.
Payback Taking into account the energy savings of the proposed new system, the financial savings at current energy prices were estimated to be more than £16,500 a year. The project cost, installing all of the required equipment and controls, was quoted at just under £72,000 and, as such, provided a simple payback of less than 4.4 years. This simple payback does not include the maintenance required for the new system, but this was more than offset by the maintenance costs that would have been needed for the cooling system that was being replaced. In addition, the costs associated with
water requirements were not taken into account in the above payback calculations. These were anticipated to be extremely low, as at their peak load each unit would
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Water circulation
EcoCooling/Celsius Design Ltd
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